Observation of Short‐Period Helical Spin Order and Magnetic Transition in a Nonchiral Centrosymmetric Helimagnet

Abstract

The search for materials exhibiting nanoscale spiral order continues to be fuelled by the promise of emergent inductors. Although such spin textures have been reported in many materials, most of them exhibit long periods or are limited to operate far below room temperature. Here, the real‐space observation of an ordered helical spin order with a period of 3.2 nm in a nonchiral centrosymmetric helimagnet MnCoSi at room temperature via multiangle and multiazimuth approach of Lorentz transmission electron microscopy (TEM) is presented. A magnetic transition from the ordered helical spin order to a cycloidal spin order below 228 K is clearly revealed by in situ neutron powder diffraction and Lorentz TEM, which is closely correlated with temperature‐induced variation in magneto‐crystalline anisotropy. These results reveal the origin of spiral ordered spin textures in nonchiral centrosymmetric helimagnet, which can serve as a new strategy for searching materials with nanoscale spin order with potential applications in emergent electromagnetism.

Strong magnetoelastic coupling in MnCoSi compounds studied in pulsed magnetic fields

“…As expected, the features of this phase diagram are like the phase diagram of μ 0 H cr as a function of the temperature. In previous studies it was found that MnCoSi has a cycloidal spiral magnetic structure at low temperature (T < 100 K) and a helical magnetic structure at intermediate temperatures (100 < T < 200 K), as initially proposed [50] and later experimentally observed [41,51]. Upon applying a magnetic field, the magnetoelastic coupling starts to significantly grow at temperatures around 280 K and below.…”

Understanding the effect of foreign atoms occupation on the metamagnetic behaviors in MnCoSi-based alloys: taking Pt-doping as an example

“…Another important information that obtained from structural refinement is the nearest Mn-Mn distance (d1, illustrated in figure 5(a)). As reported before, in the orthorhombic MnCoSi lattice, Mn is the main carrier of magnetic moment and the length of d1 determines the type of magnetism [13,20,27]. Increasing d1 stabilizes ferromagnetic coupling between two Mn moments, while shortening d1 enhances antiferromagnetic coupling [13,20,27].…”

“…As reported before, in the orthorhombic MnCoSi lattice, Mn is the main carrier of magnetic moment and the length of d1 determines the type of magnetism [13,20,27]. Increasing d1 stabilizes ferromagnetic coupling between two Mn moments, while shortening d1 enhances antiferromagnetic coupling [13,20,27]. As listed in table 1, the values of d1 in the Mn 1−x Pt x CoSi and MnCo 1−x Pt x Si display opposite trends with x: d1 increases in the Mn 1−x Pt x CoSi, while decreases in the MnCo 1−x Pt x Si.…”

Large Cryogenic Magnetostriction Induced by Hydrostatic Pressure in MnCo0.92Ni0.08Si Alloy

“…The MnCoSi-based alloys are termed as the most promising candidate owing to their lower cost and higher magnetostrictive coefficient [ 10 ]. In addition, MnCoSi-based alloys as a new type of magneto-response material have attracted increasing attention, due to their rich magnetic structure (cycloid type and helical type antiferromagnetic structure, linear ferromagnetic structure) [ 11 , 12 , 13 ] and rich functional behaviors (magnetocaloric effect [ 14 , 15 ], magnetostrictive effect [ 8 , 9 ], anomalous thermal expansion effect [ 13 , 16 ] and magnetoresistance effect [ 17 , 18 ]).…”