A research team led by associate Prof. YIN Lihua from Institute of Solid State physics, Hefei Institutes of Physical Science (HFIPS), Chinese Academy of Sciences (CAS) demonstrated clear control of magnetism (M) at low electric fields (E) at room temperature in a recent research. The E-induced phase transformation and lattice distortion were found to result in the E control of M in multiferroic BiFeO3-based solid solutions near the morphotropic phase boundary (MPB).
This research was published in Acta Materialia.
Multiferroic materials, with magnetic and ferroelectric properties, are promising for multifunctional memory devices. Magnetoelectric-based control methods in insulating multiferroic materials require less energy and have potential for high-speed, low-energy-consumption information storage applications. BiFeO3 is a room-temperature multiferroic material with potential for use in spin-electronics devices, but its weak ferromagnetic and magnetoelectric effects and high required voltage for manipulation are weaknesses.
In this research, scientists grew single crystals of multiferroic 0.58BiFeO3-0.42Bi0.5K0.5TiO3 (BF-BKT) that were located in the tetragonal region adjacent to the MPB.
"Below the Néel temperature, TN~257.5 K, the BF-BKT crystals showed antiferromagnetic behavior," said YIN, "and at room temperature, we found that BF-BKT crystals exhibited both short-range magnetic order and long-range ferroelectric order."
At room temperature, the multiferroic BF-BKT single crystals exhibited substantial and consistent control of M with E, where the magnitude of E was significantly less than the ferroelectric coercive field (EC). Additionally, high magnetic fields (H) were able to considerably reduce the degree of E control over M.
It has been found that the coupling between magnetism and ferroelectricity in BF-BKT material can be attributed to both lattice distortion and phase transformation induced by an external E, rather than just ferroelectric domain switching. At high values of H, the converse magnetoelectric effect is weakened due to the suppression of phase transformation caused by the magnetic field.
These results suggested that designing devices based on multiferroics near the MPB could be an effective way to achieve E control of M and even possible low-E switching of M for low-power spintronic applications.
High resolution X-ray diffraction patterns at in-situ applied electric fields, corresponding variation of lattice spaces with applied electric fields, and variation of magnetization at different electric fields and temepratures for the 0.58BiFeO3-0.42Bi0.5K0.5TiO3 single crystal. (Image by YIN Lihua)