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TT: Tiefe Temperaturen

TT 2: Correlated Electrons - Metal Insulator Transition

TT 2.9: Vortrag

Freitag, 4. März 2005, 12:15–12:30, TU H2053

Modelling the magnetic susceptibility of LaCoO₃ — •Thomas Möller^1,2 and Erwin Müller-Hartmann¹ — ¹Institut für Theoretische Physik, — ²II. Physikalisches Institut, Universität zu Köln

LaCoO₃ is a non-magnetic insulator, which develops a Curie susceptibility above ∼100 K. According to the Hund’s rules the ⁵D-quintet with S=2 (high spin) should form the ground state for the 3d⁶ electron configuration of Co³⁺. A sufficiently large cubic crystal field breaks Hund’s first rule, and the ground state becomes non-magnetic (S=0, low spin). However, this high-spin / low-spin scenario is not in agreement with the experimental results [1]. Radwański and Ropka [2] suggested another model for LaCoO₃. Here, the ground state is the high spin state, but this multiplet is split by spin orbit coupling and a trigonal Jahn-Teller distortion in such a way that a non-magnetic ground state develops. We calculated the magnetic susceptibility in this model and find a strong anisotropy where the Curie susceptibility disappears in the plane perpendicular to the Jahn-Teller distortion and only a large van-Vleck term remains. For a D_4h distortion, this can be explained by pure symmetry. A vanishing Curie susceptibility is found also in case of a D_3d distortion, but here the reason is still unclear. Due to its strong anisotropy the T-dependence of the averaged susceptibility χ=1/3χ_∥+2/3χ_⊥ differs from that observed in LaCoO₃.

[1] Zobel et al., Phys. Rev. B 66, 020402(R) (2002)

[2] Radwański and Ropka, Solid State. Comm. 112, 621 (1999)