Elastic, Magnetocaloric, and Magneto-Dielectric Properties of Dy3+ and La3+ Doped Co0.7Zn0.3Fe2O4 Ferrite Nanoparticles for Multifunctional Devices

This study is focused on the elastic properties, magnetocaloric effect, critical behavior, and spin interaction nature of the pristine and rare-earth-ion (Dy3+ and La3+) doped Co0.7Zn0.3Fe2O4 (CZFO) spinel ferrite nanoparticles. It also highlights an unusual dielectric behavior of the samples near the magnetic phase transition. The spinel cubic structure and nano sized grains (22–41 nm) of the samples were confirmed by an X-ray diffractometer and a transmission electron microscope, respectively. The elastic properties were analyzed using Fourier transform infrared spectroscope to determine the interatomic bond strength and thermal responses. Magnetic measurements reveal that the CZFO sample shows ferrimagnetic behavior, whereas the doped samples exhibit antiferromagnetic (AFM) behavior with second-order magnetic phase transition, below the transition temperature (T M). The Dy3+ doped sample exhibits the larger values of saturation magnetization, remanent magnetization, magnetic coercivity, the change in maximum magnetic entropy (−ΔS M max), and relative cooling power (RCP) as compared to CZFO. Critical parameters (β, γ, and δ) are estimated using Arrott plots, the Kouvel–Fisher method, and Widom scaling relation. The type of exchange interaction during magnetic phase transition is derived using renormalization group theory. The dielectric constant (ε′) exhibits an anomaly near T M for all samples, below which ε′ increases with T attributed to Maxwell–Wagner and Koop theory. Above T M, an unconventional negative ε′ behavior is observed, which can be interpreted well by the Lorentz model of dielectric resonance. These materials with large values of T M, ΔS M max, and RCP appear to be promising candidates for high temperature magnetic refrigeration technology, whereas the coexistence of AFM and magneto-dielectric behaviors can be used in designing multifunctional and spintronic devices.