I. E. Dikshtein

Shape memory effect due to magnetic field-induced thermoelastic martensitic transformation in polycrystalline Ni–Mn–Fe–Ga alloy

Abstract In Heusler-type alloy Ni 2+ x − y Mn 1− x Fe y Ga, partial substitution of Mn for Ni causes the temperatures of structural (martensitic) T M and magnetic T C (Curie point) phase transitions to converge. Close to the crossover of T M and T C , we have observed the strong strains ( Δl / l ≈2–4%) induced by the external magnetic field. This effect could be classed with colossal magnetostriction. The system exhibits the magnetic field-controlled one-way shape memory effect at fixed temperature as a result of the magnetic field-induced martensite to austenite structural phase transition.

Phase transitions in intermetallic compounds Ni-Mn-Ga with shape memory effect

The effect of a magnetic field on the formation of structural domains at martensitic transition in the intermetallic system Ni/sub 2+x/Mn/sub 1-x/Ga was studied. For the compositions x whose temperatures of structural and magnetic transitions are close this effect is most pronounced. In the field of 0.2 to 1 T the increase in the transition temperature is linear with the coefficient of 0.015 K/T. Estimates of the transition temperature shift based on thermodynamic calculations are in good agreement with the experimental data. It is shown that the switching on the magnetic field at some critical temperature induces partial transformation of austenite into martensite.

Reversible structural phase transition in Ni-Mn-Ga alloys in a magnetic field

In Ni2+xMn1−xGa shape-memory ferromagnetic alloys with coincident magnetic and structural phase transitions, a reversible structural field-induced phase transition was observed at constant temperature and pressure in magnetic fields of about 10 T. Computational results are in qualitative agreement with experiment.

Surface polaritons in composite media with time dispersion of permittivity and permeability

The propagation of electromagnetic waves in a composite medium based on an array of conducting wires in a ferromagnetic nonconducting matrix is discussed. It is demonstrated that, in certain ranges of frequencies and wavelengths, the composite under investigation can possess properties inherent in a “left-handed” medium. The regions of the existence of bulk and surface localized electromagnetic waves are explored. Consideration is given to the dispersion of surface electromagnetic waves in thick layers of the composite.

Structural and magnetic phase transitions in shape memory alloys Ni2+xMn1-xGa

Abstract The Heusler-type alloys Ni 2 + X Mn 1 − X Ga exhibit well-defined shape memory properties in a ferromagnetic state. The change of composition X moves martensitic transition temperature T M and the Curie point T C towards each other. To study this behavior, the measurements of AC magnetic susceptibility and DC resistivity were performed. The correspondence of the experimental data with calculated T—X phase diagram is discussed.

Giant magnetoresistance in a three-dimensional lattice of dipolar interacting magnetic nanoparticles

The magnetization and the giant magnetoresistance (GMR) of three-dimensional multilayered lattice of dipolar interacting fine anisotropic magnetic particles embedded in a nonmagnetic metallic matrix are numerically investigated. Using a Monte Carlo method the dependence of the magnetization curve and the GMR effect on the magnetic field H , temperature, the number of layers, the magnetic anisotropy, the separation between neighboring particles, and the particle-size distribution are examined systematically. We found that the enhanced dipolar interaction at high particle densities and for wide particle-size distributions reveals itself as a substantial suppression in the change in the negative MR with the applied field H . For out-of-plane magnetic field orientation, the negative MR is shown to increase more rapidly with H as the number of layers increases. This effect is attributed to the demagnetization field arising from the free magnetic poles forming at the sample surface. The relevance of the present results to the understanding of the magnetic and transport properties in granular composites is discussed.  2001 Elsevier Science B.V. All rights reserved.

3D surface precession solitons (surface magnetic drops) in uniaxial magnets

Abstract A new class of nonlinear excitations in magnetic materials is considered. These excitations are surface magnetic solitons or magnetic drops localised near the surface of a crystal. The dependence of the precession frequency on the magnon number is found for surface solitons in uniaxial ferro- and antiferromagnets.

Stochastic resonance of front motion in inhomogeneous media

Abstract We study the motion of a front in a bistable system with two adjacent localized attracting inhomogeneities. We assume that the front is trapped by the inhomogeneities. If the system is additionally driven by noise the front is able to perform stochastic motion and hence achieves a probability to jump between the several attracting inhomogeneities. With a small periodic force applied to the system we will observe stochastic resonance in the motion of the front. At an optimal noise level the hopping dynamics of the front becomes most coherent and the response of the system to the periodic force is maximal. This effect is proposed for the control of front motion and as techniques for measurements in inhomogeneous bistable dynamics.

Stochastic resonance of elastic string motion

A model for the motion of an elastic string is studied numerically and analytically. An elastic string in two dimensions and restricted by two pinning centers is considered. We consider two stable configurations (positively or negatively curved) with pinned ends due to the action of a bistable potential. It is further assumed that the string is driven externally by periodic and white noisy forces. The noise enables the string to flip between the two configurations. The small temporally periodic force synchronizes these flippings and the phenomenon of stochastic resonance is observed. The signal-to-noise ratio (SNR) of the output is investigated and shows a maximum for a nonvanishing intensity of the applied noise. Its dependence on the stiffness of the string is studied. The peak of SNR versus the noise intensity D is found to be more pronounced and to be shifted to small values of D with an increase in the effective stiffness of a string. The calculation is extended to stochastic resonance of vortex moti...

Magnetoelastic domain structure in a film of a rhombic ferromagnet on a nonmagnetic substrate

Abstract A ground state of a tangentially magnetized ferromagnetic film of arbitrary thickness L on a massive substrate in the vicinity of the spin-reorientational phase transition (RPT) induced by temperature is studied. A new magnetoelastic phase with spatially modulated order parameter is predicted, the existence of which is associated with the magnetostriction coupling of magnetization to lattice deformation on the crystal interface. It is demonstrated that the RPT from the uniform to the domain phase is the second order one. A domain nucleation close to the RPT temperature is analyzed. The main parameters of a developed domain structure away from the RPT temperature are determined.