Topologically protected magnetic helix for all-spin-based applications.

The recent years have witnessed an emergence of the field of all-spin-based devices without any flow of charge. An ultimate goal of this scientific direction is the realization of the full spectrum of spin-based networks as in modern electronics. The concept of energy-storing elements, indispensable for those networks, are so far lacking. Analyzing analytically the size dependent properties of magnetic chains that are coupled via either exchange or long-range dipolar or Ruderman-Kittel-Kasuya-Yosida interactions, we discover a particularly simple law: magnetic configurations corresponding to helices with integer number of twists, which are commensurate with the chain's length, are energetically stable. This finding, supported by simulations and an experimentally benchmarked model, agrees with the study [R. Skomski et al., J. Appl. Phys. 111, 07E116 (2012)] showing that boundaries can topologically stabilize structures that are not stable otherwise. On that basis, an energy-storing element that uses spin at every stage of its operation is proposed.