Tunable High-Field Magnetization in Strongly Exchange-Coupled Freestanding Co/CoO Core/Shell Coaxial Nanowires

Abstract

The exchange bias properties of Co/CoO coaxial core/shell nanowires have been investigated with cooling and applied fields perpendicular to the wire axis. This configuration leads to unexpected exchange-bias effects. Firstly, the magnetization value at high fields is found to depend on the field-cooling conditions. This effect arises from the competition between the magnetic anisotropy and the Zeeman energies for cooling fields perpendicular to the wire axis. This allows imprinting pre-defined magnetization states to the AFM, as corroborated by micromagnetic simulations. Secondly, the system exhibits a high-field magnetic irreversibility, leading to open hysteresis loops, attributed to the AFM easy-axis reorientation during the reversal (effect similar to athermal training). A distinct way to manipulate the high-field magnetization in exchange-biased systems, beyond the archetypical effects, is thus experimentally and theoretically demonstrated.

Short-Range Correlated Magnetic Core-Shell CrO2/Cr2O3 Nanorods: Experimental Observations and Theoretical Considerations

“…A usual approach in nanoscience generally involves two steps: first, the fabrication and characterization of nanomaterials, and second, employing their properties for the development of novel devices and widespread applications. In recent years, the fabrication and critical characterization of core-shell nanostructures has attracted enormous attention because of their widespread applications [ 1 , 2 , 3 , 4 , 5 ]. The enormous progress made in the field of high-density recording and nanotechnology make the study of exchange bias (EB) ferromagnetic (FM)/Antiferromagnetic (AF) core/shell system important.…”

Monte Carlo study of the exchange bias effect in Co/CoO core–shell nanowires

“…Experimental studies, demonstrated exchange bias behavior in cylindrical permalloy nanowires [17], oxidized Co nanowires [18] and nanotubes [19] with characteristic accompanying effects, such as loop shift and training effect, previously reported for exchange-biased nanoparticles [16]. The competition between shape anisotropy, cooling field and applied field directions was shown to lead to a variety of novel properties of core-shell Co/CoO nanowires, such as, tailor-made magnetic response [20] and high-field irreversibility accompanied by cooling-field dependent magnetization [21]. Furthermore, Maurer et al [18] compared the hysteresis properties of cylindrical Co and Co/CoO nanowires and demonstrated the suppression of the coercive field due to surface oxidation as well as an anomalous temperature dependence, which they attributed to the thermal fluctuations of the oxide shell.…”

Magnetic properties of nanowires with ferromagnetic core and antiferromagnetic shell

“…This latter finding is anticipated to have implications in the choice of nanowire diameters for tailoring the character of the DW as in diameter modulated nanowires [12,27]. Finally, we mention additional microstructural factors, such as core polycrystallinity, measurement conditions, such as the applied field direction [28], or sample conditions, such as the nanowire density and the concomitant inter-wire magnetostatic interactions, which are anticipated to modify the exchange biasing behavior of FM/AF core/shell nanowires. Detailed modeling in these directions is definitely highly required.…”