Hiệu ứng điện-từ trong một số vật liệu từ giảo - áp điện

Dat van de Neu ro tinh cap thiet ciia de tai hoac cac noi dung nghien cim cua de tai Vat lieu sat tir - sat dien multiferroics dugc biet den nhu nhirng vat lieu co do phan cue dien duoi

DAI HOC QUOC GIA HA NOI

DAI HOC QUOC GIA HA NOl_

TRUNG TAM I H O N G j i r ^ H H l ^ ^

00060000091

Ha Noi, nam 2008

MUC LUC

Trang

1 Bang giai thich cac chir viet t^t 1

2 Danh sach nhirng ngiroi tham gia thyc hien de tai 2

3 Danh muc cac bang so lieu ^

4 Danh muc cac hinh ^

5 Tom t^t nhii-ng kit qua nghien ciru chinh cua de tai 4

6 Bao cao tong ket 6

6.1 Dat vinda 6

6.2 Tong quan cac van de nghien cuu 7

6.2.1 Hieu img ap dien va vat lieu dien giao 7

6.2.2 Hieu ung tir giao va vat lieu tir giao 8

6.2.3 Mot so irng dung tien tien cua vat lieu tir-dien 11

6.3 Muc tieu va noi dung nghien cim cua de tai 11

A.l Che tao CoFe204 dang bot va khoi 12

A.2 Che tao vat lieu to hop dang mang PZT/CoFe204 12

A.3 Che tao mau bang tir (Feo8oCoo2o)78Sii2Bio 13

PHAN B CAC PHirONG P H A P K H A O S A T C A C T I N H C H A T 14

C.l He CoFe204 dang bot va khdi 15

C.2 He vat lieu to hgp dang mang PZT/CoFe204 17

C.3 He bang tir (Feo,8oCoo.2o)78Sii2Bio 21

KET LUAN CHUNG 24

6.4 Dia diem, thai gian va phuong phap nghien ciru 24

6.5 Ket^qua nghien cim 25

6.6 Thao luan 26 6.7 Ket luan va kien nghi 26

6.8 Tai lieu tham khao 27

7 Phu luc 28

1 BANG GIAI THICK CAC CRlf VIET TAT

1.1 Thiet bj, phirorng phap thyc nghiem

XRD (X-ray diffractometer)

AFM (atomic force microscopy)

SEM (scanning electron microscopy)

VSM (vibrating sample magnetometer)

PLD (pulsed laser deposition)

EDTA (ethylene diamine tetra acetic acid)

Nhieu xa ke tia X HiSn vi lire nguyen tir Hien vi dien tir quet Tir ke mau rung Boc bay bang xung laser

Do phan cue dien (|iC/cm )

Do phan cue dien bao hoa (|aC/cm^) magneton Bohr

Tir do (Am /kg, emu/g) Tir do bao hoa (Am /kg, emu/g) Nhiet do (°C)

Nhiet do Curie cua chat sat tir (°C) Nhiet do Curie cua chat sat dien (*^C)

3 DANH MUC CAC BANG SO LIEU

• *

Bang 1 Hang s6 mang tinh the a va kich thuoc hat CoFe204 sau khi nung

Bang 2 Tinh chit tir cua mlu bot CoFe204 nung tai cac nhiet do khac nhau va cua mau

dia det sau thieu ket

4 DANH MUC CAC HINH

Hinh 1 So d6 minh hoa cho hieu ung ap dien khi tac dung img suat len mot vat lieu ap

dien

Hinh 2 Cau true tinh the cua PZT

Hinh 3 Su phu thuoc cua do bien dang Al/I cua vat lieu tir giao vao tir truong ngoai Hinh 4 Cau true tinh the cua CoFe204

Hinh 5 So do nguyen ly ciia phuong phap PLD

Hinh 6 Gian do nhieu xa cua CoFe204: mau bot nung tai cac nhiet do tir 700 °C den

950 °C va cua dia det sau khi nung thieu ket

Hinh 7 Duong cong tir tre ciia CoFe204: mau bot nung tai cac nhiet do khac hau

va cua dTa det sau khi nung thieu ket

Hinh 8 Gian dh nhiiu xa tia X cua mang CoFe204 (280 nm)/PZT (l|im)/CoFe204 (280

Hinh 12 Su phu thuoc nhiet do cua tir dp cua ciia mang CoFe204 (280 nm)/PZT

(l^m)/CoFe204 (280 nm) do tai tir truong 0,05 T

Hinh 13 Gian do nhieu xa tia X cua bang tir Fe-Co-Si-B truac va sau khi ii nhiet tai

cac nhiet do khac nhau

Hinh 14 Anh FE-SEM ciia bang tir Fe-Co-Si-B chua u nhiet (a) va sau khi u tai Ta ^

250 °C (b)

6 BAO CAO TONG KET

6.1 Dat van de (Neu ro tinh cap thiet ciia de tai hoac cac noi dung nghien cim cua de tai)

Vat lieu sat tir - sat dien (multiferroics) dugc biet den nhu nhirng vat lieu co

do phan cue dien duoi tac dung ciia tir truong ngoai hoac co do tir hoa cam irng gay boi dien truong ngoai Hien tugng nay co dugc nho vao tuong tac dien-tir giira cac tinh chat tir va dien cua vat lieu va dugc goi la hieu irng dien-tir (magnetoelectric effect) Vat lieu sat tir - sat dien noi chung va hieu irng dien-tir noi rieng da thu hiit dugc su chu y ciia cac nha khoa hoc tren the gioi khong chi boi cac tinh chat vat ly

ly thu ma con do kha nang irng dung rong rai trong cac ITnh virc nhu cam bien kich

CO micro, luu tru thong tin va cac bo chuyen doi Mot trong cac yeu cau de co the dua vao irng dung doi voi cac vat Heu nay la co hieu ung dien-tir manh

Vat lieu sat tir - sat dien co the la mot pha don le hoac la to hgp cua mot vai pha khac nhau Cac vat lieu loai mot pha, vi du nhu BiFeOs, Cr203, YIG (Yttrium iron garnet), co hieu irng dien-tir yeu va chi co the sir dung dugc 6 nhiet do thap vi nhiet do trat tu Neel hoac Curie a duoi nhiet do phong Trong khi do, viec ket hgp giira cac pha sat tir va sat dien rieng re thanh vat lieu dang to hgp voi he so dien-tir Ion Hon "mot vai bac da tao ra mot huorig moi trong nghien cuu va mo rong kha nang irng dung do tinh da nang cua vat lieu dang nay [1, 2] Vat lieu to hgp thuong dua tren cac vat lieu c6 do tir giao Ion nhu Terfenol-D va CoFe204; va cac vat lieu

CO tinh ap dien manh nhu Pb(Zr,Ti)03 (PZT) va BaTi03 [3-5] Cac vat lieu nay cung CO nhiet do trat tu Curie len den mot vai tram do tren nhiet do phong Duoi tac dung cua tir truong ngoai, phan tir giao se bi bien dang va truyen nang lugng nay sang phan dien giao Ket qua la phan dien giao se chiu mot irng suat va tao ra do phan cue dien cam irng Hieu ung ciing co the xay ra theo Chi^u ngugc lai khi tac nhan ban dau la mot dien truong

