Effects of chemical pressure on the magnetic ground states of the osmate double perovskites SrCaCoOsO6 and Ca2CoOsO6

TL;DR

This study investigates how chemical pressure influences magnetic ground states in Sr2-xCaxCoOsO6 double perovskites, revealing a transition from antiferromagnetic to spin glass to ferrimagnetic states as Ca content increases.

Contribution

It demonstrates the impact of chemical pressure on magnetic interactions and ground states in double perovskites, with detailed structural and magnetic analysis of SrCaCoOsO6 and Ca2CoOsO6.

Findings

Magnetic ground state changes from antiferromagnetic to spin glass to ferrimagnetic with increasing Ca content.

Small changes in Co-O-Os bond angle significantly affect magnetic properties.

Two magnetic transitions observed in Sr2CoOsO6 and SrCaCoOsO6 indicating weak coupling between sublattices.

Abstract

The magnetic ground state in the double perovskite system Sr2-xCaxCoOsO6 changes from an antiferromagnet (x = 0), to a spin glass (x = 1), to a ferrimagnet (x = 2) as the Ca content increases. This crossover is driven by chemical pressure effects that control the relative strength of magnetic exchange interactions. The synthesis, crystal structure, and magnetism of SrCaCoOsO6 and Ca2CoOsO6 are investigated and compared with Sr2CoOsO6. Both compounds adopt a monoclinic crystal structure with rock salt ordering of Co2+ and Os6+ and a-a-b+ octahedral tilting, but the average Co-O-Os bond angle evolves from 158.0(3) degrees in SrCaCoOsO6 to 150.54(9) degrees in Ca2CoOsO6 as the smaller Ca2+ ion replaces Sr2+. While this change may seem minor it has a profound effect on the magnetism, changing the magnetic ground state from antiferromagnetic in Sr2CoOsO6 (TN1 = 108 K, TN2 = 70 K), to a spin glass in SrCaCoOsO6 (Tf1 = 32 K, Tf2 = 13 K), to ferrimagnetic in Ca2CoOsO6 (TC = 145 K). In the first two compounds the observation of two transitions is consistent with weak coupling between the Co and Os sublattices.