Heat-assisted magnetic recording (HAMR) promises to deliver higher storage areal density than the current perpendicular magnetic recording product. A laser is introduced to the HAMR system to heat magnetic media to reduce the media coercivity. The thermal response of the media becomes very critical for the success of the magnetic writing process. The study of thermal response time in HAMR relies on the setup configurations, such as laser spot sizes, the way that laser energy is delivered to media and the media structures. In this paper, the thermal response time of HAMR media under three different heating methods is systematically investigated through experiments and numerical analysis. A lumped model is built to simplify the heat conduction problem to understand the difference in thermal responses under various experimental conditions. Dominant layers are identified under those experimental conditions. The transient thermal response is mainly determined by the dominant layers. Engineering the dominant layers helps the most in optimizing the thermal performance of the media. Our study clearly suggests that for HAMR systems, optimizing the thermal properties of the heat sink layer is the key to reducing variations in the transient thermal process resulting from changes in the linear speed.

Thermal Response Time of Media in Heat-Assisted Magnetic Recording

Heat-assisted magnetic recording on bit patterned media dots with two magnetic structures is modeled. If the magnetic structures have different Curie temperatures two bits of information can be stored in each dot by writing at high and low temperatures. The areal density capability of the dual structure media was calculated and found to be in excess of 7 Tbit/in2, even when taking account of dot position distributions and magnetostatic fields from surrounding dots.

Heat-Assisted Magnetic Recording on Dual Structure Bit Patterned Media

We investigate the energy conversion process and subsequent thermal and bit-writing performance of a plasmonic near-field transducer (NFT) under steady-state operation within heat-assisted magnetic recording (HAMR) devices. The NFT is composed of metal-insulator-metal (MIM) layers that are designed to localize heating and produce optimal thermal gradients in order to relieve parasitic heating effects in the NFT. The thin-film MIM structure confines the electromagnetic energy in the down-track direction while cross-track confinement is achieved by tapering the insulator feature of the MIM. A comparative analysis using Gold and a number of novel Au alloys is undertaken. Modeled performance shows excellent thermal spot confinement (50 × 50 nm2) of temperatures above 650 K at an input laser power of 830 nm of less than 5 milliwatts. In addition, micromagnetic simulations using a stochastic Landau-Lifshitz-Bloch equation yield excellent signal to noise ratio with minimum jitter of under 2 nm when recording.

Optical, thermal, and bit-writing analysis of a directly coupled plasmonic waveguide for heat-assisted magnetic recording

As cloud computing and massive-data machine learning are applied pervasively, ultra-high volume data storage serves as the foundation block. Every day, nearly 2.5 quintillion bytes (50000 GB/second in 2018) of data is created and stored. Hard Disk Drive (HDD) takes major part of this heavy duty. However, despite the amazing evolution of HDD technology during the past 50 years, the conventional Perpendicular Magnetic Recording (PMR), the state-of-the-art HDD technique, starts to have less momentum in increasing storage density because of the recording trilemma. To overcome this, Heat-Assisted Magnetic Recording (HAMR) was initially proposed in 1990s. With years of advancement, recent industrial demos have shown the potential of HAMR to actually break the theoretical limit of PMR. However, to fully take advantage of HAMR and realize the commercialization, there are still quite a few technical challenges, which motivated this thesis work. Via thermal coupled micromagnetic simulation based upon Landau-Lifshitz-Bloch (LLB) equation, the entire dynamic recording process has been studied systematically. The very fundamental recording physics theorem is established, which manages to elegantly interpret the previously conflicting experimental observations. The thermal induced field dependence of performance, due to incomplete switching and erase-after-write, is proposed for the first time and validated in industrial lab. The combinational effects form the ultimate physical limit of this technology. Meanwhile, this theorem predicts the novel noise origins, examples being Curie temperature distribution and temperature distribution, which are the key properties but ignored previously. To enhance performance, utilizations of higher thermal gradient, magnetically stiffer medium, optimal field etc. have been suggested based upon the theorem. Furthermore, a novel concept, Recording Time Window (RTW), has been proposed. It tightly correlates with performance and serves as a unified optimization standard, summarizing almost all primary parameters. After being validated via spin stand testing, the theorem has been applied to provide solutions for guiding medium design and relaxing the field and heating requirement. This helps solve the issues around writer limit and thermal reliability. Additionally, crosstrack varying field has been proposed to solve the well-known transition curvature issue, which may increase the storage density by 50%.

Storage Physics and Noise Mechanism in Heat-Assisted Magnetic Recording

In this paper, we present a spin-stand testing study of heat-assisted magnetic recording (HAMR). Motivated by the understanding of the major recording noise mechanisms predicted by previous modeling, experiments were made to investigate the recording field/write current dependence of signal-to-noise ratio. The two significant noise mechanisms in HAMR, incomplete switching and erase-after-write, have been observed in the experiments and shown to be similar to the previous modeling results. Previous simulations indicate that system performance strongly correlates with recording time window (RTW). Therefore, head/media relative velocity was varied to change the RTW, and the effects of linear velocity are also compared. Further analysis has been applied to cases with different writer and media components. These results help understand the field/media requirements to optimize the HAMR recording system performance.

HAMR Noise Mechanism Study With Spin-Stand Testing

In this work, we present a systematic modeling analysis of signal-to-noise ratio (SNR) impact on recording under insufficient head field for heat assisted magnetic recording (HAMR). A typical head design in the absence of a medium soft underlayer is utilized in the modeling. The study shows that sufficient head field amplitude is critical for realization of expected HAMR recording performance. The strong correlation between recording time window and medium signal-to-noise ratio provides insightful understanding to medium and recording optimization when head field is not sufficiently high. The analysis is also performed with the inclusion of grain-to-grain Curie temperature (Tc) variation in the medium.

Analysis of signal-to-noise ratio impact in heat assisted magnetic recording under insufficient head field

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Analysis of signal-to-noise ratio impact in heat assisted magnetic recording under insufficient head field