Cho den nay cac ket qua nghien ciru ve vat lieu sat tir - dien dang X6 hgp chu

yeu van tap trung tren vat lieu gom nhieu tam tir giao va ap dien xen ke dugc chS tao bang each ket dinh hoac tren vat lieu dang khoi trong do pha tir giao hoac ap dien dugc phan bo tren nen cua pha con lai Trong phuong phap dau, do cac lop sat tir va sat dien khong tiep xuc true tiep voi nhau ma thong qua mot lop keo dinh nen tuong tac dien-tir giira chung co the bi anh Huong Con voi cac mau kh6i, kich thuoc Ion se han che viec tieu hinh hoa de ung dung trong cong nghe micro-nano

Vi vay viec nghien ciru che tao true tiep mang da lop sat tir - sat dien bang cac phuong phap hoa hoc, vat ly la rat quan trong doi voi sir phat tri6n he vat lieu nay cung nhu dap irng cac yeu cau ve irng dung hien nay va trong tuong lai cua cong nghe micro-nano

G5n day bg mon Vat lieu va Linh kien tir tinh nano (khoa Vat ly ky thuat va

Cong nghe nano, truong DHCN) da thanh cong trong viec che tao vat lieu tir

giao-dien giao Tb(Feo.55Coo.45)i.5 (TerfecoHan)/PZT trong do TerfecoHan co dang mang

con PZT 6 dang tam dugc k6t dinh voi nhau Cac tac gia quan sat thay he so dien-tir

kha lan so voi cac vat lieu to hgp khac [6] Ket qua nay la mot trong cac co so de

phat triln viec nghien ciru che tao cac mang da lop tir giao - ap dien tai don vi va

thir nghiem kha nang img dung cua cac vat lieu nay tai Phong thi nghiem muc tieu

ve Cong nghe micro va nano cua truong Dai hoc Cong nghe

6.2 Tong quan cac van de nghien cu*u (Can trinh bay nhu mot bao cao khoa hoc, neu

bat nhirng van de da nghien cim, nhirng phuong phap da ap dung cho cac nghien cim truoc,

chi ro de tai quan tam nghien cim va giai quyet nhung van de gi, nham dong gop gi)

6.2.1 Hieu irng ap dien va vat lieu dien giao

a Hieu ieng dp dien

Hieu irng ap dien (piezoelectric effect) la hien tugng mot vat lieu khi chiu tac

dung cua irng suat keo hoac nen thi trong long vat lieu se xuat hien sir phan cue dien

cam irng hoac ngugc lai, khi vat lieu chiu tac dung ciia dien truong thi vat lieu se bi

bien dang dai ra hoac ngan lai (xem hinh 1) Trong hien tugng nay, tren hai mat doi

dien cua vat lieu se xuat hien mot hieu dien the ti le voi irng suat tac dung vao [2]:

U-g33-a (1) voi g33 la he so ap dien (piezoelectric coefficient) dac trung cho tirng vat lieu va cria

irng suat tac dung (o-> 0 neu la irng suat keo, cr < 0 neu la ung suat nen)

«

H

Hinh l.Sa do minh hoa cho hieu ieng dp dien khi tac dung ieng sudt len mot vat lieu dp dien

Hieu irng ap dien dugc quan sat thay tren nhieu vat lieu tinh the nhu thach anh,

NaKC4H406 (potassium sodium tartrate), cac muoi Rochelle, Tuy nhien hieu irng

tren cac vat lieu nay nhin chung la nho Voi cac vat lieu gom co cau true tinh thi

7

perovskite thi hieu ung ap dien la rat Ion Nho dac tinh nay nen cac vat lieu gom ap dien da dugc nghien cuu manh me va dua vao ung dung rgng rai trong nhieu ITnh vuc nhu cong nghe dien tir (mang rung, cam bien, ) va thong tin (bo chuyen doi, luu tru, )

b Vat lieu dp dien PZT

Mot trong nhirng vat lieu gom ap dien da dugc sii dung rong rai nhat cho den hien nay la Lead Zirconate Titanate Pb(Zr;rTii-;f)03 (thuong dugc biet den voi ten viet tat la PZT) PZT c6 cau tnic tinh the lap phuong thuoc nhom doi xung P4mm voi hang so mang a = 4.036 A, c = 4.146 A (xem hinh 2) Trong cau true nay, ion

Tx^^/Zx ^ nam 6 vi tri bat dien (octahedral site) cua 6 co so Khi c6 tac dung ciia irng

suat ben ngoai, ion nay bi dich chuyen khoi vi tri can bang, dan den sir xuat hien ciia do phan cue dien cam ung trong vat lieu Ben canh he so ap dien Ion, PZT con

CO do phan cue dien Ion P » 36 |iC/cm^, lire khang dien nho E^ » 20 kV/cm va nhiet

do Curie cao TC(E) ^ 360-^390°C, phii hgp cho cac nghien cim ung dung

^

-Q^^^^^O^^^

Q i^

O o

Hinh 2 Cau trite tinh the cita PZT

6.2.2 Hieu irng tir giao va vat lieu tir giao

a Hieu ieng tie giao

Hieu irng tir giao (magnetostrictive effect) la hien tugng bi6n dang vl kich thuoc ciia vat lieu khi c6 sir xuat hien cua tir truong ngoai So dT co hien tugng tir giao la do duoi tac dong cua tir truong, cac momen tir trong vat lieu sap xip lai lam cho kich thuoc cua vat lieu thay doi Ngugc lai voi hieu ung tir giao la hieu ung tir giao ngugc (hieu irng Villari) trong do tinh chat tir ciia vat lieu thay d6i khi bi bi6n dang duoi tac dong cua irng suat (keo cang hoac ep lai)

Do bien dang cua vat lieu duoi tac dung cua tir truong va su thay d6i tinh chat tir ciia vat lieu duoi tac dung ciia ung suat dugc xac dinh thong qua phep do cac he

so tir giao (magnetostrictive coefficient) va do cam tir tir giao (susceptibility) Co nhirng loai vat lieu c6 he so tu giao gan bang khong nhu hgp kim Invar nhung ciing

CO nhirng vat lieu co he so tir giao bao hoa rat Ion nhu mot so hgp chat lien kim loai dat hiem - kim loai chuyen tiep De dac trung cho vat lieu tir giao nguoi ta dua vao

he so tir giao (xem hinh 3):

A = — hay A = —

trong do /, V la do dai va the tich cua vat lieu tir giao khi khong c6 tir truong, con A/

va AF la su thay doi ve do dai va the tich cua vat lieu tir giao duoi tac dung ciia tir truong ngoai

/ •

Al/1

/

Hinh 3 Su phu thuoc ciia do bien dang dl/l ciia vat lieu tit: giao vdo tit truang ngoai

