A core magnetization reversal method includes transforming the first magnetic skyrmion into a skyrmionium by applying a first alternating current (AC) magnetic field to the first magnetic skyrmion, and then transforming the skyrmionium into a second magnetic skyrmion by applying a second AC magnetic field to the skyrmionium. The first magnetic skyrmion may be formed on a hemispherical shell, which may be formed by (i) preparing a membrane having a plurality of protrusions, and (ii) stacking, on the membrane, a first layer including at least one of platinum (Pt), nickel (Ni), and palladium (Pd), and a second layer including a ferromagnetic material. The first and second AC magnetic fields may have different frequencies.