Coupled Electronic–Nuclear Magnetostatic Oscillations in Magnetic Materials

Physics of the Solid State - Magnetization dynamics in spheroidal ferromagnetic samples is studied theoretically. It is shown that, in a magnetostatic approximation, electronic-nuclear...     

Indirect interaction of nuclear spins in chiral magnets

The effective Hamiltonian of the Suhl-Nakamura interaction of nuclear spins in a helimagnet has been constructed for the case where an external magnetic field is applied perpendicular to the axis of the helicoid. The contribution from the intraboundary and intradomain spin excitations to the parameter and effective radius of this interaction has been calculated. The second moment and local broadening of the NMR absorption line, which are determined by the indirect interaction of the nuclear spins, have also been calculated.     

Vacancy ordering and oxygen dynamics in oxide ion conducting La1−xSrxGa1−xMgxO3−x ceramics: Ga, Mg and O NMR

The oxygen vacancies distribution in the rigid lattice and the thermally activated motion of oxygen atoms are studied in La_1−xSr_xGa_1−xMg_xO_3−x (x=0.00; 0.05; 0.10; 0.15 and 0.20) compounds. For that ⁷¹Ga, ²⁵Mg and ¹⁷O NMR was performed from 100 K up to 670 K, and ion conductivity measurements were carried out up to 1273 K. The comparison of the electric field gradients at the Ga- and Mg-sites evidences that oxygen vacancies appear exclusively near gallium cations as a species trapped below room temperature in local clusters, GaO_5/2-□-GaO_5/2. These clusters decay at higher temperature into mobile constituents of the structural octahedra Ga(O_5/6□_1/6)_6/2. At the same time, the nearest octahedral oxygen environment of magnesium cations persists at different doping levels. The case of two adjacent vacant anion sites is found highly unlikely within the studied doping range. The thermally activated oxygen motion starts to develop above room temperature as is observed from both the motional narrowing of ¹⁷O NMR spectra and the ¹⁷O nuclear spin-lattice relaxation rate. The obtained results show that two types of motion exist, a slow motion and a fast one. The former is a long-range diffusion whereas the latter is a local back and forth oxygen jumps between two adjacent anion sites. These sites are strongly differentiated by the probability of the vacancy formation, like the vacant apical site and the occupied equatorial site in the orthorhombic compositions x <0.15.     

Nuclear magnetic relaxation induced by the relaxation of electron spins

A physical mechanism responsible for the relaxation of nuclear spins coupled by the hyperfine interaction to relaxed electron spins in materials with spin ordering is proposed. The rate of such induced nuclear spin relaxation is proportional to the dynamic shift of the nuclear magnetic resonance (NMR) frequency. Therefore, its maximum effect on the NMR signal should be expected in the case of nuclear spin waves existing in the system. Our estimates demonstrate that the induced relaxation can be much more efficient than that occurring due to the Bloch mechanism. Moreover, there is a qualitative difference between the induced and Bloch relaxations. The dynamics of nuclear spin sublattices under conditions of the induced relaxation is reduced to the rotation of m₁ and m₂ vectors without any changes in their lengths (m ₁ ² (t) = m ₂ ² (t) = m ₀ ² (t)= const). This means that the excitation of NMR signals by the resonant magnetic field does not change the temperature T _n of the nuclear spin system. This is a manifestation of the qualitative difference between the induced and Bloch relaxations. Indeed, for the latter, the increase in T _n accompanying the saturation of NMR signals is the dominant effect.     

Breather states and compound solitons in a ferromagnet-insulator-metal structure

Nonlinear dynamic states with a fine internal structure, such as breathers, “breather lattices,” kinks, kink-antikink bound states, and their spatially periodic generalizations have been constructed in terms of a modified Korteweg-de Vries equation for a system of magnetostatic waves in a ferromagnet-insulator-metal structure. Specific features of the nucleation, interaction, and transformation of these states have been studied in layered magnetic structures.     

Specificities of Spin Wave Focusing in EuO and EuS Crystals

Physics of the Solid State - Specificities of spin wave focusing in EuO and EuS crystals are studied. It is shown that spin wave focusing is absent in the long-wave approximation: it is observed...