Evolution of Magnetic Symmetry through the BiFeO3–Ca2Fe4/3W2/3O6 Phase Diagram

Abstract

Perovskites offer vast flexibility in tuning subtle distortions in their structures through their innate ability to host a wide range of compositional combinations. Minor changes in composition can dramatically influence the properties observed through structural distortions such as octahedral tilting. In addition to understanding their properties, in magnetic materials, the magnetic structure is also tied to the nuclear structural distortions and can have more complex behavior with changing composition. In this work we report on the magnetic properties, and nuclear and magnetic structures of the solid solution (1 – x)BiFeO₃ – (x/2)Ca₂Fe_4/3W_2/3O₆. With the exception of BiFeO₃, all samples show a weak ferromagnetic behavior arising from spin canting. We find that despite only one structural phase transition occurring from R3c to Pnma in this solid solution, the magnetic phase diagram is far more complex, with four distinct magnetic phases occurring in the compositional range 0.1 < x < 1. Using a combination of neutron and X-ray diffraction, we find that a crossover between long and short Fe–O bond lengths and divergence of Fe–O–Fe bond angles with composition drive the changes in magnetic structure and can be correlated to the resulting magnetic properties.

This article investigates the effect of subtle structural distortions on the magnetic structures and properties across the (1 − x)BiFeO₃−(x/2)Ca₂Fe_4/3W_2/3O₆ solid solution. We find that not only is there a rhombohedral to orthorhombic nuclear structure phase transition with regions of phase coexistence, but multiple additional changes to the magnetic structure driven by subtle changes to the B-site bond lengths and angles with varying composition. We relate these structural distortions to the observed magnetic properties.