Spin wave excitations in the tetragonal double perovskiteSr2CuWO6

Abstract

Sr 2 CuWO 6 is a double perovskite proposed to be at the border between two-and three-dimensional magnetism, with a square lattice of S = 1 2 Cu 2+ ions. We have used inelastic neutron scattering to investigate the spin wave excitations of the system, to find out how they evolve as a function of temperature, as well as to obtain information about the magnetic exchange interactions. We observed well defined dispersive spin wave modes at 6 K, which partially survive above the magnetic ordering temperature T N = 24 K. Linear spin wave theory is used to determine the exchange interactions revealing them to be highly two dimensional in nature. Density functional theory calculations are presented supporting this experimental finding, which is in contrast to a previous ab initio study of the magnetic interactions. Our analysis confirms that not the nearest neighbor, but the next nearest neighbor interactions in the tetragonal ab plane are the strongest. Low incident energy measurements reveal the opening of a 0.6(1) meV gap below T N , which suggests the presence of a very weak single ion anisotropy term in the form of an easy axis alongâ.

Exchange Interactions Mediated by Nonmagnetic Cations in Double Perovskites

“…These results are consistent with the couplings extracted from the INS data [16]. We note that the magnon-magnon interaction, not included [15] and Sr2CuWO6 [16]. The couplings obtained from INS are from fits to SWT with a renormalization factor Zc = 1.18 as the first-order correction [44] to calculated magnetic dispersion.…”

“…In the case of a completely filled d-manifold (Te 6+ ) cation, the exchange path does not include any of its orbitals, but for the d 0 (W 6+ ) bridging cation, the SSE process via these empty orbitals is pivotal. While these conclusions corroborate with DFT+U based studies [16,45,49], it is important to know that the computed exchange couplings strongly depend on the choice of the Coulomb repulsion parameter U . We further provided the rationale for the observed exchange interactions, justifying with numerical evidence.…”

“…The Sr 2 CuTe x W 1−x O 6 for x = 0.5 and 1.0 samples were studied using MER-LIN at ISIS with E i = 45 meV [47]. Further details on Sr 2 CuTeO 6 and Sr 2 CuWO 6 INS measurements are reported elsewhere [15,16]. Figure 4 shows the inelastic neutron scattering spectra of powder Sr 2 CuTe x W 1−x O 6 that have been collected on x = {0, 0.5, 1.0} compounds.…”

“…The isostructural double perovskite copper oxides Sr 2 CuTeO 6 [12] and Sr 2 CuWO 6 [13] realise a quasi-twodimensional spin-1/2 HSL antiferromagnet, despite their three-dimensional crystal structures [14][15][16]. However, the magnetic order in the two systems is different.…”

“…However, the magnetic order in the two systems is different. While a Néel AFM (NAF) ordering is observed in Sr 2 CuTeO 6 with large AFM J 1 and small J 2 of the same sign [15,17], a columnar AFM (CAF) order is stabilized in Sr 2 CuWO 6 with small J 1 and large J 2 , both AFM [16]. Interestingly, the reported J 2 /J 1 ratio in these two compounds differs by two orders of magnitude, 0.03 and 7.92 for Sr 2 CuTeO 6 and Sr 2 CuWO 6 , respectively.…”