Electronic Structure and Transport Properties of Iron Compounds: Spin-Crossover Effects.Viktor Struzhkin

CollaborationsM. Eremets, I. EremetsMax-Planck Institute, Mainz, GermanyA. Gavriliuk, I. LyubutinInstitute of Crystallography, RAS, Moscow, RUSSIA

Optics and Theory A. Goncharov, GL S. Ovchinnikov Institute of Physics, Siberian Branch of RAS, Krasnoyarsk, RUSSIA

NFS, XESW. Sturhahn, J. Zhao, S. Kharlamova, P. Chow, M. Y. HuAPS, ANL, Argonne, USAJ. F. Lin LLNL

Spins and MagnetismP < PcP > PcScope: electronic structure of Fe2+ and Fe3+ in octahedral sites

Theoretical approachIn the Mott-Hubbard theory charge fluctuations din djn din-1 djn+1 are completely suppressed due to strong exchange and Coulomb d - d interaction U

J.Zaanen, G.Sawadzky, J.Allen [PRLett 1985] showed that an another type of charge transfer () can be considered din din+1 L, where L is a hole in p valence band of anion

Depending on the ratio of parameters, which are related to hybridization , the system can be (from the point of view the nature of the gap gap) :1)Mott-Hubbard insulator d-d type U < (gap U),2)insulator (or semiconductor) with charge transfer U > (gap ),3)d metal < U and U < W/24)p metal U < and < W

Bandwidth- versus filling-controlledmetal-insulator transition(Fujimori)

Mott-Hubbard transition under high pressure: bandwidth control

Tanabe-Sugano diagram for Fe+3 ion andSpin crossoverFe3+ - LS (S = 1/2)Fe3+ - HS (S = 5/2)Usp

Magnetic collapse in transition metal oxides

Cohen, Mazin, Isaak, Science 1997R. E. Cohen et al., MRS Symp proc. 1998High-spin to low-spin transitionI. Jackson and A. E. Ringwood (1981)G = E PV + TS

E = Nn{ - (r)}, ~ 0(r0/r)5 For cubic (B1) FeO: Ptr=50 GPa

X-ray emission spectroscopy as a local magnetic probe

High-spin to low-spin transition in FeS J.-P. Rueff , C.-C. Kao,V. V. Struzhkin, J. Badro, J. Shu, R. J. Hemley, and H. K. Mao , Phys. Rev. Lett. (1999)

J. Badro et. al., Science (2003) Mg0.83Fe0.170

Spin-crossover transition in ferropericlase

Nuclear inelastic scattering set-up (W. Sturhahn, E. Alp, M. Hu)

FeBO3 Mssbauer spectroscopy and NFS (Lyubutin et al.)

10Dq

Reduced radiative conductivityof low-spin (Mg,Fe)O in the lower mantleA. Goncharov, V. Struzhkin, and S. Jacobsen

The observed changes in absorption are in contrast to prediction and are attributed to d-d orbital charge transfer in the Fe2+ ion. The results indicate low-spin (Mg,Fe)O will exhibit lower radiative thermal conductivity than high-spin (Mg,Fe)O, which needs to be considered in future geodynamic models of convection and plume stabilization in the lower mantle.

Theory

Comparison of Mssbauer and X-ray emission results for FeOM. P. Pasternak et al . Phys. Rev. Lett.(1997)J. Badro et al. Phys. Rev. Lett. (1999)

NFS FeO (wstite)

Magnetic phase diagram of FeO

41 GPa113 GPaInsulator-metal transition in FeO

Fe B O3

R Fe3 (BO3)4 (R = Gd)

Y3 Fe5 O12

Fe3+ Samples: Singe crystals enriched with the Fe-57 isotope

Changes in the crystal color under pressure increase and decrease19 GPa41 GPa50 GPa13 GPa0 GPa32 GPaElectronic transitionY3Fe5O12

at P = 46 GPa the insulator- semiconductor transitionFeBO3Structural, magnetic, electronic and spin transitions at high pressuresat 53 GPa collapse of the unit-cell volume by ~ 9 %

at P = 46 GPa magnetic collapse with the HS LS transition

at P = 43 GPa the insulator- semiconductor transitionGdFe3(BO3)4Structural, electronic and spin transitions at high pressuresat 26 GPa collapse of the unit-cell volume by ~ 8 %at P = 43 GPa the HS LS transition

at P = 50-55 GPa the insulator- metal transitionStructural, magnetic, electronic and spin transitions at high pressuresat 48 GPa srtuctural amorphyzationat P = 48 GPa magnetic collapse with the HS LS transitionY3Fe5O12

BiFeO3 - belongs to ferro-magneto-electric materials (multiferroics) which have both a spontaneous electrical polarization and a spontaneous magnetization.

Between known multiferroics, it has a record high the antiferromagnetic Neel temperature (TN = 643 K) and the ferroelectric Curie temperature (TC = 1083 K) Bi Fe O3 : Multiferroic

BiFeO3Electronic transition from the insulating to highly conducting state. Mott ?7.2 GPa54.5 GPa

Pressure temperature dependence of resistivityBiFeO3At 40 55 GPa the resistance drops by 107 (metallization)

at P = 45-55 GPa the insulator- metal transitionStructural, magnetic, electronic and spin transitions at high pressuresnear 45 GPa srtuctural transitionat P = 47 GPa magnetic collapse with the HS LS transitionBi Fe O3

Main parameter is the effective Hubbard energy Ueff

Ueff = E0(d 4) + E0(d 6) - 2 E0(d 5)

LPP P < Pc S = 2 S = 2 S = 5/2 HPP P > Pc S = 1 S = 0 S = 1/2

S. G. Ovchinnikov [JETP Letters, 2003]

Theoretical approach

ELECTORON STRUCTURE of FeBO3 and GdFe3(BO3)4 [S.G. Ovchinnikov and S.A. Kharlamova, JETP Letters, 2003; 2004] SEC for Fe: ) d - d - transitions b) charge transfer transitions p6d5 p5d6 electron creation Fe3+ Fe2+: = E (52, d6) E (6A1, d5) hole creation Fe3+ Fe4+: = E0 (6A1,d5) E0 (6A1,d4)

By Raccah parameters : = d + 5 A + 14 B 0.4 = d + 4 A 14 B + 0.6 Then the Hubbard effective parameter is: Ueff = c = + 28 = 4.2 eV

The effective Hubbard parameter:

Ueff = c - = E0(d4) +E0(d6) -2E0(d5)

PPc S=2 S=2 S=5/2

PPc S=1 S=0 S=1/2

Ueff = c - = + 9 -7 1.45 eV ELECTRON STRUCTURE of FeBO3 and GdFe3(BO3)4 inMULTIELECTRON MODEL at AMBIENT and HIGH PRESSURE7S.G.Ovchinnikov. JETP Lett. (2003)

S. G. Ovchinnikov [JETP Letters, 2003]

Theoretical approachesFe2+Fe3+FeO?

Bandwidth- versus filling-controlledmetal-insulator transition(Fujimori)HS-LSU-control