Unconventional exchange bias in CoCr2O4/Cr2O3 nanocomposites

Abstract

Unconventional exchange bias (EB) has been studied in CoCr2O4/Cr2O3 nanocomposites, in which the Curie temperature of the ferrimagnetic CoCr2O4 is much lower than the Néel temperature of the antiferromagnetic Cr2O3. A negative EB field of about 2.5 kOe at 5 K is achieved upon cooling in a field of 30 kOe. Meanwhile, the coercivity of the CoCr2O4 nanoparticles has been enhanced significantly by coupling with Cr2O3. The effect of the cooling field on the EB field and coercivity at 10 K has also been investigated. The domain-state model is used to interpret the unconventional EB. Cooling field may play a decisive role in the creation of the interfacial spin configuration for the unconventional EB, not only by exchange interaction between the induced magnetization of a polarized paramagnet and interfacial spins of an antiferromagnet but also by Zeeman interaction between the domain-state surplus magnetization and the external field.

Exchange bias and its training effect in Ni/NiO nanocomposites

“…According to the domain-state model [13,14], EB acts as a result of a domain state in the AFM phase carrying an irreversible domain-state magnetization. In this model, the formation of AFM domain states is crucial, which can be enhanced by defects introduced during mechanical milling [12]. After annealing at 573 K and 673 K, the number of these defects reduces, leading to a weakening of the EB effect.…”

“…The mixtures of about 4 g were put in argon atmosphere in a hardened-steel vial with steel balls of 12 mm diameter. Mechanical alloying was carried out using a high-energy ball mill which was rotated in two dimensions perpendicular to the horizontal plane [10][11][12]. The rotation speed of the mill was chosen to be 600 rpm.…”

Tailoring Interfacial Exchange Anisotropy in Hard–Soft Core-Shell Ferrite Nanoparticles for Magnetic Hyperthermia Applications

“…The direct exchange interaction between the core and shell spins was prevented by the It is interesting that numerous research studies revealed the occurrence of (unconventional) EB. For example, unconventional EB with T N > T C has been observed in some systems such as core-shell nanoparticles and thin-film heterostructures [41][42][43][44]. In addition, EB was reported to occur in systems cooled from temperatures below T N [45].…”

Study of exchange bias and training effect in NiCr 2 O 4

“…There is a great deal of interest in exploring the EB effect because of its relevance in applications such as magnetic read heads, spintronics devices, etc. [25][26][27]. In NiCr 2 O 4 , a few authors have observed an asymmetry in M-H loops, however so far to our knowledge no attempt has been made to study the exchange bias field in this system [28,29].…”