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In heat-assisted magnetic recording (HAMR) technology, it is necessary to heat the magnetic layer of disks at a temperature that exceeds the Curie temperature (Tc). When the disk is laser irradiated, the lubricating film and diamond-like carbon (DLC) protective film on the disk surface are heated at high temperatures (300 °C–500 °C). If the lubricant film, DLC thin film, or organic contamination on the disk surface evaporates or thermally decomposes upon laser heating, it adheres as a smear on the slider surface. In view of the negative effect exerted thereof, the solution to this problem is, therefore, critical for the successful application of HAMR. Furthermore, recently developed helium-enclosed hard disk drives are currently utilized in industries. It is, thus, expected that the aforementioned novel HAMR technology will be employed in helium-enclosed drives. In this study, the effects of DLC thin films on the smear characteristics upon the laser heating of disks in air and He are experimentally investigated, and the manner with which these films on the disk surface affects the smear characteristics is clarified. Moreover, the technical countermeasures necessary to reduce the smear with respect to the hydrocarbons from the DLC thin films in HAMR are elucidated and proposed in this article. Simply put, the technical countermeasures depend on the heating temperature, and the use of a mixture of He and air or oxygen gases is found to be effective. This method, however, may not be significantly useful when the heating temperatures exceed 500 °C. [ABSTRACT FROM AUTHOR]

The control of the magnetization at the microscale by pure optical means is fundamentally interesting and promises faster speeds for data storage devices. Although several experiments have shown that it is possible to locally reverse the magnetization of a ferromagnetic system by means of laser pulses, a completely theoretical description of these all-optical switching (AOS) processes is still lacking. Here, we develop an advanced micromagnetic solver that is applied to the numerical study of the AOS. The solver is based on the Landau–Lifshitz–Bloch equation that governs the dynamics of the magnetization coupled the microscopic three-temperature model, which describes the temporal evolution of the temperatures of the subsystems as caused by laser heating. The helicity-dependent magnetization switching is evaluated by a magnetooptical effective field caused by the inverse Faraday effect when a circularly polarized laser is applied to the sample. All the other usual terms of a full micromagnetic model are included (exchange, anisotropy, and Dzyaloshinskii–Moriya interaction). As a test, the model is used to describe the local magnetization switching of thin-film samples with high perpendicular anisotropy. The results are in a good agreement with available experimental observations. [ABSTRACT FROM AUTHOR]

One of the challenges in heat-assisted magnetic recording (HAMR) is the formation of write-induced head contamination at the near-field transducer. A possible mechanism that has been proposed for this contamination is the transfer of lubricant from the disk to the head due to temperature driven evaporation/condensation. Most previous studies on lubricant depletion due to laser heating have assumed the lubricant to be a viscous fluid and have modeled its behavior using the traditional lubrication theory. However, perfluoropolyether lubricants are viscoelastic fluids and are expected to exhibit a combination of viscous and elastic behavior at the time and length scales of HAMR conditions. In this paper, we use a modified Reynolds lubrication equation for the viscoelastic fluid that employs the linear Maxwell constitutive model. We use this modified lubrication equation to develop a model that predicts the disk-to-head lubricant transfer during HAMR writing. This model simultaneously determines the thermocapillary stress driven deformation and evaporation of the viscoelastic lubricant film on the disk, the diffusion of the vapor phase lubricant in the air bearing, and the evolution of the condensed lubricant film on the head. We investigate the effects of lubricant type (Zdol versus Ztetraol), head/disk temperature, initial lubricant thickness, and laser spot size on the lubricant transfer process. Simulation results show a significant difference between the rates of transfer for Zdol (timescale of nanoseconds) versus Ztetraol (timescale of microseconds). The amount of transfer increases with the disk temperature and the initial lubricant thickness. [ABSTRACT FROM AUTHOR]

