Effect of rare earth elements addition on magnetic properties of nickel-zinc ferrites

Abstract

Magnetic materials have an important place in today's technological developments, as they are widely used in applications in various industrial fields, from telecommunications to energy production, and data storage. In many engineering fields such as aerospace, and electric-electronics they are required on a very large scale and in different types as core materials of coils, transformers and transducers, or as protective materials of switching and storage devices. Ferrites offer various benefits, such as high electrical resistivity, low eddy current losses, high saturation magnetization and high permeability. Spinel ferrites are soft magnetic materials with diverse applications. Their general formula is represented by MeFe2O4. Soft ferrites are ferrimagnetic substances that lose their magnetization when the magnetic field is took out, meaning they only exhibit ferromagnetism if there is an external magnetic field. Hard ferrites retain their magnetism even after the magnetizing process, thanks to this ability they are also mentioned to as permanent magnets. The properties of ferrites are affected by many parameters like chemical compositions and the preparation methods employed. Ni-Zn ferrite (NZF) is one of the most significant type of soft ferrites and they recognized by a mixed spinel structure. Within these ferrite structures, iron (Fe3+) and zinc ions (Zn2+) take part A-sites, that is tetrahedral sites, while nickel ions (Ni2+) and ferromagnetic iron ions (Fe3+) take part B-sites, that is octahedral sites. NZFs have low coercivity, superior corrosion strength, highly elevated resistivity, and permeability. The characteristics of these ferrite materials such as physical appearance and magnetic properties are greatly affected by structure and composition, and of course that are highly dependent on the synthesis methods utilized. The preparation process, sintering circumstances, and levels of metal oxides, impurities, or doping elements play crucial roles in determining these properties. The improvement of electric and magnetic characteristics of NZFs can be acquired by doping of rare earth (RE) oxides, known for their insulating properties and high resistivities. Therefore, the motivation of this work is to investigate the influence of different RE elements addition on magnetic properties of NZFs. Six different RE elements such as gadolinium (Gd), yttrium (Y) and europium (Eu), dysprosium (Dy), samarium (Sm) and scandium (Sc) were added to the Ni0.5Zn0.5RExFe(2-x)O4 compound; where x, the addition amounts were determined as 0.025 and 0.05. The compositions 0.10 and 0.15 was tried only for the Sc dopant. The powder samples were produced by solid-state method. The phase analysis of the produced samples was conducted with X-ray diffractometer (XRD), and morphological investigation was conducted by using scanning electron microscopy (SEM). Magnetic characteristics were observed by using vibrating sample magnetometer (VSM). According the XRD results, the addition of rare earth dopant increased, the formation of second phase also increased. This is because the dopants added after passing a certain saturation level could not dissolve in the lattice and form secondary phases called REFeO3. The homogeneous particle distribution was observed in morphology examinations. From the SEM pictures, it was obtained that the addition of dopant improved the sinterability of the powders. As a result of VSM analyses, all types and amounts of additives resulted in a decrease in saturation magnetization for both atmospheres compared to the pure sample. The reason for this decrease in saturation magnetization is that RE3+ ions, which have larger ionic radius, replace Fe3+ ions and reducing the net magnetic moment of the material. Coercivity showed a slight increase in samples with additives that sintered in N2 atmospere compared to sample without additives. This increase in coercivity value may be caused by parameters such as the number of metal cations and ion interactions in the spinel lattice. On the contrary, with the addition of dopant, the coercivity value decreased for all elements and amounts for air atmosphere, since smaller grains were obtained after the sintering in air atmosphere. An exception was noted with the Sc additive, unlike other elements, the increase in saturation magnetization value when the addition amount increases from 0.025 to 0.05. When Sc3+ took place in the octahedral region, the distance between the atoms decreased. As a result of the decrement in distance, a stronger A-B interaction emerged and magnetization increased.