Transition between long and short-range helical orders in mixed B20 cubic helimagnets

TL;DR

This paper models how defect bonds in B20 helimagnets affect magnetic order, showing that defects can disrupt long-range helical order and induce short-range ordering, aligning with experimental observations.

Contribution

It introduces a model accounting for defect-induced distortions in B20 helimagnets and explains the transition from long-range to short-range helical order.

Findings

Defects cause dipolar-like distortions in magnetic order.

Finite defect concentration modifies the spiral vector.

Strong defects can destroy long-range order, leading to short-range helical phases.

Abstract

A model of B20 helimagnet with strong (frustrating) defect bonds is considered. Single defect provides dipolar field-like distortion of the helical magnetic ordering. At finite defect bond concentrations, the spiral vector acquires correction to its value in the pure system. Moreover, it is shown that the strong defects of sufficient but small concentration are able to destroy long-range order driving the system to the phase with short-range helical ordering. It is argued that the developed approach allows describing main experimental observations in Mn$_{1-x}$Fe$_x$Si and Mn$_{1-x}$Co$_x$Si compounds.