Giant exchange bias in a single-phase magnet with two magnetic sublattices

Exchange bias phenomenon is generally ascribed to the exchange coupling at the interfaces between ferromagnetic and antiferromagnetic layers. Here, we propose a bulk form of exchange bias in a single-phase magnet where the coupling between two magnetic sublattices induces a significant shift of the coercive field after a field cooling. Our experiments in a complicated magnet YbFe2O4 demonstrate a giant exchange bias at low temperature when the coupling between the Yb3+ and Fe2+/Fe3+ sublattices take places. The cooling magnetic field dependence and the training effect of exchange bias are consistent with our model. In strong contrast to conventional interfacial exchange bias, this bulk form of exchange bias can be huge, reaching the order of a few Tesla.

Theoretical Modeling of ME effect at Low frequency and Resonance Frequency for Magnetoelectric Laminates with Anisotropic Piezoelectric Properties

A new theory is developed for the magnetoelectric (ME) coupling in a symmetric 2-2 ME laminate having a representative piezoelectric crystal (PMN-PT) particularly with anisotropic piezoelectric properties. Considering the average field method, the theoretical expressions for the transverse ME voltage coefficients at low and resonance frequencies were derived. The theory takes into account the anisotropic properties of the piezoelectric materials providing two different expressions of transverse ME voltage coefficients for different in-plane magnetic fields both at low and resonance frequencies. The numerical simulations show multiple resonance frequencies and phase differences between transverse ME voltage coefficients showing good agreement with the experimental results. Our theory should be generally applicable to other ME laminates with any piezoelectric with anisotropic piezoelectric coefficients.