Ya. B. Bazaliy

Dynamics of domain walls in magnetic nanostrips.

We express the dynamics of domain walls in ferromagnetic nanowires in terms of collective coordinates, generalizing Thieles steady-state results. For weak external perturbations the dynamics is dominated by a few soft modes. The general approach is illustrated on the example of a vortex wall relevant to recent experiments with flat nanowires. A two-mode approximation gives a quantitatively accurate description of both the steady viscous motion of the wall in weak magnetic fields and its oscillatory behavior in moderately high fields above the Walker breakdown.

Magnetic and structural properties of spin-reorientation transitions in orthoferrites

Magnetic and structural characteristics of ErFeO3, TmFeO3, and YbFeO3 single crystals were studied over a wide temperature range. Magnetic measurements found that the spin-rotation transitions in all crystals are well described by the earlier proposed theory with no fitting parameters. Additionally, they have shown the absence of the magnetic compensation point in TmFeO3 and a noticeable growth of the c-axis magnetization at low temperatures in TmFeO3 and ErFeO3. The x-ray measurements found no symmetry-lowering lattice distortions during the reorientation. Overall, the measurements cover a wide range of material parameters and demonstrate the generality of the modified mean field theory of the Γ4→Γ24→Γ2 orientation phase transitions in orthoferrites.

Dynamics of a vortex domain wall in a magnetic nanostrip: application of the collective-coordinate approach

The motion of a vortex domain wall in a ferromagnetic strip of submicron width under the influence of an external magnetic field exhibits three distinct dynamical regimes. In a viscous regime at low fields the wall moves rigidly with a velocity proportional to the field. Above a critical field the viscous motion breaks down, giving way to oscillations accompanied by a slow drift of the wall. At still higher fields the drift velocity starts rising with the field again but with a much lower mobility

The role of erbium magnetization anisotropy during the magnetic reorientation transition in ErFeO3

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Measurements of spin reorientation in YbFeO3 and comparison with modified mean-field theory

than in the viscous regime. To describe the dynamics of the wall, we use the method of collective coordinates that focuses on soft modes of the system. By retaining two soft modes, parametrized by the coordinates of the vortex core, we obtain a simple description of the wall dynamics at low and intermediate applied fields that applies to both the viscous and oscillatory regimes below and above the breakdown. The calculated dynamics agrees well with micromagnetic simulations at low and intermediate values of the driving field. In higher fields, additional modes become soft and the two-mode approximation is no longer sufficient. We explain some of the significant features of vortex-domain-wall motion in high fields through the inclusion of additional modes associated with the half antivortices on the strip edge.

Precession states in planar spin-transfer devices : The effective one-dimensional approximation

Magnetization of ErFeO3 single crystal was measured by a super conducting quantum interference device magnetometer with greatly improved precision. A dramatic (70%) increase of magnetization was observed in the spin-reorientation interval (88–97 K). This and the temperature dependence of the spin-rotation angle are accurately described by the modified mean field theory, which uses the key fact of the magnetic anisotropy of erbium subsystem. Calculated temperature dependence of the rotation angle shows a remarkable correspondence with the experiment with no fitting parameters. Proposed model is general and can be used to analyze orientation transitions in many orthoferrites.

Staggered superconductivity in UPt3: A new phenomenological approach.

Precise measurements of YbFeO_3 magnetization in the spin-reoirentation temperature interval are performed. It is shown that ytterbium orthoferrite is well described by a recently developed modified mean field theory developed for ErFeO_3. This validates the conjecture about the essential influence of the rare earth ions anisotropic paramagnetism on the magnetization behavior in the reorientation regions of all orthoferrites with Gamma{4} ->Gamma{24} ->Gamma{2} phase transitions.

Planar approximation for spin transfer systems with application to tilted polarizer devices

Current induced precession states in spin-transfer devices are studied in the case of large easy plane anisotropy (present in most experimental setups). It is shown that the effective one-dimensional planar description provides a simple qualitative understanding of the emergence and evolution of such states. Switching boundaries are found analytically for the collinear device and the spin-flip transistor. The latter can generate microwave oscillations at zero external magnetic field without either special functional form of spin-transfer torque, or “field-like” terms, if Gilbert constant corresponds to the overdamped planar regime.

Magnetotransport near a quantum critical point in a simple metal

We present a new Ginzburg-Landau theory for superconductivity in UPt{sub 3}, based upon a multicomponent order parameter transforming under an irreducible space group representation; the phase is staggered in real space. Our model can explain the {ital H}-{ital T}-{ital P} phase diagram including the tetracritical point for all field directions. We motivate this unconventional superconducting state in terms of odd-in-frequency pairing that may arise in one- or two-channel Kondo models, and suggest experimental tests.

Two scenarios of spin-transfer switching and criteria for the corresponding threshold currents

Planar spin-transfer devices with dominating easy-plane anisotropy can be described by an effective one-dimensional equation for the in-plane angle. Such a description provides an intuitive qualitative understanding of the magnetic dynamics. We give a detailed derivation of the effective planar equation and use it to describe magnetic switching in devices with tilted polarizer.