Crystallographic structure and magnetic ordering inCaMn1−xRuxO3

Alexander I. Shames

¹

,

E. Rozenberg

²

,

C. Martin

³

et al.

Abstract

Neutron powder diffraction (NPD), ac susceptibility and electron magnetic resonance (EMR) techniques were employed for studying the crystallographic structure and magnetic ordering in CaMn 1−x Ru x O 3 ͑x ഛ 0.40͒ manganite system. It is shown that CaMn 1−x Ru x O 3 crystallizes in an orthorhombic Pnma perovskite structure within the temperature interval 1.5ഛ T ഛ 300 K independently on the level of Ru-doping ͑x͒. It means that the changes of the magnetic ordering in this system are solely determined by doping of Mn sites with Ru in parent CaMnO 3 compound. The NPD data show also that the long-ranged ferromagnetic (FM) ordering is developed in x ജ 0.10 compounds within antiferromagnetically (AFM) ordered matrix. The volume of this FM phase increases with x at the expense of the AFM one. The ac susceptibility ͑͒ demonstrates broadened peaks on ͑T͒ curves for x = 0.10, 0.15 samples and characteristic two-peak shape for x = 0.40 compound. The frequency dependence of ͑T͒ curves is also observed for x ജ 0.10 compounds. The complementary data of EMR indicate, in addition, the complex character of FM ordering, i.e., appearance of some nonequivalent FM phases, differ on its Curie temperatures and magnetocrystalline anisotropies in x ജ 0.15 samples. The best description of all these results could be done in the frame of the model of phase separated FMϩAFM ground state developing in the considered CaMn 1−x Ru x O 3 system for Ru concentrations x ജ 0.10.

EMR Study of Electronic and Magnetic Ordering in Doped CaMn1-x,yMx,yO3(M = Ru, Mo) Perovskites

“…As a whole, these energy diagrams (Fig. 4) are consistent with the magnetic and conductive properties of Ru-and Mo-doped CaMnO 3 [4][5][6][7][8], but the detailed consideration with this respect will be presented elsewhere. Let us outline the spin subsystems in CMRO and CMMO, which play the main role in EMR in these systems.…”

“…1-3). The following valence formulae [4,5] 3+ ions in CMRO is strongly supported by the absence of OO/CO states for x up to 0.50 [4,8]. It advocates the energy diagram, in which the deep trap level, with symmetry other than e g , appears below the conduction band with Ru-doping (Fig.…”

“…The synthesis of polycrystalline samples of CMRO and CMMO with 0 ≤ x ≤ 0.50 and 0 ≤ y ≤ 0.14, respectively, has been described previously (see [4][5][6][7][8] and refs. therein).…”

“…Above noted mostly pronounced low temperature broadening of ∆H pp in CMRO (x ≤ 0.06) and CMMO (y ≤ 0.10), shown in Figs. 3c and d, coincides with the transition to AFM state upon cooling at T < T N ≈ 125 K [4,8] and at T < T N ≈ 150 K [5,6] in CMRO and CMMO, respectively. Such broadening correlates also with the notable reduction of the corresponding DIN values at low T in both CMRO and CMMO (see Fig.…”

“…It is evident that, for obtaining a deeper insight into the magnetic ordering in these systems and for better understanding of underlying physics, microscopic probes, capable to identify signatures of different exchange interactions, are required. For example, our measurements [7,8] of electron magnetic resonance (EMR, comprising both electron paramagnetic resonance -EPR -for T > T C , the Curie point, and ferromagnetic resonance -FMR -for T < T C ) in CMRO with x ≤ 0.40 show that EMR parameters differ drastically for AFM and AFM+FM samples with respective Ru-doping x ≤ 0.06 and x ≥ 0.10.…”