Ru doping of the Mn site in La_(0.4)Ca_(0.6)MnO_3 perovskite: Electron magnetic resonance study of electronic and magnetic ordering

摘要

X-band (v = 9.4 GHz) electron magnetic resonance (EMR) measurements were carried out in polycrystalline La_(0.4)Ca_(0.6)Mn_(1-x)Ru_xO_3 (0 ≤ x ≤ 0.16) samples at 100 K ≤ T ≤ 550 K, aiming to study magnetic/electronic ordering induced by Ru doping. EMR indicates that such doping modifies even the paramagnetic state of La_(0.4)Ca_(0.6)Mn_(1-x)Ru_xO_3 series: the linewidth of resonance signal increases with doping. The initial charge-ordered (CO) antiferromagnetic (AFM) ground state is also drastically modified by doping. At Ru contents x ≥ 0.04, the ferromagnetic (FM) EMR signal is observed below former T_(CO). It evidences that the CO transition transforms into the FM one. The magnetic ground state of La_(0.4)Ca_(0.6)Mn_(1-x)Ru_xO_3 remains definitely inhomogeneous due to the coexistence of FM and AFM phases up to, at least, x = 0.10. The data obtained are compared with known ones for CaMn_(1-x)Ru_xO_3 system and discussed in the framework of the energy diagram model for Ru-doped manganites.