The experimental observation of direct and reverse martensitic transformation due to ultrasound processing of Ni–Mn–Ga alloy is discussed. It was found that martensite–austenite as well as austenite–martensite structural transitions can be induced by the intense ultrasound at constant temperature. During the experiments low magnetic field susceptibility measurements and optical detection of twin domains arising due to martensitic transformation were performed in situ. The non-thermal nature of the effect is confirmed making use of the pulsed ultrasound technique.

The magnetic and thermodynamic properties of a Ni2.19Mn0.81Ga alloy with coupled magnetic and structural (martensitic) phase transitions were studied experimentally and theoretically. The magnetocaloric effect was measured by a direct method in magnetic fields 0–26 kOe at temperatures close to the magnetostructural transition temperature. For theoretical description of the alloy properties near the magnetostructural transition a statistical model is suggested, that takes into account the coexistence of martensite and austenite domains in the vicinity of martensite transformation point.

A model for the motion of a single ferromagnetic domain is studied numerically and analytically. A single strip in two dimensions and pinned at two inhomogeneities is considered. We suppose two stable configurations (positively or negatively curved with pinned ends) due to the action of a bistable potential. Further, it is assumed that the domain is driven externally by periodic and noisy magnetic fields. The noise makes the domain able to flip between the two configurations. The small temporally periodic fields synchronize these flippings and the phenomenon of stochastic resonance is observed. The signal to noise ratio of the output is investigated and shows a maximum for a nonvanishing intensity of the applied noise. Its dependency on the stiffness of the domain is studied.

Anomalous decrease of the sound velocity and the important role that nonlinear processes play near the spin-reorientational phase transitions (OPT) in the limited ferrimagnetic (FM) and antiferromagnetic (AF) crystals make such crystals promising materials for use in electronic devices [1]. The e5ciency of such devices can be raised considerably by using surface waves, since the energy of such waves is concentrated within a thin surface layer. The study of the spectra of magnetoelasic (ME) waves in limited specimens of FM and AF makes it possible to determine the type of soft mode involved in OPT.

A study is made of magnetization distribution and surface magnetoelastic waves (Love waves) propagation in a ferromagnetic film of arbitrary thickness on a bulk substrate in the vicinity of the reorientational phase transition induced by an external magnetic field. A new phase with spatially modulated parameter of order is predicted, the existence of which is associated with magnetostriction coupling of the magnetization to lattice deformation on a crystal interface

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.

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.

We study the motion of a small-angle domain wall (DW) in a rhombic ferromagnet with localized attracting inhomogeneities in the vicinity of the reorientational phase transition induced by temperature. Usually DW can be trapped by the inhomogeneities. If the system is additionally driven by noisy magnetic field the DW is able to perform stochastic motion and hence there is a nonzero probability of DW jumps between several attracting inhomogeneities. With small periodic magnetic field applied to the system we will observe stochastic resonance in the motion of the DW. At an optimal noise level the hopping dynamics of the DW becomes most coherent and the response of the system to the periodic force is maximal.

It is well known that in linear theory, surface spin waves (SW) do not exist in a pure exchange-coupled ferromagnet for the case of free spins at the surface. However, in these approximations of the linear theory the plane volume spin waves (VW), propagating along the surface of a ferromagnet, satisfies not only the Landau–Lifshitz equation for the magnetization motion, but the boundary conditions for the free surface spins. Such VW can be unstable and can be transformed into SW under small changes of a magnetic medium, e.g., if the surface spins are partly pinned. In the present work a new type of self-localized SW in the ferromagnet has been considered. The existence of such waves is conditioned entirely by the nonlinear properties of a ferromagnet. The penetration length of such SW is proportional to 1/A, where A is a maximum of the magnetization amplitude on the surface of the crystal. The dispersion equations have been obtained for pure exchange and dipole-exchange nonlinear SW. In the latter case the influence of the second harmonic generation on the wave propagation at the fundamental frequency was studied. The conditions when the SW excites the VW, carrying the energy into the volume of the crystal, are derived. The nonlinear Schrödinger equation for the SW envelope amplitude was derived and its solitonic solutions are obtained. The estimations of threshold values for the wave numbers of the propagating waves are provided.

Surface spin waves, localizing near the surface of magnets as a consequence of nonlinear properties of material, have been studied in Ref. . According to the Lighthill criterion this wave is modulationally unstable. This can lead to the creation of nonunidimensional surface states. In this work, a new class of nonlinear exitations in a pure exchange-coupled uniaxial ferro- and antiferromagnets is considered. These exitations are 3D surface precession solitons or ‘‘magnetic drops’’ localized near the surface of a crystal. Such solitons are the space localized solutions of the Landau–Lifshits equation of motion for magnetization field with appropriate boundary conditions for the spins on the surface of magnetics. They keep their dynamic structure during the motion in space. The conditions of their stability are found. The problem of soliton motion is considered. It is shown that energy and precession frequency for surface 3D solitons is less than for volume 3D solitons, which was studied in Ref. . The possibility of experimental registration of such solitons is discussed.