Study of polycrystalline bulk Sr$_3$OsO$_6$ double-perovskite insulator: comparison with 1000 K ferromagnetic epitaxial films

TL;DR

This study compares the magnetic properties of bulk and epitaxial film Sr$_3$OsO$_6$, revealing that bulk is antiferromagnetic while ferromagnetism in films is interface-driven, highlighting the influence of synthesis conditions on magnetic behavior.

Contribution

It provides the first detailed comparison between bulk and film Sr$_3$OsO$_6$, elucidating the role of interfaces in inducing ferromagnetism in epitaxial films.

Findings

Bulk Sr$_3$OsO$_6$ is antiferromagnetic, unlike ferromagnetic films.

High low-temperature specific heat suggests fermionic-like excitations.

Magnetism differs despite identical lattice and insulating state.

Abstract

Polycrystalline Sr$_3$OsO$_6$, which is an ordered double-perovskite insulator, is synthesized via solid-state reaction under high-temperature and high-pressure conditions of 1200 $^\circ$C and 6 GPa. The synthesis enables us to conduct a comparative study of the bulk form of Sr$_3$OsO$_6$ toward revealing the driving mechanism of 1000 K ferromagnetism, which has recently been discovered for epitaxially grown Sr$_3$OsO$_6$ films. Unlike the film, the bulk is dominated by antiferromagnetism rather than ferromagnetism. Therefore, robust ferromagnetic order appears only when Sr$_3$OsO$_6$ is under the influence of interfaces. A specific heat capacity of 39.6(9) 10$^{-3}$ J mol$^{-1}$ K$^{-2}$ is found at low temperatures ($<$17 K). This value is remarkably high, suggesting the presence of possible fermionic-like excitations at the magnetic ground state. Although the bulk and film forms of Sr$_3$OsO$_6$ share the same lattice basis and electrically insulating state, the magnetism is entirely different between them.