Increasing the density of data storage is crucial to the future of inexpensive digital technology. The large majority of storage in the “Cloud” consists of magnetic hard-disk drives. The continued evolution of this USD$30 billion industry depends on the commercial introduction of heat-assisted magnetic recording (HAMR). This technology uses heat from a laser beam confined well below the diffraction limit, <50-nm wide, to write to media near 450°C with high magnetic anisotropy that would normally be unwriteable under available magnetic fields. This high anisotropy guarantees thermal stability even for grain sizes around 5-nm diameter, which are necessary for major increases in storage density. In this article and in the articles in this issue, we introduce HAMR requirements and discuss its numerous interdisciplinary materials challenges, including high-temperature/efficient plasmonic materials, low-loss optical materials, highly ordered/thermally anisotropic nanoscale magnetic grains, block copolymers for directed assembly below 10 nm, high-temperature nanometer-thick coatings/lubricants, materials/interfaces to control heat flow at nanometer length scales, and advanced spintronic materials.

Heat-assisted magnetic recording (HAMR) is being developed as the next-generation magnetic recording technology. High anisotropy granular media such as FePt-C have been demonstrated as HAMR media for ∼2 Tbpsi (terabits per in2) recording density. In order for this technology to reach its full potential of 4–5 Tbpsi, more progress and innovations are needed for the key requirements for HAMR media, including microstructure, design, magnetic distribution, and thermal design. Beyond granular media, heated-dot magnetic recording (HDMR) is planned to extend areal density toward 10 Tbpsi. HDMR combines similar advanced recording layer materials with advanced patterning techniques to fabricate <10-nm rectangular dot media.

Heat-assisted magnetic recording (HAMR) is the next-generation technology that is required to deliver areal densities in excess of 2 terabit/in2 for high-capacity, low-cost hard drives.The recording process relies on spatially and temporally localized heating of the media surface to lower its coercivity during the magnetic writing process. This scheme drives substantial changes to the recording head write element architecture, combining the conventional electromagnet structure with integrated optical light delivery layers, focusing optics, and plasmonic nanostructures to generate subwavelength optical spots. Power losses associated with the strong optical fields required for heating the media can cause local temperatures in excess of 400°C at the recording head surface. Coupled with high pressures, an oxidative/corrosive air-bearing environment, and a sub-3 nm head-media spacing, this introduces new challenges for the functional materials in recording heads required to balance performance and long-term reliability demands. Here, we briefly review specific challenges associated with HAMR heads, highlighting the major requirements, failure modes, and needed innovations for the near-field transducer and optical-waveguide subsystems.

This article reviews progress in magnetoresistive (MR) read sensor technology for hard-disk drives (HDDs). MR reader technology has progressed from the anisotropic magnetoresistance sensor, to the current-in-plane giant magnetoresistive (CIP-GMR) sensor, to today’s current-perpendicular-to-plane (CPP) tunneling magnetoresistance (TMR) sensor. This evolution has driven the continuous growth of the areal density of HDDs from 2 Gbpsi (gigabits/in2) in early longitudinal recording to ∼1 Tbpsi (terabits/in2) currently in perpendicular magnetic recording. For further increases in the areal density, a transition to energy-assisted recording is expected in the near future. Further technical challenges for the read sensor technology toward 2 Tbpsi and then 5 Tbpsi areal densities are discussed based on recent promising experimental work on CPP-GMR using Heusler alloys, and CPP-GMR’s laterally expanded version, the lateral spin valve (LSV). To realize large MR output and narrow shield-to-shield spacing requirements for higher density recording, materials selection and optimization of interface structures of CPP-GMR and LSV devices are critical.

Heat-assisted magnetic recording (HAMR) relies on careful management of heat flow at the nanoscale. This article describes the heat-transfer aspects of such a system that must be considered above and beyond standard Fourier’s Law-based heat conduction. A background on nanoscale heat transport is provided that discusses energy carriers and the role of interfaces and microstructure in nanoscale conduction. These heat-transport concepts are applied to the key components of the HAMR system—the head (principally, the near-field transducer [NFT]) and the magnetic medium. This analysis frames the central challenge of thermal engineering for a HAMR system—getting the medium hot enough while maintaining a NFT that it is cool enough to avoid degradation over time. Of particular note are discussions on the role of the interface thermal conductance in the NFT and the importance of thermal anisotropy in the medium due to its granular microstructure.

The heat-assisted magnetic recording (HAMR) head–disk interface is a unique operating environment that combines nanoscale spacings, high shear rates, high-temperature gradients, and high optical fluxes in a mass-produced device. One of the greatest challenges is to develop materials for the head–disk interface that enable the required head–media spacing while also providing reliability. Traditional head–disk interface materials, engineered and optimized for conventional magnetic recording hard-disk drives, are challenged to provide the needed performance at the high temperatures that HAMR involves. We review some of the primary materials used in conventional magnetic recording, how high temperatures challenge their performance, and some of the current understanding and strategies to develop a reliable HAMR head–disk interface.