μSR investigation of magnetism and magnetoelectric coupling in Cu2OSeO3

Abstract

A detailed zero-and transverse-field muon spin rotation investigation of magnetism and the magnetoelectric coupling in Cu 2 OSeO 3 is reported. An internal magnetic field B int (T = 0) = 85.37(25) mT was found, in agreement with a ferrimagnetic state below T c = 57.0(1) K. The temperature dependence of the magnetic order parameter is well described by the relation2 )β with an effective exponentβ 0.39(1), which is close to the critical exponent β 1/3 for a three-dimensional (3D) magnetic system. Just above T c the muon relaxation rate follows the power law λ(T ) ∝ (T /T c − 1) −ω withω = 1.06(9), which is characteristic for 3D ferromagnets. Measurements of B int (T ) with and without an applied electrostatic field E = 1.66 × 10 5 V/m suggest a possible electric-field effect of magnitude B V = B V (0 V) − B V (500 V) = −0.4(4) mT.

Transverse field muon-spin rotation signature of the skyrmion-lattice phase inCu2OSeO3

“…This is consistent with the long lengthscale dynamics observed via Lorentz microscopy [24], which suggest rotations of the skyrmion texture take place on a 0.1 s timescale. Consistent with the observation that the muon signal below T c is dominated by the the distribution of static internal magnetic fields are the results of the previous zero-field μ + SR study of this material [20]. Those measurements showed sizable transverse relaxation of the muon precession signal, which decreased as the transition was approached from below, consistent with the decrease of the internal field with increasing temperature.…”

“…A previous zero-field μ + SR study of this material [20] we take the magnetic moment to be 0.25μ B , consistent with that found in a previous study [17]. For comparison with the measured spectra, the distributions were convolved with a simulated instrument function, generated with the WIMDA program.…”

“…In this material, spins are located on the Cu 2+ ions, which are arranged in four tetrahedra within the unit cell. Ferrimagnetic (FiM) ordering of these spins is favored, with one Cu ion (Cu1) oriented in the opposite direction to that of the others (Cu2) [17,20]. This ordered configuration persists when we build more complicated spin configurations described in the following [21].…”

“…7 arise from the SkX phase spin textures, we may consider the dipole fields produced by a skyrmion at individual muon sites. In Cu 2 OSeO 3 , this is complicated by the large number of inequivalent muon sites [20] and the ferrimagnetic arrangements of Cu 2+ spins that form the basis of the skyrmion spin texture. Figures 8(a) and 8(b) show examples of the magnitude of the dipole field found at two of the five crystallographically distinct muon sites, evaluated field distribution at each site, with spectral weight skewed towards high fields.…”

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

“…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].…”