Experiment and Theoretical Study of Critical Behavior in Magnetic Multilayers

Abstract

Ni/NM multilayers (with noble metal NM = Au, Ag and Cu) were prepared by the electron beam evaporation method under ultra high vacuum conditions. The magnetic properties of Ni/NM multilayers are examined as a function of Ni layer thickness t Ni . The temperature dependence of the spontaneous magnetization M(T ) is well described by a T 3/2 law in all multilayers. A spin-wave theory has been used to explain the temperature dependence of the magnetization and the approximate values for the bulk Exchange interaction J b and surface exchange interaction J s for various Ni layer thicknesses have been obtained.In the other hand we have used the high-temperature series expansion technique, to analyze the phase transition and the critical phenomena of a ferromagnetic a two-component multilayer, through three models: Ising, XY and Heisenberg. The critical reduced temperature τ c (ν) is studied as function of the thickness of constituents in the unit cell of the mul-R. Masrour ( ) Laboratory of Materials, Processes, Environment and Quality, tilayer. In the two-component multilayer τ c (ν) is studied as function of the exchange interaction in each material and within the interface J s , J b and J ⊥ , respectively. A critical value of the surface exchange interaction in the film and interface exchange interaction in the multilayer above which the surface and the interface magnetism appears is obtained. The dependence of the reduced critical temperature on the thickness of the film and the unit cell of multilayer has been investigated. The effects of an amorphous magnetic surface on the critical properties of the film of simple cubic lattice have been studied. A number of characteristic behaviors, such as the possibility of the existence of a critical length of the unit cell thickness at which the temperature of the multilayer remains insensitive to the exchange coupling within interface, are reported.In a defined range of the exchange interactions, the values of γ are comparable to the universal ones and are independent of the film thickness. The asymmetry of the structure and the competition of the effects of the exchange coupling are important for the magnetic properties of the system.