Magnetic Properties of Nanocomposite Particles of FePt/FeRh

The magnetic properties of selected compositions of FePt, FeRh, and their composites, prepared by the solution phase method, were investigated. A high-resolution transmission electron microscopy study revealed that the average size of monodispersed FePt and FeRh are 3-5 nm in the prepared state while average sizes are larger in the annealed state. In the case of FeRh, X-Ray diffraction studies show the disordered fcc phase in the as prepared which transforms into the CsCl structure through annealing. Similarly, in the case of FePt, X-Ray diffraction studies show the fee structure in as a deposited case with the L1₀ phase in the annealed state. The temperature-dependent magnetization of composite FePt/FeRh shows a significant decrease in the coercivity which starts at around 30degC and decreases rapidly with increasing temperature. This result reveals a strong exchange coupling between ferromagnetic (FePt) and antiferromagnetic (FeRh) phases. The thermal hysteresis width; Delta H of annealed FePt/FeRh shows about 5degC while that of FeRh in the single particles state is 135degC. The shift in transition temperature toward the lower side, in the presence of the magnetic field, implies the role of an applied magnetic field. The entropy change associated with this transition is estimated to be 185 mJ/Kcc.