Enhanced Magnetic Properties in Antiferromagnetic-Core/Ferrimagnetic-Shell Nanoparticles

Abstract

Bi-magnetic core/shell nanoparticles are gaining increasing interest due to their foreseen applications. Inverse antiferromagnetic(AFM)/ferrimagnetic(FiM) core/shell nanoparticles are particularly appealing since they may overcome some of the limitations of conventional FiM/AFM systems. However, virtually no simulations exist on this type of morphology. Here we present systematic Metropolis Monte Carlo simulations of the exchange bias properties of such nanoparticles. The coercivity, HC, and loop shift, Hex, present a non-monotonic dependence with the core diameter and the shell thickness, in excellent agreement with the available experimental data. Additionally, we demonstrate novel unconventional behavior in FiM/AFM particles. Namely, while HC and Hex decrease upon increasing FiM thickness for small AFM cores (as expected), they show the opposite trend for large cores. This presents a counterintuitive FiM size dependence for large AFM cores that is attributed to the competition between core and shell contributions, which expands over a wider range of core diameters leading to non-vanishing Hex even for very large cores. Moreover, the results also hint different possible ways to enhance the experimental performance of inverse core/shell nanoparticles for diverse applications.

Doping of Ga in antiferromagnetic semiconductor α-Cr2O3 and its effects on magnetic and electronic properties

“…The peak at about 365 nm is associated with the conventional band gap ( 3 eV) of α-Cr 2 O 3 [13]. The absorption peaks at around 460 nm and 600 nm correspond to 4 A 2g → 4 T 1g and 4 A 2g → 4 T 2g 3d 3 electronic transitions of octahedral Cr 3+ ions [22]. It is difficult to classify whether the peaks are due to direct or indirect electronic transitions for wide band gap semiconductors, like α-Cr 2 O 3 .…”

“…Recently, antiferromagnetic (AFM) systems (NiO, CoO, Fe 2 O 3 , Cr 2 O 3 ) in nanoparticle (NP) form have received a significant amount of research interest for fundamental understanding of new magnetic phenomena, such as surface superparamagnetism, size-induced ferromagnetism, quantum confinement effect [1][2][3][4][5][6][7]. The enhanced ferromagnetism and magnetic exchange bias effect has provided the experimental evidence of modified spin order (core-shell structure) and magnetic anisotropy in AFMNP [2][3][4].…”

“…The enhanced ferromagnetism and magnetic exchange bias effect has provided the experimental evidence of modified spin order (core-shell structure) and magnetic anisotropy in AFMNP [2][3][4]. From application point of view, increase of ferromagnetic (FM) component in AFMNP is important for the development of magnetic semiconductor with reasonably large ferromagnetic moment, tunable band gap in the UV-Vis range of light and electrical field controlled electronic properties at room temperature [8][9][10][11][12].…”

Off-axis spin orientation in goethite nanoparticles

“…Of particular interest are nanocomposites, where different types of magnetic materials are combined on the nanoscale, e.g., in core-shell structures or by embedding one material in a matrix of another. This is a promising and active field of research [1][2][3][4][5][6][7][8][9][10].…”

“…Below a Néel temperature of about 400 K, the Fe 3+ spins order antiferromagnetically. In nonstoichiometric goethite and in goethite samples with small crystallite sizes, the 2469-9950/2017/96(10)/104426 (10) 104426-1 ©2017 American Physical Society…”