Press Release: Electric-field control of magnetism

May 27, 2016

To implement multifunctional, low-power consumption, and ‘green’ nanoelectronics, electrical control of the spin degree of freedom is an intriguing route to explore. Promising approaches as well as a rich field of new physics focus on employing magnetoelectric multiferroics, in which an electric field can be used to switch or alter inherent magnetic order. The control of magnetism via an electric-field has attracted significant attention because of potential applications in magnetoelectronics, spintronics, and high-frequency technologies, providing new varieties to next-generation electronic devices.

While single-phase magnetoelectric multiferroics – materials that show spontaneous magnetization and polarization simultaneously – are favored, they remain elusive at ambient conditions. Two alternate pathways to obtain multiferroicity have been widely adopted. One is to start with intrinsic magnetic materials, such as manganites, and then to strategically develop improper ferroelectricity therein. The other is to add magnetic ions to a traditional ferroelectric material, such as BaTiO3, to induce magnetic moment. Although both approaches have been demonstrated conceptually, they share common challenges: 1) the ordering temperature of the developed materials is in most cases too low for practical applications; 2) the induced magnetization/ferroelectricity cannot be arbitrarily modulated by external electric/magnetic fields due to weak coupling between magnetization and ferroelectricity.

In a recent study done via intense collaboration between the MPI CPfS research team led by Dr. Zhiwei Hu (Physics of Correlated Matter) and the Taiwan research team led by Prof. Ying-Hao Chu, we demonstrate a controllable way to enhance the magnetization in highly strained BiFeO3 thin films at room-temperature. This is accomplished via 1) a highly distorted BiFeO3 phase to reduce the antiferromagnetic superexchange interaction, which manifests itself in a reduced antiferromagnetic Néel temperature as determined by x-ray linear dichroism (XLD); 2) an electric-field driven rotation of the ferroelectric polarization to enhance the Dzyaloshinskii-Moriya (DM) interaction as supported by the density functional theory calculations. The enhanced moment is detected by x-ray magnetic circular dichroism (XMCD) and the strong magnetoelectric coupling is revealed by photoemission electron microscopy (PEEM). Our study adds a new scenario to the electric field control of magnetism and sheds the light on next-generation and low-power spintronics.

JCY ; CYK ; ZH ; YHC / CPfS

Schematic change of magnetization induced by the electric field: (a) for as-grown BFO/NGO, polarization along [111]pc and canting angle of 3° giving M= 0.21 mB from D-M interaction. (b) after poling canting angle is up to 5° and polarization rotates towards [001]pc leading to M=0.35 mB. XMCD-PEEM images (c) for the poled (yellow-square areas) and un-poled (as-grown) regions BFO thin film.  X-ray absorption spectroscopy (XAS) of BFO thin films: (d) temperature dependence XAS linear dichroism ILD. Inset shows XAS measured at 27 oC and 300 oC at Fe L2 edge with E//c (orange line) and E^c (black line). (e) Fe-L3 XAS with E//c and Ec of as-grown (solid line) and poled (dotted line) BFO/NGO films. Inset: Change in c-axis, orbital and structure.

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