Study of Magnetic Properties of NdMn_1-xCo_xO₃

It is a well known fact that ferromagnetism (FM) gets induced in LaMnO₃ on Co doping at Mn site; yet, there is no general agreement on exchange mechanism responsible for it . We investigated the magnetic properties of Co doped NdMnO₃ to study the effect of Co doping on it; Nd being magnetic as compared to La.

We synthesized polycrystalline NdMn_1-xCo_xO₃ (x = 0.0, 0.3, 0.7) samples using ceramic method. Rietveld refined X- ray diffraction pattern revealed the single phase orthorhombic crystal structure of all the samples with space group Pbnm. Temperature dependent magnetic measurements performed in field cooled (FC) and zero field cooled (ZFC) mode at 0.05T exhibit the transition from FM to paramagnetic (PM) phase at Curie temperature T_c which increases with increasing Co concentration. The ZFC magnetization display maximum (T_m) and thereby starts decreasing resulting in the cusp. The sharp peak in the ZFC curve and huge difference between the ZFC and FC measurements at lower temperatures are suggestive of antiferromagnetic (AFM) coupling. It is seen that there is a decrease in peak magnetization in x = 0.7 sample as compared to x = 0.0 & 0.3 samples. The hysteresis at 10 K suggest the FM interactions at small fields and at higher fields a typical AFM character is seen which is more prominent in x = 0.7 sample. The magnetic properties are very well explained in terms of the mixed valence states of Mn and Co confirmed using X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) studies.