Shujun Ye

Magnetoelectric switching energy in Cr2O3/Pt/Co perpendicular exchange coupled thin film system with small Cr2O3 magnetization

We investigated perpendicular exchange bias switching by a magnetoelectric field cooling process in a Pt-spacer-inserted Cr2O3/Co exchange-coupled system exhibiting small Cr2O3 magnetization. Although higher magnetoelectric switching energies with decreasing Cr2O3 thickness due to the exchange bias were reported in Cr2O3/Co all-thin-film systems, in this study, we demonstrated low-energy switching in a magnetoelectric field cool process regardless of the exchange-bias magnitude; we balanced the exchange-bias energy with the Zeeman energy associated with finite magnetization in Cr2O3. We proposed a guideline for realizing low-energy switching in thin Cr2O3 samples.

Control of lateral ferromagnetic domains in Cr2O3/Pt/Co thin film system with positive exchange bias

We investigated the switching of perpendicular exchange bias (PEB) from a negative to a positive value in an exchange-coupled Cr2O3/Pt/Co heterostructure. With varying the Pt spacer layer thickness or the measurement temperature, two types of intermediate states were found during the switching process: a double hysteresis loop indicating a local PEB and a single hysteresis loop indicating an averaged PEB. We propose a way to control the lateral ferromagnetic domain, which is associated with the type of the intermediate state, through the control of the exchange coupling magnitude.

Large perpendicular exchange bias and high blocking temperature in Al-doped Cr2O3/Co thin film systems

We investigated the effect of Al doping on the perpendicular exchange bias in Cr2O3/Co thin film systems. By Al doping, a large unidirectional anisotropy energy (J K ~ 0.74 erg/cm2) and a high blocking temperature (T B) were obtained simultaneously. The variations in J K and T B induced by Al doping were discussed on the basis of Mauris model and explained from an increase in magnetic anisotropy and a decrease in the exchange stiffness constant of Cr2O3. Our first-principles calculations suggest a factor to improve the magnetic anisotropy of Cr2O3 markedly, which is different from the previously established lattice strain effect.

Inserted metals for low-energy magnetoelectric switching in a Cr2O3/ferromagnet interfacial exchange-biased thin film system

An inserted metal (IM) layer (such as Pt, Ru, or Cr) is typically fabricated between Cr2O3 and the ferromagnet in magnetoelectric switched antiferromagnet/ferromagnet exchange-biased thin film systems. The IM layer is used as a “spacer layer” to prevent oxidization of Co and enhance the blocking temperature. In this work, we found that the magnetic properties of these thin film systems vary depending on the type of IM, and they could be reproduced by bilayers or multilayers of Co and IM thin films. We also found that the IM layer was spin-polarized by the Co ferromagnetic layer based on X-ray magnetic circular dichroism data. These results suggest that the IM does not work separately as a “spacer layer”, but rather it is an integral component of Co-based stacked ferromagnetic films in magnetoelectric switched Cr2O3/ferromagnet exchange-biased systems. Furthermore, we found that some stacked ferromagnetic films easily exhibit a low unidirectional anisotropy energy (Jk), which may be a good way to decrease the magnetoelectric switching energy of antiferromagnets for practical device applications.