Analysis of magnetization processes in composite media grains

Abstract

Composite grains, consisting of a subgrain with high anisotropy field coupled with a subgrain with zero anisotropy, are analyzed using a two-spin model. An analytical expression is given for the exchange coupling between the subgrains that minimizes the field required to reverse the magnetically hard layer. The results of the two-spin model are compared with those of a spin chain that represents an “exchange spring magnet.” The limitations of the two-spin model are worked out.

The influence of magnetostatic interactions in exchange-coupled composite particles

“…In Ref. [8], the figure of merit does not exceed 2 whereas some cc m values in our study do exceed 2. This difference in the figure of merit maxima again highlights the effects of magnetostatic interactions in the magnetic response of ECC particles.…”

“…Richter et al [8] introduced a model for ECC particles that neglects magnetostatic interactions. For modeling purposes, micromagnetic simulations are generally the method of choice [7,[9][10].…”

“…Equations (6)(7)(8) were derived based on the integral form of the dipolar coupling factor, as discussed in [11] and [12]. The demagnetization factors of cylinders and shells can be expressed as combinations of elliptic integrals [11,16].…”

“…From this dependence, we can determine the optimum exchange coupling strength corresponding to a maximum switching field reduction. Knowing the optimum switching field and the energy barrier at zero applied field, one can then compute a figure of merit, as defined in [4,8].…”

“…Since thermal stability is related to the energy barrier at zero applied field, both the switching field and the energy barrier have to be evaluated. For this purpose, the concept of "figure of merit" was defined in references [4,8] …”