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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