Temperature dependence of the entropy variation DSMwas calculated from the isothermal magnetization.. Introduction The temperature change of a magnetic material, associated with an exter
Trang 1Journal of Magnetism and Magnetic Materials 300 (2006) e385–e387
The substitution effect of Cr about large magnetocaloric effect in
amorphous Fe–Si–B–Nb–Au ribbons S.G Mina, L.G Ligayb, K.S Kima,c, S.C Yua, , N.D Thod, N Chaud
a Department of Physics, Chungbuk Nat’l University, Cheongju, 361-763 Korea
b Department of Physics, Nat’l University, of Uzbekistan, Tashkent 700-174 Uzbekistan
c
Basic Science Research Institute, Chungbuk Nat’l University, Cheongju, 361-763, Korea
d
Center for Materials Science, Department of Physics, Hanoi University of Science, 334 Nguyen Trai, Hanoi, Vietnam
Available online 16 November 2005
Abstract
The magnetization behaviors have been analyzed for amorphous Fe73.5xCrxSi13.5B9Nb3Au1(x ¼ 0, 3, 5) alloys An amorphous phase was formed after quenching by melt spinning with a copper wheel surface speed of 30 m/s The structure analysis of as-cast was performed using X-ray diffractometer The magnetic properties of the ribbons were measured by VSM The Curie temperature is decreased from 629 to 491 K with increasing Cr concentration (x ¼ 025) Temperature dependence of the entropy variation DSMwas calculated from the isothermal magnetization The maximum of DSMwas found to appear in the vicinity of the Curie temperature of the amorphous phase The DSMvalue is 1.7, 1.13 and 0.94 J/kg K at x ¼ 0, 3, and 5, respectively
r2005 Published by Elsevier B.V
Keywords: Magnetocaloric effect; Isothermal magnetization; Amorphous ribbon
1 Introduction
The temperature change of a magnetic material,
associated with an external magnetic field change in an
adiabatic process, is defined as the magnetocaloric effect
(MCE) The thermal effect was discovered in 1881 by
Warburg when he applied varying magnetic field to metal
later and suggested achieving an ultralow temperature by
later and suggested achieving an ultralow temperature by
to magnetic solids and is induced via the coupling of the
magnetic sublattice with the magnetic field, which alters the
magnetic part of the total entropy due to a corresponding
change in the magnetic field It can be measured and/or
[4–6] The MCE is a function of both temperature T and the
magnetic field change DH and is usually recorded as a function of temperature at a constant DH
Recently, a search for new magnetic materials, which exhibit a significant change in the magnetic entropy in response to the change of magnetic field under isothermal conditions, has become an important task in applied physics Traditionally, diluted paramagnetic slats and rare earth intermetallic compounds that display significant MCE were considered as attractive materials for cryogenic
Fe73.5xCrxSi13.5B9Nb3Au1(x ¼ 0, 3, 5) compounds were investigated These kind of amorphous materials have many useful properties that are attractive for application as magnetic refrigerants
2 Experiments
(x ¼ 0, 3, 5) alloys have been prepared by rapid quenching technology on a single copper wheel The linear speed of the copper wheel was 30 m/s The ribbon had the width of
7 mm and the thickness of 16.8 mm The structure analysis
www.elsevier.com/locate/jmmm
0304-8853/$ - see front matter r 2005 Published by Elsevier B.V.
doi:10.1016/j.jmmm.2005.10.125
Corresponding author Tel.: +82 43 261 2269; fax: +82 43 265 6416.
E-mail address: scyu@chungbuk.ac.kr (S.C Yu).
