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Studies on magnetic oxyhydrides have been almost limited to perovskite-based lattices with corner-sharing octahedra with a M−H−M (M: transition metal) angle of θ ∼ 180°. Using a high-pressure method, we prepared BaCrO 2 H with a 6H-type hexagonal perovskite structure with corner-and face-sharing octahedra, offering a unique opportunity to investigate magnetic interactions based on a θ ∼ 90°case. Neutron diffraction for BaCrO 2 H revealed an antiferromagnetic (AFM) order at T N ∼ 375 K, which is higher than ∼240 K in BaCrO 3−x F x . The relatively high T N of BaCrO 2 H can be explained by the preferred occupancy of H − at the face-sharing site that provides AFM superexchange in addition to AFM direct exchange interactions. First-principles calculations on BaCrO 2 H in comparison with BaCrO 2 F and BaMnO 3 further reveal that the direct Cr−Cr interaction is significantly enhanced by shortening the Cr−Cr distance due to the covalent nature of H − . This study provides a useful strategy for the extensive control of magnetic interactions by exploiting the difference in the covalency of multiple anions.

Abstract.We investigate composite Fe-SrF 2 films to explore new materials showing the granular type tunneling magnetoresistance (TMR) effect. The films are composed of Fe nano-particles embedded in a SrF 2 matrix. The electromagnetic properties of the ferromagnetic metal-insulator films are confirmed, including super-paramagnetism, tunnel conduction, and TMR. We obtain a TMR of 3% at RT and 5% at 77 K. The film resistivity is much higher than that of oxide-based granular film. We also fabricate the nanostructures of granular films and aim at the application of the single-electron transistor. As a result, we observed Coulomb blockade (CB) region and CB oscillation at low temperature.

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