Orbital and spin correlations in Ca${}_{2-x}$Sr${}_x$RuO${}_4$: A mean field study

Abstract

The alloy Ca${}_{2-x}$Sr${}_x$RuO${}_4$ exhibits a complex phase diagram with peculiar magnetic metallic phases. In this paper some aspects of this alloy are discussed based on a mean field theory for an effective Kugel-Khomskii model of localized orbital and spin degrees of freedom. This model results from an orbital selective Mott transition which in the three-band system localized two orbitals while leaving the third one itinerant. Special attention is given to the region around a structure quantum phase transition at $x\approx 0.5$ where the crystal lattice changes from tetragonal to orthorhombic symmetry while leaving the system metallic. This transition yields, a change from ferromagnetic to antiferromagnetic spin correlations. The complete mean field phase diagram for this transition is given including orbital and spin order. The anisotropy of spin susceptibility, a consequence of spin-orbit coupling and orbital correlation, is a tell-tale sign of one of these phases. In the predominantly antiferromagnetic phase we describe a metamagnetic transition in a magnetic field and show that coupling of the itinerant band to the localized degrees of freedom yields an anomalous longitudinal magnetoresistance transition. Both phenomena are connected with the evolution of the ferromagnetic and antiferromagnetic domains in the external magnetic field and agree qualitatively with the experimental findings.

arXiv comment12 pages, accepted for publication in EPJ B

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Cited by in corpus (10)

• Spin, charge and orbital fluctuations in a multi-orbital Mott insulator
• Orbital-selective Mott transitions in the anisotropic two-band Hubbard model at finite temperatures
• Finite-temperature Mott transitions in multi-orbital Hubbard model
• Metal-insulator transition in the two-orbital Hubbard model at fractional band fillings: Self-energy functional approach
• Severe Fermi Surface Reconstruction at a Metamagnetic-Transition in Ca${}_{2-x}$Sr${}_x$RuO${}_4$ (for $0.2\le x\le 0.5$)
• Mott transitions in the multi-orbital systems
• Phase diagram of orbital-selective Mott transitions at finite temperatures
• Field-induced Orbital Patterns in Ferromagnetic Layered Ruthenates
• Orbital-selective Mott transitions in the 2-band J_z-model: a high-precision quantum Monte Carlo study
• Interplay of metamagnetic and structural transitions in Ca${}_{2-x}$Sr${}_x$RuO${}_4$