Vat lieu co he so tir giao Ion co the irng dung lam cac vi cam bien (microsensor) de do bien dang co hoc hoac de dieu khien su dich chuyen ciia cac he

o kich thuoc micromet Voi cac irng dung nay, yeu cau doi vai vat lieu la co he so tir giao bao hoa Idn de co tin hieu Ion va c6 do cam tir giao ciing phai Ion de co the hoat dong trong tir truong nho Noi chung cac vat lieu tir deu co he so tir giao trong dai 10"^ nhung co nhung vat lieu tir giao khong 16 (giant magnetostriction) vai he so tir giao co 10'\ Ion gap hang nghin lan vat lieu tir giao thong thuong Vat lieu loai nay moi dugc phat hien vao nhung nam 80 cua the ki truoc dua tren hgp kim (Dy,Tb)Fe2 va thuong dugc biet voi ten thuong mai Terfernol

b Vat lieu tie giao spinel AB2O4

Ben canh cac hgp chat lien kim loai dat hiem - kim loai chuyen tiep hien dac tinh tir giao, cac vat lieu oxit cau true dang spinel voi cong thirc cau tao chung

AB204=AỌB203 da va van dugc quan tam nghien cuu do co cac tinh chat tir va dien phong phụ Mot trong nhirng dac tinh dang chii y cua cac oxit cau true dang spinel la co cau tnic tinh the lap phuong kep thuoc nhom doi xung Fd3m vai hang

so mang a ~ 8,3^8,4 A (xem hinh 4) Do do neu tinh cho mot nira 6 co so thi "hang

so mang" con khoang 4,1^4,2 A, rat gan voi hang so mang cua PZT va la co so cho viec nghien cuu che tao vat lieu to hop tir giao-ap dien dang mang da lop AB2O4/PZT voi dinh huong tinh the cao, luu giii dugc cac tinh chat uu viet ciia tirng lop thanh phan

^ A-ntoins

"^ rptiahedinl sites

PTinh 4 Cau true tinh the cua CoFe204

Trong cong thirc tong quat AB2O4 thong thuong A la cac nguyen to kim loai

CO hoa tri 2+ nhu Co, Fe, Mn, Zn, Mg, Cu, Ni, Cd; B la nguyen to kim loai co hoa tri 3+ nhu Fẹ Cac ion Oxy co ban kinh Ion Hon nhieu so voi cac ion kim loai A va

B (^1,32 A so voi 0,6-~0,8 A) nen gan nhu nam sat nhau tao thanh mang lap phuong tam mat xep chat Theo quan diem ve hoa tri, cac ion kim loai co the phan bo 6 hai nhom vi tri ben trong nhu sau (cau tnic spinel thuan - normal spinel):

- nhom A: vi tri mang 8a, goi la vi tri tir dien (tetahedral site), 6 do moi ion kim loai Â"^ dugc bao boc boi 4 ion Ố

- nhom B: vi tri mang 16d, goi la vi tri bat dien (octahedral site), o do m6i ion kim loai B"^"" dugc bao bgc boi 6 ion Ố

Tuy nhien trong thuc te thuong quan sat thay hien tugng mot nira cac ion Fê"^ nam 6 vi tri 8a, con nira con lai ciing voi cac ion Â"^ nam 6 vi tri 16d (cau true spinel dao - inverse spinel): Fe" [Me Fe"" ]04 " Do sir phu thuoc goc cua tuong tac sieu trao doi am nen cac momen tir 0 hai phan mang A va B phan bo phan song

song Trong cau tnic spinel dao, do ion Fe"*"^ co mat o ca hai phan mang voi so lugng bang nhau nen momen tir cua vat lieu chi phu thuoc vao ion B^^

Trong cac spinel dao, CoFe204 dugc dac biet chii y do co momen tir kha Ion (My = 3,7 p-B so voi 4,1 I^B cua Fe304) va he so tir giao Ion nhat I ^ I = 590x10'^

Ben canh do CoFe204 con c6 nhiet do Curie kha cao TC(M) ^ 520°C, phii hgp cho cac

nghien cim voi muc dich img dung tren nhiet do phong

6.2.3 Mot so irng dung tien tien ciia vat lieu tir-dien

Voi uu the c6 cac tinh chat to hgp dien va tir ma cac vat lieu don le thuong khong CO, vat lieu tir-dien co cac kha nang irng dung phong phii, gan voi cac nganh cong nghiep dien tir, thong tin hay y sinh, Mot so irng dung co ban co the ke den nhu sau:

- c a c sensor do tir truong nho, do dong dien;

- Cac cam bien de phat hien nhanh cac phan tir sinh hoc;

- Bo chuyen doi nang lugng;

- Bo nho luu tru du lieu,

6.3 Muc tieu va noi dung nghien ciru cua de tai

Trong xu Huong chung hien nay, cac linh kien dien tir ngay cang phai co kich thuoc nho gon Hon va it tieu ton nang lugng Vi vay doi voi phan Ion cac irng dung

de cap o tren, vat lieu tir-dien sau khi che tao can phai dugc tieu hinh hoa o mot mire do nao do De co the tien hanh viec tieu hinh hoa thi vat lieu phai dugc che tao duoi dang mang mong voi do min cao de qua trinh khac (quang khac, an mon, )

CO the tien hanh thuan Igi Do do muc tieu chinh dat ra trong de tai nay la khao sat, nghien ciiu lam chii cong nghe che tao vat lieu to hgp tir - dien dang mang da lop c6 tinh chat tir va dien tot

Vat lieu to hgp dang mang da lop tir giao - ap dien se dugc nghien ciru che tao bang cac phuong phap vat ly sir dung cong nghe boc bay xung laser Ben canh viec tap trung che tao va nghien cuu cac tinh chat tir va dien cua vat lieu to hgp dang mang da lop tir giao - ap dien CoFe204/PZT thi nhom tac gia nghien ciru ciing

CO du dinh che tao vat lieu to hgp dang mang da lop tir giao - ap dien (Feo.8oCoo2o)78Sii2Bio/PZT Tuy nhien trong qua trinh thuc nghiem, do mot s6 kho khan ve viec chuan bi bia cua vat lieu de diing cho viec tao mang tir giao nen chiing toi moi chi tam dirng o viec che tao va nghien cuu cac tinh chat ciia bang tir (Feo.8oCoo.2o)78Sii2Bio Cac tac gia ciing du dinh nghien ciru tinh toan ly thuylt v6 he

II

vat lieu nay nhung do mot so han che ve thai gian va nhan lire nen moi chi dirng a mot so khao sat ban dau

Trong phan tiep theo nay chung toi se trinh bay nhung noi dung nghien cuu chinh trong de tai theo thu tu nhu sau:

- Phan A Cac phuong phap che tao vat lieu

- Phan B Cac phuong phap khao sat cac tinh chat

- Phan C Ket qua va thao luan

Phan A CAC PHirONG PHAP CHE TAO MAU

A.l Che tao CoFe204 dang hot va khoi

Cac hat CoFe204 dugc tong hgp thong qua phuong phap tao phuc (complexometric method) Trong phuong phap nay, cac chat ban dau la cac dung dich muoi nitrat ciia cac kim loai tuong ung Co(N03)2 va Fe(N03)3 voi ty le thanh phan cac muoi ban dau dugc lira chon phii hgp voi thanh phan kim loai tuong ung trong hgp chat CoFe204 Dung dich Hon hgp muoi kim loai tren dugc bo sung EDTA de tang cuong viec tao phirc va phan tan dong nhat cho cac ion kim loai Hon hgp gel

se dugc lam kho, say a nhiet do trung gian (200^300 "^C) va cuoi ciing nung 6 cac

nhiet do khac nhau (850^1050 °C) de thu dugc cac hat spinel voi cac kich thuoc khac nhau

