A New Twist in an Old Material: Novel Magnetic States in MnSi/Si(111)

Ted Monchesky (Dalhousie University, Canada)

Chiral interactions in magnetic thin films create twists in the magnetic structure that have yet unexplored opportunities for magnetic storage technologies. These interactions lead to self-organization of the magnetic structure into stable 1-dimensional or 2-dimensional solitonic units that are nanoscale in size that can be manipulated by electrical currents that are orders of magnitude smaller than those required to move conventional domain walls.

In epitaxial MnSi thin films, polarized neutron reflectometry (PNR) measurements show that the chiral interactions create particle-like magnetic vortex states (skyrmions) over a broad range of fields and temperatures. At the lowest temperatures, these 2D textures are replaced by a 1D winding of the magnetic structure, known as a helicoid. These helical states exhibit novel behavior in a magnetic field where they unwind via discrete transitions to states with a quantized number of turns of the magnetization, in contrast to the continuous evolution observed in bulk helimagnets. Furthermore, we demonstrate the concept of a novel helicoid magnetic memory where information can be stored in the number of turns in the helicoid and the discrete states can be read by electronic means.

Our study establishes that MnSi thin films are a system where anisotropy and finite size effects can be used to engineer novel magnetic textures. Since these films are grown on Si substrates, this opens the possibility to investigate spin-dependent transport effects in chiral magnetic heterostructures.

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