Substrate for magnetic disk, magnetic disk, and hard disk drive apparatus

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 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 provided on a surface of the substrate main body such that the film is formed continuously over the main surfaces and the outer circumferential edge surface, wherein
• the disk shape has an outer diameter of 90 mm or more,
• a thickness T of the substrate, which includes film thicknesses of sections of the film provided on the main surfaces, is 0.520 mm or less,
• a total thickness D (mm), which is a sum of the film thicknesses of the sections of the film provided on the main surfaces, and the thickness T (mm) of the substrate satisfy Equation (1) below,
• D≥0.0082/T−0.0015 (1),
• and
• the substrate main body at the outer circumferential edge surface forming an interface with the film provided on the outer circumferential edge surface has a surface roughness maximum height Rz of 0.5 μm or more.