De che tao CoFe204 duoi dang cac bia hinh dTa det diing cho viec che tao mang mong, truoc het cac hat spinel dugc nghien co hoc, sau do dugc ep di Huong (16 MPa) va dang Huang (4000 MPa) de dinh khuon dang Tiep theo vat lieu se dugc

nung thieu ket 6 nhiet do khoang 1200-^1300 °C de tao san pham cuoi cimg la cac

bia voi kich thuoc khoang (j)25x3 mm Rieng doi voi PZT, cac bia hinh dTa det voi kich thuoc tuong tu dugc chuan bi tir bot PZT thuong mai (do sach 3N) cung c^p boi TRS Ceramics Technologies (USA)

A.2 Che tao vat lieu to hgp dang mang PZT/CoFe204

Cac mang da lop tir giao/ap dien dugc che tao dua tren cong nghe boc bay bang xung laser (pulsed laser deposition) sir dung thiet bi PLD General (TST B.V.) tren d^ SrTi03 (100) hoac de Nb-SrTi03 (100) tiiy theo muc dich sir dung Cac d6 truoc khi su dung deu dugc xir ly hoa hoc va ii nhiet a 950°C de lam xuat hien lop Ti02 [7] So do minh hoa ve cong nghe boc bay bang xung laser dugc chi ra tren hinh 5

beam

Piirl with

qiianz window

Ht-atablc sample siagc

V:tcuum ciianibcr

Hinh 5 Sa do nguyen ly cua phuang phap PLD

Buong tao mau cua he PLD dugc hiit chan khong den gia tri co so vao khoang 5x10"*^ mbar truoc khi dua khi O2 voi ap suat pO? vao Sau do nhiet do de dugc tang

len den gia tri Ts voi toe do tang nhiet 15°C/phut Cac thong so ky thuat da su dung

trong qua trinh che tao cac lop vat lieu tuong irng nhu sau:

- CoFe204: nhiet do da T^ = 400-^700 °C, ap suat O2 p02 -0.02^0.1 mbar, nang lugng xung 2.5 J/cm^ va tan so xung 5 Hz

Thong so dugc chon la: Ts = 600 °C va p02 = 0.05 mbar

- PZT: nhiet do da Ts = 500-^700 °C, ap suat O2 PO2 =0.05^0.2 mbar, nang

lugng xung 3.5 J/cm va tan so xung 10 Hz

Thong so dugc chon la: Ts = 600 °C va p02 = 0.1 mbar

De khao sat anh Huong cua do day cac lop len tinh chat ciia mang da lop, do day cac mang dugc thay doi trong khoang tir 70 nm den 280 nm cho CoFe204 va 250

nm den 1 \im cho PZT Do day cua mang dugc tinh toan theo toe do tao mau tai cac

diau kien khac nhau va dugc kiam tra lai bang phep chup anh cat lop hian vi dien tir quet (SEM)

A.3 Che tao mau bang tir (Feo.8oCoo.2o)78Sii2Bio

Mau bang tir giao (Feo.8oCoo.2o)78Sii2Bio dugc che tao sir dung cong nghe nguoi nhanh (rapid cooling, melt-spinning) hay con dugc goi la phuang phap lam lanh nhanh hoac toi nhanh (rapid quenching) Day la mot phuang phap luyen kim diing

da che tao cac bang hgp kim hoac kim loai v6 dinh hinh bang each lam lanh nhanh hgp kim hoac kim loai nong chay voi toe do thu nhiet rat Ion (tir lO'^ K/s dan 10^

13

K/s), Toe do lam lanh nay dam bao qua trinh kat tinh se khong xay ra trong hgp kim hoac kim loai

Hgp kim (Feo.8oCoo.2o)78Sii2Bio dugc cha tao tir cac kim loai co do sach cao nhu

Fe 99.9%, Co 99.9%, Si 99.5% va B 99.5% Cac kim loai ban dau nay dugc can theo thanh phan danh dinh, sau do dugc nau chay bang dong dien cam irng cao tan trong mot noi bang thach anh c6 voi phun Sau khi nong chay a 1130 C, hgp kim long dugc nen bang khi tro Ar (p.,^ = 200 mbar) roi chay qua voi va phun lan mot mat trong dong dang quay voi toe do 20 m/s de tao ra cac bang hgp kim Bang tir (Feo.8oCoo.2o)78Sii2Bio cha tao bang phuang phap nay co kich thuoc dian hinh day 30

pm va rong 8 mm Sau khi cha tao, mot so bang tir (Feo.8oCoo.2o)78Sii2Bioda dugc xir

ly nhiet bang each ii nhiet trong chan khong tai cac nhiet do 160 ^C, 250 ^C va 350

**C trong thoi gian 30 phut

PHAN B CAC PHlTcnSfG PHAP KHAO SAT CAC TINH CHAT

B.l Phiro'ng phap nhieu xa tia X

Gian do nhiau xa tia X dugc do tran may Siemens D5005 (Bruker AXS) sir dung birc xa CU-KQ voi buoc song A, = 1,5406 A Goc quet 20 nam trong khoang 10° den 120° voi dien ap sir dung 30 kV, dong dien 30 mA, toe do quet 0.05°/s cho mau bot Doi voi mau mang, thiat bi dugc sir dung la XRD Enraf-Notius CAD4 (Bruker AXS) voi dien ap 40 kV, dong 40 mA, t6c do quet 0.01°/s

B.2 Khao sat kich thu'ac hat va do phan bo

Kich thuoc trung binh cua cac hat bot cha tao dugc cung nhu su phan bo kich thuoc hat dugc khao sat bang thiet bi Mastersizer 2000 vai phan mam cung cap boi Malvern instruments

B.3 Hiln vi dien tu quet (SEM)

Cac anh SEM cua vat lieu dugc chup tren kinh hien vi dien quet JOEL-3000 co dien tha tir 20 ^ 35 kV, do phong dai tir 20 ^ 100.000 i k

B.4 Hien vi lu*c nguyen tu* (AFM)

Hinh thai hoc ba mat cua cac mang cha tao dugc nghien ciru sir dung hien vi lire nguyen tir AFM MultiMode (Vecco)

B.5 Ttf k§ m l u rung (VSM)

Cac ket qua do tinh chat tir ciia vat lieu Fe304 dugc thuc hien tren he tir ka mau rung Oxford (Oxford Instruments) Cac phep do dugc thuuc hien tai nhiet do phong trong dai tir truang len den 2.400 kA/m Momen tir cua cac mau dugc do theo hai phuang vuong goc va song song voi tir truong ngoai voi do chinh xac toi 1 pemu

B.6 Tir ke can Faraday

c a c phep do tir nhiet cua cac mang dugc tian hanh tran tir ke can Faraday tai nhiet do phong trong tir truang 0.05 T

