Abstract
The influence of spin-orbit coupling (SOC) on the physical properties of the 5d2 system Sr2MgOsO6 is probed via a combination of magnetometry, specific heat measurements, elastic and inelastic neutron scattering, and density functional theory calculations. Although a significant degree of frustration is expected, we find that Sr2MgOsO6 orders in a type I antiferromagnetic structure at the remarkably high temperature of 108 K. The measurements presented allow for the first accurate quantification of the size of the magnetic moment in a 5d2 system of 0.60(2) μB –a significantly reduced moment from the expected value for such a system. Furthermore, significant anisotropy is identified via a spin excitation gap, and we confirm by first principles calculations that SOC not only provides the magnetocrystalline anisotropy, but also plays a crucial role in determining both the ground state magnetic order and the size of the local moment in this compound. Through comparison to Sr2ScOsO6, it is demonstrated that SOC-induced anisotropy has the ability to relieve frustration in 5d2 systems relative to their 5d3 counterparts, providing an explanation of the high TN found in Sr2MgOsO6.
Highlights
Ba2YMoO620,21 which do not fit into this framework
Sr2MgOsO6 crystallizes in the tetragonal I4/m space group as previously reported[27,28] and shown in Fig. 1, which is common to a number of other Sr2BOsO6 compositions[42,43,44,45,46]
The I4/m space group is associated with the a0a0c− Glazer tilt system, where out of phase tilting occurs about the c-axis[47]
Summary
Ba2YMoO620,21 which do not fit into this framework. Investigation of magnetism due to the d4 configuration has begun, such as in A2BIrO6 (A = Sr, Ba; B = Sc, In, Y), where questions have arisen concerning the strength of SOC and the magnetism of the resulting ground state[22,23,24,25]. Density functional theory (DFT) confirms that this substantial reduction in moment occurs through a combination of both covalency and SOC, and predicts that SOC-induced anisotropy is essential in the selection of the magnetic ground state. The presence of this anisotropy is experimentally confirmed by the observation of a spin gap in the magnetic excitation spectrum via inelastic neutron scattering. Ground mixtures of up to 3 g were contained in high-density alumina tubes and sealed in evacuated silica ampoules (approximate volume 40 mL with 3 mm thick walls) for heatings of 48 hours at 1000 °C in a box furnace located within a fumehood This was followed by regrinding and identical reheating for an additional two cycles. Powdered Sr2MgWO6 samples were synthesized in air following the procedure outlined in the literature[32]
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