Rare-earth-iron nanocrystalline magnets E.Burzo 1) , C.Djega 2) 1) Faculty of Physics, Babes-Bolyai University, Cluj-Napoca 2) Universite Paris XII, France 1. General 2. Sample preparation 3. Crystal structure and microstructure 4. Magnetic properties of R 2 Fe 17 compounds 5. Magnetic properties of Sm-Fe-Si-C alloys 6. Mössbauer effects 7. Technical applications
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General Sample preparation Crystal structure and microstructure
Rare-earth-iron nanocrystalline magnets E.Burzo 1) , C.Djega 2) 1) Faculty of Physics, Babes-Bolyai University, Cluj-Napoca 2) Universite Paris XII, France. General Sample preparation Crystal structure and microstructure Magnetic properties of R 2 Fe 17 compounds - PowerPoint PPT Presentation
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-High magnetization MFe 2.1-2.2 B/atom-Planar anisotropyRombohedral structure: space groupSm:6c, Fe:6c, 9d, 18f, 18hdifferent local environments
Increase Tcvalues by:- replacement of iron involved in negative exchange inteactions- increase volume: interstitial atoms (C,N)Uniaxial anisotropy
m3R
i j
dj5d5d5d5di3d5d5d3 S)0(SJ2)0(S)0(SJ2H
M5d(0)=a MFe
4f-5d-3d Exchange interactions
Band structure calculations
Preparation. Crystal structureHigh energy ball milling and annealingSm2Fe17-xSix; Sm2Fe17-xSixC for Ta>850 oCMetastable Sm1-s(Fe,Si)5+2s P6/mmm type structure
Statistical occupation of Si in the 3g site and random distribution in the 2e dumbbell atoms have been simulated by using an appropriate P6/mmm subgroup, P1 with a’=3a, b’=3a, c’=2c
2e0 3g0 6l0
Six sextets:2e ; 3g ; 6l
2e1 3g1 6l1
Mean 57Fe hyperfine fields decrease with Si content
Hhf2e > Hef6l > Hhf3g
correlate with number of NN Fe atoms
Mean isomer shifts: δ2e>δ3g>δ6l
δ2e, δ6l increase with Si substitution
δ3g remains nearly constant
preferred occupation of Si sites
(3g)
Technical parameters
1. Uniaxial anisotropy is induced in 1:9 phase
2:17 phaseCoercive fields SmFe9-xSixC
X = 0.25 Hc=1.2 MA/m Ta=750 oC
x = 0.50 Hc = 1.04MA/m Ta=800 oC
The maximum in Hc values:
•Too low Ta hinders the complete solid-state reaction for forming a perfect metastable phase responsible for magnetic hardening
•Increasing Tc
- number of surface defects of hexagonal P6/mmm phase is reduced Hc
- the domain size increases Hc
2. Curie temperature increases
Tc 700 K for SmFe8.75Si0.25C
3. Induction resonance
Br 0.68 Bs
High energy product is expected with a smaller temperature coefficient than Nd-Fe-B alloys