Spiral magnets with Dzyaloshinskii-Moriya interaction containing defect bonds

Abstract

We present a theory describing spiral magnets with Dzyaloshinskii-Moriya interaction (DMI) subject to bond disorder at small concentration $c$ of defects. It is assumed that both DMI and exchange coupling are changed on imperfect bonds. Qualitatively the same physical picture is obtained in two models which are considered in detail: B20 cubic helimagnets and layered magnets in which DMI leads to a long-period spiral ordering perpendicular to layers. We find that the distortion of the spiral magnetic ordering around a single imperfect bond is long-range: values of additional turns of spins decay with the distance $r$ to the defect as $1/r^2$ being governed by the Poisson's equation for electric dipole. At finite concentration of randomly distributed imperfect bonds, we calculate correction to the spiral vector. We show that this correction can change the sign of spin chirality even at $c\ll 1$ if defects are strong enough. It is demonstrated that impurities lead to a diffuse elastic neutron scattering which has power-law singularities at magnetic Bragg peaks positions. Then, each Bragg peak acquires power-law decaying tails. Corrections are calculated to the magnon energy and to its damping caused by scattering on impurities.

19 pages, 7 figures

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• Localized and propagating excitations in gapped phases of spin systems with bond disorder
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• Destabilization of U(1) Dirac spin-liquids on two dimensional non-bipartite lattices by quenched disorder
• Observation of magnetic skyrmion lattice in Cr${}_{0.82}$Mn${}_{0.18}$Ge by small-angle neutron scattering
• Random-bond disorder in two-dimensional non-collinear XY antiferromagnets: From quasi-long-range order to spin glass
• Antiferromagnets with random vacancies and substitutional spins on the triangular lattice
• Defect-induced spin textures in magnetic solids
• Ferromagnetic monolayer with interfacial Dzyaloshinskii-Moriya interaction: magnon spectrum and effect of quenched disorder