Spin-polarized Current-induced Instability in Spin-Valve with Antiferromagnetic Layer

In the framework of phenomenological model we consider dynamics of a compensated collinear antiferromagnet (AFM) in the presence of spin-polarised current. The model is based on the assumption that AFM spins are localised and spin torque is transferred to each magnetic sublattice independently. It is shown that in AFM spin current i) can be a source of the "negative friction"; and ii) modifies spin-wave frequencies. Equilibrium state of AFM can be destabilized by the current polarized in parallel to AFM vector. Threshold current at which the loss of stability takes place depends upon the magnetic anisotropy of AFM.Comment: 9 pages, 3 figures, submitted to J. Mag. Soc. Japa

Shift of close-packed basal planes as an order parameter of transitions between antiferromangetic phases in solid oxygen: II. Temperature/pressure dependence of sound velocities and lattice parameters

In the present paper we generalised a phenomenological model developed in \cite{gomo:2005} for the description of magnetostructural phase transitions and related peculiarities of elastic properties in solid oxygen under high pressure and/or low (below 40 K) temperature. We show that variation of all the lattice parameters in the vicinity of $\alpha\beta$-phase transition is due to both the shift of basal closed packed planes and appearance of the long-range magnetic order. Competition between these two factors from one side and lattice compression below $T_{\alpha\beta}$ from another produces non monotonic temperature dependence of lattice parameter $b$ (along monoclinic axis). Steep decrease of the sound velocities in the vicinity of $T_{\alpha\beta}$ can be explained by the softening of the lattice with respect to shift of the close-packed planes (described by the constant $K_2$) prior to phase transition point. We anticipate an analogous softening of sound velocities in the vicinity of $\alpha \delta$-phase transition and non monotonic pressure dependence of sound velocities in $\alpha$-phase.Comment: 11 pages, 8 figures, to appear in Low Temperature Physics, v.33, N6, 2007, materails presented at the Conference CC-2006, Kharkov, 200