Substrate for magnetic disk and magnetic disk

A substrate for a magnetic disk, the substrate comprising:

• a substrate main body having two opposing main surfaces and an outer circumferential edge surface, the outer circumferential edge surface including a side wall surface, which is orthogonal to the main surfaces, and chamfered surfaces, which are disposed between the main surfaces and the side wall surface, the substrate main body being a glass substrate main body or an aluminum alloy substrate main body, the substrate main body having a disk shape;
• and
• a film that is an alloy film containing Ni and P, and is provided on a surface of the substrate main body such that the film is formed continuously over the main surfaces, the chamfered surfaces, and the side wall surface of the substrate main body,
• wherein the substrate has a thickness (T+D) of 0.520 mm or less, the thickness (T+D) being the sum of a thickness T of the substrate main body and a thickness D of the film formed on the main surfaces of the substrate main body,
• the disk shape has an outer diameter of 90 mm or more,
• a ratio D/T of the thickness D of the film to the thickness T of the substrate main body is 0.025 or more, and
• a surface roughness maximum height Rz of the film formed on the outer circumferential edge surface of the substrate main body is smaller than a surface roughness maximum height Rz of the substrate main body at the outer circumferential edge surface of the substrate main body.