Magnetic coercivity is often viewed to be lower in alloys with negligible (or zero) values of the anisotropy constant. However, this explains little about the dramatic drop in coercivity in FeNi alloys at a non-zero anisotropy value. Here, we develop a theoretical and computational tool to investigate the fundamental interplay between material constants that govern coercivity in bulk magnetic alloys. The two distinguishing features of our coercivity tool are that: (a) we introduce a large localized disturbance, such as a spike-like magnetic domain, that provides a nucleation barrier for magnetization reversal; and (b) we account for magneto-elastic energy—however small—in addition to the anisotropy and magnetostatic energy terms. We apply this coercivity tool to show that the interactions between local instabilities and material constants, such as anisotropy and magnetostriction constants, are key factors that govern magnetic coercivity in bulk alloys. Using our model, we show that coercivity is minimum at the permalloy composition (Fe21.5Ni78.5) at which the alloy's anisotropy constant is not zero. We systematically vary the values of the anisotropy and magnetostriction constants, around the permalloy composition, and identify new combinations of material constants at which coercivity is small. More broadly, our coercivity tool provides a theoretical framework to potentially discover novel magnetic materials with low coercivity.
Bibliographical noteFunding Information:
The authors acknowledge the Minnesota Supercomputing Institute at the University of Minnesota (Dr. David Porter), and the Advanced Research Computing at the University of Southern California for providing resources that contributed to the research results reported within this paper. The authors acknowledge the support of NSF (DMREF-1629026), ONR (N00014-18-1-2766). R.D.J and A.R.B, respectively, acknowledge the support of a Vannevar Bush Faculty Fellowship and a Provost Assistant Professor Fellowship. Finally, the authors thank anonymous reviewers for their insightful comments that have helped improve this manuscript.
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- Nucleation barrier