Magnetoelectric Coupling in Single CrystalCu2OSeO3Studied by a Novel Electron Spin Resonance Technique

Abstract

The magneto-electric (ME) coupling on spin-wave resonances in single-crystal Cu2OSeO3 was studied by a novel technique using electron spin resonance combined with electric field modulation. An external electric field E induces a magnetic field component µ0H i = γE along the applied magnetic field H with γ = 0.7(1) µT/(V/mm) at 10 K. The ME coupling strength γ is found to be temperature dependent and highly anisotropic. γ(T ) nearly follows that of the spin susceptibility J M (T ) and rapidly decreases above the Curie temperature Tc. The ratio γ/J M monotonically decreases with increasing temperature without an anomaly at Tc. PACS numbers: 75.85.+t, 76.50.+g, Magneto-electric (ME) materials exhibiting coupled and microscopically coexisting magnetic (M) and electric (P) polarizations have attracted considerable interest in recent years [1][2][3][4]. This coupling allows one to influence the magnetic state of a ME material via an external electric field, thus opening a broad range of possible technical applications of such materials [3,5]. Moreover, it is very interesting to investigate the microscopic mechanism of ME coupling, since P and M tend to exclude each other [4]. In order to detect the ME effect, sensitive and reliable experimental techniques are required, since this coupling is generally quite small. Usually, for the determination of the ME coupling either the dielectric properties of ME materials are measured as a function of magnetic field or the magnetization is studied as a function of an applied electric field [3].Cu 2 OSeO 3 is a paraelectric ferrimagnetic material with a Curie temperature of T c 57 K [6][7][8]. The ME effect in Cu 2 OSeO 3 was first observed by magnetocapacitance experiments [6]. Later on, a small abrupt change of the dielectric constant below T c was reported by infrared reflection and transmission studies [9,10]. Recent µSR investigations showed a rather small change of the internal magnetic field by applying an electric field [8]. X-ray diffraction [6] and nuclear magnetic resonance [11] studies revealed no evidence of any lattice anomaly below T c , suggesting that lattice degrees of freedom are not directly involved in the ME effect. Moreover, a metastable magnetic transition with enhanced magnetocapacitance was observed [6] and later on was also investigated under hydrostatic pressure [12]. Very recently, ME skyrmions were observed in Cu 2 OSeO 3 by means of Lorentz transmission electron microscopy [13] and small angle neutron scattering [14].Here we report a study of the ME coupling in single crystal of Cu 2 OSeO 3 . For this investigation a novel microscopic method for the direct determination of the ME effect based on the standard FMR/EPR technique combined with electric field modulation was developed. As a result, to our knowledge for the first time spin-wave resonance (SWR) excitations [15] were detected via ME coupling. The linear ME coupling strength γ was determined quantitatively in Cu 2 OSeO 3 . In particular, the temperature and angular dependence of γ and the SWR...

Dynamical magnetoelectric phenomena of multiferroic skyrmions

“…Note that these magnetic-phase evolutions are not affected by the H-direction. We find that all the magnetically ordered states can induce finite ferroelectric polarization P along [111] The phase evolutions and magnetoelectric nature of Cu 2 OSeO 3 discussed here have been confirmed by several experimental techniques such as electron spin resonance (ESR) measurements [69], magnetoelectric susceptibility measurements [70,71], resonant soft x-ray scatterings [72], and muon-spin [111] , (b) ac magnetic susceptibility χ , and (c) [111] component of ferroelectric polarization P [111] for bulk samples of Cu 2 OSeO 3 measured under…”

Establishing the Fundamental Magnetic Interactions in the Chiral Skyrmionic Mott InsulatorCu2OSeO3by Terahertz Electron Spin Resonance

“…Extrapolating the frequency-field dependences of modes A, B, and C to zero field, on the other hand, gives the zero-field gaps of 95, 202, and 263 cm −1 , respectively. The mode G corresponds to the expected Goldstone mode that has also been seen in low-frequency studies [19,28,29,33]. Now, we would like to notice a fine structure of the resonance absorption observed at 142 cm −1 in magnetic fields ∼ 50-60 T (Fig.…”

“…While most of the well-known skyrmionic helimagnets, such as MnSi [1,2], Fe 1−x Co x Si [3,4], and FeGe [5] are metallic, the recent discovery [6][7][8] of skyrmionic mesophases in Cu 2 OSeO 3 , a strongly correlated insulator with localized Cu 2+ spins [15][16][17], has opened a route to explore skyrmion physics in Mott insulators. In addition Cu 2 OSeO 3 manifests a magnetoelectric coupling [6,18,19] which brings exciting perspectives on the application front, since it allows to manipulate skyrmions by an external electric field [20][21][22].Another very attractive aspect rooted in the insulating nature of Cu 2 OSeO 3 is that a reliable modeling of its magnetic interactions becomes possible which, in conjunction with powerful experimental techniques like the one presented below, offers the unique opportunity to gain a precise understanding of the microscopic magnetic structures and interactions in this skyrmionic material. Having a noncentrosymmetric space group P 2 1 3, the magnetic Cu 2+ ions in Cu 2 OSeO 3 reside at the vertices of a distorted pyrochlore lattice, featuring two symmetry-inequivalent Cu sites, Cu1 and Cu2, with ratio 1:3 (in total there are 16 Cu sites per unit cell), see Fig.…”

Microscopic description of twisted magnet Cu2OSeO3

“…First of all, having the space group P2 1 3 without centre of inversion, this crystal becomes a cubic helimagnet below the critical temperature of about 58 K. Moreover, it is the first cubic crystal beyond the class of itinerant magnets with B20 crystal structure [1][2][3][4], for which an A-phase, associated with a Skyrmion lattice [5][6][7], has been recently observed [8][9][10][11][12][13][14]. Secondly, being an insulator, Cu 2 OSeO 3 has magnetic-electric properties [14][15][16][17][18][19][20], which provide a new physical significance in comparison with the B20 crystals. The interconnection between magnetization gradients and electric polarization makes this crystal potentially applicable for data storing devices and spintronics [21][22][23][24].…”