Origin and consequence of an unpinned helical magnet: application to partial order in MnSi under pressure

Abstract

We study a classical ferromagnetic Heisenberg model in the presence of Dzyaloshinskii-Moriya interactions on the corner-shared triangle lattice formed by the Mn sites of MnSi. We show that a sizable spin helicity can be obtained only when the microscopic Moriya vectors lie parallel to the Mn-Mn bonds. Further, such vectors are shown to produce an unpinned helical order characterized by a particular ordering wavevector magnitude but unpinned direction, dubbed partial order, at physically realizable temperatures. A consequence of such an unpinned helical ordering is that the neutron scattering intensity is sharply peaked at this wavevector magnitude. The surface formed by connecting these wavevectors is a sphere, around which the neutron scattering weight is spread. We further show that the observed neutron scattering intensity can be anisotropic along this surface and that this anisotropy is dependent on the experimentalist's choice of lattice Bragg peak through a geometric factor. A neutron scattering measurement near the Bragg point ($\frac{2\pi }{a}$,$\frac{2\pi }{a}$,0) naturally leads to a highest intensity along the (1,1,0) direction consistent with the observed anisotropy in MnSi [Pfleiderer {\it{et al.}} Nature {\bf{427}} 227 (2004)]. A possible mechanism for pinning the helical order, and a way to distinguish an ordered and a partially ordered state in the context of neutron scattering are discussed.

6 pages, 4 figures, added new Fig. 1, expanded discussion

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Cited by in corpus (15)

• Skyrmions and Anomalous Hall Effect in a Dzyloshinskii-Moriya Spiral Magnet
• Magnetic Blue Phase in the Chiral Itinerant Magnet MnSi
• Out-of-Plane Spin-Orientation Dependent Magnetotransport Properties in the Anisotropic Helimagnet Cr${}_{1/3}$NbS${}_2$
• Weak antiferromagnetic ordering and pure magnetic reflections induced by Dzyaloshinskii-Moriya interaction in MnSi-type crystals
• Frustrated magnetic helices in MnSi-type crystals
• Multi-shell contribution to the Dzyaloshinskii-Moriya spiralling in MnSi-type crystals
• Bose-Luttinger Liquids
• Phase transitions in chiral magnets from Monte Carlo simulations
• Skyrmions and spirals in MnSi under hydrostatic pressure
• Evolution of Helimagnetic Correlations when approaching the Quantum Critical Point of Mn${}_{1-x}$Fe${}_x$Si
• Antiferromagnetic spin cantings as a driving force of ferroelectricity in multiferroic Cu2OSeO3
• A general model of MnSi-like spiral magnets
• Partial Antiferromagnetic Helical Order in Fe${}_3$PO${}_4$O${}_3$
• Experimental determination of the spin Hamiltonian of the cubic chiral magnet MnSi
• The influence of antiferromagnetic spin cantings on the magnetic helix pitch in cubic helimagnets