Heisenberg Hamiltonian description of multiple-sublattice itinerant-electron systems: General considerations and applications to NiMnSb and MnAs

Abstract

We consider magnetic systems where the magnetic sublattices can be unambiguously separated into sublattices of inducing and induced moments. The concrete numerical calculations are performed for half-metallic ferromagnetic Heusler compound NiMnSb and hexagonal phase of MnAs. In both systems, Mn atoms possess a robust atomic moment that is much larger than the induced moments of other atoms. It is shown that the treatment of the induced moments as independent variables of the Heisenberg Hamiltonian leads to artificial features in the spin-wave spectrum. We show that the artificial features of the model do not have a dramatic influence on the estimated value of the Curie temperature. This is demonstrated within both mean-field approximation and random-phase approximation. It is shown that the calculational scheme where the induced moments are assumed to fully adjust their values and directions to the adiabatic magnetic configurations of the inducing moments is free from the artificial feature in the spin-wave spectra. In this scheme, the exchange interaction between the inducing and induced moments appears as renormalization of the exchange interactions between inducing moments. It is shown that the redistribution of the exchange interactions has strong influence on the estimated value of the Curie temperature because of the decreased number of the degrees of freedom in the thermodynamic model. Different schemes of the mapping of the systems on the Heisenberg Hamiltonian are examined. The similarities and differences in the properties of NiMnSb and MnAs are discussed.

First-principles theoretical studies of half-metallic ferromagnetism in CrTe

“…saturates at a value of 4.0 µ B , as the HM state is achieved, while the local moments on the Cr-and Te-sublattices increase in magnitude, remaining opposite in sign. Sandratskii et al 55 have discussed the problem associated with such 'induced moments' in calculating the Curie temperature. LMTO-ASA results using LDA for the ZB and RS structures are presented in Fig.8.…”

Finite-temperature magnetism ofFexPd1−xandCoPolesya1, Mankovsky2, Šipr3 et al. 2010Phys. Rev. B452370View full textAdd to dashboardCite

“…Lezaic et al [18] emphasized the need to account for longitudinal fluctuations of magnetic moments induced on Ni atoms for a proper description of the temperaturedependence of the spin-polarisation at the Fermi energy E F in the half-metallic ferromagnet NiMnSb. Sandratskii et al [19] investigated several ways for accounting for the induced magnetic moments within the spin-spiral approach used for the calculation of the exchange coupling parameters in NiMnSb and MnAs. Using these results Sandratskii et al [19] have studied finite-temperature magnetic properties of NiMnSb; their findings are consistent with the findings of Lezaic et al [18].…”

“…Sandratskii et al [19] investigated several ways for accounting for the induced magnetic moments within the spin-spiral approach used for the calculation of the exchange coupling parameters in NiMnSb and MnAs. Using these results Sandratskii et al [19] have studied finite-temperature magnetic properties of NiMnSb; their findings are consistent with the findings of Lezaic et al [18].…”

Ab initio electronic and magnetic properties of half-metallic NiCrSi and NiMnSi Heusler alloys: The role of defects and interfaces

“…22 Moreover taking into account also the reconstruction at the surfaces and interfaces can have an important effect on their properties. 26 Finally we should note that several other aspects of NiMnSb have been studied using first-principles calculations like the exchange constants and Curie temperatures, 27,28,29 the quasiparticle states 30 and the dynamical effects, 31 the defects and doping, 32,33,34 the structural stability, 35,36 the effect of spin-orbit coupling, 37 the fit of model Hamiltonians to describe NiMnSb, 38,39 orbital magnetism, 40 the pressure and thermal expansion effects, 41 the temperature effect 42 and the magneto-optical properties. 43,44 The half-metallic character of NiMnSb in single crystals has been well-established experimentally.…”