B,7 Cac tinh chat dien

Dien dung tai nhiet do phong dugc khao sat nhu mot ham cua dien tha su dung

he do HP 4275A LCR va LCR 3550 (Tegam) voi tan s6 do dian hinh la 10 kHz Gia tri hang so dien moi dugc tinh tir gia tri dien dung tai viing dien truong thap

PHAN C KET QUA NGHIEN ClTU C.l He CoFe204 dang bot va khoi

a Cau true tinh the, cau true vi mo

Gian do nhiau xa tia X ciia mau bot CoFe204 sau khi che tao dugc trinh bay tran hinh 5 Tir gian do nhieu xa tia X co tha nhan thay trong viing nhiet dp nung nhiet

do tir 750 °C dan 950 °C cau tnic tinh tha thu dugc tuong ung voi cau tnic lap

phuong cua CoFe204 d viing nhiet do thap Hon, vi du 700 °C, nhirng dinh nhieu xa

voi cuong do yau ciia mot pha a-Fe203 xuat hien (dugc danh dau bang dau * tran hinh 6)

10 (111)

20

{220)

(311)

(440) (511) {400)

Hinh 6 Gian do nhieu xg cua CoFe204: mau bot nung tai cac nhiet do tit 700 T din 950

X^ vd cua dia det sou khi nung thieu ket

15

Hang so mang tinh tha ciia cac mau nau tren dugc tinh toan sir dung chuong trinh Rietveld refinement va trinh bay tran bang 1 Kat qua nay cung cho thay sir phii hgp ve hang so mang tinh tha neu so sanh voi cau tnic CoFe204 chuan

Bang 1 Hang so mang tinh tha a va kich thuoc hat CoFe204 sau khi nung

Kich thuac trung binh (|am) 2.1 3.7 5.2

Kich thuoc ciia cac hat CoFe204 sau khi nung say tai cac nhiet do khac nhau dugc khao sat tran thiat bi Mastersizer 2000 (Malvern instruments) Ket qua do dugc biau dian tran bang 1 cho thay cac hat co kich thuoc trung binh mot vai pm, khi tang nhiet do nung thi kich thuoc tang lan do sir Ion lan ciia cac hat

b Tinh chat tie

Duong cong tir tra cua CoFe204 dang mau bot sau khi nung tai cac nhiet dp khac nhau va mau dang dia sau khi thiau kat dugc do tran tir ke mau rung VSM Oxford tai nhiet do phong va dugc biau dien lai tren hinh 7

1 f

H (kA/m)

Hinh 7 Duang cong tie tre cua CoFe204: mau bot nung tai cdc nhiet do khac hau

vd ciia dia det sau khi nung thieu ket

Mot so ket qua chinh thu dugc tir cac phep do tir nay dugc tong ket tren bang

2, trong do dang chu y la:

- Tir do bao hoa Ion nhat Ms == 81.2 Am^/kg dugc quan sat thay tran mau nung tai nhiet do 850 °C

- Mau sau khi nung o 950 °C co lire khang tir Ion nhat la 120 kA/m (0.15 T)

Bang 2 Tinh chat tir cua mlu hot CoFe204 nung tai cac nhiet do khac nhau va cua

mau dia det sau thiau kat (M^: tir do bao hoa He', luc khang tir)

Nhiet do nung

850 °C

950 °C

1050 °C sintered

M,(Am'/kg) 81.2 79.3 77.7 80.4

He (kA/m)

109.4 120.5 75.2 25.0

Nhu vay cac hat bot CoFe204 da dugc cha tao thanh cong va co tha sir dung lam nguyen lieu da cha tao bia dang dia det Day la buoc chuan bi can thiat giup cho qua trinh cha tao mang mong tir giao CoFe204 noi rieng ciing nhu cha tao mang

da lop tir giao-ap dien noi chung dugc chii dong va linh boat

C.2 He vat lieu to hgp dang mang PZT/CoFe204

a Cau triic tinh the, can true vi mo

Kat qua do nhiau xa tia X ciia mot mang da lop PZT/CoFe204 dian hinh dugc trinh bay tran hinh 8 Chung ta thay rang cac dinh nhiau xa thu dugc dau thuoc ho (001) cua cac tinh the PZT va CoFe204 Kat qua nay cho thay rang mang to hgp cha tao dugc co dinh Huong uu tien theo phuong tinh the cua da SrTi03 Diau nay co tha dugc giai thich do su lech mang khong qua Ion giira CoFe204 va PZT so voi hang so mang tinh the cua da SrTiOs (cau tnic tinh the lap phuong voi a =- 3.905A )

17

DAI HOC QUOC GIA HA NQl^ TRUNG 1AM THONG TIN THU VtEN

CCC(.CCCCCS.>

i(001)PZT

'c

u -d

FTinh 8 Gian do nhieu xg tia X cua mang CoFe204 (280 nm)/PZT (lpm)/CoFe204 (280

nm)/PZT(ipm) (CFO: CoFe204, STO: SrTiOs)

Tiap theo, chung toi tian hanh nghien cuu hinh thai hoc ba mat cua cac mang

cha tao dugc sir dung ky thuat hien vi luc nguyen tir Lop mang tir giao dau tian

CoFe204 dau CO ba mat rat mln vdrdg nhap chi khoang 0,5 nm va moc theo dung

cac buoc (steps) cua Ti02 (xem hinh 9a) Tuy nhian sau khi tao tiap lop thir hai la

PZT thi ba mat tro nan tho Hon vai do rap vao khoang rms % 2,5 nm nhu trinh bay

tran hinh 9b cho mang CoFe204 (70 nm)/PZT (250 nm)/CoFe204 (70 nm) Su thay

doi nay la do sir hinh thanh cac hat PZT kat tinh a nhiet do quanh 600 °C

(a) (b) Hinh 9 Anh AFM cita mang dan CoFe204 (70 nm) vd mang da lap

CoFe204 (70 nm)/PZT (250 nm)/CoFe204 (70 nm)

b Tinh chat dien

Mot trong cac tinh chat dugc quan tam cua he mang da lop tir giao - ap dien do

la cac dac trung dien cua chiing do sir Han quan den kha nang ung dung trong cac linh kien dien tir Tren hinh 10 cho thay kat qua do sir phu thuoc cua dien dung vao dien tha (dien truong) ngoai C-V ciia mot mang da lop CoFe204 (280 nm)/PZT (lpm)/CoFe204 (280 nm) Duong cong co dang dac trung "butterfly'^ ciia cac vat lieu sat dien (ferroelectrics) Tir gia tri dien dung tai goc toa do chung ta co tha tinh dugc hang so dien moi cua vat lieu vao khoang 800, gan voi gia tri ciia PZT dang khoi Diau nay cho thay rang he mang cha tao co tinh chat dien kha tot

Ban canh do, chiing toi ciing quan tam dan dac trung dong-tha I-V cua he mang

da lop nay Cac kat qua khao sat cho thay gia tri ciia dong ro tren cac mang da lop

do dugc tai dien the 30 V va tan so 10 kHz la thap, vao khoang 10'"* A/cm^, dap ung dugc yeu cau sir dung trong cac linh kien dien tir

c Tinh chat tir

Ben canh cac tinh chat dien dugc khao sat cua he mang tir giao - ap dien thi mot tinh chat khac ciing dugc dac biet quan tam do la tir tinh ciia he vat lieu Tran hinh

