Structural and magnetic properties of Ca3Mn2−xRuxO7(0<x≤0.9)

Abstract

We here report on the study of the crystallographic and magnetic properties of layered perovskites ${\mathrm{Ca}}_{3}{\mathrm{Mn}}_{2\ensuremath{-}x}{\mathrm{Ru}}_{x}{\mathrm{O}}_{7}$ ($x\ensuremath{\le}0.9$). We observe a solid solution between Mn and Ru atoms in the whole series and all samples present the same orthorhombic structure independently of the Ru content. Different magnetic structures, depending on the Ru content in the sample, have been determined using neutron powder diffraction. For low Ru doping ($x\ensuremath{\le}0.1$), there is a dominant $G$-type antiferromagnetic ordering in the perovskite bilayers but, differently from undoped ${\mathrm{Ca}}_{3}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$, the magnetic moments are located on the $ab$ plane. For higher Ru concentration ($x\ensuremath{\ge}0.3$), the predominant $G$-type ordering is preserved along the $y$ axis while an $A$-type component is developed along the $x$ axis and its intensity increases as Ru content does. This component is characterized by a ferromagnetic ordering in the $a$ direction of one of the $Mn(\mathrm{Ru}){\mathrm{O}}_{6}$ layers, coupled antiferromagnetically with the neighbor $\mathrm{Mn}(\mathrm{Ru}){\mathrm{O}}_{6}$ layer within the same bilayer. The study of the macroscopic magnetic properties shows that ferromagneticlike correlations are enhanced with increasing Ru content as deduced from the shift to higher temperature of the onset of the magnetic transition temperature. The magnetic transitions take place in two steps. At higher temperatures (140--200 K), short-range magnetic correlations are established. Tiny spontaneous magnetization is observed in the hysteresis loops with small coercive field. At ${T}_{\mathrm{N}}\ensuremath{\approx}115--125\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, long-range antiferromagnetic ordering is developed. The ferromagnetic component remains with a strong increase of coercivity. We discuss in the paper the possible origins of this ferromagnetic contribution.