Giant magnetocaloric effect and magneto-crystalline coupling. Luana Caron

Transcription

1 Giant magnetocaloric effect and magneto-crystalline coupling Luana Caron

2 Outlook Magneto-crystalline coupling How to change the coupling: Fe2P chemical pressure x physical pressure Fe2P to (Fe,Mn)2(P,?) similarities and differences What information can we obtain from it? Conclusions

3 Magneto-crystalline coupling magnetic interaction is dependent on interatomic distance Pauli s exclusion principle H = 0 E E H > 0

4 Chemical pressure: Fe2P Fe1 - tetrahedral 1.03 μb Fe2 - pyramidal 1.91 μb Per Nordblad, PhD thesis Uppsala University 1982

5 Chemical pressure: Fe2P! % I I I I 1, TEMPERATURE IK) Lundgren et al. Physica Scripta 1978

6 Chemical pressure: FeMnP Fe - tetrahedral 0.5 μb Mn - pyramidal 2.6 μb antiferromagnetic Co2P - orthorhombic Watanabe et al. JPSJ 1973

7 Chemical pressure FeMnP1-xAx A = As, Ge, Si MnFeP1-xAsx ferromagnetism and Fe2P structure are recovered Tegus, PhD thesis University of Amsterdam

8 Chemical pressure FeMnP1-xAx Ref. 4. A = As, Ge, Si y c/a T hys K T c K S m,max J kg 1 K 1 RCP J kg Gadolinium a a Reference 4. Mn2-yFeyP0.75Ge0.25 ferromagnetism and Fe2P structure are recovered Appl. Phys. Lett. 94, (2009)

9 Probing the coupling with pressure Fe, P 1. P=O kbar 2. Pz Pz Ps P= P P P P-11.0 a. P= TEMPERATURE ( K ) Fujiwara et al. JMMM 1980

10 dc-susceptibility (a.u.) Probing the coupling 3.6 with pressure x= T MnFeP 0.65 As 0.35 µ 0 H = 20 mt cooling Brück et al. JMMM 2007 T (K) 0 GPa 0.47 GPa 1.07 GPa M (µ B /f.u.) - S (J/kgK) MnFeP 1-x As x x= T x= T x= T T = 10 K P (GPa) Fig. 2. Magnetization of MnFe(P, As) at 10 K vs. pressure MnFeP 0.65 As 0.35 µ 0 H = 0-5 T T (K) 0 GPa 0.50 GPa 0.84 GPa 1.08 GPa Fe2P- like behavior Fig. 3. Magnetic entropy change in the case of MnFeP 0.65 As 0.35 for a field change of 5 T, under different applied pressures.

11 Probing the coupling with pressure Yabuta et al. JMMM 2007

12 Probing the coupling with pressure Yabuta et al. JMMM 2007

13 Probing the coupling with pressure Mn 1.16 Fe 0.84 P 0.75 Ge 0.25

14 Probing the coupling with pressure " V # " M # $ % = $ % & B' & P ' T T FeyMn2-yP0.75Ge0.25 Why no change in TC?? Hydrostatic pressure

15 Why no change in TC? " V # " M # $ % = $ % & B' & P ' T T Fe0.84Mn1.16P0.75Ge0.25

16 Why no change in TC? Fe0.84Mn1.16P0.75Ge0.25

17 Conclusions? Fe2P-based compounds present different behaviors under pressure chemical pressure is not always equivalent to physical pressure how to understand the entire picture?

18 Acknowledgements The Delft magnetocalorics group: Ekkes Brück, Jürgen Buschow, Lian Zhang, ZhiQiang Ou, Trung T. Nguyen, Dung Nguyen, Anton Lefering, O. Tegus, D. T. Cam Thanh, Bastian Knoors, Merien Uitterhoeve, Remco Addink Uppsala s Angstrom group: Per Nordblad, Roland Mathieu, Matthias Hudl, Viktor Höglin UNICAMP group: Sérgio Gama and Adelino de Aguiar Coelho Thank you for your attention!