Abstract
Below the Néel temperature, TN ∼ 220 K, at least two nano-scale antiferromagnetic (AFM) phases coexist in the polar polymorph of the BiFe0.5Sc0.5O3 perovskite; one of these phases is a weak ferromagnetic. Non-uniform structure distortions induced by high-pressure synthesis lead to competing AFM orders and a nano-scale spontaneous magnetic phase separated state of the compound. Interface exchange coupling between the AFM domains and the weak ferromagnetic domains causes unidirectional anisotropy of magnetization, resulting in the exchange bias (EB) effect. The EB field, HEB, and the coercive field strongly depend on temperature and the strength of the cooling magnetic field. HEB increases with an increase in the cooling magnetic field and reaches a maximum value of about 1 kOe at 5 K. The exchange field vanishes above TN with the disappearance of long-range magnetic ordering. The effect is promising for applications in electronics as it is large enough and as it is tunable by temperature and the magnetic field applied during cooling.
Highlights
Multiferroic materials with polar and magnetic orders combine spontaneous magnetization and electric polarization and offer a unique opportunity to effectively cross-control these parameters.the search for new multiferroics has attracted the attention of many research groups worldwide.1–3The compositions derived from the “classical” type-I multiferroic BiFeO3 are the best studied materials.4,5 Cation substitutions in the crystallographic positions of bismuth result mainly in a change scitation.org/journal/adv in the temperature of the ferroelectric transition, while the ironsite substitutions allow variation of the magnetic transition
According to both scanning electron microscope (SEM) observations and XRD study, as well as the neutron diffraction data measured in a wide temperature range,13 the annealed BiFe0.5Sc0.5O3 ceramics were homogeneous and single-phase with the polar Ima2 perovskite structure
All loops recorded after ZFC turned out to be centered about the origin of coordinates H and M (Fig. S3 in the supplementary material), while the loops after FC are shifted to the negative direction of the H-axis (Fig. 1)
Summary
Multiferroic materials with polar and magnetic orders combine spontaneous magnetization and electric polarization and offer a unique opportunity to effectively cross-control these parameters. The as-prepared perovskite BiFe0.5Sc0.5O3 phase is the antipolar Pnma polymorph that can be irreversibly converted to the polar Ima one by annealing within a temperature range of 820–920 K at ambient pressure. The polar Ima modification is a rare case of canted ferroelectrics, which combines both ferroelectric- and antiferroelectric-like displacements of cations along different crystallographic axes. This polymorph definitely deserves a detailed study. We report on a detailed study of the EB effect in the polar Ima polymorph of the metastable BiFe0.5Sc0.5O3 perovskite and demonstrate that the effect is associated with nano-sized magnetic phase separation in this material
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