The spacing between the flying head and the rapidly rotating disk in hard disk drives continues to decrease in order to grow the areal density. In heat-assisted magnetic recording (HAMR), the spacing control complexity is compounded by the additional protrusion resulting from the laser heating. Compared to the writer induced and thermal fly-height control protrusion, the near-field transducer (NFT) protrusion is a faster and more local protrusion that requires new HAMR-specific spacing control techniques. In this paper, we will review the simulation and experimental studies which shed light on both the steady-state and transient characteristics of the NFT protrusion. Simulation analysis reveals the scale of the protrusion and its effects on spacing control. Experimentally, we have demonstrated a novel technique to characterize the NFT protrusion and assist in setting the spacing for each HAMR head. Based upon the knowledge gleaned from characterization, compensation schemes have been developed. Some of the schemes have already been successfully demonstrated. [ABSTRACT FROM AUTHOR]

Structural and molecular weight changes to lubricant picked up the following laser heating in heat-assisted magnetic recording (HAMR) were analyzed using time-of-flight secondary ion mass spectroscopy. The average molecular weight of the disk lubricant increased by laser heating at temperatures over 500 °C and that of the picked up lubricant increased at temperatures over 400 °C. The presence of end-group fragments with low molecular weight (CH3O+) increases in both the disk and picked up lubricants, whereas at high temperature the concentration of the end-group component (C3H7O2+) decreases in the disk lubricant and increases in the picked up lubricant. Overall, the results presented herein suggest that the chemical and thermal stability of the terminal ends of lubricants should be improved in order to decrease depletion of the lubricant film and the lubricant pickup by the laser heating in HAMR. [ABSTRACT FROM AUTHOR]

We investigated the laser-heating-temperature dependence of the friction characteristics of magnetic disks coated with boundary lubricant films by using a pin-on-disk tester and discussed the fundamental characteristics observed. In the contact area of the glass pin and disk, we observed the area that showed a buildup and depletion of the lubricant film thickness. The amount of buildup and depletion increased with increasing heating temperature. It was found that the friction coefficient of each lubricant film initially decreased as the temperature increased. Thereafter, the minimum value of the friction coefficient of each test lubricant occurred at a specific temperature, resulting in an increase in the friction coefficient inversely as the temperature further increased. It was suggested that the specific temperature corresponds to the transition temperature at which the test lubricant film evaporates. In addition, it was also suggested that the thermal durability of the lubricant film improved because of ultraviolet treatment. [ABSTRACT FROM AUTHOR]

Heat-assisted magnetic recording (HAMR) is a technique for overcoming the superparamagnetic limit and enabling large increases in the storage density of hard disk drives. A tiny area of the magnetic recording media has to be heated up to a high temperature with a laser to lower the coercivity temporarily before information can be written on the area. The possible degradation of the ultrathin media carbon overcoat induced by the laser heating is a concern. In this paper, the laser heating-induced degradation of ultrathin a-C:Nx, a-C:Hx, and a-C overcoats on HAMR media is studied. Surface topography changes induced by the laser heating are evaluated with atomic force microscopy and structure changes with the visible Raman spectrum and X-ray photoelectron spectroscopy (XPS). Laser heating areas are analyzed with time-of-flight secondary ion mass spectrometry and XPS to reveal the underlying mechanism of the degradations. It is found that at a proper HAMR writing temperature and for a total laser heating duration corresponding to a five-year drive life, the surface topography, structure, and composition of the a-C:Nx overcoat are changed by the laser heating. However, the surface topographies of the a-C:Hx and a-C overcoats are not changed. The structure and composition of the a-C:Hx and a-C overcoats are also not changed much. Interlayer diffusion between the carbon overcoat and the underlying magnetic layer is confirmed in the laser heating area for all the three overcoats. [ABSTRACT FROM AUTHOR]

