Microscopic description of twisted magnet Cu2OSeO3

Abstract

a b s t r a c tTwisted structures of chiral cubic ferromagnets MnSi and Cu 2 OSeO 3 can be described both in the frame of the phenomenological Ginzburg-Landau theory and using the microscopical Heisenberg formalism with a chirality arising from the Dzyaloshinskii-Moriya (DM) interaction. Recent progress in quantum firstprincipal methods allows us to calculate interatomic bond parameters of the Heisenberg model, namely isotropic exchange constants J ij and DM vectors D ij , which can be used for simulations of observed magnetic textures and comparison of their calculated characteristics, such as magnetic helix sense and pitch, with an experimental data. In the present work, it is found that unaveraged microscopical details of the spin structures (local canting) have a strong impact on the global twist and can significantly change the helix propagation number. Coefficients and of the phenomenological theory and helix propagation number k /2 = are derived from interatomic parameters J ij and D ij of individual bonds for MnSi and Cu 2 OSeO 3 crystals and similar cubic magnets with almost collinear spins.

Low-energy magnon dynamics and magneto-optics of the skyrmionic Mott insulator Cu2OSeO3

“…The resulting effective unit cell then consists of four S = 1 spins arranged in the Trillium lattice, a structure identical to that of the B20 helimagnets, revealing why such similar phase diagrams result from seemingly dissimilar compounds 11 . The magnetic phase diagram can then be understood as competition between the "weak" Heisenberg and "weak" DM exchange interactions between these effective S = 1 spins 29,44,45 . With |D ij | < |J ij |, the resultant magnetic order in zero field onsets at T c ≈ 58K in the form of a long wavelength helix (λ ≈ 50 nm) 12,46 as shown in Figure 1 (c).…”

Optically probed symmetry breaking in the chiral magnetCu2OSeO3

“…The magnetization 23 , of Cu 2 OSeO 3 shows that the S = 1 clusters are fully aligned along the applied field in the ferrimagnetic phase, i.e., already for moderate magnetic fields of 0.2 T. This reflects that the magnetocrystalline anisotropy is weak in this cubic magnet with small spin-orbit coupling. As a result, the helical or conical domains can be easily reoriented, 48 even when the magnetic field is applied along the 111 hard axis. This in turn is reflected in a large magnetic susceptibility χ m , and hence a large magneto-optical susceptibility χ MO .…”

Magnon spectrum of the helimagnetic insulator Cu2OSeO3

“…Understanding the complex magnetic phase diagram of Cu 2 OSeO 3 therefore requires detailed knowledge of the spin Hamiltonian with precise quantitative estimates of all interaction parameters, which can be obtained from measurements of the spin-excitation spectrum. Microscopic theoretical models that were recently proposed for the description of spin arrangements in Cu 2 OSeO 3 include five magnetic exchange integrals and five anisotropic DM couplings between neighbouring S = 1 2 copper spins [12][13][14][15][16] , yet their experimental verification was so far limited to thermodynamic data 14 , terahertz electron spin resonance (ESR) 15 , far-infrared 17 and Raman spectroscopy 18 that can only probe zone-center excitations in reciprocal space. Here we present the results of inelastic neutron scattering (INS) measurements that reveal the complete picture of magnetic excitations in Cu 2 OSeO 3 accessible to modern neutron spectroscopy over the whole Brillouin zone and over a broad range of energies and demonstrate good quantitative agreement with spin-dynamical model calculations both in Figure 1 | Simplified structure of the magnetic Cu sublattice in Cu 2 OSeO 3 and Brillouin zone unfolding.…”