Structural, magnetic and thermo-magnetic properties of NiMn Y-Type strontium nano-hexaferrites

Abstract

Six chemical compounds of poly-crystalline NiMn Y-type strontium nano hexaferrites doped with hybrid Ti4+Co2+, having chemical formula Sr2NiMnFe12-X(TiCo)X/2O22 (0 ≤ x ≤ 2.5 and Δx = 0.5) synthesized by sol-gel auto-combustion through microwaves and calcined at 950 °C for 5 h. The refined XRD analysis shows compounds are in single Y-type hexagonal phase. The lattice parameter ‘a’ slightly increases and easy magnetized ‘c’ axis undergoes more expansion with the content of TiCo. The grain size measured from XRD data is in the range of 41 nm–71 nm. The microstructure was visualized and studied by SEM, TEM, HRTEM and SAED. TEM images show that the compounds are in hexagonal shape with grain size in the range of 42 nm–89 nm.Saturation magnetization (Ms), Retentivity (Mr) and Coercivity (Hc) were observed through vibrating sample magnetometer (VSM). All the six compounds are found to be ferrimagnetic at the room temperature and remain so up to the transition temperature (TM). Above this transition temperature the compounds start becoming paramagnetic. The transition temperature (TM) was determined from the derivative of the thermo-magnetic susceptibility curve. The strong (negative) derivative peak confirmed a single magnetic phase and the narrow peak profile predicts magnetic homogeneity of the compounds.