Structural and magnetic properties of Ca3Mn2−xRuxO7(0<

Abstract

We here report on the study of the crystallographic and magnetic properties of layered perovskites Ca 3 Mn 2−x Ru x O 7 (x 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 0.1), there is a dominant G-type antiferromagnetic ordering in the perovskite bilayers but, differently from undoped Ca 3 Mn 2 O 7 , the magnetic moments are located on the ab plane. For higher Ru concentration (x 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(Ru)O 6 layers, coupled antiferromagnetically with the neighbor Mn(Ru)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 N ≈ 115-125 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.

Chemical pressure induced spin reorientation in the magnetic structure of Ca 3 Mn

“…Studies on single crystals of the undoped compound indicate that this metamagnetic behaviour is due to a spin-flop transition of the moments from along the a-axis to along the b-c plane [29]. However, investigations on Ru-doped Ca 3 Mn 2 O 7 , where moments have re-oriented into the b-c, plane also demonstrate a change in slope of the M-H curve [24]. Thus, further investigations on single crystalline doped compounds would be required to uncover the nature of metamagnetism and its relationship with anisotropy in these compounds.…”

“…Chen et al and Zhang et al have shown that co-substitution of Fe/Al and Nb at the Mn or Ti sites of Ca 3 (Mn/Ti) 2 O 7 leads to an enhancement in the ferroelectric polarization owing to increased oxygen octahedral distortions [22,23]. More recently, ruthenium doping at the Mn site of Ca 3 Ru x Mn 2−x O 7 (0.05 ⩽ x ⩽ 0.9) was investigated by Blasco et al [24]. They reported an intriguing finding that the spins aligning along the out-of-plane direction (along the long axis) in the undoped compound were observed to be aligned in-plane upon doping.…”