Journal of Magnetism and Magnetic Materials 304 2006 e179–e181Ultrasoft magnetic properties in nanocrystalline alloy Finemet with Au substituted for Cu N.. The DSC curves show the first p
Trang 1Journal of Magnetism and Magnetic Materials 304 (2006) e179–e181
Ultrasoft magnetic properties in nanocrystalline alloy
Finemet with Au substituted for Cu
N Chau , N.Q Hoa, N.D The, P.Q Niem Center for Materials Science, College of Science, Vietnam National University, Hanoi, 334 Nguyen Trai, Hanoi, Vietnam
Available online 6 March 2006
Abstract
The amorphous ribbon Fe73.5Si13.5B9Nb3Au1has been prepared by rapid cooling on a copper wheel The ribbon is 16.8 mm thick and
7 mm wide The DSC curves show the first peak at 547–579 1C (corresponds to the crystallization of a-Fe(Si) phase) depending on heating rate from 10 to 50 1C/min which is a little higher than that of pure Finemet (542–570 1C, respectively) From the Kissinger plot, the crystallization activation energy is determined and shown to be 2.8 eV for a-Fe(Si) phase, less than that of Finemet (E ¼ 3:25 eV) By annealing at 530 1C for 30, 60 and 90 min, the crystallization volume fraction of a-Fe(Si) phase increased from 73% to 78% and 84%, respectively After appropriate annealing, the ultrasoft magnetic properties are achieved The maximum magnetic entropy change, jDSmjmax, showed a giant value of 7.8 J/kg K which occurred at around Curie temperature of amorphous phase of the ribbon
r2006 Published by Elsevier B.V
PACS: 75.50.Tt; 75.30.Sg; 71.55.Jv; 73.63.Bd
Keywords: Nanocrystalline alloy; Soft magnetic amorphous system; Nanoparticle; Magnetocaloric effect
Excellent soft magnetic properties of nanocrystalline
It was shown that Cu and Nb play a very important role to
produce the nanocrystalline structure A small amount of
Cu facilitates to form a-Fe(Si) phase as crystallization
nucleation but Nb with high melting temperature is
ascribed to hinder the grain growth
In the previous work, we have studied the crystallization
present our study on the influence of Au substituted for Cu
in Finemet on the crystallization and properties of alloy
This alloy has been fabricated by rapid quenching
technology on a single copper wheel The ribbon is
16.8 mm thick (observed by SEM) and 7 mm wide The
X-ray diffraction (XRD) analysis showed that the as-cast
ribbon is amorphous
The DSC measurements on as-cast samples were performed with different heating rates from 10 to 50 1C/
corresponds to the crystallization of a-Fe(Si) phase and the second one relates to the forming of boride phase From the Kissinger’s linear dependence, the crystallization
a-Fe(Si) phase is a little higher than that of pure
Finemet, Cu forms the cluster prior to the primary crystallization reaction of a-Fe(Si) phase and Cu-enriched
that the role of Au in studied sample is similar to that
of Cu on the crystallization in Finemet but with high diffusion coefficient, Au facilitating the crystallization
The crystallization feature of the studied ribbon could
be observed by measurement of thermomagnetic curves
www.elsevier.com/locate/jmmm
0304-8853/$ - see front matter r 2006 Published by Elsevier B.V.
doi:10.1016/j.jmmm.2006.01.225
Corresponding author Tel.: +84 4 5582216; fax: +84 4 8589496.
E-mail address: chau@cms.edu.vn (N Chau).
Trang 2(Fig 2) It can see fromFig 2that the Curie temperature
also there is a single phase structure in the M(T) curve
measured along cooling cycle whereas in the case of Ag and
Zn substituted for Cu in Finemet, the multiphase structure
clearly seen that after annealing, the crystallization of
a-Fe(Si) phase occurred Using Scherrer expression, the
grain size of a-Fe(Si) nanocrystallites is determined and
shown to be in range of 10.8–11.6 nm for above keeping
time which is less than ferromagnetic exchange interaction length in Finemet (35 nm)
Based on DSC measurements, and Leu and Chin
fraction of the a-Fe(Si) phase to be 73%, 78% and 84%, respectively, for the above annealing conditions
Fig 4shows the hysteresis loops of as-cast and annealed
Obviously, different from pure Finemet, here hysteresis loop of as-cast sample has quite high rectangular coeffi-cient of more than 90% by pinning of domain wall
mechanical strain of Au atoms locating at grain bound-aries The magnetic parameters of as-cast and annealed
50 °C/min
40 °C/min
30 °C/min
20 °C/min
10 °C/min
714 °C
710 °C
705 °C
698 °C
687 °C
568 °C
579 °C
574 °C
559 °C
547 °C
T( °C)
Fig 1 DSC curves of as-cast ribbons Fe 73.5 Si 13.5 B 9 Nb 3 Au 1 measured
with heating rate from 10 to 50 1C/min.
0
20
40
60
80
100
120
(2) (1)
H = 50 Oe
T ( °C)
Fig 2 Thermomagnetic curves of as-cast ribbon (1): heating cycle, (2):
cooling cycle.
0 20 40
60
α-Fe(Si)
2 Theta (deg.)
Fig 3 X-ray diffraction pattern of annealed ribbon: T a ¼ 530 1C for
90 min.
-12 -8 -4 0 4 8 12
2.5 2.0 1.5 1.0 0.5 0.0 0.3 0.6 0.9
as-cast
H (Oe)
H (Oe)
as-cast annealed
Fig 4 Hysteresis loops of as-cast and annealed samples (at 530 1C for
30 min).
Trang 3ribbons are collected inTable 1 After annealing, ultrasoft
From a series of isothermal magnetization curves
measured at different temperatures, giant magnetocaloric
effect (GMCE) was firstly discovered by us for amorphous
studied sample has been determined depending on the
7.8 J/kg K This value belongs to GMCE We note that this GMCE has reached at quite low magnetic field variation of 13.5 kOe
In conclusion, the magnetic ribbon with Cu fully substituted by Au in Finemet is prepared with amorphous structure The ribbon exhibits higher plasticity, higher solidity and more easy to bend in comparison with those of Finemet The appropriate annealing leads to nanocompo-site state in the sample with ultrasoft magnetic properties
T ¼ 342 1C has been discovered The studied sample could
be considered as a good magnetic refrigerant material working at high temperature
The authors would like to thank Vietnam National Fundamental Research Program for financial support (Project 811204)
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[6] K Hono, D.H Ping, M Ohnuma, H Onodera, Acta Mater 47 (1999) 997.
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[8] M.S Leu, T.S Chin, MRS Symposium Proceedings 577 (1999) 557 [9] N Chau, N.D The, C.X Huu, in: Proceedings of the Second International Workshop on Nanophysics and Nanotechnology (IWONN’04), Hanoi, Vietnam, October 22–23, 2004, p 51.
Table 1
The magnetic characteristics of studied samples (as-cast sample and
samples annealed at 530 1C for different time)
m i m max H c (Oe) M s (emu/g)
0
3
6
9
7.8 J/kgK
Sm
T ( °C)
Fig 5 Magnetic entropy change jDS m j of the studied sample versus
temperature.