Volume 34, Issue 8, August 2008
Index of content:
- LOW-TEMPERATURE MAGNETISM
Charge ordering, internal structural parameters, and magnetic susceptibility of : driving forces of a phase transition34(2008); http://dx.doi.org/10.1063/1.2967506View Description Hide Description
The temperature dependences of the long diagonals of the octahedron and the magnetic susceptibility of in the temperature interval are investigated. The functions and are found to have anomalies in the charge-ordering range . The sharp decrease of the diagonal agrees with phase-transition notions, according to which the spatial modulation of the charge density is due to the modulation of the Mn–Mn bond lengths. The most likely driving forces of the transition are the Peierls lattice instability and Jahn–Teller stability of the octahedron at the ions. The hysteresis of the temperature dependence in the paramagnetic region shows indirectly that structuralphase separation occurs together with the transition. The parameters of the function indicate that ferromagnetic clusters consisting of one, two, or three ion pairs – form in the system in the temperature intervals , , and , respectively.
34(2008); http://dx.doi.org/10.1063/1.2967507View Description Hide Description
The magnetic and magnetoresonance properties of a new single-crystal compound are studied. Measurements of the magnetization and magnetic susceptibility of the crystal in a wide temperature range make it possible to conclude that is a quasi-two-dimensional antiferromagnet with the easy magnetization axis directed perpendicular to the crystallographic plane and a magnetic ordering temperature . Resonancemeasurements at in wide range of frequencies and magnetic field (up to ) permit us to obtain the frequency-field dependence of the AFMR spectrum for a field applied along the easy magnetization axis . It is shown that a magnetic field directed along the antiferromagnetic axis induces a magnetic phase transition of the spin-flop type, which is found to occur at . The magnetic resonance experimental data are described qualitatively in the model of a biaxial antiferromagnet.
34(2008); http://dx.doi.org/10.1063/1.2967508View Description Hide Description
The influence of the kinematic interaction and indirect exchange of electrons on the magnetic structure of a narrow-band Hubbard magnet is investigated using diagrammatic perturbation theory. All contributions to the combined population and the spin Green’s function are examined to the first order of perturbation theory. A self-consistent equation is found for the order parameter of the phases. All contributions to the mass operator are determined with effective “dressing” of the interaction lines taken into account. The effect of indirect anti-ferromagnetic exchange on the spin wave spectrum and the damping of elementary excitations are investigated for ferromagnetic and paramagnetic phases. The correction to the frequency of spin-wave excitations at zero temperature and for hole concentrations, proportional to , is calculated for a ferromagnetic structure. As indirect exchange increases in magnitude, the spin-wave excitation frequencies decrease linearly, in agreement with the results obtained by Nagaoka and Zaitsev. It is found that the spin-wave spectrum near the Fermi level is coherent. The transverse dynamic susceptibility of the system is calculated for uniform ferromagnetic and paramagnetic structures.
34(2008); http://dx.doi.org/10.1063/1.2967509View Description Hide Description
The magnetic properties of , a layered metal with a hexagonal structure of the crystal lattice, are measured, and the change of those properties after irradiation with high-energy electrons is investigated. It is shown that the main part of the magnetic susceptibility comes from the Pauli paramagnetism of free charge carriers. The low-temperature deviations from Pauli paramagnetism are explained by dangling interatomic bonds, which are present in small numbers even in the unirradiated samples.