Design, synthesis and properties of Chiral Magnets From Complexes to inorganic materials

Orateur : Katsuya INOUE (Center for Chiral Science, Hiroshima University, Japon)

By quantum mechanics, particles behave as linear waves with quantum phase. The coherent quantum phase control is one of the key issues to create for new stage of materials. The quantum phase coherence easily lost in centro-symmetric crystal, but protected in non centro-symmetric crystal. This protection coming from difference topological number of systems. Chirality is commonly found in nature, from particle physics to molecular chemistry, and one of the non centro-symmetric systems. It is characterized by a reflection asymmetry that we are most familiar with in terms of our left hand being the mirror opposite of our right hand. When this kind of handedness appears in the structure of atoms or molecules in a solid, it affects the way that the magnetic moments of unpaired electrons organize themselves through the Dzyaloshinskii-Moriya (DM) interactions[1-3]. In a symmetric structure, these interactions cancel out, but in a chiral lattice they do not. The DM interactions stabilize a screwlike helical arrangement of the magnetic moments, but they must compete with ferromagnetic exchange, which tries to align all the magnetic moments in the same direction.[4] The result is a helical magnetic arrangement with a winding period of several tens or hundreds of nanometers, which is much longer than the lattice constant. Therefore, even though the chiral properties depend on the symmetry of the lattice, they can be understood and manipulated at the mesoscopic level, independently of the structural details. The properties of these magnetic arrangements are similar to that of chiral liquid crystals. Both materials have helical structures, and they both contain extremely stable excitations called solitons. Solitons are nonlinear excitations that behave like particles, maintaining their shape and energy as they propagate, as exemplified by tsunamis that travel across entire oceans. In chiral magnets, solitons take the form of one-dimensional kinks or two-dimensional vortices called skyrmions[5]. These solitonic excitations are stabilized by temperature and magnetic fields. They are extremely robust and can be manipulated by electric currents or even condense to form a regular lattice, such as the lattice of skyrmions found in MnSi and other related systems [5]. In this paper, we would like to introduce how can stabilize chiral magnetic structures by the structural chirality.

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