Theoretical studies of the magnetic multivalued recording in coupled multilayers

Abstract

In this paper, we discuss the possibilities of realizing the magnetic multi-valued (MMV) recording in a magnetic coupled multilayer. The hysteresis loop of a double-layer system is studied analytically, and the conditions for achieving the MMV recording are given. The conditions are studied from different respects, and the phase diagrams for the anisotropic parameters are given in the end.

Phase transitions in random magnetic bilayer with the mean-field approximation

“…Evidently this is due to expected triviality of results (just one magnetic state) for the identical slabs without randomness (yet see Ref. [6]). The present study show that random competing exchange can essentially complicate the variety of phase states in the simplest layered heterostructure.…”

“…The form of the potential in Eq. (6) implies that all its extrema are minima, so all solutions to eqations of state correspond to stable phases. Their stability regions and the equilibrium potential values are:…”

“…Thin films of layered magnets and artificial heterostructures composed of alternating magnetic and nonmagnetic layers can have a variety of stable magnetic states and switching between them can be achieved by different regimes of magnetic field variation 1,2,3 . This opens vast possibilities for numerous technical applications of such structures 4,5,6 and makes theoretical description of their magnetic states and properties of these states very actual. In particular, such description for finite number of layers can be achieved in some variants of mean-field approximations 6,7 or using numerical methods 8,9 , yet the study of ideal homogeneous systems can be insufficient for the description of experimental data.…”

“…This opens vast possibilities for numerous technical applications of such structures 4,5,6 and makes theoretical description of their magnetic states and properties of these states very actual. In particular, such description for finite number of layers can be achieved in some variants of mean-field approximations 6,7 or using numerical methods 8,9 , yet the study of ideal homogeneous systems can be insufficient for the description of experimental data. Indeed, impurities and defects in interlayer space modify generally the exchange constants, which could essentially transform magnetic state of layered structure.…”

Quantum approach for magnetic multilayers at finite temperatures

“…Theoretically, a basic model which considers the exchange energy, the uniaxial anisotropy, and the Zeeman energy has been popularly adopted to discuss various properties of the magnetic multilayers. [8][9][10][11][12][13][14][15][16] Recently, a quantum theory based on this model was established to calculate the hysteresis loop and the coercivity of a magnetic multilayer, 14 and was applied to give a basic consideration of the magnetic multivalued ͑MMV͒ recording in double-film structures 15 and in magnetic granular film. 16 Some authors have tried to extend their methods to finite temperature, for example, using the molecular-field approximation which is good for the hightemperature case, 9 naively applying the Bose-Einstein statistics which is better for the very-low-temperature case 11 or some other assumptions.…”