Inducing Ferrimagnetism in Insulating Hollandite Ba1.2Mn8O16

Published

January 27, 2015

Author(s)

Amber M. Larson, Pouya Moetakef, Karen Gaskell, Craig Brown, Graham King, Efrain E. Rodriguez

Abstract

Folded triangular lattices connecting magnetic metal centers can be realized in the so-called hollandite type structure, providing a new platform for multifunctional behavior in transition metal oxides. The microporous oxide BaMn₈O₁₆ has been tuned from a complex antiferromagnet with T_N=25 K to a ferrimagnet with T_c = 180 K via colbalt substitution for 1/8 of the manganese sites. Both Ba_xMn₈O₁₆ and Ba_xCo_yMn_8-yO₁₆ were prepared by slat flux methods, and combined neutron and X-ray diffraction confirm a distorted hollandite-type structure for both oxides, with monoclinic space group I2/m. X-ray photoelectron spectroscopy reveals that the Co²⁺ substitution drives the average Mn oxidation state from 3.7 to nearly 4.0, thereby changing the d-electron count. Magnetization and resistivity measurements suggest that the cobalt-doped material belongs to the rare class of ferromagnetic insulators, with an unusually high magnetic transition temperature of 180 K. The magnetic structure Ba_xMn₈O₁₆ as solved by constant-wavelength neutron diffraction consists of a complex antiferromagnet, likely with helical ordering, with a large magnetic unit cell and magnetic propagation vector k = (1/4 1/8 1/4). Upon subsituting coblat into manganese, the magnetic structure changes dramatically, with a magnetic structure that is no long a supercell of the chemical unit cell, and ferromagnetic alignment of the Mn centers along the tunnel direction. The observed hysteresis at base temperature for Ba_xCo_yMn_8-yO₁₆ is explained as arising from uncompensated spins aligned along the (200) crystallographic planes.

Citation

Chemistry of Materials

Volume

27

Issue

2

Pub Type

Journals

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Keywords

neutron diffraction, magnetism, structure

Citation

Larson, A. , Moetakef, P. , Gaskell, K. , Brown, C. , King, G. and Rodriguez, E. (2015), Inducing Ferrimagnetism in Insulating Hollandite Ba_1.2Mn₈O₁₆, Chemistry of Materials, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=917732 (Accessed July 18, 2024)