Abstract
The effects of chemical pressure on the structural and magnetic properties of the triple perovskite are investigated by substituting ions for ions. Two phases could be stabilized via a solid-state reaction at ambient pressure (AP) in air. The with pairs with pairs (cubic with corner-sharing octahedral, ) sequence of structural phases occurs with increasing Sr content, i.e., chemical pressure, which is like that previously reported for pure samples of obtained under increasing high physical pressure (HP). For the phase, using combined Rietveld refinements of powder x-ray and neutron diffraction patterns, precession electron diffraction tomography data collected on thin crystals, aberration-corrected high-angle annular dark field scanning transmission electron microscopy coupled to energy dispersive x-ray spectroscopy mapping, we reach the conclusion that the structure features corner-sharing octahedra and pairs of face-shared octahedra (or Ni-Sb dumbbells) with either a random orientation of the Ni-Sb dumbbells or nanosized chemical correlations for the dumbbell arrangement. As observed in HP produced through synthesis at 9 GPa, AP crystallizes in a double perovskite cubic structure where , and sites are occupied by (Ba + Sr), Sb, and atoms, respectively. The sites, which are randomly occupied by spin-1 and diamagnetic , form a face-centered-cubic (FCC) sublattice where the amount stays above the site percolation threshold. Weiss temperatures ( and K for and , respectively) indicate that dominant magnetic interactions between spins are antiferromagnetic with magnitudes like those observed in the corresponding HP phases of pure . As for the HP compound, in , muon spin relaxation measurements identify a dynamic magnetic state down to the base temperature (95 mK), consistent with a previously published inelastic neutron scattering study. For and nuclear magnetic resonance measurements both indicate the presence of a transition to a static magnetic state below K with a significant amount of disorder in this frozen state, in contrast to the spin-liquid state previously suggested for the HP phase of . Consistently, a broad maximum is observed in the specific heat at the same temperature. Building on the structural data, the magnetic properties of HP and AP are discussed in light of recent works on triangular and honeycomb systems with or without quenched disorder. We are led to the conclusion that the driving force toward a spin-liquid-like state is quenched disorder which needs to be incorporated in honeycomb models. Our evidence of a magnetic transition to a frozen magnetic ground state for the AP Sr-doped phase is in line with models for geometrically frustrated FCC antiferromagnets. This calls for a better experimental and possibly theoretical understanding of the HP phase.
9 More- Received 3 June 2022
- Accepted 16 November 2022
DOI:https://doi.org/10.1103/PhysRevMaterials.6.124408
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