Heat-assisted magnetic recording (HAMR) is a promising approach for enabling large increases in the magnetic data storage density. Amorphous carbon is the principal overcoat material of thin-film disks and magnetic heads in the HAMR systems. In this paper, we investigated the recording performance of media with a chemical vapor deposition (CVD) carbon overcoat (COC) and a sputtered COC. We observed that the carbon type has a significant impact on the HAMR recording performance and the heat absorption. Tunneling current atomic force microscopy analysis results show higher surface roughness and peak current in the disk with the sputtered carbon. Track profile and magnetic signal measurement results indicate 90% of the optimized laser current is not enough to fully write the disk with the CVD carbon, while the tracks on the sputtered carbon disk can be written using the same laser current. The difference in the two types of COC can be attributed to the difference in the carbon bonding structure, the optical and electrical properties, the roughness, and the heat absorption behavior. [ABSTRACT FROM AUTHOR]

Due to poor thermal performance of media, it is difficult for heat-assisted magnetic recording (HAMR) to achieve densities greater than 3 Tb/in ^ 2 for continuous-wave laser heating. Short-pulse laser heating is an attractive approach to improve the thermal response of media. In this paper, the recording performances of HAMR using short-pulse laser heating are studied by dynamic micromagnetic simulations solving the Landau–Lifshitz–Bloch equation. The results show that the magnetic damping constant of the media, $\alpha $ , and applied magnetic field, H$ , exhibit significant effects on recording quality at a pulse-width of 100 ps. From analyses of the relationships among readout signal and noise ratio, recorded track width, \alpha $ , and H is achievable for FePt recording media. [ABSTRACT FROM AUTHOR]

This paper investigates the depletion of a thin lubricant film subjected to laser heating in an inert gas environment, and we experimentally elucidate the fundamental characteristics and mechanisms related to lubricant depletion in air and inert gas environments. In addition, fundamental experimental studies are conducted to understand the structural stability or degradation, such as through oxidation and graphitization of diamond-like carbon (DLC) thin films subjected to laser heating, in an inert gas environment compared to air environment. The degradation and its mechanisms are investigated using Raman spectroscopy. The results suggest that less degradation would occur by oxidation for a DLC thin film in an inert gas environment than air environment. It is found that, from the view point of the reliability in the head/disk interface, the lubricant depletion issue is more crucial than DLC thin-film degradation for thermally assisted magnetic recording in an inert gas environment. [ABSTRACT FROM AUTHOR]

The write field requirements in heat-assisted magnetic recording (HAMR) using FePt media are studied using an atomistic model. Langevin dynamics simulations of laser-induced thermal demagnetization and magnetization recovery are performed on a single L \(1_\mathbf {o}\) -ordered FePt grain. We show that the minimum heat temperature for thermal overwrite of information is a cooling rate-dependent temperature \(\boldsymbol T\!_\mathbf {o}\) , larger than the Curie temperature of the grains. If \(\boldsymbol T\!_\mathbf {o}\) is exceeded, memory effects can be neglected in HAMR since the characteristic pulse time is long compared with the mean first passage time of thermal demagnetization. The minimum write field \(\boldsymbol H_{\boldsymbol {\rm w}}\) to attain sufficiently high thermoremanence \(\boldsymbol M\!_{\boldsymbol Z}\boldsymbol =\mathbf {0.9}\boldsymbol M\!_{\boldsymbol S}\) is then independent of the heating process. We study the variation of \(\boldsymbol H_{\boldsymbol {\rm w}}\) with cooling rate, damping, field orientation, and grain size \(\boldsymbol L\) , and explore the phase space of the parameters \(\boldsymbol H\) , \(\boldsymbol T\) , and \(\boldsymbol L\) , also resulting in thermal stability of the recorded information during storage. [ABSTRACT FROM AUTHOR]

A custom microcoil was used to generate a magnetic field pulse and a continuous wave (CW) laser was used as a heating source to study the heat-assisted effect in magnetization switching on GdFeCo thin films. Four different pulsed field strengths were chosen, and the power of the CW laser heating was varied from 0 to 180 mW. The heat-assisted enhancement was not observed when the pulsed field strength was 2400 Oe. The enhancement was visible when the pulsed field strength was reduced to 2160 Oe, and became obvious when the pulsed field strength was 1750 and 1350 Oe. These interesting results prove that CW laser heating could provide a marked improvement to the magnetization switching when the switching field is relatively small, thus making it a more applicable and economic alternative to pulsed laser heating. Simulations based on the Landau–Lifshitz–Bloch equation have also been performed and agreed well with the experimental data. The CW laser heating scheme provides a more economic and practical way to realize heat-assisted magnetization switching, which could be used for potential future heat-assisted magnetic recording technology. [ABSTRACT FROM AUTHOR]

