Inducing Ferrimagnetism in Insulating Hollandite Ba1.2Mn8O16
Amber M. Larson, Pouya Moetakef, Karen Gaskell, Craig Brown, Graham King, Efrain E. Rodriguez
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 TN=25 K to a ferrimagnet with Tc = 180 K via colbalt substitution for 1/8 of the manganese sites. Both BaxMn8O16 and BaxCoyMn8-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 BaxMn8O16 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 BaxCoyMn8-yO16 is explained as arising from uncompensated spins aligned along the (200) crystallographic planes.
, Moetakef, P.
, Gaskell, K.
, Brown, C.
, King, G.
and Rodriguez, E.
Inducing Ferrimagnetism in Insulating Hollandite Ba<sub>1.2</sub>Mn<sub>8</sub>O<sub>16</sub>, Chemistry of Materials, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=917732
(Accessed December 9, 2023)