Electronic, Magnetic, and Structural Properties of Sr 2 MnRuO 6 and LaSrMnRuO 6 Double Perovskites

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Abstract
The perovskites Sr 2 MnRuO 6 and LaSrMnRuO 6 have been investigated and their properties compared with those of the broader family of A 2 MRuO 6 double perovskites (A=Sr, La; M=Cr, Mn, Fe, Co, Ni). Neutron powder diffraction shows that both phases lack long‐range Mn/Ru order. Sr 2 MnRuO 6 exhibits a cooperative Jahn–Teller distortion, conductivity that proceeds via variable‐range hopping, and antiferromagnetic (AFM) order (C‐type structure, T N ≅200K, 2.05(1) μ B per transition metal). LaSrMnRuO 6 exhibits nearly undistorted octahedra, conductivity that proceeds via diffusion‐assisted small‐polaron hopping, and ferromagnetic (FM) order ( T C ≅220K, 1.60(4) μ B transition metal). Band structure calculations show that AFM Mn–O–Ru coupling optimizes polarization of the Ru t 2 g orbitals, while FM coupling favors delocalization of the Ru t 2 g electrons. The transition from antiferromagnetism to ferromagnetism is linked to a loss of orbital order and stabilized over competing glassy states by delocalization of Ru t 2 g electrons.

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