Parasitic Magnetism in Magnetoelectric Antiferromagnet

Parasitic magnetism plays an important role in magnetoelectric spin switching of antiferromagnetic oxides, but its mechanism has not been clearly investigated. Unlike the widely obtained surface boundary magnetization in magnetoelectric Cr₂O₃ antiferromagnet, we previously reported that Al doping could produce volume-dependent parasitic magnetism (M_para) in Cr₂O₃ with the remaining magnetoelectric effect and antiferromagnetic properties. In this work, we systematically investigated the magnetic properties of M_para in Cr₂O₃ through its different exchange coupling characteristics with the ferromagnet at various conditions. The columnar grain boundaries cause an antiferromagnetic sublattice breaking to produce uncompensated spins and thus are considered to be responsible for M_para in both undoped and Al-doped Cr₂O₃. Finally, a model was proposed for the formation mechanism of the parasitic magnetism in Cr₂O₃, which explains the reported magnetic characteristics of Cr₂O₃, and some current topics such as the domain formation and motion in Cr₂O₃ during magnetoelectric spin switching. This work contributes to a deep understanding of antiferromagnetic spintronics and provides a method to realize the low-energy operation of antiferromagnetic-based magnetic random access memory.

Spin glass like transition and the exchange bias effect in Co3O4 nanoparticles anchored onto graphene sheets

We have synthesized Co3O4 nanoparticles having 40 nm average size, which are anchored on reduced graphene oxide. X-ray diffraction, FESEM, TEM and Raman spectroscopy are performed for the characterization. The temperature dependence of field cooled (FC) and zero field cooled (ZFC) magnetization curves exhibits antiferromagnetic (AFM) transition around ∼30 K, as observed for bulk Co3O4. The exchange bias effect is observed below ∼30 K. A significant change in the exchange bias effect is noted around ∼8 K, which is close to a spin-glass-like transition. The spin-glass-like phase has been confirmed by the memory effects observed by different experimental protocols. The possible origin of exchange bias is discussed in the manuscript.