Design of magnetic spirals in layered perovskites: extending the stability range far beyond room temperature

TL;DR

This paper demonstrates how combining chemical disorder with lattice control in layered perovskites can significantly raise the magnetic spiral ordering temperature, approaching 400 K, and establishes a universal relationship between spiral wave vector and transition temperature.

Contribution

It introduces a novel design strategy for magnetic spirals in layered perovskites that achieves higher transition temperatures and provides general rules for engineering these phases for practical use.

Findings

Achieved spiral ordering temperatures close to 400 K in Cu-Fe layered perovskites.

Discovered a linear, universal relationship between spiral wave vector and transition temperature.

Identified a paramagnetic-collinear-spiral triple point limiting maximum ordering temperature.

Abstract

In insulating materials with ordered magnetic spiral phases, ferroelectricity can emerge due to the breaking of inversion symmetry. This property is of both fundamental and practical interest, in particular with a view to exploiting it in low-power electronic devices. Advances towards technological applications have been hindered, however, by the relatively low ordering temperatures $T_\mathrm{spiral}$ of most magnetic spiral phases, which rarely exceed 100 K. We have recently established that the ordering temperature of a magnetic spiral can be increased up to 310 K by the introduction of chemical disorder. Here we explore the design space opened up by this novel mechanism by combining it with a targeted lattice control of some magnetic interactions. In Cu-Fe layered perovskites we obtain $T_\mathrm{spiral}$ values close to 400 K, comfortably far from room temperature and almost 100 K higher than using chemical disorder alone. Moreover, we reveal a linear, universal relationship between the spiral's wave vector and the onset temperature of the spiral phase. This linear law ends at a paramagnetic-collinear-spiral triple point, which defines the highest spiral ordering temperature that can be achieved in this class of materials. Based on these findings, we propose a general set of rules for designing magnetic spirals in layered perovskites using external pressure, chemical substitutions and/or epitaxial strain, which should guide future efforts to engineer magnetic spiral phases with ordering temperatures suitable for technological applications.