three-dimensional magnetization process in hofe 11 ti
DESCRIPTION
Three-dimensional magnetization process in HoFe 11 Ti. Yuri Janssen, J.C.P. Klaasse, E. Br ü ck, F.R. de Boer, K.H.J. Buschow, J. Kamar á d 1 , N.V. Kudrevatykh 2. I. M. II. B. 1: Institute of Physics, Praha 2: Institute of Physics and Applied Mathematics, Ekaterinburg. Outline - PowerPoint PPT PresentationTRANSCRIPT
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Three-dimensional magnetization process in HoFe11Ti
Yuri Janssen, J.C.P. Klaasse, E. Brück, F.R. de Boer, K.H.J. Buschow,J. Kamarád1, N.V. Kudrevatykh2
1: Institute of Physics, Praha2: Institute of Physics and Applied Mathematics, Ekaterinburg
B
MI
II
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Outline
- Introduction- Experiment- Results- Conclusion
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Research of rare-earth (R) – transition-metal (T) compounds
Modern permanent magnets: - SmCo5 (1960s) - Nd2Fe14B (1984) - RFe11Ti (1990s)
Requirements: - large magnetization- high ordering temperature- high coercivity
large magnetocrystalline anistropy
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Magnetic R-T coupling essential for coupling between:
- large magnetization (T) - high anisotropy (R)
Hund’s rules ==>
Light-R (Nd, Sm) – T : parallel coupling => ferromagnets
Heavy-R (Gd, ..Ho, Tm) – T : antiparallel coupling => ferrimagnetsMTMR
M
M
MTMR
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HoFe11Ti
Tetragonal crystal structure: ThMn12-type (s.g. I4/mmm)Ti stabilizes crystal structure
[001]
[100] [010]
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HoFe11Ti: R-T coupling strong!
Ho and Fe sublattice moments remain antiparallel
B
[001][001]
MFe = 20 B/f.u.
MHo = 10 B/f.u.
M = 10 B/f.u.
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Strong coupling HoFe11Ti excellent system for research on magnetocrystalline anisotropy
Eanisotropy = K1sin2 + K2 sin4 + K3 sin6 + K4 sin4cos4 + K5sin6cos4
Tetragonal structure
[100]
[010]
[001]
Ho has large orbital momentum==> at low temperature, higherorder K play a role
HoFe11Ti: easy-axis system ( M // [001] )
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Magnetic free energy determines equilibrium magnetization
F = Eanisotropy + EZeeman = Eanisotropy - B.M
Only K1 Higher order K
MS
0
B // [100]
B // [001]
M
B
MS
0
B // [100]
B // [001]
M
B
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Outline
- Introduction- Experiment- Results- Conclusion
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Magnetization B // main directions
Different in-plane results! K4, K5 important
Magnetic-phase transition when field in plane
0 1 2 3 4 50
2
4
6
8
10
B // [100]
B // [110]
B // [001]
T = 5 K
HoFe11Ti
MZ ( B
/f.u
.)
B (T)
Bdem ~ 0.3 TMS
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HoFe11Ti : possible 3D-process
3D magnetometry (SQUID, high-field magnet)
Requirements:
- Pickup coils in three directions
- Sample single domain (homogeneous magnetization)
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Bdem.=NM[001]
M
[001]
[001]
Bsingle=Bdem./cos
Choose [001] = 75° single domain when B ~ 1.1 T
Sample single domain: projection of B on [001]
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Magnetizationfor B in(110) plane
Above 1.1 T, sample single domainTransition occurs above 1.1 T
0 1 2 3 4 50
2
4
6
8
10
12
B in (110)[001] = 75°
HoFe11
Ti
T = 5 K
MZ ( B
/f.u.
)
B (T)
MS sin 75
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0 1 2 3 4 50
2
4
6
8
10
12
B in (100)
[001] = 73°
HoFe11
Ti
T = 5 K
MZ ( B
/f.u.
)
B (T)
Above 1.1 T, sample single domainTransition occurs above 1.1 T
Magnetizationfor B in(100) plane
MS sin 73
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Measurement configuration
Mz // B
Mx near [001]
My Mx Mz
After measurement:
project Mx, My, Mz
on [100], [010], [001]
Mtot
Mz
Mx
[001]
[001]
B
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Outline
- Introduction- Experiment- Results- Conclusion
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0 2 4 6 8 10 12 14
0
2
4
6
8
10
12
Mz
My
Mx
Mtot
HoFe11TiB in (110)[001] = 75°
T = 4.2 K
M ( B
/f.u
.)
B (T)
My nearly zero
Conclusion: 2D process
Magnetizationfor B in(110) plane
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Magnetization for [100] and [010] equal, as expected
0 2 4 6 8 10 12 140
2
4
6
8
10
12Mtot.
M[001] M[010]
M[100]
HoFe11
TiB in (110)
[001] = 75° T = 4.2 K
M ( B
/f.u.
)
B (T)
Magnetizationfor B in(110) plane
Projectiononcrystalaxes
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My becomes non-zero! 3D process
Magnetizationfor B in(100) plane
0 2 4 6 8 10 12 14
0
2
4
6
8
10
12
Mtot.
Mx
My
Mz
T = 4.2 K
HoFe11Ti B in (100)[001]= 73°
M ( B
/f.u
.)
B (T)
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B in (100) plane: 3D process
0 2 4 6 8 10 12 14
0
2
4
6
8
10
12
M[010]
Mtot.
M[001]
M[100]
T = 4.2 K
HoFe11
Ti B in (100)
[001]= 73°
M ( B
/f.u
.)
B (T)
Magnetizationfor B in(100) plane
Projectiononcrystalaxes
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Transition: first-order (follows from coexistence) Outlook: mechanism for coexistence ? microscopy
0 2 4 6 8 10 12 14
0
2
4
6
8
10
12B in (110)
[001] = 75°
Coexistence High-field phase
Low- field phase
M ( B
/f.u.
)
B (T)
2 4 6 8 100.0
0.5
1.0
B (T)
f
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Abadìa et al., J. Phys.:Condens. Matter 10 (1998), 349 Calculations: M.-H. Yu
B = 3 T
B = 4 T
Calculations based on anisotropy parameters*
B in (110) plane
2D process
First order
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B in (100) plane
3D process
First order
B = 5 T
B = 6 T
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Conclusions:
-At the magnetic phase transition, a 3D magnetization process occurs- This phase transition is first order
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* Asti and Bolzoni, J. Magn. Magn. Mater. 20 (1980), 29
M // [001] M [001]
0 30 60 90
B = 0.45
B = 0.417
B = 0.35
K1 = 1 a.u.
K2/K
1 = -1.5
K3/K
1 = 1
B = 0
Mag
net
ic e
ner
gy (
a.u
.)
(deg)
Some combinations of K1, K2, K3 (..K4, K5) ==> local minima inmagnetic energy as a function of angle with [001] ==> First order magnetization
process (FOMP)*