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It is shown that non-Heisenberg exchange interaction should be taken into account to reproduce the magnetic phase diagram of La1−xAxMnO3 (A = Ca,Sr) using only effective exchange parameters and spins. The formation of the four-spin exchange arises from carrier hopping and coincides with the critical concentration metal–dielectric transition. The two- and four-spin exchange parameters are determined by Monte Carlo simulations.

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The temperature dependence of resistivity and the bulk modulus are calculated on the Kondo lattice, with ring exchange between localized spins, using the spin-polaron and adiabatic approximation. Peak and zero values of the bulk modulus as functions of temperature and concentration are determined below the temperature of the transition to the paramagnetic state. The effects of the nearest order between transverse spin components and a value of the ring exchange between localized spins on magnetoresistivity are estimated.

No abstract