Dresden 2009 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 3: Magnetic Half Metals and Oxides

MA 3.4: Vortrag

Montag, 23. März 2009, 11:45–12:00, HSZ 401

Correlation effects in p-electron magnets: the case of RbO₂ — •Roman Kováčik and Claude Ederer — School of Physics, Trinity College Dublin, Dublin 2, Ireland

The development of spintronics in recent years has triggered a need for new materials such as half metallic (HM) ferromagnets. HM materials with 2p-magnetism were proposed from electronic structure calculations, e.g. Rb₄O₆ [1]. However, recent measurements indicate that Rb₄O₆ is a magnetically frustrated system that exhibits spin-glass-like behavior in a magnetic field [2]. This discrepancy was attributed to inadequate treatment of the molecular states within the local spin density approximation (LSDA). This assumption was supported by calculations for RbO₂, known to be an insulating antiferromagnet, which turns out to be HM in LSDA as well. According to [2], this outcome could not be corrected within LDA+U even for U=13.6 eV.

We present results of LDA+U calculations for RbO₂, which show that, when allowing the system to reduce its symmetry, an orbitally polarized insulating state is favored for U>2 eV, consistent with experiment. Furthermore, we discuss an alternative treatment of on-site correlations in RbO₂, using an effective tight-binding model corresponding to a molecular orbital basis, which is constructed via maximally localized Wannier functions. In this case, the insulating state is obtained for significantly lower U>0.5 eV. In addition, we discuss a possible orbital ordering driven by correlation effects.

[1] J. J. Attema et al., J. Am. Chem. Soc. 127, 16325 (2005).

[2] J. Winterlik et al., J. Phys. Condens. Matter 19, 1 (2007).