Coercivity of Ultrathin Magnetic Films with Perpendicular Anisotropy

Abstract

The calculation of the temperature dependence of the domain wall coercivity of ultrathin magnetic films with perpendicular anisotropy is reported. In this case, the magnetization reversal is supposed to occur through domain wall motion. The proposed model takes into account thermal bending fluctuations of the domain wall , which is pinned by crystal defects such as grain boundaries. A fitting procedure, applied to recently published experimental data on the field induced domain wall velocity in Au/Co films, allows us to find out realistic values of the involved parameters.PACS numbers: 75.60. 75.60.Ch, 75.70.Ak In many experiments, which had been performed for ultrathin ferromagnetic films and multilayers, either a nonlinear or almost linear law of the coercivity decrease with the increase in the film temperature has been found (for a review see Refs. [1][2][3][4]). This decrease can be understood as coming from a mechanism of thermally activated domain wall (DW) motion. Indeed, the DW coercivity at T = 0 is determined by a value of the energy barrier which separates two different positions of a DW segment. At T > 0 the energy of thermal oscillations of the . DW segment favours to overcome the coercivity barrier and decreases its effective value.The goal of this paper is to thermodynamically examine the bending oscillation of DW and the mechanism of their movement in ultrathin magnetic films with a perpendicular anisotropy. The basis is the DW vibration model similar to that applied in Ref. [5] for the description of the bend fluctuations of long molecules.Let us suppose that a segment of the DW is pinned to two defects (or to grain boundaries) and that the distance between them is 2R. We consider a limp type of DW and a weak DW pinning regime. For T > 0 the DW can change its form owing to the effect of the temperature fluctuations. We will describe the form of the DW bend by the following equation y = b/ch(x/R) (here b is the amplitude of the DW bending). The magnetic field is directed perpendicular to the film surface.(471)

Giant spin Hall effect and magnetotransport in a Ta/CoFeB/MgO layered structure: A temperature dependence study

“…where H 0 is the coercivity at 0K and the constant a depends on the activation energy of DW motion [29][30][31]. Fig.7(b) shows that between 5K and 150K, Eq.…”

Analysis of Magnetic Domain Sizes in Ultrathin Ferromagnetic Films

“…The points corresponding to p(t 3 ) and p(t 2 ) were connected by the dotted line to give a qualitative p(t) dependence in this t 3 < t < t 2 thickness range. It is difficult to apply the above presented results to analysis in a micrometer scale (available using an optical microscope) of domain structures in presently available ultrathin samples characterized by large local coercivity [11] out of the reorientation region. Shape and size of a domain strongly depend on sample magnetic and thermal history.…”