Because the diamond-like carbon (DLC) thin film overcoat on a hard disk surface plays an important role in maintaining the reliability and durability of the head-disk interface, DLC degradation is a critical issue in thermally assisted magnetic recording (TAMR). The use of helium in hard disk drives (HDDs) is being developed to decrease air-induced structural vibrations, windage loss, and temperature rise. TAMR technology is suggested to be put to practical use in a helium environment in HDDs. In this paper, fundamental experiments have been conducted to understand the structural stability or degradation of an ultrathin DLC overcoat subjected to laser heating in an inert gas environment. An inert gas environment was simulated using nitrogen gas. The degradation of DLC thin films fabricated through chemical vapor deposition was investigated by varying the laser irradiation duration and controlling the intensity of the laser, and it was evaluated through Raman spectroscopy. The differences in the damage mechanisms between an inert gas and air environments were elucidated. We found that the degradation of DLC thin films by oxidation would be significantly less in an inert gas environment than in an air environment. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulation coupled with a modified coarse-grained bead-spring model is employed to investigate the diffusion-related degradation of lubricant film under laser heating. The lubricant surface morphology and depletion profiles during laser heating are studied. It is observed that lubricant film degrades due to thermal diffusion and undergoes severe depletion with increasing laser heating duration, resulting in raised ridges around the depleted zone. The diffusion width and depth are evaluated to further explore diffusion-related degradation instability. As expected, the diffusion depth increases rapidly with the heating duration and the laser power, while the width would fluctuate around a constant value after initial rapid rise and following slight reduction. In addition, a Gaussian temperature gradient is formed in the radial direction due to the thermal transfer between the heated and surrounding beads. It is also shown that the laser power plays an important role in the temperature gradient and hence greatly influences the diffusion-related degradation of lubricant film on a solid surface. [ABSTRACT FROM AUTHOR]

In heat assisted magnetic recording, the thermal gradient at the recording point determines the quality of the written transitions. We developed an experimental technique that enables us to find the thermal gradients in both the down- and the cross-track directions, where the laser power is modulated during the recording process. It is explained in detail how quantitative information on the gradients can be obtained from the measured data. It is found that strong heat-sinking of the media increases the thermal gradient and that the gradient measurement reacts sensitively to the shape of the thermal profile. [ABSTRACT FROM AUTHOR]

Thermal flying-height control (TFC) technology has been used in the last few years in hard disk drives (HDDs) to achieve a lower flying height for higher storage areal density. In this paper a slider with dual thermal protrusions, one produced by the laser used to heat the disk in HAMR and the other one used for TFC, is studied. The flying height modulations (FHM) due to disk waviness and external disturbances are compared for the dual protrusions, single protrusion and no protrusion sliders. The protrusions provide additional force and torque excitation to the slider. The protrusions can be viewed as a passive feedback loop to compensate the disturbance. The gain of the feedback loop depends on the stiffness of the protrusions, which is determined by the protrusions' heights and positions. Thus the complicated air bearing slider system with protrusions is simplified by casting the protrusion perturbation as a feedback loop and this simplified model helps to speed up the optimization of the TFC protrusion height and position. The numerical simulation results show that FHM of the dual protrusion slider is reduced significantly when the TFC protrusion height and location are optimized. External disturbance induced FHM can be suppressed as well. This scheme for dual protrusion optimization and analysis described in the work can benefit HAMR head design because the optimized dual protrusion provides a more consistent flying height and a greater ability to compensate external disturbances. [ABSTRACT FROM AUTHOR]