11 trinh bay duong cong tir tra do tai nhiet do phong tren mang CoFe204 (280 nm)/PZT (l|im)/CoFe204 (280 nm) theo hai phuong song song va vuong goc voi mat mang Tir sir khac nhau giira hai duong cong nay, chiing ta c6 tha thay mang CoFe204/PZT CO di Huong tir trong mat phang kha Ion voi luc khang tir vao khoang

200 kA/m Nguon goc ciia di Huong tir nay co tha dugc giai thich tran co so sir xuat

hien ciia irng suat trong he mang, gay boi su khac nhau \t hang s6 mang tinh tha

19

giua lop CoFe204 thu nhat va da SrTi03 cung nhu sir khac nhau nay nhung giira cac

lop CoFe204 va lop PZT Nhu chung ta da Xhky 6 tran, "hang s6 mang tinh tha'^ ciia CoFe204 vao khoang 4.1 -^ 4,2 A la Ion Hon so voi cac gai tri tuong ung cua dt SrTi03 (a = 3.905 A) hoac Nb-SrTi03 (a = 3.91 A) va lop PZT (a = 4.036 A, c -

4.146 A) Vi vay khi cac lop tir giao nay hinh thanh va phat triln tao mang tren da hoac tren ba mat lop PZT thi nhin chung se chiu mot ung suat nen trong mat phang mang Mat khac vat lieu CoFe204 lai co tir giao am nan duoi tac dung ciia mot irng suat nen, mot di huong tir trong mat phang se dugc thiat lap, dan dan cac kat qua quan sat thay 6 tran

(/) -

nm va chiau day lop PZT duoi 1 pm thi khong quan sat thay su khac thuong nao Nhung voi cac he mang da lop du day thi kat qua thu dugc la rat ly thu (xem hinh

12) Nhu thong thuong chung ta quan sat thay tir do giam VQ gia tri bang khong o quanh nhiet do Curie tir TC{M) =^ 520^530 °C cua CoFe204 Ban canh do a truoc

nhiet do TC(M) tran duong cong tir nhiet xuat hien mot di thuong tai do gia tri tir do

tang lan, dat cue dai o nhiet do khoang T=^ 369 °C roi quay tro va xu huong truoc

do Nau so sanh thi chung ta thay gia tri nay rat gan voi nhiet do Curie dien ciia PZT

la TcrE) =^ 360-^390 °C Nhu da da cap dan trong bai bao va he vat lieu dang cac ong

xen ke CoFe204/BaTi03 dang tran tap chi Science [4] thi hien tugng nay co tha dugc xem nhu gay boi su tuong tac giua cac tinh chat tir giao va dien giao

Tai viing nhiet do duoi gia tri TQE), do sir khac nhau va hang so mang tinh tha so voi lop PZT cau true tu giac, lop CoFe204 se chiu tac dung cua mot irng suat nen

trong mat phang mang Doi voi viing nhiet do tran gia tri Tc(Eh chuyan pha dien

giao cua PZT ciing keo theo chuyen pha tir cau tnic tu giac sang cau true lap

phuong Trong chuyen pha cau tnic nay hang so mang theo true a ciia PZT se tang lan trong khi hang so mang theo true c thi giam di, nhu vay lop CoFe204 luc nay lai

chiu mot ling suat nen nho Hon truoc Chinh diau nay lam thay doi manh sir lech

mang giua cac lop PZT va CoFe204 quanh viing gia tri TC(E) va chung ta quan sat

thay tuong tac giua cac thong so trat tu cua hai pha tir giao va ap dien thong qua di thuong nau tren

Hinh 12 Suphu thuoc nhiet do cita tic do cita cita mang CoFe204 (280 nm)/PZT

(lpm)/CoFe204 (280 nm) do tai tie truang 0,05 T

Mot diam can nhan manh o day la cho dan nay, hieu irng nay moi chi quan sat thay tren cac vat lieu to hgp tir giao-ap dien dang cau true cot xen ke nhau ma chua tirng dugc quan sat tran cac vat lieu dang mang da lop tir giao-ap dien

C.3 He bang tir (Feo.8oCoo.2o)78Sii2Bio

Trong phan cuoi nay chiing toi muon da cap dan mot so kat qua nghian cuu ban dau tran he bang tir giao (Feo.8oCoo2o)78Sii2Bio Day la loai vat lieu co tinh tir mam Ion nan cac tinh chat tir se bao hoa trong mot tir truong nho hon nhiau so Terfenol-

D va do do CO tha irng dung trong he vi co dien tir

21

a Cau triic tinh the, cau true vi mo

Ket qua do nhiau xa tia X cua cac bang tir (Fe8oCo2o)78Sii2B|o, bao gom mau

chua u nhiet va cac mlu ii nhiet tai cac nhiet do Ta = 160 °C, 250 °C va 350 °C,

dugc trinh bay tren hinh 13 Chiing ta thay rang tren gian do nhieu xa thu dugc cua mau chua u nhiet khong xuat hien dinh nhiau xa nao, diau nay chung to sau khi che tao mau 6 trang thai v6 dinh hinh

Sau khi ii nhiet, mot dinh nhiau xa da xuat hien tai goc nhiau xa 20 = 52.4° Khi tang nhiet do ii mau, dinh nhiau xa tro nan sac net vai cuong do dugc tang cuong Nguyen nhan cua su xuat hien dinh nhieu xa nay la do su hinh thanh va Ion len cua hat tinh the (Fe, Co) trong qua trinh u nhiet

Pfinh 13 Gian do nhieu xg tia X cita bang tic Fe-Co-Si-B truac vd sau khi u nhiet

tai cdc nhiet do khac nhau

Mot so mau tieu biau nhu cac mau u nhiet tai nhiet do 250 °C da dugc khao

sat cau triic vi mo bang kinh hian vi phat xa truang FE-SEM Anh vi cau true cua cac mau nay dugc chup lai tran hinh 14 Chung ta co tha nhan thay rang voi mau sau khi ii nhiet 6 250 °C, cac hat tinh tha (Fe, Co) co kich thuoc trung binh la 10 nm

va phan bo deu tren toan bo be mat mau Cac kat qua nay la phii hgp voi cac kat qua nghien cuu ve cau tnic tinh tha sir dung nhiau xa tia X trinh bay o phan tran

Hinh 14 Anh FE-SEM cua bang tic Fe-Co-Si-B chua u nhiet (a)

vd sau khi u tai Ta ^ 250 X! (b)

b Tinh chat tie

Phep do duang cong tir tre dugc tian hanh tran tir ka mau rung VSM tai nhiet

do phong trong tir truang lan dan 1600 kA/m (2 T) theo hai phuang song song va vuong goc voi mat bang tir Tir phep do nay chiing ta thu dugc cac kat qua sau:

- Nhin chung doi voi cac mau (Fe8oCo2o)78Sii2Bio chua u va sau khi ii nhiet, phuong song song voi mat bang tir la phuang da tir hoa nen tir do ciia cac mau bao hoa trong mot tir truang kha nho, co 40 kA/m (0.05 T) (xem hinh 3.4a~^d) Tuy nhian khi do theo phuong vuong goc voi mat phang mlu (phuang kh6 tir hoa) chung ta can mot tir truang Ion dan 2 T de tir do bao hoa

