In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

Publisher Summary This chapter discusses the magnetocaloric effect (MCE) in the vicinity of phase transitions Magnetothermal properties of materials were demonstrated because of their significance for the development of fundamental and applied magnetism These phenomena have a strong influence on the character of the behavior of such fundamental physical quantities as the entropy, specific heat, and thermal conductivity, and could lead to a number of extra anomalies in the dependencies of the material properties on temperature, magnetic field, and some other external parameters The MCE is the change of the initial temperature of a magnetic material as an external magnetic field is applied under conditions of constant total entropy of the material It describes the processes of entropy variation of the magnetic subsystem The chapter discusses the character of the MCE behavior in different magnetic materials and reviews the studies of this effect The materials with magnetic moments of either band or localized origin, and materials where the magnetic ordering can have collinear, and more complicated character, such as helical are reviewed in the chapter The MCE is utilized in magnetic refrigeration machines

Chapter 4 Magnetocaloric effect in the vicinity of phase transitions

A unified approach has been developed to study nonlinear dynamics of a 1D lattice of particles with long-range power-law interaction. A classical case is treated in the framework of the generalization of the well-known Frenkel–Kontorova chain model for the non-nearest interactions. Quantum dynamics is considered following Davydov's approach for molecular excitons. In the continuum limit the problem is reduced to dynamical equations with fractional derivatives resulting from the fractional power of the long-range interaction. Fractional generalizations of the sine-Gordon, nonlinear Schrodinger, and Hilbert–Schrodinger equations have been found. There exists a critical value of the power s of the long-range potential. Below the critical value ( s 3 , s ≠ 1 , 2) we obtain equations with fractional derivatives while for s ⩾ 3 we have the well-known nonlinear dynamical equations with space derivatives of integer order. Long-range interaction impact on the quantum lattice propagator has been studied. We have shown that the quantum exciton propagator exhibits transition from the well-known Gaussian-like behavior to a power-law decay due to the long-range interaction. A link between 1D quantum lattice dynamics in the imaginary time domain and a random walk model has been discussed.

Nonlinear fractional dynamics on a lattice with long range interactions

A consistent consideration of ferromagnetic alloys undergoing a cubic-tetragonal martensitic transformation on cooling is carried out within the framework of Landau theory. The concept of two different Curie temperatures, corresponding to the parent (austenitic) and resultant (martensitic) phases, is substantiated by taking into account the volume magnetostriction of an alloy. The difference in these two temperatures is evaluated for different alloys from the Ni-Mn-Ga family typifying ferromagnetic martensites. A statistical dispersion of the local Curie temperatures reflecting the heterogeneity of martensitic states is introduced. The qualitatively different temperature dependencies of the magnetization are predicted theoretically and observed experimentally under an applied magnetic field of about 10 kOe. Quantitative agreement between the theoretical and experimental curves is achieved.

Ferromagnetism of thermoelastic martensites: Theory and experiment

This paper presents an investigation of the self-focusing of cosh-Gaussian laser beam in a plasma with linear absorption taking into account the combined effects of relativistic and ponderomotive type nonlinearities. Nonlinear parabolic partial differential equation governing the evolution of complex envelope in slowly varying envelope approximation is solved using variational approach. Self-focusing and self-phase modulation as well as self-trapping of cosh-Gaussian beam are studied at various values of decentered parameter b, with different absorption levels ki′. Numerical analysis shows that these parameters play vital role on propagation characteristics.

V.P. Silin

Papers

Third-harmonic generation in a laser-pre-excited gas: the role of excited-state neutrals

Theory of nonlocal heat transport in fully ionized plasma

Stimulated brillouin scattering in weakly collisional plasmas

On small perturbations of stationary states in a nonlinear nonlocal model of a Josephson junction

About smooth phase transitions in ferromagnetic Invar alloys