Compensating holes inCa2+-doped yttrium iron garnet and their influence on magnetic properties of the system

Abstract

Assuming that the holes compensating the Ca + doping charge in Ca +-doped yttrium iron garnet (Ca +: YICx} are located in the p states of oxygen, we study their influence on the superexchange antiferromagnetic d-d coupling, starting with the Anderson periodic Hamiltonian for a system of the narrow-band and wideband electrons, with the p-d hybridization term. Using canonical perturbation theory, we derive explicit expressions for the Kondo-like interaction between a localized iron spin and a p hole, and for the antiferromagnetic superexchange coupling between iron spins. They are based on the second-order and fourth-order p-d hybridizations, respectively. The systematical analysis of the superexchange coupling is performed at T =0 K for both pure and doped YICx. It is shown that the presence of compensating holes can result in a significant decrease in the strength of the superexchange coupling. At a certain concentration of the Ca + ion a change of the sign of the coupling constant is obtained. It turns out that for the charge-transfer model and the Mott-Hubbard insulator model the d-d magnetic coupling is not only different in its value, but also the change of its sign occurs for a different concentration of the doping ions.

Properties of the Semi Spin Glass Ground State of Garnets

“…As already shown before [2], compensating holes produced by the doping, can influence profoundly the superexchange interaction between spins of the d electrons, not destroying, however, the translational symmetry of the system. Thus (233) follows importance or even a necessity for obtaining a phase diagram of the magnetic ground state, in terms of varying superexchange parameters.…”

“…It seems to be challenging to propose a new model which could explain at least some of the changes. Recently we have concentrated on an analysis of the change in magnetic properties which is displayed by YIG on the valence-uncompensated doping.As known, pure YIG is an insulating ionic crystal with ferrimagnetic collinear order.Magnetic properties of the system can be studied with the two-sublattice Heisenberg Hamiltonian [1,2] S is the S = 5/2 iron spin operator localized either at the sites of the octahedral (i, j) or tetrahedral (k,1) sublattice. Both the intra-and inter-sublattice coupling constants are limited to nearest neighbours, only, and denoted by J a , Jd and Jad, respectively.…”

“…Magnetic properties of the system can be studied with the two-sublattice Heisenberg Hamiltonian [1,2] S is the S = 5/2 iron spin operator localized either at the sites of the octahedral (i, j) or tetrahedral (k,1) sublattice. Both the intra-and inter-sublattice coupling constants are limited to nearest neighbours, only, and denoted by J a , Jd and Jad, respectively.…”