Electrical detection of emergent magnetization dynamics in artificial spin ice

Artificial spin ices (ASIs) consisting of 72 stadium-shaped magnetic tunnel junction (MTJ) cells arranged in a honeycomb lattice were fabricated. The magnetization state of each cell was electrically detected using magnetoresistance. Measurements on the MTJ-based ASIs with a lattice constant a ranging from 980 nm to 2 μm confirmed the following: (1) the switching field of the cells depends on the angle of the long axis of the cell with respect to the field direction, reflecting the shape anisotropy of the free layer in the MTJ cells; (2) the switching field distribution was ∼10% of the mean value; and (3) the magnetic coupling increased monotonically with the reduction in a and reached ∼1 mT for the smallest a, which was close to the switching field distribution. Furthermore, during the magnetization of this ASI, reversed cells aligned in a string appeared, corresponding to the dipole strings previously reported for ASIs fabricated with single-layer ferromagnetic films. The appearance of a dipole string connecting emergent monopoles is a feature of the ASI dynamics. The observation of such emergent dynamics in the ASIs microfabricated using MTJ arrays highlights their potential for advancing the development of novel functional devices.