The magnetic transitions and dynamics in the multiferroic Lu 0.5 Sc 0.5 FeO 3
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The magnetic transitions and dynamics in the multiferroic Lu0.5Sc0.5FeO3 Junjie Yang1, Chunruo Duan1, John R. D. Copley2, Craig M. Brown2,3 and Despina Louca1 1 Department of physics, University of Virginia, Charlottesville, VA 22903, U.S.A. 2 Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, U.S.A. 3 Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716, U.S.A. ABSTRACT In spite of its frustrated lattice, the multiferroic Lu0.5Sc0.5FeO3 exhibits two consecutive magnetic transitions at TN1 ป 175 K and TN2 ป 70 K determined from neutron diffraction. In the ordered state, magnetic fluctuations are present, most likely arising from the in-plane frustrated interaction of the Fe hexagonal lattice. Furthermore, a crossover of the magnetic intensity is observed from elastic to inelastic upon warming, indicating that magnetic fluctuations persist well above TN1, a common feature in hexagonal multiferroics. INTRODUCTION Multiferroics of the kind that exhibit successive ferroelectric and magnetic orders have captivated the research community in large part due to their unique properties. Among the various multiferroic materials, one of the earliest examples is that of the hexagonal RMnO3 family (R is a rare earth ion with small radius such as Y, Lu, Ho, and Yb) with space group P63cm.[1-6] Recently, the isostructural RFeO3 (R=Y, Yb and Lu) family has been made with an antiferromagnetic transition near 440 K and ferroelectric transition near 1050 K.[7] In bulk form hexagonal RFeO3 is metastable thus the sample synthesis is quite difficult. Very recently, it was found that the hexagonal phase of RFeO3 can be stabilized when doped with 50% Sc in Lu1xScxFeO3.[8] Moreover, Lu0.5Sc0.5FeO3 (LSFO) was reported to exhibit a dielectric anomaly associated with a weak ferromagnetic transition at 162 K, the mechanism of which is not understood at present. Here, we present evidence from a neutron scattering experiment on a powder sample of Lu0.5Sc0.5FeO3, that two successive antiferromagnetic transitions occur instead, one at TN1 ป 175 K and another one at TN2 ป 70 K. From inelastic neutron scattering measurements, we observed that the scattering intensity under the magnetic (100)M reflection change from elastic to inelastic as a function of increasing temperature. The magnetic (100)M reflection most likely arises from the *1 or *3 magnetic structure, which has the spin orientation arranged in a 120q configuration in the a-b plane. Critical magnetic scattering appears at temperatures well above TN1, and disappears below as the system globally orders. The broad inelastic scattering, which appears in the same region in momentum space as the (100)M reflection, shows an asymmetric shape below TN1 indicating that the magnetic fluctuations are confined in two dimensions. This is consistent with our previous results on LuMnO3.[9]
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