Role of interfacial layer on exchange-coupled magnetic properties of bi-magnetic nanostructures: An experimental and theoretical approach

• Published in: Journal of magnetism and magnetic materials 2023-12, Vol.587, p.171306, Article 171306
• Main Authors: Panda, Soumyakanta, Das, Malaya Kumar, Mohapatra, Niharika
• Format: Article
• Language: English
• Subjects: Bi-magnetic nanostructures; Coercivity; Density functional theory; Exchange bias effect; Magneto crystalline anisotropy; Training effect
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2023.171306

[Display omitted] •A simple hydrothermal one-pot synthesis route successfully produced heteronanostructures of magnetically contrasting Fe3O4 and NiO phases.•XRD, FESEM, and TEM data analysis reveals the embedded Fe3O4 nanoparticles in the NiO matrix.•A strong exchange bias and significant enhancement of coercive field were demonstrated in the field-cooled magnetization.•DFT band structure calculations indicate the role of cation intermixing at the interface with a narrowed band gap, which was also supported by the UV–Vis spectroscopy studies.•Analysis of the training effect suggests the role of both rotatable and frozen spins. Bi-magnetic hetero-nanostructures exhibiting significant exchange bias effects are highly desirable for technological advancement in spin valves, memory devices, data storage, biomedicine, and hyperthermia-based cancer treatment. As the interfacial spin interaction and the resulting anisotropy play a central role in these phenomena, investigating the tailored physical properties of hetero-structures of magnetically contrasting nanoparticles in different architectures is extremely useful. In this work, we report the formation of microspheres containing nano-aggregates of ferrimagnetic Fe3O4 and antiferromagnetic NiO phases. We demonstrate that this kind of bi-magnetic hetero-structures provide a conducive atmosphere for strong interfacial coupling giving rise to an extensive exchange bias effect (∼1.6 kOe). In addition, we also observe a substantial enhancement of the coercive field, indicating the onset of an additional unidirectional anisotropy under the field-cooled condition. Our first-principle density functional theory calculations reveal the role of cation intermixing at the interface of the two phases, being the source of an additional higher magneto-crystalline anisotropy than the original phases. This cation intermixing at the interface also causes a narrowed energy band, which was demonstrated by UV–Vis spectroscopy and first principle calculations. Having these technologically essential features with a tunable band gap, the embedded hetero-nanostructures are envisioned to cater to the requirement of high-density data storage and memory devices.