Domain wall displacements in amorphous films and multilayers studied with a magnetic force microscope

Abstract

The magnetic force microscope (MFM) was used to study the displacement of domain walls (DW) in amorphous TbFe alloy films and Co/Pd multilayer films with high spatial resolution. The reversible bending of domain wall segments pinned to defects and irreversible, jumplike displacement of domain wall segments were imaged with the MFM in an applied magnetic field. The maximum reversible displacement of domain walls was 50–100 nm and the length of the segments which reversibly curved in the field was about 150 nm. Measurement of the change in radius of curvature of a DW segment in response to an applied field allowed estimation of the DW energy density and self-demagnetizing field of the film acting on the DW. The DW energy density for the TbFe films was about 1 erg/cm2. It was shown that the self-demagnetizing field acting on a domain wall depends on the domain structure surrounding the studied DW segment. For instance, for a film with saturation magnetization 100 G and thickness 80 nm, which exhibited a mazelike domain structure, the demagnetizing field varied from 100 G in the center of a mazelike domain to 400 G near the edge of a domain. The irreversible displacement of a DW was not a continuous process. The 200–400 nm long DW segments exhibited jumplike motion over distances of 100–150 nm.

Magnetization reversal at elevated temperatures in Co/Pt multilayer thin films

“…It should be noted that care has to be taken in obtaining and interpreting MFM images, as the imaging process is intrinsically invasive. Due to the tip being magnetic, and therefore possessing a stray field, the imaging of a sample may itself alter the domain configuration within the sample [35]. The tip stray field could be at least 620 Oe [36] and may therefore cause domain walls to move, or in the worst case, saturate the area being imaged and hence erase any domains.…”

Length Scale Coupling for Nonlinear Dynamical Problems in Magnetism

“…At larger length scales (microns), the magnons propagate into the bulk of the sample carrying away significant energy. Such multiscale phenomena are encountered in the depinning of DW [1,2,3,4], the influence of surfaces and interfaces on the spins in the bulk [5,6,7,8], etc. These phenomena determine basic magnetic properties such as the coercive field and the dynamics of magnetization reversal.…”

“…where Q is the statistical integral, and the torques F j and G j are determined from the conditions of local equilibrium: µ f µ,j α 1µ = α 1j , and µ f µ,j α 2µ = α 2j , where the angular brackets mean the statistical averaging with the distribution function (2).…”