Exchange bias in Co-Cr2O3 nanocomposites

Abstract

The possibility of using exchange bias in ferromagnetic-antiferromagnetic system to over come the effect of superparamagnetism in small cobalt nanoparticles is explored. We have prepared Co-Cr 2 O 3 nanocomposite powders using a chemical method. It is shown that in this system the effect of superparamagnetism in cobalt nanoparticles could be overcome.The superparamagnetic blocking temperature of 3 nm cobalt particles has been increased to above room temperature. The choice of Cr 2 O 3 is vital as its T N is higher compared to other antiferromagnetic materials used for this purpose such as CoO. The field cooled and zero field cooled hysteresis measurements of the samples confirm the existence of exchange bias interaction in this system. PACS

High Temperature Magnetic Stabilization of Cobalt Nanoparticles by an Antiferromagnetic Proximity Effect

“…Despite the foreseeable change of recording paradigm from continuous to patterned media, where each bit is recorded in an individual nanostructure [7], the key for sustained storage density increase will remain the introduction of progressively more anisotropic (high K) materials [8], which allow for magnetic stability at very small volumes, V (i.e., blocking temperature, T B ∝ KV, above room temperature, RT). Two main strategies are largely investigated to achieve high K (both of them with implications in other active technologies beyond information storage, such as permanent magnets, magnetic hyperthermia or even sensors [5,[9][10][11]): (i) the use of compounds with intrinsically high magnetocrystalline anisotropy (such as FePt [3,8]) and (ii) the design of exchange-coupled nanocomposites [4,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29].Unfortunately, most high-K materials require high-temperature annealing processes to obtain the desired phase, which could hamper their implementation in certain structures. Thus, FM-AFM exchange coupling alternatives may be an appealing option.…”

Exchange bias effect in ball milled Co–Cr2O3 FM–AFM nanocomposites

“…Significant enhancement in exchange bias field, H E , and coercivity, H c , below T N of Cr 2 O 3 are observed in ball milled FM-AFM nanocomposites over similar composites prepared via wet-chemical method [13,14]. Also, the role of interparticle dipolar-dipolar interaction and surface-spin disorder on overall magnetic properties of composites clearly emerges from this study.…”

“…Although, blocking temperature in this system has increased up to the room temperature but the system lacks adequate coercivity and exchange bias field necessary for any practical applications. Composites synthesized using wet-chemical method [13,14] indeed showed improvement in blocking temperature but these techniques suffer from low yield and hence could not be extended to a large scale production of EB nanocomposites such as hard-magnetic materials [15]. It is thus interesting to explore and study exchange coupled magnetic nanocomposites where judicious selection of FM and AFM components and novel synthesis route can optimize the exchange bias properties of the composite.…”

Effects of Cu dilution in NiO on the magnetic properties of NiFe2O4/Ni1−xCuxO nanocomposites

“…However, with decreasing the particle size, the anisotropy energy, which keeps the particle magnetization in the easy anisotropy axis direction, becomes comparable to the thermal energy, and thus makes the particle magnetization flip in all easy directions. As a result, the magnetic nanoparticles lose their stable magnetic order states and become superparamagnetic [2]. This is the so-called "superparamagnetic limit" [3] which limits the use of ultrafine particles for various applications.…”