- Dang va do Ion cua cac duong cong tir tra do theo phuang song song hoac vuong goc vai mat bang ciia cac mau khong khac nhau nhiau Tir duong cong tir tre do trong mat phang mau chiing ta tinh dugc gia tri cua tir do bao hoa cua cac mau vao khoang 175 emu/g, con lire khang tir co do Ion co 1 kA/m (10 Oe) dac trung cho tinh chat tir mam ciia vat lieu

23

KET LUAN CHUNG

Cac kat qua chinh thu dugc trong da tai gom co:

- Nghien cim xay dung quy trinh cong nghe cha tao vat lieu to hgp dang mang

da lop tir giao - ap dien (multiferroics) CoFe204/PZT sir dung phuang phap boc bay bang xung laser, anh huong ciia cac dieu kien che tao lan cac tinh chat dien va tir cua mang CoFe204/PZT

- Lan dau tien quan sat thay di thuong va tir do tran duong cong tir nhiet tren

he mang da lop Thong qua cac khao sat nay da tim hiau va hieu irng tir dien va giai thich hien tugng tran co so tuong tac trao doi giira cac thong so trat tu cua cac pha tir giao va ap dien

Nghian ciru mot so tinh chat ban dau cua bang tir giao (Fe8oCo2o)78Sii2Bio, lam CO so cho cac nghian ciru tiap theo tran cac vat lieu to hgp dang mang tir giao - ap dien

6.4 Dia diem, thai gian va phacng phap nghien ciru (ghi ro ten, ky ma hieu, ma so

quan ly cua phuong tien nghien cim nhu: cac trang thiet bj, he thong thiet bi, chuong trinh,

he thong phan mem da sir dung trong khi thuc hien de tai, dac biet la nhirng phuong tien dugc dau tu tai don vi qua cac du an)

Cac nghian ciru dugc thuc hien tai truong Dai hoc Cong nghe, cac truong Dai hoc va vien nghien ciru hgp tac trong va ngoai nuoc:

a Trirang Dai hoc Cong nghe va tru-crng Dai hoc Khoa hoc ty nhien (DHQGHN):

- Nghian ciru cha tao vat lieu CoFe204 dang bot da lam bia cha tao mang mong: he tao mau tu cha tao dung phuang phap complexometric

- Nghian cuu cac cau tnic tinh tha va vi cau tnic cua bot va vat lieu bia cha tao dugc: Siemens D5005 (Bruker AXS), Mastersizer 2000 (Malvern instrument)

- Nghian ciru mot so tinh chat dien cua mang cha tao dugc: he do LCR 3550 (Tegam)

b Tryong Dai hoc tong hgp Twente (Ha Lan):

- Nghien ciru vi cau triic cua bia cha tao dugc: SEM JEOL-3000

- Nghian ciru cha tao mang tir giao va dien giao; thiat bi cha tao mang dua tran cong nghe xung laser PLD General (TST B.V.)

- Nghien cuu cac cau tnic tinh tha, vi cau tnic cua cac mang: XRD Notius CAD4 (Bruker AXS), AFM MuUiMode (Vecco)

Enraf Nghien cuu mot so tinh chat tir cua vat lieu: VSM Oxford (Oxford Instruments)

d Trircrng Dai hoc tong hgp Amsterdam (Ha Lan):

Nghien cuu mot so tinh chat tir nhiet ciia mang che tao dugc: he do tir nhiet

tu che tao dua tran nguyan ly can Faraday

6.5 Ket qua nghien ciru (gom cac phan)

6.5.1 Cac cong bo lien quan den ket qua cua de tai (chi chap nhan cdc bao

coo, bai bao hoac cdc tai Hieu chuyen khao cong bo tren cdc on pham khoa hoc cong nghe co ghi ro thuc hien trong khuon kho cua de tai vd mot phan duac tai tra tie de tai)

- P.D Thang, M.T.N Pham, G Rijnders, D.H.A Blank, N.H Due, J.C.P

Klaasse and E Briick, Multiferroic CoFe O -Pb(Zr,Ti)0 nanostructure, J

Korean Phys Soc 52 (2008) 1406

- P.D Thang, D.T Huong Giang, B.C Tinh, T.M Danh, N.H Tuan and

N.H Due, Magnetoelastic properties of nanostructured ribbons FeCoSiB

using for high-sensitive stress sensors, Phys Stat Sol (c) 4 (2007) 4585

- P.D Thang, N.H Tuan, D.T.H Giang, T.M Danh va N.H Dire, Nghien

cieu che tao sensa do ung sudt dua tren bang tir can triic nano Fe-Co-Si-B,

Tuyan tap Hoi nghi Vat ly Chat ran toan qu6c lan thir 5, 12-14/11/2007, Viing Tau, Viet Nam, trang 887

6.5.2 Ket qua dao tao cua De tai (Giai thieu danh muc va noi dung chinh cac

luan van ThS (LV), cac khoa luan (KL) cua SV da hoan thanh trong qua trinh thuc hien de tai, cac LV, KL nay trong lai noi dau can ghi ro la da dugc hoan thanh hoac mot phan dugc hoan thanh trong khuon kho de tai Ma so QC.07.08)

Ten KLTN: Nghien ciru mot so tinh chat ciia bang tir Fe-Co-Si-B

Sinh vien: Pham Thanh Tiing

Khoa: QH-2003-I/CQ-V Chuyen nganh: Vat ly ky thuat

Tom tat noi dung: Khoa luan tot nghiep nay trinh bay cac ket qua nghien cim va cac

tinh chat ciia bang tir dua tren hgp kim (Feo.8oCoo2o)78Sii2Bio Trong khoa luan,

25

chiing toi da khao sat cin tnic tinh the va cau tnic vi mo cua bang tir sau khi che tao

va sau khi xu ly nhiet 6 nhiet dp T^ < 350°C bang cac phep do nhieu xa tia X va

chup anh FE-SEM Kat qua do duong cong tir tre tren cac mau cho thay phuong tir hoa de nim trong mat phang mau Gia tri tir do bao hoa va lire khang tir cua cac mau vao khoang 175 emu/g va 10-^15 Oe Cac nghian cuu ve hieu img tir giao ngugc tren cac bang tir dua tran hgp kim (Fe8oCo2o)78Si|2Bio chi ra rang senso sir dung mau dugc xir ly nhiet 6 250 °C c6 do nhay cao nhat la 4.2 mV/MPa Ket qua nay mo ra mot huong moi ve img dung vat lieu bang tir (Fe8oCo2o)78Sii2Bio nhu cac senso do img suat c6 do nhay cao

6.5.3 Ket qua irng dung cua De tai (neu co, neu ro kha nang trien khai rong rai, hieu

qua cua viec irng dung ket qua ciia de tai)

6.6 Thao luan (tiiy theo mire do va quy mo cua de tai, bao cao de tai can thao luan danh

gia ve cac ket qua da dat dugc ciia de tai: lam ro nhung noi dung, nhung diem moi trong phuong phap nghien cim, so sanh voi cac ket qua cua cac nghien cim truoc do hoac tinh doc dao (originality) cua ket qua de tai)

