Coercivity mechanism in (CoPt) and (CoPd) multilayers

Abstract

Two approaches are discussed to understand the coercivity mechanism of multilayer ($\text{Co}\text{Pt}$) and ($\text{Co}\text{Pd}$) films with high coercivity and high perpendicular magnetic anisotropy. One approach follows the phenomenological model proposed by Kronmüller et al^(1,2), and the other is the one based on the relaxation mechanism⁽³⁾. The first approach provides the size of the pinning region. Using the measured values of coercivity, magnetization and perpendicular magnetic anisotropy constant as a function of temperature, and assuming the exchange constant and anisotropy of a pinning region to be a half the matrix value, and zero, respectively, one obtains a few Å for a pinning size in the multilayers. The second approach is based on the dependence of apparent coercivity on sweep speed of magnetic field. It is shown that the Barkhausen volume is of the order of 10⁻¹⁸cm³ for those multilayers. The results are compared to the case of Tb₂₆(FeCo)₇₄ amorphous films.