Download presentation

Presentation is loading. Please wait.

Published byJacob Barnes Modified over 3 years ago

1
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

2
Permanent magnets: cobalt based: SmCo 5, Sm 2 Co 17 - high Curie temperatures - good energy product SmCo 5 (BH) max 200 kJ/m 3 Sm 2 Co 17 240 kJ/m 3 - very expensive iron based: Nd-Fe-B - low Curie points, T C - high energy product at RT (BH) max 360 kJ/m 3 - high decrease of Energy Product with T T<100 o C - low cost

3
Directions of researches: nanocrystalline systems iron based with rare-earths iron based without rare-earth spring magnets RCo 5 /α-Fe

4
Iron based magnets with rare-earth R-Fe system RFe 2, RFe 3, R 6 Fe 23, R 2 Fe 17 no RFe 5 phases are formed R 2 Fe 17 -Low Curie temperatures, T c < 477 K for Gd 2 F 17 -High magnetization M Fe 2.1-2.2 B /atom -Planar anisotropy Rombohedral structure: space group Sm:6c, Fe:6c, 9d, 18f, 18h different local environments Increase T c values by: - replacement of iron involved in negative exchange inteactions - increase volume: interstitial atoms (C,N) Uniaxial anisotropy

6
M 5d (0)=a M Fe 4f-5d-3d Exchange interactions Band structure calculations

7
Preparation. Crystal structure High energy ball milling and annealing Sm 2 Fe 17-x Si x ; Sm 2 Fe 17-x Si x C for T a >850 o C Metastable Sm 1-s (Fe,Si) 5+2s P6/mmm type structure s = 0.22TbCu 7 T a = 650 o C-850 o C s = 0.33Sm 2 Fe 17 s = 0.36-0.38SmFe 9 (new) Carbonation: mixture of alloys and C 14 H 10 powders 420 o C in vacuum Grain sizes: SmFe 9-y Si y : 22-28 nm SmFe 9-y Si y C: 18-22 nm Rietveld analysis C 3f sites (1/2,0,0); (0,1/2,0); (1/2,1/2,0) Sm at (0,0,0) is occupied by 0.64-0.62 atoms Si 3g sites

8
R 1-s M 5+2s P6/mmm

9
SmFe 8.75 Si 0.25 Electron microscopy: distribution of elements particle dimensions

11
y=2 y=0 y=2 y=0 z=0 z=1

13
Curie temperature: effect of Si T c increases by Si substitution in noncarbonated samples T c decreases in carbonated sample Volume effects: Localized moment of iron moments Molecular field approximation Fe mainly localized magnetic behaviour 16.4 1:9 22.9 2:17 25 1:9 30 2:17

14
Intrinsic magnetic properties Magnetic measurements: H 9T T4.2 K initial magnetization curves - inflection typical for pinning effects coherent precipitates with matrix impede the motion of domain walls Band structure calculations: LMTO-LDA method M Sm =-0.66 B /atom M Fe (6c) > M Fe (18h) M Fe (18f) > M Fe (9d) Mean magnetic moment of Fe in field of 9T increases with Si content Noncarbonated: 1.50 B (y=0.25); 1.75 (y=1.0) Carbonated: 1.88 B (y=0.25); 1.97 (y=1.0) Asymmetric filling of Fe 3d band by Si3p electrons

15
Mössbauer effect studies SmFe 9-x Si x C P6/mmm type structure Analysis of spectra local environment relationship between isomer shift, δ, and WSC volumes x = 1.0 WSC volume in (Å 3 ) Sm1a (33.96); Fe2e (19.87); Fe3g (13.45); Fe6l (13.39) Larger isomer shifts=larger WSC volumes 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 2e 0 3g 0 6l 0 Six sextets:2e ; 3g; 6l 2e 1 3g 1 6l 1

17
Mean 57 Fe hyperfine fields decrease with Si content H hf 2e > H ef 6l > H hf 3g correlate with number of NN Fe atoms Mean isomer shifts: δ 2e >δ 3g >δ 6l δ 2e, δ 6l increase with Si substitution δ 3g remains nearly constant preferred occupation of Si sites (3g)

19
Technical parameters 1.Uniaxial anisotropy is induced in1:9 phase 2:17 phase Coercive fields SmFe 9-x Si x C X = 0.25H c =1.2 MA/mT a =750 o C x = 0.50H c = 1.04MA/mT a =800 o C The maximum in H c values: Too low T a hinders the complete solid-state reaction for forming a perfect metastable phase responsible for magnetic hardening Increasing T c - number of surface defects of hexagonal P6/mmm phase is reduced H c - the domain size increases H c

20
2. Curie temperature increases T c 700 K for SmFe 8.75 Si 0.25 C 3. Induction resonance B r 0.68 B s High energy product is expected with a smaller temperature coefficient than Nd-Fe-B alloys

23
Thank you very much for your attentions.

Similar presentations

Presentation is loading. Please wait....

OK

The basics for simulations

The basics for simulations

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on nepal culture Ppt on switching devices with verizon Ppt on effective leadership skills Ppt on digital image processing fundamentals Free ppt on smart note taker pdf Ppt on railway reservation system in java Ppt on condition based maintenance technologies Ppt on business environment nature concept and significance definition A ppt on storage devices Ppt on inhabiting other planets warming