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Magnetic Iron Oxide Nanoparticles for Biomedical Applications
Published in Ashwani Kumar, Mangey Ram, Yogesh Kumar Singla, Advanced Materials for Biomechanical Applications, 2022
Vikram Hastak, Suresh Bandi, Ajeet K. Srivastav
The coating of a magnetic material on magnetic nanoparticles imparts great influence on its magnetic properties. This approach leans toward the formation of magnetic nanocomposites. Thereby, a remarkable feature “exchange bias effect” (shift of hysteresis loop at the interface) occurs [76]. The exchange bias effect generally materializes whenever there exists an interface between the core of a ferromagnetic material and the shell of an antiferromagnetic material or vice versa. Fe3O4–CoO (ferrimagnetic–antiferromagnetic) is an example of such a nanocomposite. The exchange bias effect has its advantages in permanent magnets, spintronics, and recording media. Not only are the magnetic properties of nanoparticles influenced by their shape, size distribution, surface effects, and phase morphology, but also there are numerous complications which add up to the contribution.
A Theoretical Overview of the Quantum Phenomena at Oxide Interfaces: The Role of Spin and Charge
Published in Tamalika Banerjee, Oxide Spintronics, 2019
Carmine Autieri, Biplab Sanyal
In this section, we will discuss an unusual phenomenon of the large vertical shift in exchange bias occurring in a specific oxide heterostructure. Exchange bias is one such outcome of interfacial coupling across two different magnetic states [46], usually antiferromagnetic and ferromagnetic phases. In perovskite-based heterostructures, magnetic interactions are particularly fascinating as they can show interface ferromagnetism between two antiferromagnets or between an antiferromagnet and a paramagnet [47]. Competing magnetic interactions, which give rise to proximity coupling such as exchange bias have found technological applications in magnetoresistive sensors, however, its microscopic origin often raises debates particularly regarding the coupling configurations at the interface [46].
Magnetism of Complex Oxide Interfaces
Published in Evgeny Y. Tsymbal, Igor Žutić, Spintronics Handbook: Spin Transport and Magnetism, Second Edition, 2019
Satoshi Okamoto, Shuai Dong, Elbio Dagotto
Exchange bias is a widely observed unusual effect corresponding to ferromagnetic-antiferromagnetic interfaces [106]. In principle, the pinning effect by the antiferromagnetic interface is expected to bias the hysteresis loop of the attached ferromagnetic layer, as sketched in Figure 11.8a. However, the origin of this effect is still under much discussion. For example, for a fully compensated antiferromagnetic interface, such as the (001) surface of a G-type antiferromagnetic perovskite (Figure 11.8b–c), it intuitively appears that the antiferromagnetic moments are symmetrically distributed with respect to their orientations, and thus they cannot bias the neighboring ferromagnetic moments. Several possible mechanisms have been proposed to understand the exchange bias effect. Extrinsic factors are often considered, such as interface roughness, spin canting near the interface, as well as frozen interfacial and domain pinning, but there is no universally accepted explanation for this exotic phenomenon [107–111]. Recent experiments demonstrated the presence of exchange bias in BiFeO3/La0.7Sr0.3MnO3 heterostructures [61, 112], as well as in other BiFeO3/ferromagnetic alloys [113]. More interestingly, it was observed that this exchange-bias can be affected by the switching of the ferroelectric polarization of BiFeO3. This new ingredient cannot be well understood by any of the traditional theories of exchange bias.
Study of the structural and magnetic properties at high temperature of Ni-Co-Mn-Al Heusler alloy prepared by an unconventional route
Published in Philosophical Magazine, 2023
The effect of heat treatment on the structural and magnetic characteristics of Ni-Mn-Al-based Heusler alloys has been the subject of several scientific works. Outcomes confirmed that the magnetic properties of this alloy system are highly dependent on the chemical composition, crystal structure, and applied heat treatments [20]. The structural order of the austenite, more precisely the B2 structure, has a major impact on the magnetic properties of NiMnAl alloys [21]. The effect of growth temperature on structural and magnetic properties of Ni2MnAl Heusler alloy was investigated by X.Y. Dong et al. [22]. It was found that films, grown at lower temperatures, were paramagnetic with a B2-type crystal structure, while a higher growth temperature (673 K) resulted in ferromagnetic films with an L21-type structure. In another related work, Ni48Mn39.5Sn9.5Al3 ribbons were subjected to various applied heat treatments in order to detect their response to magnetic magnetization following the evolution of the magneto-structural order [23]. As a result, the exchange bias phenomenon progressively degrades as the antiferromagnetic/ferromagnetic domains grow in size with increased ordering and the temperature of thermal treatment. The control of magnetic coercivity by heat treatment in Ni-Mn-based heusler alloys has been widely studied by L.Straka et al. [24]. Findings confirmed that increasing the density of thermal antiphase boundaries provides a method to increase the magnetic coercivity without deteriorating the magnetic shape memory functionality.
Synthesis of nickel nanothorn particles by the hydrothermal method
Published in Journal of Dispersion Science and Technology, 2020
Salih Ugur Bayca, Haydar Altinok, Aysun Akcay
Magnetization hysteresis cycles shifted to a slightly negative area. This shift may result from the exchange bias effect due to the magnetic exchange interaction between the ferromagnetic and antiferromagenetic phases.[21,22]