Magnetic order and spin-orbit entanglement in Sr3NiIrO6

Orateur : Émilie LEFRANCOIS

Oxides of the family A3MM’O6 (A = alkaline-earth metal, M, M’ = transition metal) attracted a lot of attention because of their unconventional magnetic properties linked to the coexistence of low dimensionality, magnetic frustration and magneto crystalline anisotropy. In these compounds, the M and M’ ions form chains which are distributed on a triangular lattice. In consequence, the magnetism of the compounds with an easy-axis of anisotropy, which confines the magnetic moments along the chains direction, should be strongly frustrated. We studied the 5d-based compound Sr3NiIrO6, where the strong spin-orbit coupling on the Ir4+ ions might induce unexpected behaviors through spin-orbit entanglements. Single crystal magnetization, powder neutron diffraction and single crystal resonant inelastic scattering (RIXS) measurements were performed. The magnetization measurement revealed the existence of a large easy-axis anisotropy confining the Ni2+ and Ir4+ magnetic moments along the chains. Besides the zero-field cooled and field-cooled measurements show that there are two characteristic temperatures : T1 = 70 K and T2 = 17 K. The first temperature is associated with a deviation from a Curie-Weiss behavior and the appearance of magnetic order with propagation vector k=(0,0,1). At T2, the susceptibility reaches a maximum followed by a sudden drop. The magnetic structure can be determined from powder neutron diffraction only up to a global phase. However, symmetry arguments allowed determining the exact nature of the magnetic ground state below T2, thus clarifying the universal magnetic properties of this family of compounds [1]. In addition, RIXS measurements allowed probing the electronic and magnetic excitations inside the t2g triplet thus estimating the strength of the spin-orbit coupling as well as the amplitude of the trigonal distortion of the IrO6 octahedra. From these parameters, we were able to determine that the spin-orbit entanglement is maximized in this compounds thanks to the trigonal elongation [2].

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