- Nhom tac gia tham gia thuc hien d& tai da nghian ciru xay dung quy trinh

cong nghe cha tao vat lieu to hgp dang mang da lop tir giao - ap dien (multiferroics) CoFe204/PZT sir dung phuong phap boc bay bang xung laser Trong xu Huong nghian ciru ve cac vat lieu moi chuc nang hien nay, viec lam chu cong nghe cha tao nay la rat can thiet da co tha chii dong trien khai cha tao vat lieu va thir nghiem cac kha nang irng dung tai Viet Nam

- Lan dau tian da quan sat thay di thuong va tir do tran duong cong tir nhiet tran he mang da lop tir giao - ap dien Thong qua cac khao sat nay da tim hiau ve hieu irng tir - dien va giai thich hien tugng tran co so tuong tac trao doi giira cac thong so trat tu ciia cac pha tir giao va ap dien Ket qua nghian ciru da dugc xuat ban tran tap chi chuyan nganh quoc te

6.7 Ket luan va kien nghj

v a CO ban nhom tac gia thuc hien da tai da hoan thanh cac nhiem vu dugc giao, thanh quyat toan va tai chinh theo dung cac quy dinh cua Nha nuoc

6.8 Tai lieu tham khao (phin nay viet theo qui dinh cua Tap chi KH - DHQGHN)

Tai lieu tieng nuoc ngoai

[1] T.H O'Dell, Electronics and Power 11 (1965) 266

[2] J Van Suchetelene, Philips Research Report 27 (1972) 28

[3] K Uchino, in Comprehensive Composite Materials: Piezoelectric Composites,

Elsevier, Amsterdam, 2000; va cac tai lieu trich dan

[4] H Zheng, J Wang, S.E Lofland, Z Ma, L Mohaddes-Ardabili, T Zhao, L Salamanca-Riba, S.R Shinde, S.B Ogale, F Bai, D Viehland, Y Jia, D.G Schlom, M Wuttig, A Roytburd and R Ramesh, Science 303 (2004) 661

[5] P.D Thang, G Rijnders and D.H.A Blank, J Magn Magn Mater 295 (2005) 251 [6] N.H Due and D.T Huong Giang, J Alloys Compd 449 (2008) 214

[7] G Koster, B.L Kropman, G.J.H.M Rijnders, D.H.A Blank and H Rogalla, Appl Phys Lett 73 (1998), 2920

27

7 Phu luc:

Cac phu luc chuyen mon lien quan dan noi dung da tai (trinh bay theo thu tu 1,

2, 3 ) bao gom:

1 Cac so lieu goc, hinh anh minh hoa, bao cao ciia cac dQ tai nhanh v v

2 Ban sao cac bai bao, bao cao khoa hoc da cong bo; Ban sao trang bia va trang loi cam on cua LV, KL tot nghiep ciia HVCH va SV Han quan dan de tai

3 Ban sao Hgp dong thuc hien da tai nghian cuu da dugc phe duyet va cac phieu Phe duyet cac thay doi (neu co)

4 Bao cao tom tat kat qua nghian ciru ciia da tai bang tiang Anh va tiang Viet

5 Phiau dang ky ket qua nghian ciru KHCN

.Journal of t h e Korean Physical Society, Vol 52 No 5 May 2008 pp 1406-1409

Multiferroic CoFe204-Pb(Zr,Ti)03 Nanostructures

Faculty of Chemistry College of Natural Science Vietnam National University,

10 Le Thanh Tong, Hoan Kiem, Hanoi, Vietnam

(Received 15 July 2007 in final form 25 \ugust 2007)

Multiferroic C o F e ) 0 ^ - P b ( Z r T i ) O j films were prepaied on T i O j - t e r m i n a t e d (001) Nb-doped SrTiO.i substrates by using pulsed laser deposition (PLD) T h e films were epitaxial and exhibited

a large in-plane magnetic anisotropy and good ferroelectric properties A decrease in t h e

magneti-zation around rhe ferroelectric Curie temperature indicated magnetoelectric coupling between the

magnetostrictive and the piezoelectric phases, which allows interconversion of energy stored in the

electric and t h e magnetic fields and provides great potential for applications as next-generation

nmltr-functional devices

FAGS numbers: 72.80.Tm, 74.25.Ha, 75.80.-^q, 77.65.-j

Keywords: Multiferroics, Magnetic anisotropy, Magnetostriction, Piezoclectrics

1 I N T R O D U C T I O N t h e i r wide a p p l i c a t i o n s in t h e fields of t r a n s d u c e r s ,

sen-sors a n d d a t a s t o r a g e [1-3]

A few single-pha.se multifferoics, s u c h as C r ^ O a a n d Multiferroics a r e single-pha.se or c o m p o s i t e m a t e r i a l s BiFeOa c a n b e used only a t low t e m p e r a t u r e d u e t o t h e i r

t h a t can possess a s p o n t a n e o u s d i e l e c t r i c p o l a r i z a t i o n a s low Neel or C u r i e t e m p e r a t u r e [4-6] B y c o m b i n i n g

sepaa r e s p o n s e t o sepaa n sepaai>plied m sepaa g n e t i c field or sepaa m sepaa g n e t i z sepaa l sepaa t e f e r r o m sepaa g n e t i c sepaa n d ferroelectric p h sepaa s e s , t h e c o m p o s tion i n d u c e d by a n e x t e r n a l electric field Such m a t e r i a l s ite offers m o r e possibilities in a p p l i c a t i o n s t h a n k s t o its have a t t r a c t e d significant a t t e n t i o n b e c a u s e of not only m u l t i f u n c t i o n a l i t y [ 1 , 2 , 7 , 8 ] R e c e n t l y , t h e r e h a s b e e n

-t h e i r i n -t e r e s -t i n g m a g n e -t o - e l e c -t r i c a l p r o p e r -t i e s b u -t also ^ revival of m u l -t i f e r r o i c c o m p o s i -t e s [ 3 , 9 11] A m o n g

._, t h e m , m a g n e t o s t r i c t i v e m a t e r i a l s , foi e x a m p l e C'nrrespr)iidint> Aiitlior: pdthiiiigt!i\'nu.edu.\ii; D a n d ferrites a n d p i e z o e l e c t n c s , for e x a m p l e B a T i O ^

Terfenol-Tel: +84-.1 75-t'y:i:j-2')66.'S; Fax- +84-4 754 74<iU; ^^^ P b ( Z r , T i ) 0 3 ( P Z T ) a r e p a r t i c u l a r l y i n t e r e s t i n g d u e

Vietnam Niitionai University, College of Technology, Faculty ol En t o t h e i r large m a g n e t o s t r i c t i o n , high p i e z o e l e c t r i c p r o p ginecring Physics and Nanoteclinology, DepartinenL of Nano Mag- e r t i e s a n d h i g h C u r i e t e m p e r a t u r e In t h e s e multifer-

-notir Materials and Devices, Building E3 144 Xuan Thuy Cau j-^j^g^ ^^.^^^ ^^^ m a g n c t O S t r i c t i v e p a r t s a r e d e f o r m e d

UU-Gia\ Hanoi, Vietnam