Control method for magnetic disk device, magnetic disk device, and magnetic disk

According to one embodiment, a control method for a magnetic disk device includes writing data by varying a phase of the array period of the plurality of magnetic elements or a phase of the time period of the recording signal in one section of the track from a corresponding phase in another section of the track, reading a reproduction signal from the track, and determining a phase shift between the array period of the plurality of magnetic elements and the time period of the recording signal, based on a reproduction signal read from the one section and a reproduction signal read from the other section. In another embodiment, a magnetic disk includes a track in which magnetic elements are magnetically separated and arranged in an array period, and a phase of the array period in one section is different from a phase in another section of the track.