Study of polycrystalline bulk Sr$_3$OsO$_6$ double-perovskite insulator: comparison with 1000 K ferromagnetic epitaxial films (2002.06743v1)

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.

• The paper demonstrates that polycrystalline Sr3OsO6 synthesized under high-pressure conditions exhibits dominant antiferromagnetic interactions, in contrast to the strong ferromagnetism in epitaxial films at 1000 K.
• The research employs high-pressure synthesis and comprehensive X-ray diffraction analysis to confirm a triclinic structure with similar lattice parameters across bulk and film forms.
• The study reveals semiconducting transport and unusual thermal properties suggesting fermionic-like excitations, which open avenues for further exploration in spintronic applications.

Analysis of Polycrystalline Sr$_3$OsO$_6$ Double-Perovskite Insulator: A Comparative Study with High-Temperature Ferromagnetic Films

The paper investigates the synthesis and characterization of the polycrystalline Sr$_3$OsO$_6$ double-perovskite insulator, drawing a comparative analysis with epitaxially grown films exhibiting ferromagnetic properties at temperatures above 1000 K. The paper aims to elucidate the underlying mechanisms of high-temperature ferromagnetism found in these films by examining the bulk form, which showcases contrasting magnetic properties predominated by antiferromagnetism.

Synthesis and Structural Characterization

The polycrystalline Sr$_3$OsO$_6$ was synthesized via a solid-state reaction under high-pressure (6 GPa) and high-temperature (1200 °C) conditions. The structural investigations were carried out using X-ray diffraction analysis with both commercial apparatus and synchrotron XRD. The XRD patterns confirmed that both the film and bulk forms share the same lattice basis, yet remarkably different magnetic characteristics. The refined structure of the polycrystalline form, best described by a triclinic symmetry (P-1 space group), further emphasizes the similarities in the lattice parameters when compared to the film.

Magnetic and Thermal Properties

A key finding of the research is the distinct lack of long-range ferromagnetic (FM) order in the bulk form at temperatures above 2 K, contrary to the strong ferromagnetic behavior of the film. This difference in magnetic ground states is primarily associated with the interfaces present in the film, which are absent in the bulk. The magnetic susceptibility measurements displayed a glassy transition or a weak ferromagnetic component at approximately 12 K. The absence of significant ferromagnetic characteristics in the bulk form, as indicated by the reduced magnetization and negative Weiss temperature (-47 K), alludes to dominating antiferromagnetic (AFM) interactions influenced by the structure and composition.

The charge transport properties, characterized by electrical resistivity, demonstrated a semiconducting-like behavior in the bulk, with resistivity trending under the Efros-Shklovskii variable range hopping model indicating disorder and long-range Coulomb interactions. Furthermore, specific heat capacity measurements revealed an unusually high γ value, suggesting potential fermionic-like excitations at the magnetic ground state.

Implications and Future Directions

The findings have profound implications on our understanding of magnetism in perovskite materials, highlighting the unique role of interface effects in driving FM behavior. The absence of high-temperature FM order in the bulk Sr$_3$OsO$_6$ underscores the necessity to investigate the interplay of structural, electronic, and spin dynamics at interfaces.

The observed large γ value and potential fermionic-like excitation prompt further theoretical and experimental studies to explore unconventional magnetic ground states, possibly linked to spin-liquid phases in 5d transition metal oxides. Future work could focus on understanding the spin-orbit coupling's influence on magnetism and the potential for exploiting such characteristics in spintronic applications.

Overall, the paper sheds light on the complex magnetic behavior of Sr$_3$OsO$_6$ and provides a framework for exploring interface-driven phenomena in oxide materials. This research contributes to the broader context of material science by reinforcing the importance of structural details in determining electronic and magnetic properties, paving the way for the development of advanced functional materials.