Electric field control of magnetism

Controlling the magnetic state using electric field rather than conventional magnetic field has couple of advantages. Besides being more energy efficient, using electric field allows a more local control of magnetic state resulting in better scalability of the magnetic device. The material, which possess both ferroelectric and ferromagnetic order, known as multiferroics, are scarce in nature [1]. However, fabricating artificial multiferroics heterostructures consisting of thin layers with relevant ferroic order is a promising alternative. Such heterostructual multiferroics may be categorized based on the effecting mechanism of multiferroicity as charge-mediated [2], exchange bias [3, 4], and strain-driven [5] multiferroics.

In strain-driven artificial multiferroics heterostructures consisting of a piezoelectric material combined with a ferromagnetic element, the applied electric field across the piezoelectric material generates strain, which will be transferred then to the magnetostrictive nanostructures. By means of a magnetic imaging technique, here Photo-Emission Electron Microscopy (PEEM), a magnetic contrast can be obtained using X-ray Magnetic Circular Dichroism (XMCD).  As shown in Figure 1, XMCD-PEEM images of a Ni (magnetostrictive nanostructure) on PMN-PT (piezoelectric material) reveal that the magnetic configuration of Ni can be manipulated only by applying DC electric field across the piezoelectric substrate. The domain walls in the square-shaped nanostructures are in Landau state, whose domain size can be altered by induced anisotropy [6].

Figure 1. (a) XMCD-PEEM images of a 2-μm-wide Ni square, at different applied electric fields. The blue and yellow arrows indicate the directions of the compressive and tensile strains, respectively. (b) Micromagnetic simulations of a 2-μm-wide Ni square, assuming different uniaxial anisotropies. The gray scale bar and the red arrows indicate the direction of the magnetic contrast, while the green arrow indicates the direction of the uniaxial anisotropy applied in the micromagnetic simulations. (c) Schematic of the heterostructures.


Alternatively, if an AC electric field is applied to the piezoelectric substrate, surface acoustic waves (SAWs) can be generated. These are propagating strain waves that can also couple with the magnetization dynamics of magnetostrictive nanostructures. As shown in Figure 2, XMCD-PEEM allows the simultaneous direct observation of both strain waves and magnetization modes in Ni nanostructures with high spatial and temporal resolution [7].

Figure 2. (a) PEEM (top row) and XMCD-PEEM (lower row) images of a 2x2µm2 Ni square at different phases of the SAW. (b) Analysis of the domain configuration from multiple Ni squares of 2x2µm2 as a function of the individual phase with respect to the SAW for a configuration with square sides aligned with SAW propagation direction.


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[2]. C.A.F. Vaz et al., Phys. Rev. Lett. 104, 127202 (2010).
[3]. Y-H. Chu et al., Nat. Mater. 7, 478 (2008).
[4]. M. Vafaee et al., Appl. Phys. Lett. 108, 072401 (2016).
[5]. A. Tkach et al., Appl. Phys. Lett. 106, 062404 (2015).
[6]. S. Finizio et al., Phys. Rev. Appl. 1, 021001 (2014).
[7]. M. Foerster et al., Nat. Commun. 8, 407 (2017)