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![The effect of electronic doping on the
magnetisation and thermopower
properties of Ba2FeMoO6
Jibu Stephen a,b,c, Grant Williams b,c, Ben Ruck b,c, K. Rutherford a
Industrial Research, Lower Hutt, New Zealand
The MacDiarmid Institute
Victoria University of Wellington
Outline
[1] Double Perovskite Ba2FeMoO6
[2] ASD & Magnetisation
[3] Magnetoresistance
[4] Thermopower
a b c](https://image.slidesharecdn.com/14-00o8jstephen-111110215645-phpapp01/85/14-00-o8-j-stephen-1-320.jpg)
![The effect of electronic doping on the
magnetisation and thermopower
properties of Ba2FeMoO6
Jibu Stephen a,b,c, Grant Williams b,c, Ben Ruck b,c, K. Rutherford a
Industrial Research, Lower Hutt, New Zealand
The MacDiarmid Institute
Victoria University of Wellington
Outline
[1] Double Perovskite Ba2FeMoO6
[2] ASD & Magnetisation
[3] Magnetoresistance
[4] Thermopower
a b c](https://image.slidesharecdn.com/14-00o8jstephen-111110215645-phpapp01/75/14-00-o8-j-stephen-1-2048.jpg)
![Magnetoresistance
MR = Δρ/ρ = [(ρ(0) - ρ(H))/ρ(0)]
Magnetoresistance model in polycrystalline
samples,
∆ρ/ρ = −P2mgb(H)2 / (1 + P2mgb(H)2 )
P - degree of spin polarisation
mgb(H) - magnetisation from a disordered region
near the grain boundaries
H - applied field.
mb mgb mgb mb
E. K. Hemery, G. V. M. Williams, and H. J. Trodahl, Physica B 390, 175 (2007).](https://image.slidesharecdn.com/14-00o8jstephen-111110215645-phpapp01/85/14-00-o8-j-stephen-9-320.jpg)
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14.00 o8 j stephen
- 1. The effect ofelectronic doping on the magnetisation and thermopower properties of Ba2FeMoO6 Jibu Stephen a,b,c, Grant Williams b,c, Ben Ruck b,c, K. Rutherford a Industrial Research, Lower Hutt, New Zealand The MacDiarmid Institute Victoria University of Wellington Outline [1] Double Perovskite Ba2FeMoO6 [2] ASD & Magnetisation [3] Magnetoresistance [4] Thermopower a b c
- 3. Double perovskites • Ba2FeMoO6 (BFMO)/ Sr2FeMoO6 (SFMO) – tetragonal - alternating Fe and Mo surrounded by oxygen octahedra. • Ba/Sr occupy every hole created by 8 BO6 octahedra Crystal structure of ordered double perovskite: A2BB’O6 Ba/Sr Fe Mo O
- 4. Double perovskites • Halfmetallic band structure – conduction electrons 100% spin polarised • The Fe3+ 3d5 electrons are localised and the Mo5+ 4d1 electrons are itinerant. E E E EF EF EF N(E) N(E) N(E) NM FM HM
- 5. Double perovskites Intergrain-type tunneling magnetoresistance Highferromagnetic ordering temperature (Tc) (~310 K for HM I HM HM I HM BFMO) Large MR + high Tc - promising applications: Read head for magnetic hard disk, magnetic sensors and R R magnetic RAM. B No applied field B Applied field
- 6. Synthesis • Solid statesynthesis • Mix appropriate proportions of A(NO3)2 (A = Sr, Ba), Fe2O3 and MoO3 to satisfy stoichiometry. • Grind, denitrate and press into pellets • Sinter at 1200 C in air • Regrind, repellet and sinter at 1150 C in 5% H2/95% N2 several times • XRD on sample at each stage to check phase homogeneity
- 7. ASD and Magnetisation 4 5K Ordered 3 2 1 /f.u.) Disordered 0 B M ( -1 -2 -3 -4 -6 -4 -2 0 2 4 6 Field (T)
- 8. ASD and Magnetisation Antiferromagnetic coupling model: Fe3+ 3d5 - Mo5+ 4d1 = 5 – 1 = 4μB/f.u. Ms 4.0 9 ASD Low ASD
- 9. Magnetoresistance MR = Δρ/ρ= [(ρ(0) - ρ(H))/ρ(0)] Magnetoresistance model in polycrystalline samples, ∆ρ/ρ = −P2mgb(H)2 / (1 + P2mgb(H)2 ) P - degree of spin polarisation mgb(H) - magnetisation from a disordered region near the grain boundaries H - applied field. mb mgb mgb mb E. K. Hemery, G. V. M. Williams, and H. J. Trodahl, Physica B 390, 175 (2007).
- 10. Thermopower Thermoelectric power, S=ΔV/ΔT Intragrain phenomena rather than intergrain
- 11. Thermopower Electron diffusion – Mottequation Sd Phonon drag – at low temperatures (at a fraction of the Debye temperature)
- 12.
- 13. Thermopower – Electrondoped Hemery et al., PRB 74, 054423 (2006)
- 14. Thermopower – nearTc Tc
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- 18. Conclusions • Electron dopingof BFMO does not have a significant impact on ASD • Thermopower of BFMO changes with La doping • BFMO exhibits magnetothermopower