Electric-Field-Induced Skyrmion Distortion and Giant Lattice Rotation in the Magnetoelectric InsulatorCu2OSeO3

Abstract

Uniquely in Cu 2 OSeO 3 , the Skyrmions, which are topologically protected magnetic spin vortexlike objects, display a magnetoelectric coupling and can be manipulated by externally applied electric (E) fields. Here, we explore the E-field coupling to the magnetoelectric Skyrmion lattice phase, and study the response using neutron scattering. Giant E-field induced rotations of the Skyrmion lattice are achieved that span a range of ∼25°. Supporting calculations show that an E-field-induced Skyrmion distortion lies behind the lattice rotation. Overall, we present a new approach to Skyrmion control that makes no use of spin-transfer torques due to currents of either electrons or magnons. [12,13]. All have the chiral-cubic space group P2 1 3, a weak magnetocrystalline anisotropy, and common phase diagrams with a helimagnetic ground state. Despite these similarities, the diverse transport properties lead to material specific mechanisms for Skyrmion manipulation and the associated dynamics. In the well-studied itinerant compounds, spin-transfer torques (STTs) exerted by the conduction electrons of an ultralow current density, j ≲ 10 6 A·m −2 drive the Skyrmion motion [5,[14][15][16][17][18][19]. More generally, in both MnSi and insulating Cu 2 OSeO 3 , Skyrmion lattice (SKL) rotations are observed to be driven by STTs exerted by the magnon currents induced by a thermal gradient [20]. Even though electric currents and thermal gradients have been established to generate Skyrmion motion, it remains vital to find new control mechanisms which may lead to further efficient Skyrmion-based functionalities.In the insulating SKL host compounds, the chiral lattice promotes a magnetoelectric (ME) coupling between electric (E) and magnetic orders which can be expected to lie at the heart of new Skyrmion control paradigms. The use of ME coupling for Skyrmion manipulation is also attractive for applications since losses due to Joule heating are negligible. Presently, however, open questions remain concerning the basic understanding of how an applied E field can manipulate the Skyrmion spin texture. To address this issue, we have used small-angle neutron scattering (SANS) to study the giant E-field-induced SKL rotations generated in a bulk sample of ME Cu 2 OSeO 3 . Surprisingly, the rotations saturate at an angle dependent on both the size and sign of the E field. With supporting calculations, we explain our observations, and show that an E-field-induced Skyrmion distortion leads to the observed rotations. This amounts to a new approach for Skyrmion control that does not require STTs.In Cu 2 OSeO 3 , the ME coupling exists in all magnetic phases [12,[21][22][23][24][25][26][27][28], and is generated by the d-p hybridization mechanism [12,24,29,30]. This mechanism dictates a particular ME coupling anisotropy; for a magnetic field μ 0 H∥½110 or [111], an electric polarization P emerges ∥½001 or [111], respectively [24]. In our experiments, we chose E∥½111 (which corresponds to a negative applied voltage) or ∥½111 (positive voltage). T...

Relaxation dynamics of modulated magnetic phases in the skyrmion host GaV4S8 : An ac magnetic susceptibility study

“…The emergence of the skyrmion lattice phase was identified in the close vicinity of the paramagnetic-helical phase boundary of cubic chiral helimagnets, known as B20 compounds with a P 2 1 3 space group [3][4][5][6][7]. Cu 2 OSeO 3 , belonging to the same space group with a different crystal structure [8] is an insulating material demonstrated to host skyrmions [9,10], with a magnetoelectric character [11][12][13][14]. Since their experimental discovery, skyrmions have attracted much attention owing to their potential application as magnetic bits in high-capacity and low-consumption memory devices [15][16][17][18][19].…”

Quantized transport for a skyrmion moving on a two-dimensional periodic substrate

“…Skyrmion motion can be directly observed with Lorentz microscopy 7,10 or deduced from changes in the transport properties, permitting the construction of effective skyrmion velocity versus applied force curves that show that the skyrmion velocity increases with increasing current 20 . Other methods to move skyrmions include the use of temperature gradients [27][28][29][30][31] , electric fields 32,33 , and coupling to a magnetic tip 15 .…”

Charged skyrmions on the surface of a topological insulator

“…30 ) and, more importantly, an electric field is easier to manipulate than a temperature gradient. It has also been shown that in multiferroic materials, which include Cu 2 OSeO 3 , skyrmion textures have an intrinsic dipole moment which enables them to couple to to the gradient of electric field 29,35,36,45 . Regardless of the difficulty of applying a gradient in electric field, the estimated Hall velocity v H in our approach is two orders of magnitude greater than v H due to magnetoelectric coupling 29 , where v H ≈ (λR S /2πS )∆E ∼ 10 −3 mm/s with R S = 25 nm, dipolar coupling λ ∼ 10 −33 ≈ C · m 34 , and field strength difference ∆E ∼ 10 2 V/m.…”