A heat-assisted magnetic recording (HAMR) disk has a magnetic recording layer (typically a FePt chemically-ordered alloy), a seed-thermal barrier layer (typically MgO) below the recording layer, a heat-sink layer, and an optical-coupling multilayer of alternating plasmonic and non-plasmonic materials between the heat-sink layer and the seed-thermal barrier layer. Unlike a heat sink layer, the multilayer has very low in-plane and out-of-plane thermal conductivity and thus does not function as a heat sink layer. The multilayer's low thermal conductivity allows the multilayer to also function as a thermal barrier. Due to the plasmonic materials in the multilayer it provides excellent optical coupling with the near-field transducer (NFT) of the HAMR disk drive.

A heat-assisted magnetic recording (HAMR) disk has a magnetic recording layer (typically a FePt chemically-ordered alloy), a seed-thermal barrier layer (typically MgO) below the recording layer, a heat-sink layer, and an optical-coupling multilayer of alternating plasmonic and non-plasmonic materials between the heat-sink layer and the seed-thermal barrier layer. Unlike a heat sink layer, the multilayer has very low in-plane and out-of-plane thermal conductivity and thus does not function as a heat sink layer. The multilayer's low thermal conductivity allows the multilayer to also function as a thermal barrier. Due to the plasmonic materials in the multilayer it provides excellent optical coupling with the near-field transducer (NFT) of the HAMR disk drive.

A magnetic-disk substrate has a pair of main surfaces and arithmetic average roughnesses Ra of the main surfaces are each 0.11 nm or less. Also, in surface unevenness of the main surfaces, an average area of regions occupied by a plurality of protrusions having a height of 0.1 [nm] or more from an average plane of the surface unevenness is 25 [nm.sup.2/protrusion] or less. The arithmetic average roughness Ra and the surface unevenness are measured using an atomic force microscope with a probe having a probe tip provided with a carbon nanofiber rod-shaped member.

A magnetic-disk substrate has a pair of main surfaces and arithmetic average roughnesses Ra of the main surfaces are each 0.11 nm or less. Also, in surface unevenness of the main surfaces, an average area of regions occupied by a plurality of protrusions having a height of 0.1 [nm] or more from an average plane of the surface unevenness is 25 [nm.sup.2/protrusion] or less. The arithmetic average roughness Ra and the surface unevenness are measured using an atomic force microscope with a probe having a probe tip provided with a carbon nanofiber rod-shaped member.

A magnetic disk substrate includes an aluminum alloy including one type or two or more types of Fe: 8.5 mass % or less, Mn: 2.5 mass % or less, Ni: 6.5 mass % or less, and Mg: 4.5 mass % or less, a balance being Al and unavoidable impurities, wherein, when f (Hz) is a resonance frequency, ρ (g/cm.sup.3) is a density, and t (mm) is a plate thickness, (f×ρ/t) is 3800 or greater; and a magnetic disk using the magnetic disk substrate.

A magnetic disk substrate includes an aluminum alloy including one type or two or more types of Fe: 8.5 mass % or less, Mn: 2.5 mass % or less, Ni: 6.5 mass % or less, and Mg: 4.5 mass % or less, a balance being Al and unavoidable impurities, wherein, when f (Hz) is a resonance frequency, ρ (g/cm.sup.3) is a density, and t (mm) is a plate thickness, (f×ρ/t) is 3800 or greater; and a magnetic disk using the magnetic disk substrate.

A non magnetic substrate for a magnetic disk includes a substrate main body having two opposing main surfaces and being a glass substrate main body or an aluminum alloy substrate main body, and a metal film made of an Ni—P alloy and provided on the main surfaces and an outer circumferential edge surface of the substrate main body. The non magnetic substrate has a thickness (T+D) of 0.57 mm or less, which is the sum of a thickness T of the substrate main body and a thickness D of the metal film. The non magnetic substrate has a diameter of 90 mm or more. A ratio D/T is 0.025 or more. The outer circumferential edge surface of the substrate main body forming an interface with the metal film has a surface roughness maximum height Rz of 0.5 μm or more.

A non magnetic substrate for a magnetic disk includes a substrate main body having two opposing main surfaces and being a glass substrate main body or an aluminum alloy substrate main body, and a metal film made of an Ni—P alloy and provided on the main surfaces and an outer circumferential edge surface of the substrate main body. The non magnetic substrate has a thickness (T+D) of 0.57 mm or less, which is the sum of a thickness T of the substrate main body and a thickness D of the metal film. The non magnetic substrate has a diameter of 90 mm or more. A ratio D/T is 0.025 or more. The outer circumferential edge surface of the substrate main body forming an interface with the metal film has a surface roughness maximum height Rz of 0.5 μm or more.

Magnetic recording media including a soft magnetic underlayer (SUL) formed over a plasma-polished substrate or pre-seed layer. In some examples, the substrate or pre-seed layer is plasma-polished using an inert gas such as krypton so that the roughness of the surface on which the SUL is deposited is reduced. The roughness reduction can lead to improved crystallographic texture within subsequently deposited media films, and consequently, to increased recording performance of the media. In particular, media signal-to-noise ratio (SNR), linear recording density, and areal recording density or areal density capacity (ADC) can be improved. In one aspect, a carbon deposition/etching apparatus may be modified to polish the substrate or pre-seed layer with krypton or other inert gases, rather than be used to deposit carbon overcoat.

A magnetic-disk substrate has an average value of squares of inclinations that is 0.0025 or less, and a frequency at which squares of inclinations are 0.004 or more is 15% or less, in a case where samples of inclinations on a main surface are obtained at intervals of 10 nm. The main surface is configured to receive at least a magnetic recording layer thereon. The magnetic-disk substrate includes an outer circumferential end portion and an inner circumferential end portion, and the outer circumferential end portion and the inner circumferential end portion have chamfered portions.