Oxide electronics

Abstract:

© 2020 American Physical Society. Powder neutron-diffraction experiments have been employed to establish the effects of site-selective magnetic dilution in the Sm2MnMnMn4-xTixO12 A-site columnar ordered quadruple perovskite manganites (x=1, x=2, and x=3). We show that in all three compositions the Mn ions adopt a collinear ferrimagnetic structure below 27, 62, and 34 K, respectively. An unexpected increase in the ordering temperature was observed between the x=1 and x=2 samples, which indicates a considerable departure from mean-field behavior. This result is corroborated by large reductions in the theoretical ground-state magnetic moments observed across the series, which indicate the presence of spin fluctuations and/or disorder. We show that long-range magnetic order in the x=3 sample, which occurs below the percolation threshold for B-B exchange, can only be understood to arise if it is mediated via both A-B and B-B exchange, hence confirming the importance of A-B exchange interactions in these materials. Finally, we show that site-selective magnetic dilution enables the tuning of a ferrimagnetic compensation point and the introduction of temperature-induced magnetization reversal.

Abstract:

We present a combined polarized neutron and x-ray scattering study on two enantiopure langasite single crystals aimed at the determination of their absolute structural and magnetic chiralities and the coupling between them. Our respective data sets unambiguously reveal two samples of opposite structural chirality, where the magnetic handedness is pinned by the structural one. Simple energy considerations of the magnetic exchange and single-ion anisotropy parameters reveal that it is not the Dzyaloshinskii-Moriya interaction but the local single-ion anisotropy on a triangular plaquette which plays a key role in stabilizing one of the two magnetic helices.