V. S. Vlasov

Nonlinear excitation of hypersound in a ferrite plate under the ferromagnetic-resonance conditions

The nonlinear problem of excitation of hypersound by an alternating magnetic field in a normally magnetized ferrite plate is considered. The plate is characterized by uniaxial and cubic anisotropies and exhibits magnetostriction. The equations of motion and boundary conditions for the magnetization components and for the elastic displacement are obtained for the case of the arbitrary angle of the magnetization-vector precession. The obtained system is solved by means of the Runge-Kutta method. It is shown that, in the nonlinear regime, the amplitude of the excited hypersound may exceed the amplitude observed in the linear regime by three or four orders of magnitude and that, simultaneously, the range of effectively excited frequencies extends by a factor of one and a half or two.

Multiregime character of the nonlinear precession of the second-order magnetization under the conditions for the orientational transition

The forced nonlinear precession of the magnetization vector in the normally magnetized magnetic plate is considered under the conditions for the orientational transition. The time dependences and precession patterns of the oscillations of magnetization are presented. Five regimes of precession are revealed: small-amplitude circular precession, precession of the equilibrium position without encircling of center, undamped precession of equilibrium position with encircling of center, damped precession of equilibrium position with encircling of center, and full-scale circular precession. The transitions between the regimes are studied using the 3D model of potential. The domains of the regimes of precession are determined on the plane decay parameter-ac field amplitude. It is demonstrated that a variation in the amplitude of the ac field leads to the stepwise dynamic orientational transition from the fourth regime to the fifth regime. The recommendations for the practical applications are worked out using the results.

Nonlinear dynamics of the magnetization in a ferrite plate with magnetoelastic properties under the conditions for orientational transition

The nonlinear dynamics of the orientational phase transition of the magnetization vector in a magnetoelastic medium is analyzed. It is demonstrated that the transition involves the precession of the magnetization vector accompanied by the elastic oscillations at the same frequency. The critical constants of magnetoelasticity, elasticity, and magnetization needed for the transition are determined. It is shown that, in real materials, the magnetoelastic interaction leads to an increase in the field of transition by several or several tens of oersteds. The conditions for and the possibility of an increase in this field by hundreds of oersteds are revealed.

Nonlinear excitation of ultrasound in a two-layer ferrite structure under ferromagnetic resonance conditions

The nonlinear problem of excitation of hypersound in a normally magnetized structure is considered. The structure consists of two ferrite layers, its elastic properties are constant across the entire structure thickness, and the magnetic properties of the layers can be different. The equations of motion and boundary conditions for the magnetization components and elastic displacement are obtained for the case of an arbitrary angle of the magnetization vector precession. Using the decomposition in eigenmodes, the problem is reduced to a system of an infinite number of second-order differential equations. In the case when the first elastic mode is excited, the complete problem is reduced to a system of thirty nonlinear first-order differential equations solved numerically by means of the Runge-Kutta method. The time evolution and amplitude-frequency characteristics of excited oscillations are considered. Conditions under which the amplitude of nonlinear-mode elastic vibrations exceeds the amplitude of linear-mode elastic vibrations by a factor as large as 70 and the bandwidth increases by a factor as large as five are revealed.

Asymmetric forced nonlinear precession of magnetization under the conditions for the orientational transition

The forced nonlinear precession of the magnetization vector in the normally magnetized magnetic plate is analyzed under the conditions for the orientational transition in the presence of the asymmetric static field. The excitation conditions for the precession of the equilibrium position of the magnetization vector are determined. It is demonstrated that the precession pattern of oscillations represents a large circular ring filled with small rings with the nonuniform densening whose position depends on the field asymmetry. The precession of the equilibrium position substantially depends on the degree of asymmetry. When the field exceeds a certain threshold level, the precession of equilibrium is changed by the conventional circular precession with a relatively large amplitude. The domains of existence with respect to dc and ac fields are analyzed for the precession of the equilibrium position. The dependence of the precession period on the degree of asymmetry of the dc field is studied. The main features of the above effects are qualitatively interpreted using complementary (energy and vector) models.

Forced nonlinear precession of the magnetization vector under the conditions of an orientation transition

Forced nonlinear precession of the magnetization vector in a normally magnetized magnetic plate under the conditions of an orientation transition is considered. It is shown that, in the field lower than the form demagnetization field, the variable circularly polarized field causes precession of the equilibrium position of the magnetization vector. It is demonstrated based on a vector model in which the precession period of the equilibrium position is inversely proportional to the squared amplitude of the variable field and the sine of the angle of deviation of the equilibrium position of magnetization from the constant field. It is shown that the critical parameters necessary for excitation of precession of the equilibrium position are the amplitude and frequency of the variable field. Diagrams determining domains of existence of precession of the equilibrium position for different saturation magnetization of a magnetic plate are constructed in terms of the coordinates variable field amplitude-frequency. The role of dissipation of magnetization oscillations in the determination of the critical parameters is elucidated. The features of precession in the presence of asymmetric excitation and in the presence of anisotropy in the plane of the plate are noted.

Second-order magnetization precession in an anisotropic medium. Part 1: Uniaxial anisotropy

A second-order precession of the magnetization vector in a normally magnetized magnetic plate with a uniaxial anisotropy whose axis is tilted at an angle to the plate normal is considered. Under the conditions for the orientational transition, precession pattern of the forced oscillation in the form of a large ring filled, along the ring generator, with small rings is obtained. A relationship between the observed crowding and sparseness of small rings and the tilt of the anisotropy axis to the normal to the plate plane is established and explained on the basis of the potential-energy model. It is shown that the crowding and sparseness can be compensated by a constant transverse field. It has been found that the phenomenon is critically sensitive to the axis orientation and to the value of the anisotropy constant as well as to the strength of the constant field. It is indicated that the observed phenomena can be put to practical use.

Asymmetric excitation of the two-order magnetization precession under orientational transition conditions

The forced nonlinear precession of magnetization vector in the normally magnetized magnetic plate is examined. Investigations are performed under orientational transition conditions at the asymmetric orientations of transverse and longitudinal ac fields. It has been revealed that the precession of equilibrium position exhibits pulse-like behavior under the action of two types of field. This feature manifests itself as the nonuniform bunchings of phase trajectories in the precession pattern. It is demonstrated that the nonuniformity of precession can be compensated by applying the asymmetric dc field. It should be emphasized that the compensation is highly sensitive to the dc field amplitude and reaches several hundredths of a percent of its total value. Recommendations are given to observe the discussed phenomena in the experiment. The possibility of their practical application is discussed.

Magnetic and Relaxation Properties of (CO45Fe45Zr10)x(Al2O3)1-x Thin Films

The work is devoted to the research of the magnetic resonance properties of composite (metal-dielectric) films and revealing their relationship with the nanostructure characteristics and degree of crystallinity. The FMR line width and resonance position for two series of composite films have been investigated. First films series has a small metal crystal phase content. The second one contains metal oxide and amorphous. The results of work shows that oxidation of a metal phase displaces percolation bound to area of the big metal concentration. Strong changes of FMR properties of the films are observed below the percolation bound. The significant changes of FМR properties are connected to nanostructural transformations in the ferromagnetic granules topology and presence of metal phase oxide.

Second Order Precession in the Plate with Cubic Anisotropy and Magnetoelastic Properties

The paper considers the second order precession of the magnetization vector in a perpendicular magnetized anisotropic ferrite plate with magnetoelastic properties. The boundaries of the precession regimes on the frequency and amplitude of the alternating field were defined. The features of the precession of the magnetization vector regimes associated with magnetoelastic properties were revealed.