Magnetostrictive sensor, magnetic structure and production method thereof, motor drive device provided with magnetostrictive sensor, and motorassisted bicycle

A magnetostrictive sensor, comprising:

• a magnetic structure, including
• a columnar substrate extending along an axis, and
• a magnetostrictive portion disposed on an outer peripheral surface of the substrate, and containing a plurality of elements, wherein
• the magnetostrictive portion including a plurality of portions that have different concentrations of at least one of the plurality of elements, the portions being so arranged as to satisfy at least one of
• a first requirement that in a first cross sectional view of the magnetostrictive portion orthogonal to the axis, the portions having different concentrations of the at least one element are arranged clockwise about the axis,
• a second requirement that in the first cross sectional view, the portions having different concentrations of the at least one element are arranged in a thickness direction of the magnetostrictive portion, and
• a third requirement that, in a second cross sectional view of the magnetostrictive portion that is orthogonal to the first cross sectional view and passes through the axis, the portions having different concentrations of the at least one element are arranged along the axis.