Theory of magnetic resonance as an orbital state probe

Abstract

It is demonstrated that magnetic resonance in a magnetically ordered state is a sensitive indirect method for the investigation of the orbital ground state. This idea is illustrated for two perovskite titanates: LaTiO 3 and YTiO 3 . In contrast to the spin-wave energy spectra, antiferromagnetic resonance spectra in an external magnetic field reveal clear dependence on the orbital state and it can distinguish the state with strong orbital fluctuations from the static orbital order. Our theoretical analysis is based on the model, which explicitly takes into consideration the strong correlation among lattice, orbital, and magnetic degrees of freedom.

Hyperfine interactions in titanates: Study of orbital ordering and local magnetic properties

“…They proposed the orbital liquid model that explains the reduction of the magnetic moment of titanium of about 0.5μ B in LaTiO 3 [5] and an isotropic spectrum of spin waves [8]. However, the model contradicts the NMR experimen tal results for 47,49 Ti [9], some calculations in the crys tal field model [3,10], and band calculations [11]. The results of calculations show that the ground level of the Ti 3+ ion is an orbital singlet separated from the The NMR experiments on the 47,49 Ti nuclei allow the detection of the local orbital order, whereas NMR on 139 La( 89 Y) depends on the entire picture of the orbital and magnetic orders.…”

“…The orbital structure determines the type and code of the magnetic order in titanate crystals [3,10]. Orbital fluctuations can change the code of the mag netic structure [10]. The type and code of the mag netic structure are responsible for the magnitude and direction of the induced magnetic field on the nuclei of La and Y diamagnetic cations detected in the NMR experiments [13].…”

“…Thus, the role of orbital fluctuations in titanates is incompletely clear. The orbital structure determines the type and code of the magnetic order in titanate crystals [3,10]. Orbital fluctuations can change the code of the mag netic structure [10].…”

Specific features of magnetic structure formation in orbitally degenerate BiMnO3 manganite

“…The strong influence on mixing angle Φ n of the wavefunctions can be produced by interactions of some other types. According to [12,13,15], these are (i) interaction with nearest neighbors in the octahedral environment of higher orders: (4) where Q θn , Q εn are the symmetrized coordinates of e g type distortions of the nearest neighbor oxygen envi ronment of the nth Mn 3+ ion and Q xn , Q yn , Q zn are the symmetrized coordinates of t 1g type distortions of the ) have not been estimated, but their possible influence on the orbital and magnetic states of the crystal can be considered. Table 3 presents data for the symmetrized distortions of the environment of man ganese ions as calculated from experimental data [8].…”

“…The orbital structure will be described using a model of electron vibrational (vibronic) interactions as described by the following Hamiltonian [12,13]: (2) Let us consider partial contributions stipulated by this model. The main linear contribution from the near est neighbor oxygen environment of manganese ion can be written as and V e = -1.29 eV/Å is the linear vibronic interaction constant determined in [14].…”