Ultrafast demagnetization excited by laser pulses introduces the technological possibility for controlling the magnetic properties of materials on sub-picosecond regime. In this paper, the demagnetization dynamics of amorphous ferrimagnetic TbFeCo alloy is modeled by using the stochastic Landau-Lifshitz-Gilbert equation on an atomistic level. The transition metal (Fe, Co) and rare earth (Tb) atoms are constructed by two different sub-lattice systems. Laser-heating induced demagnetization processes are clearly demonstrated by a series of snapshots. Our simulations show that full demagnetization on the sub-picosecond time scale requires a temperature over the Curie point, and the demagnetization time increases with the Tb content. [ABSTRACT FROM AUTHOR]

Heat-assisted magnetic recording (HAMR) is likely the successor of perpendicular magnetic recording (PMR) technology. The quality of HAMR writing is dominated not by the magnetic field gradient (as in PMR), but by the high thermal gradient generated by the laser heating spot. Knowledge of temperature dependence of magnetic parameters: anisotropy field Hk(T), saturation moment Ms(T) and anisotropy field distribution (\sigma Hk) in the proximity of Curie temperature (Tc) is crucial for media development. Here we describe a new system to probe the magnetic properties close to Tc, as well as a semianalytical model to explain the results. The model takes into account the thermal fluctuations; input into the model are experimentally measured data for Ms(T), Hk(T), mean field demagnetization factor, \sigma Hk and grain size distribution. In the paper we present two types of data: 1) thermal erasure in the absence of a magnetic field; and 2) thermomagnetic writing, allowing the estimate of the switching field distribution at high temperatures. [ABSTRACT FROM AUTHOR]

Through a novel temperature measurement method, this paper studies the lubricant film property subjected to heat-assisted magnetic recording (HAMR) laser heating. The material characterization of lubricant film under HAMR ultra-fast heating rate and ultra-short heating period condition has been compared with that after conventional thermal heating. The relationship of lubricant degradation and decomposition with the heating rate and heat duration and the reaction of the lubricant with the metal used for the temperature sensor has been studied and discussed. [ABSTRACT FROM PUBLISHER]

This paper concerns the effect of a thin overcoating layer on the temperature increase in heat-assisted magnetic recording disk structure induced by laser heating. The optical absorption model, which derived from Maxwell's equation, is applied to quantify local energy absorption by the media. The numerical simulations indicate that the presence of a 2-nm overcoating layer results in additional 5% temperature increase in the disk, compared with the same media structure without overcoating layer. This temperature increase is resulted from the laser energy absorbed by the overcoating layer and the low thermal conductivity of the overcoating layer. The temperature difference between the overcoating layer and its neighbor layer is negligible small. This paper indicates that besides its mechanical properties, the thermal and optical properties of the overcoating material are important design factors. [ABSTRACT FROM PUBLISHER]

Thermally assisted magnetic recording (TAMR) is one of the novel technologies that are employed for achieving magnetic recording densities higher than 1 Tb/in2. With regard to this novel technology, it has been suggested that there exists a critical head-disk interface (HDI) issue associated with the use of ultrathin liquid lubricant films on the disk surface. This problem is attributed to the fact that these films are heated to high temperatures by using laser beams in order to reduce magnetic coercivity. In this study, a fundamental research on the lubricant depletion caused due to laser heating in TAMR systems was conducted. That is, the effect of lubricant film materials on lubricant depletion was investigated. In this experimental study, four types of lubricant film materials—Zdol2000, Zdol4000, Ztetraol2000, and A20H2000-were used, and the differences in the characteristics of lubricant depletion for each tested lubricant film were investigated. The effect of the molecular weight as well as the end group of the lubricant on the lubricant depletion was discussed and clarified by analyzing the obtained experimental results. In addition, it was found that the depletion characteristics of ultrathin liquid lubricant films could be explained by using experimental results obtained from the thermogravimetric analysis for each bulk lubricant material [ABSTRACT FROM AUTHOR]