Interplay between spin-orbital coupling and electron-correlation: induction of phase transitions and giant magnetic anisotropy in strained LaSr 1- x Ca x NiReO 6 .

In recent decades, 3d-5d based double perovskite oxides (DPO) have received considerable attention due to the existence of the Mott-insulating (MI) state, which is due to the spin-orbit coupling (SOC) and strong electron-correlation (EC) effects. They provide a small stray field and ultra-fast spin moments, which play a key role in the design of magnetic tunnel junctions. Herein, we examined the physical properties of the unstrained and biaxial ([110]) strained LaSr 1- x Ca x NiReO 6 ( x = 0.0 (Sr-dop.), 0.5 (SrCa-dop.), and 1.0 (Ca-dop.)) motifs with a high formal charge state of Re 5+ (5d 2 )/Ni 2+ (3d 8 ) using ab initio calculations. Interestingly, our results revealed that the combined effect of SOC and EC is essential to define both the electronic and magnetic ground states of the structures. The unstrained x = 0.0/0.5 and 1.0 systems displayed a MI ferromagnetic (FM) and ferrimagnetic (FiM) behavior with energy band gaps of 0.14/0.12 and 0.35 eV, respectively, which is in good agreement with the recent experimental observations [S. Jana, P. Aich, P. A. Kumar, O. K. Forslund, E. Nocerino, V. Pomjakushin, M. Maansson, Y. Sassa, P. Svedlindh and O. Karis, et al. , Sci. Rep. , 2019, 9 , 18296]. Most importantly, a giant magnetic anisotropy constant of 0.2/0.4/3.7 × 10 8 erg cm -3 with an easy axis of [001]/[001]/[101] for x = 0.0/0.5/1.0 is achieved, which is jointly associated with SOC and distorted Ni-O-Re bond angles. Strikingly, an insulator-to-metal transition occurs for x = 0.0 and 0.5 under the influence of a critical compressive strain of -3%. Furthermore, the systems ( x = 0.0 and 0.5) again exhibit a transformation from FM metal to the antiferromagnetic (AFM) MI state with -5% strain. Similarly, a FiM MI to AFM MI transition is also predicted for x = 1.0 at a critical strain of -6%. Thus, the present investigations proposed that strain modulated properties of the LaSr 1- x Ca x NiReO 6 DPOs further enhance their potential realization for high-density magnetic memory devices.