Trang 2of ribbons was performed using X-ray diffractometer
Bruker 5005 using Cu-Ka radiation The thermal transition
was examined by SDT 2960 TA Instrument The magnetic
properties of the ribbon were measured by VSM
According to thermodynamic theory, the magnetic
entropy change caused by the variation of the external
0
qS qM
T
From Maxwell’s thermodynamic relationship:
qM
qT
H
qH
T
Eq (1) can be rewritten as follows:
0
qM qT
H
Numerical evaluation of the magnetic entropy change
was carried out from formula (3) using isothermal
magnetization measurements at small discrete field and
approxi-mately from Eq (3) by
i
Thus, the magnetic entropy changes associated with
applied field variations can be calculated from Eq (4)
3 Results and discussion
It is known that the favorable soft magnetic properties of
Fe-based nanocrystalline alloys come from extremely small
magnetic anisotropy and magnetostriction due to small
grain size For this purpose, much work has been done on
the Fe-based amorphous alloys by annealing process for
very good soft magnetic properties Among the
nanocrys-talline materials, conventional Fe–Nb–Cu–Si–B type
(FI-NEMET) alloys were reported to exhibit excellent soft
magnetic properties with a high saturation magnetization
substitution of Cr and Au in the FINEMET systems
improved coercive force and core loss at high frequency
devitrification process of the studied alloy is analogous to
that of the usual amorphous Fe–Cr–Si–B–Nb–Au type
materials In order to gain further insight into the MCE of
carried out magnetization studies
It takes place in two main stages, as evidenced by the two
well-resolved exothermal peaks in the DSC curve The first
exotherm corresponds to the appearance of the (Fe,Si)
crystals which remain embedded in the remaining
amor-phous matrix The second crystallization process is related
to the formation of boride-type phases and
The influence of the presence of Cr on the devitrification process is an enhancement of the stability of the alloy against crystallization, as observed in the increase of 40 K
in the peak temperature of the first exothermal maximum
was found to be 629, 545 and 491 K for x ¼ 0, 3 and 5 of
Fe73.5xCrxSi13.5B9Nb3Au1, respectively With an increase
system, the Curie temperature decreases According to
thermal stability is enhanced and Curie temperature is reduced, due to the reduce in coupling between the nanocrystals in amorphous matrix
Isothermal M2H curves have been measured at various temperatures in the vicinity of Curie temperature (see the
According to the Banerjee criterion, the negative slope in
temperature region 626–668 K are clearly seen in the lower
the materials displaying a first-order transition
In evaluating the magnetocaloric properties of the
Fe73.5xCrxSi13.5B9Nb3Au1 (x ¼ 0, 3, 5) samples, the magnetic entropy change, a function of temperature, and magnetic field, produced by the variation of the magnetic
Fig 3, with a magnetic field varying from 0 to 1.5 T, the
0 10 20 30 40 50 60 70
Temperature (K)
Fe73.5-xCrxSi13.5B9Nb3Au1 x=0
x=3 x=5
Hdc= 50 Oe
Fig 1 Temperature dependence of the magnetization measured at 50 Oe for Fe Cr Si B Nb Au (x ¼ 0, 3, 5).
Trang 31.13, 0.94 J/kg K for x ¼ 3, 5 at 545 and 491 K (the Curie
temperature), respectively
4 Conclusion
The magnetic properties and entropy changes of
Fe73.5xCrxSi13.5B9Nb3Au1(x ¼ 0, 3, 5) amorphous alloys
were investigated The Curie temperature and the
max-imum value entropy change decreases with increasing Cr
concentration, and the peaks of entropy change appear at
the Curie temperature region The maximum value of
entropy change decreases with increasing Cr concentration
Our results show that these amorphous samples are useful
for application as magnetic refrigerants
Acknowledgement This work was supported by Korea science and Engineering Foundation through the Research Center for Advanced Magnetic Materials at Chungnam National University
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0 2000 4000 6000 8000 10000 12000 14000 16000
0
20
40
60
80
Magnetic Field (Oe)
574 584 594 602 608 614 620 626 632 638 648 658 668
0 1000 2000 3000 4000 5000 6000
0
200
400
600
800
1000
1200
1400
Fe73.5-xCrxSi13.5B9Nb3Au1 x=0
M2 (emg/g)2
574 584 594 602 608 614 620 626
1 632
A 635
a 638 643 653 663
Fig 2 Top panel: Isothermal magnetization curves in the vicinity of Curie
temperature for Fe 73.5 Si 13.5 B 9 Nb 3 Au 1 Bottom panel: The H=M vs M 2
plots for the isotherms of Fe 73.5 Si 13.5 B 9 Nb 3 Au 1
440 460 480 500 520 540 560 580 600 620 640 660 680 0.2
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
SM
Temperature (K)
Fe73.5-xCrxSi13.5B9Nb3Au1 x=0
x=3 x=5
∆ H =1.5T
Fig 3 Temperature dependence magnetic entropy obtained under a field change from 0 to 1.5 T, for x ¼ 0, 3, 5 of Fe 73.5x Cr x Si 13.5 B 9 Nb 3 Au 1
(x ¼ 0, 3, 5).