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"The effect of Fe substitutions on
the microstructure of Gd5Si2Ge2"
2007 MRS Fall Meeting November 26 - 30, 2007,Boston
Benjamin Podmiljak1, Paul McGuiness1, Spomenka Kobe1, Irena kulj21Josef Stefan Institute, Ljubljana, Slovenia
2Institute of metals and technology, Ljubljana, 1000, Slovenia
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S
N
Magnetocaloric effect Magnetocaloric effect (MCE) is defined as the heating or cooling of a
magnetic material due to the application of a magnetic field.
magnetocaloric
Apply magnetic fieldSpins alignSm, Sl
Temperature increases
Remove magnetic fieldSpins ramdomize
Sm, Sl Temperature decreases
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Gd5Si2Ge2
36 atoms per unit cell,
which arrange in slabs
The bonding arrangements between slabs have a greateffect on the properties of the material
Giant MCE magnetic and structual transformation
Orthorhombic() < 276 K < Monoclinic structure()
T
H
2007 MRS Fall Meeting November 26 - 30, 2007,Boston
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Sample preparation
Ar
Ge99,9999%
Si99,9995%
Gd
99,95%
cooling
Power
supply
+
_
Power
supply
+
_
Fe99,98%
3-5 g buttonsI = 80 A, 6x remelted
heattreatment1300 Cfor 1hin Ar
2007 MRS Fall Meeting November 26 - 30, 2007,Boston
Arc-melting
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Gd5(Si1-xFex)2Ge2
1. XRD
2007 MRS Fall Meeting November 26 - 30, 2007,Boston
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
2 ()
Intensity
(/)
Fe=0
Fe=1
Fe=0.75
Fe=0.5
Fe=0.25
Fe=0.125
5:2:2
5:3
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Gd5(Si1-xFex)2Ge2
2. Optical
X=0 X=0,25 X=0,5
X=0,75 X=1
2007 MRS Fall Meeting November 26 - 30, 2007,Boston
1 cm
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Gd5(Si1-xFex)2Ge2
3. SEM
2007 MRS Fall Meeting November 26 - 30, 2007,Boston
X=0
X=0.5
X=0.75
X=0.125X=0.25X=0.5X=0.75X=1
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Gd5(Si1-xFex)2Ge2
3. SEM
2007 MRS Fall Meeting November 26 - 30, 2007,Boston
X=0 X=0.125 X=0.25
X=0.5 X=0.75 X=1
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0
2
4
6
8
10
200 250 300
Temperature (K)
S
(J/kgK)
0.125
0.25
0.5
Gd
Gd5(Si1-xFex)2Ge2
4. Magnetic measurements: CurieT and Sm
2007 MRS Fall Meeting November 26 - 30, 2007,Boston
0
100
200
300
0 0.25 0.5 0.75 1X (amount of iron)
Temperature(K)
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0
20
40
60
80
100
0 4000 8000 12000 16000
Field (G)
Moment/Mass(emu/g)
270K
275K
280K
285K
290K
295K
300K
305K
310K
X=0
0
20
40
60
80
100
120
0 4000 8000 12000 16000
Field (G)
Moment/Mass(emu/g)
240K
245K
250K
255K
260K
265K
270K
275K
280K
Gd5(Si1-xFex)2Ge2
4. Magnetic measurements: hysteresis losses
2007 MRS Fall Meeting November 26 - 30, 2007,Boston
X=0.125
0
20
40
60
80
100
0 4000 8000 12000 16000
Field (G)
M
oment/Mass(emu/g)
270K
275K
280K
285K
290K
295K300K
305K
310K
X=0
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Conclusions
Fe substitutions
The addition of iron influences the macro and microstructure of the material. The crystal structure changes from the 5:2:2 to the 5:3 structure.
No hystereisis losses can be seen after the addition of iron.
2007 MRS Fall Meeting November 26 - 30, 2007,Boston