Controlling the exchange bias field in Co core/CoO shell nanoparticles

Co nanoparticles inserted into a porous carbon amorphous matrix: the role of cooling field and temperature on the exchange bias effect

“…Contrary to other reported values 30 on Co-based nanostructured systems, in which a large discrepancy for M s respect to the bulk-Co value was attributed to size effects and enhanced surface-to-volume ratio, the proper quantification of analyisis (see Fig. 3) may be responsible for a coupling between the FM Co-core and the AFM CoO (or SPM due to the small size of the CoO grains) interface/shell 33,34 . According to recent studies 35 the Néel temperature of CoO can be reduced down to 235 K (or lower) from the value of 15 their bulk counterpart [T N (CoO) ~ 290 K].…”

Probing core and shell contributions to exchange bias in Co/Co<inf>3</inf>O<inf>4</inf> nanoparticles of controlled size

“…The behavior of the three samples is similar, showing irreversibility up to the highest measured temperature of 300 K, which indicates that the nanoparticles have blocking temperatures above this value due to their relatively large size. Note that both curves decrease monotonously below 300 K and do not display any peak characteristic of the Néel temperature of CoO, which should be in the range of 235-293 K depending on the particle size [26,39,40]. However, below ∼40 K, a weak anomaly marked by an upturn of the magnetization can be observed in both the ZFC and FC curves, which could be ascribed to the onset of the antiferromagnetic order [26] in crystallites forming the shell since Co 3 O 4 orders antiferromagnetically around 40 K [41].…”

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

“…[2][3][4]7 It is worth mentioning that due to its large exchange coupling the Co/CoO system has been used as a reference material in exchange bias studies in thin films, lithographed structures or core/shell nanoparticle or nanowires. [1][2][3][4][7][8][9][10][11][12][13] Remarkably, compared to the existing literature on exchange biased thin films [2][3][4] and isotropic bi-magnetic core/shell nanoparticles, 7,14 the amount of studies dealing with exchange biased anisotropic nanostructures (i.e., rods, nanowires) is relatively scarce. [15][16][17] Nonetheless, interesting new phenomena arising from the competition between shape anisotropy and exchange bias may be anticipated in these structures, thus providing an extra degree of freedom to enhance the current functionalities of these materials while adding large potential for novel, unforeseen, applications.…”