In an MR element, each of a pinned layer and a free layer includes a
Heusler alloy layer. The Heusler alloy layer has two surfaces that are
quadrilateral in shape and face toward opposite directions. The Heusler
alloy layer includes one crystal grain that touches four sides of one of
the two surfaces. In a method of manufacturing the MR element, a layered
film to be the MR element is formed and patterned, and then heat
treatment is performed on the layered film patterned, so that crystal
grains included in a film to be the Heusler alloy layer in the layered
film grow and one crystal grain that touches four sides of one of the
surfaces of the film to be the Heusler alloy layer is thereby formed.