Spin, Orbital and Lattice Coupling in the Double Perovskite Ba 2 154 SmMoO 6
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1148-PP04-02
Spin, Orbital and Lattice Coupling in the Double Perovskite Ba2154SmMoO6
A. C. Mclaughlin The Chemistry Department, University of Aberdeen, Meston Walk, Aberdeen, AB24 3UE.
ABSTRACT
An unexpectedly high antiferromagnetic transition temperature (TN = 130 K) has been observed in the double perovskite Ba2154SmMoO6 as a result of a strong interplay between spin, orbital and lattice degrees of freedom. A variable temperature neutron diffraction study of Ba2154SmMoO6 demonstrates that the orbital order below TN is as a result of a Jahn-Teller distortion of the MoO6 octahedra.
INTRODUCTION
Exotic electronic, magnetic and structural phenomena have been observed in doped transition metal oxides in recent years; one such example is colossal magnetoresistance (CMR). CMR materials undergo a large reduction in the electrical resistance upon application of a magnetic field and are used in spintronics devices. CMR is established in perovskite manganites such as La1xSrxMnO3
for Mn oxidation states of 3.2 – 3.5 [1]. LaMnO3, the parent compound to the CMR
manganites contains the Jahn-Teller active Mn3+ ion and a strong interplay between spin, orbital and structural degrees of freedom is observed as the co-operative Jahn Teller distortion is accompanied by C-type orbital ordering and A-type antiferromagnetism. In contrast to the examples above in which orbital order of the eg states occurs, the observation of a co-operative Jahn Teller distortion in materials with unevenly filled t2g orbitals is much less common. Most recently ferromagnetism has been observed at low temperature in the Mott insulator Ba2NaOsO6 [2] as a result of orbital ordering where Os7+ has the 5d1 electronic configuration. We have previously studied the magnetic and electronic properties of the Mo based oxides, Ba2REMoO6
(RE = Sm, Eu, Gd, Dy)[3], in which Mo is pentavalent and has the electronic configuration t2g1 which is sensitive to a Jahn-Teller instability. These materials were originally synthesised by Brandle et al but the magnetic and electronic properties had not been studied [4]. All samples were found to be electronically insulating. Antiferromagnetic order was observed from dc susceptibility measurements on Ba2SmMoO6 and Ba2EuMoO6 with anomalously high TN of 130 K and 112 K respectively [3]. There was no evidence of magnetic order for Ba2REMoO6 (RE = Gd – Yb, Y) [5, 6]. Preliminary neutron diffraction results demonstrated that the unexpectedly high antiferromagnetic transition temperature observed in Ba2154SmMoO6 as a result of a strong interplay between spin, orbital and lattice degrees of freedom [7]. In this paper a full structural study of Ba2154SmMoO6 is presented between 4 K and 353 K. EXPERIMENT
Sample preparation has been described elsewhere [3]. Neutron diffraction patterns were recorded at a wavelength of 1.5943 Å on instrument SuperD2B at the ILL, Grenoble. A 1g sample was inserted into an 8mm vanadium can and neutron diffraction patterns were recorded with an acquisition time of one hour at several temperatures betwee
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