Year-end Sale % OFF 
Abstract
Magnetic ceramics are important for numerous technologically relevant applications with a detailed understanding of structure, property, and processing inter-relationships playing a critical role in tailoring magnetic properties. Spinel ferrites are a particularly interesting class of magnetic ceramics of chemical formula AB2O4, with applications including biomedical hyperthermia and high frequency electrical power conversion. In this contribution, we seek to investigate a unique class of Co-ferrites in which spinodal decomposition can produce a ferrite nanocomposite with chemistry and stress state fluctuating within the interior of crystalline grains on the nm-scale, resulting in corresponding fluctuations of intrinsic magnetic properties as well as exchange and magnetostatic interactions. Structural and magnetic characterization of spinel ferrite samples are carried out (1) in the as-milled state prior to thermal processing, (2) after chemical and structural homogenization with a thermal calcination step, and (3) in the spinodal decomposed state following a subsequent annealing treatment within the Co-ferrite miscibility gap. Of note is the formation of a wasp-waisted hysteresis loop which emerges for the spinodal decomposed Co-ferrite sample, indicative of more complex magnetization reversal processes at relatively large applied fields than for homogeneous Co-ferrite samples of similar particle size and identical nominal chemistry. First order reversal curve (FORC) analysis is applied to further characterize the magnetization response, and a conventional interpretation of observed features in the FORC contrast is presented to discuss potential dominant magnetization mechanisms. The work described here represents the first application of FORC to spinodal decomposed magnetic ceramics and provides a strong foundation for future investigations seeking to quantitatively describe the impacts of nm-scale chemical, structural, and magnetic fluctuations on magnetization processes in ferrite spinel nanocomposite systems.
Highlights
Magnetic ceramics play an important role in numerous applications spanning permanent magnets, biomedical hyperthermia and drug delivery, magnetic field sensing, and high frequency soft magnets for power and radio frequency communications.1–3 In all cases, a detailed understanding of structure, property, and processing inter-relationships plays a critical role in tailoring magnetic properties
Spinel ferrites are an example class of magnetic ceramics of chemical formula AB2O4 corresponding to a face centred cubic (FCC) crystal structure which can be defined by FCC packing of oxygen anions with A corresponding to tetrahedral and B corresponding to octahedral interstices occupied by transition metal cations
For as-milled samples, observed peaks are identified as a mixture of the initial Fe3O4 (PDF no: 01-080-6402) and Co3O4 (PDF no: 01-080-1541) starting feedstock powders in the cubic spinel phase, with distinct lattice parameters corresponding to each of the constituent phases indicating a lack of homogenization during the milling
Summary
Magnetic ceramics play an important role in numerous applications spanning permanent magnets, biomedical hyperthermia and drug delivery, magnetic field sensing, and high frequency soft magnets for power and radio frequency communications. In all cases, a detailed understanding of structure, property, and processing inter-relationships plays a critical role in tailoring magnetic properties. Prior work has demonstrated that magnetic properties of spinodal decomposed Co-ferrites are complex and dependent upon specific details of thermal processing and chemistry.. Separate investigations have reported a decrease or increase in the intrinsic coercivity of spinodal decomposed ferrites subjected to controlled thermal aging treatments as compared to nominally single-phase samples rapidly quenched through the miscibility gap.. In case of cryogenic measurements, dramatically increased coercivities have been reported by Takahashi and Fine.. In case of cryogenic measurements, dramatically increased coercivities have been reported by Takahashi and Fine.9 This was attributed to (1) domain wall pinning due to local variations in chemistry and magnetic properties or (2) through formation of single domain regions enriched in Fe with large shape anisotropy and separated by paramagnetic regions enriched in Co. It was noted that spinodal decomposition was not inhibited even upon water quenching
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
