A solution to the permalloy problem

TL;DR

This paper explains why permalloy with 78.5% Ni exhibits a significant reduction in hysteresis despite no obvious change in material constants, using a new coercivity analysis tool.

Contribution

It introduces a theoretical explanation for the permalloy problem by linking local instabilities and material constants to hysteresis behavior.

Findings

The coercivity tool successfully models the hysteresis drop at 78.5% Ni.

Local instabilities are crucial for understanding hysteresis reduction.

The results align with experimental observations of permalloy.

Abstract

We propose a solution to the longstanding permalloy problem$-$why the particular composition of permalloy, Fe$_{21.5}$Ni$_{78.5}$, achieves a dramatic drop in hysteresis, while its material constants show no obvious signal of this behavior. We use our recently developed coercivity tool to show that a delicate balance between local instabilities and magnetic material constants are necessary to explain the dramatic drop of hysteresis at 78.5% Ni. Our findings are in agreement with the permalloy experiments and, more broadly, provide theoretical guidance for the discovery of novel low hysteresis magnetic alloys.