Frustrated magnetic helices in MnSi-type crystals

Article

关键词: ANISOTROPIC SUPEREXCHANGE INTERACTION;    WEAK FERROMAGNETISM;    PHASE;   

DOI  :  10.1103/PhysRevB.85.014421

来源: SCIE

【 摘 要 】

The spiral magnetic order in cubic MnSi-type crystals is described analytically using the model of classical Heisenberg ferromagnetics with an extra interaction of the Dzyaloshinskii-Moriya (DM) type between neighboring atoms. For all shortest Mn-Mn bonds the DM vectors D are expressed via the D vector of an arbitrary chosen bond, in accordance with the P2(1)3 space group of these crystals and bond directions. After minimization of the magnetic energy it is found how the propagation vector k of magnetic helices depends on D: for any helix direction k = 2(D-x - 2D(y) - D-z)/(3J) where J is the exchange interaction constant and k vector is in the units of the inverse lattice constant. The propagation number k determines both the sign and strength of global spiraling, whereas locally, within a unit cell, the helical order is shown to be frustrated so that the twist angles between neighboring ferromagnetic layers may be even of different signs. Conical deformations of helices caused by an arbitrary directed external magnetic field are also considered within the same model. The critical field of helix unwinding is found and it is shown that even in the unwound state there remains a residual periodic canting of magnetic moments with the canting angle proportional to (D-x + D-z)/J which can be measured by diffraction methods. It is also demonstrated how the usually used continuous picture of moment distribution can be obtained from the discrete one in a coarse grain approximation.

【 授权许可】

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