Exchange bias using a spin glass

Abstract

Exchange bias is commonly manifested as the hysteresis-loop shift observed when a ferromagnet is in contact with an antiferromagnet. Here, we report observations of exchange bias with unusual features of a ferromagnet in contact with a spin glass, demonstrating that this is a phenomenon of greater generality. The easily measured properties of the ferromagnet allow access to the internal magnetic degrees of freedom of the glass to which they are coupled. Our results show that a Co/CuMn bilayer system exhibits all the rich phenomena of coercivity enhancement, bias-field shifts and training effects associated with a conventional ferromagnet/antiferromagnet system. Nevertheless, striking differences arise, such as an orientation reversal of the bias field in a small temperature range just below the blocking temperature. We argue that all features can be understood within the context of a random-field model for long-ranged oscillatory Ruderman-Kittel-Kasuya-Yosida (RKKY) coupled spins.

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

“…It can be easily observed the completely different radial structure functions. While that of Co foil shows the well-defined peaks corresponding to the 25 first four Co-Co neighbour distances, the FT of the Co-NPs sample resembles that of Co 3 O 4 oxide, 28,29 with peaks around 1.6, 2.5 and 3 Å, associated with the six Co-O bonds, the four Co-Co bonds (edge-shared CoO 6 octahedra) and the 8 Co-Co bonds (corner-shared CoO 6 octahedra), respectively. 30 However, the contribution of both metallic Co-cores and the CoO thin shell can only be appreciated as sight broadening of the FT peaks and/or shoulder-like features.…”

“…[1][2][3] Magnetic NPs can be easily manipulated by external magnetic field gradients and thus, be used for separation of different catalytic solids, hyperthermia 25 treatments or magnetic resonance imaging. [4][5][6] In order to use innovative magnetic NPs for artificial engineering, a systematic characterization is needed to control not only the magnetic properties of an individual particle, but also the collective behavior of an ensemble of interacting magnetic 30 NPs.…”

“…20 Other possibility is that the presence of AFM small grains with uncompensated spins and disorder generated by grain boundaries are likely at a very thin (< 1 nm) CoO layer, due to the roughness and intermixing at the interface. 36, 37 Therefore, the maximum seen in the FC and the EB effect could be 25 associated with the transition into a frozen state of the spinglass (SG) Co-oxide shell. 38 In contrast, at higher temperatures, the curve exhibits a broad maximum centered at 220 K, which could be a signature of a 35 progressive unfrozen process of the magnetic moments in the oxide SG shell.…”

Interplay between microstructure and magnetism in NiO nanoparticles: breakdown of the antiferromagnetic order

“…The research developed by Ali et al on exchange-biased bilayered FM/SG systems revealed that H EB increased monotonically with the SG thickness until it is saturated at a certain value, while H C exhibits a maximum well below the saturation point of H EB . 67 Therefore, in the case of FM/SG interfaces, the degree by which a region of the glass is bound to the FM depends on the characteristics of the spin configuration at the interface. The H EB is provided by the glassy regions that remain largely intact on reversal the FM, whereas those that change on reversal of the FM contribute to H C .…”

Effects of coexisting spin disorder and antiferromagnetism on the magnetic behavior of nanostructured (Fe79Mn21)1−xCux alloys

“…10 Within this uncompensated AFM/disordered region description, the moments at intergrain boundaries freeze below T ZFC and align with the uncompensated ones. Thus, analogously to the case of the EB effect observed in oxide nanoparticles, 22,23 here the EB might arise from coupling interactions at the interface between the AFM phases and the spin-glass-like intergrain boundaries.…”