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Mixed Nd4+/3+ and Cluster Magnetism in Hexagonal Perovskite 12R-Ba4NdMn3O12-γ
Liam A V Nagle-Cocco1, Madeline G Port1,2, James Eujin Park3
1Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California94025, United States.
Abstract:
Hexagonal perovskite oxides with 12R stacking host well-separated face-sharing octahedral metal trimers with short metal-metal distances, leading in some cases to large degrees of magnetic frustration and cluster magnetism. Introducing magnetic ions in proximity to these trimers can influence the degree of frustration and cluster magnetism, but the extent to which the magnetism can be tuned by varying neighboring metal cations remains an open question. In this work, we test the impacts of using Nd in proximity to Mn trimers in the hexagonal perovskite 12R-Ba4NdMn3O12-γ. Given this stoichiometry, Nd should assume the 4+ oxidation state with a spin state of S = 1, which would be the first realization of Nd4+ in an oxide environment. Through detailed bulk magnetic, X-ray absorption spectroscopic, and powder neutron diffraction (PND) measurements, we find that Nd4+ is realized in this material, but there is also partial reduction to Nd3+, which is charge-balanced by O vacancies. Magnetometry measurements indicate an antiferromagnetic ordering temperature TN ≈ 16 K, and PND measurements reveal a surprising collinear antiferromagnetic structure with magnetic space group Pc2/m (no. 10.49 in BNS notation), which has not previously been seen in this class of materials. Our results represent a comprehensive analysis of the structural, electronic, and magnetic properties of 12R-Ba4NdMn3O12-γ, showing the first observation of partial Nd4+ in an oxide, and demonstrating that this structural class can host a broad range of magnetic structures which are not easily predicted based on compositional trends.
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