A detailed zero- and transverse-field muon spin rotation investigation of magnetism and the magnetoelectric coupling in Cu2OSeO3 is reported. An internal magnetic field Bint(T=0)=85.37(25) mT was found, in agreement with a ferrimagnetic state below Tc=57.0(1) K. The temperature dependence of the magnetic order parameter is well described by the relation Bint=B(0)(1−(T/Tc)2)β̃ with an effective exponent β̃≃0.39(1), which is close to the critical exponent β≃1/3 for a three-dimensional (3D) magnetic system. Just above Tc the muon relaxation rate follows the power law λ(T)∝(T/Tc−1)−ω̃ with ω̃=1.06(9), which is characteristic for 3D ferromagnets. Measurements of Bint(T) with and without an applied electrostatic field E=1.66×105 V/m suggest a possible electric-field effect of magnitude ΔBV=BV(0 V)−BV(500 V)=−0.4(4) mT.
©2011 American Physical Society