Magnetoelectric effects in single crystals of the cubic ferrimagnetic helimagnet Cu2OSeO3

Abstract

We present magnetodielectric measurements in single crystals of the cubic spin-1/2 compound Cu${}_2$OSeO${}_3$. A magnetic field-induced electric polarization ($\vec{P}$) and a finite magnetocapacitance (MC) is observed at the onset of the magnetically ordered state ($T_c=59$ K). Both $\vec{P}$ and MC are explored in considerable detail as a function of temperature (T), applied field ${\vec{H}}_a$, and relative field orientations with respect to the crystallographic axes. The magnetodielectric data show a number of anomalies which signal magnetic phase transitions, and allow to map out the phase diagram of the system in the $H_a$-T plane. Below the 3up-1down collinear ferrimagnetic phase, we find two additional magnetic phases. We demonstrate that these are related to the field-driven evolution of a long-period helical phase, which is stabilized by the chiral Dzyalozinskii-Moriya term $D \vec{M} \cdot(\bs{\nabla}\times\vec{M})$ that is present in this non-centrosymmetric compound. We also present a phenomenological Landau-Ginzburg theory for the ME${}_H$ effect, which is in excellent agreement with experimental data, and shows three novel features: (i) the polarization $\vec{P}$ has a uniform as well as a long-wavelength spatial component that is given by the pitch of the magnetic helices, (ii) the uniform component of $\vec{P}$ points along the vector $(H^y{H}^z,H^z{H}^x,H^x{H}^y)$, and (iii) its strength is proportional to ${\eta }_{\parallel }^2-{\eta }_{\perp }^2/2$, where ${\eta }_{\parallel }$ is the longitudinal and ${\eta }_{\perp }$ is the transverse (and spiraling) component of the magnetic ordering. Hence, the field dependence of P provides a clear signature of the evolution of a conical helix under a magnetic field. A similar phenomenological theory is discussed for the MC.

References in corpus (11)

• Spin current and magneto-electric effect in non-collinear magnets
• Spontaneous Skyrmion Ground States in Magnetic Metals
• Role of the Dzyaloshinskii-Moriya interaction in multiferroic perovskites
• Magnetically driven ferroelectric order in Ni${}_3$V${}_2$O${}_8$
• Ferroelectric polarization flop in a frustrated magnet MnWO${}_4$ induced by magnetic fields
• Ferrimagnetism of the magnetoelectric compound Cu${}_2$OSeO${}_3$ probed by ${}^{77}$Se NMR
• Metallic State in Cubic FeGe beyond its Quantum Phase Transition
• Multiferroicity induced by dislocated spin-density waves
• Microscopic origin of Magnetic Ferroelectrics in Nonlinear Multiferroics
• Chiral criticality in doped Mn${}_{1-y}$Fe${}_y$Si compounds
• Ultrasonic studies of the magnetic phase transition in MnSi

Cited by in corpus (3)

• Electric field-induced Skyrmion distortion and giant lattice rotation in the magnetoelectric insulator Cu2OSeO3
• Strong Dzyaloshinskii-Moriya Interaction and Origin of Ferroelectricity in Cu2OSeO3
• Magnetoelectric Resonances and Predicted Microwave Diode Effect of Skyrmion Crystal in Multiferroic Chiral-Lattice Magnet