Magnetoresistance effect element

A magnetoresistance effect element comprising:

• a laminate which includes a first ferromagnetic layer, a nonmagnetic layer, and a second ferromagnetic layer;
• an insulating layer which surrounds the laminate when viewed from a laminating direction;
• and
• a sidewall layer which is provided between the laminate and the insulating layer and surrounds at least a part of the laminate when viewed from the laminating direction,
• wherein at least one of the first ferromagnetic layer and the second ferromagnetic layer contains a Heusler alloy, and
• wherein the sidewall layer is any one of a composite layer in which metal particles containing a metal contained in the Heusler alloy or a metal contained in the nonmagnetic layer are dispersed within metal oxide, a multilayer film including a metal oxide layer containing metal oxide and a metal layer containing the metal contained in the Heusler alloy or the metal contained in the nonmagnetic layer, and a metal layer containing low diffusion coefficient metal selected from a group consisting of Ta, Ru, W, Ir, Pt, Au, and Mo.