Terry McDaniel

Heat Assisted Magnetic Recording

Heat-assisted magnetic recording is a promising approach for enabling large increases in the storage density of hard disk drives. A laser is used to momentarily heat the recording area of the medium to reduce its coercivity below that of the applied magnetic field from the recording head. In such a system, the recording materials have a very high magnetic anisotropy, which is essential for the thermal stability of the magnetization of the extremely small grains in the medium. This technology involves new recording physics, new approaches to near field optics, a recording head that integrates optics and magnetics, new recording materials, lubricants that can withstand extremely high temperatures, and new approaches to the recording channel design. This paper surveys the challenges for this technology and the progress that has been made in addressing them.

Light Delivery Techniques for Heat-Assisted Magnetic Recording.

Heat-assisted magnetic recording (HAMR), also known as hybrid recording, has been proposed to enable storage densities greater than 1 Tb/in2 in hard disc drives while circumventing the superparamagnetic limit. Light is delivered in the near field to the recording medium to heat just the spot which is to be recorded. Techniques based on apertures, antennas, waveguides, and solid immersion lenses have been suggested for delivering substantial amounts of optical power into subwavelength spots in the near field. A practical transducer for HAMR may require a combination of techniques.

Characteristics of thermally assisted magnetic recording

Extensive thermally assisted recording measurements were performed on isotropic longitudinal media. The dynamic coercivity decrease provided by thermal assistance was quantified by spin stand measurements. Thermally assisted recording performance was found to equal the performance of conventional (nonthermally assisted) recording at significantly reduced values of write current. This reduction in write current is consistent with the coercivity decrease that occurs during the thermally assisted writing process.

Application of Landau-Lifshitz-Bloch dynamics to grain switching in heat-assisted magnetic recording

Magnetization dynamics in heat-assisted magnetic recording (HAMR) involves magnetization collapse and re-formation under rapid local temperature excursion in a temporally varying applied magnetic field, with temperature likely moving above and below the medium Curie point on nanosecond timescales. Traditional micromagnetic simulation of the writing process in magnetic data storage has been restricted to isothermal processes in which macrospin magnetization dynamics are handled with the well-established Landau-Lifshitz-Gilbert (LLG) algorithm or close variants. Classical LLG treats the magnitude of material magnetization M as fixed (at zero Kelvin), so initial attempts at micromagnetic analysis of HAMR have typically dealt with the effects of temperature variation in HAMR in a somewhat ad hoc manner (e.g., insertion of M(T), A(T), K(T)), and have not been rigorous. A much improved treatment of this problem substitutes the Landau-Lifshitz-Bloch (LLB) algorithm in which thermally driven magnetization variati...

Areal density limitation in bit-patterned, heat-assisted magnetic recording using FePtX media

The future evolution of magnetic recording data storage toward its ultimate limit is expected to involve a combination of energy-assisted recording on bit-patterned media, according to recent publications. In this work, we assess the effectiveness of single magnetic grain reversal under heat-assisted recording conditions by analyzing macrospin magnetization dynamics with the Landau-Lifshitz-Bloch equation. The simulations reported pertain to FePtX recording media and recording system parameters constrained by expected practical limitations. The approach adopted is assessment of the patterned media writing error rate as a function of applied bias field and areal density (AD), taking account of the relevant physics of the heat-assisted recording process. Additionally, we require that long-term thermal stability of recorded information be maintained, and that sufficient thermal and effective writing field gradients to support AD targets are available. For the long-time analysis, an Arrhenius-Neel model of si...

Effect of gradient alignment in heat assisted magnetic recording

Heat assisted magnetic recording (HAMR) is one of the leading technologies to extend magnetic storage. Significant progress has been achieved in head and media fabrication [M. Seigler et al., IEEE Trans. Magn. 44, 119 (2008); Y. Peng et al., TMRC, Seagate Research, 2008], resulting in a basic technology demonstration (C. Hardie et al., ODS Conference Proceedings, 2008) of HAMR. Both field and field-gradient limitations of a conventional perpendicular recording are overcome by engineering the thermal profile (notably the gradient) and recording at a temperature near Tc (thus requiring a smaller head field). We have used a micromagnetic recording model to study the effect of thermal and field-gradient alignment in HAMR by varying the separation between the thermal spot and the leading edge of the head field. The output of the recording model includes transition jitter, which is based on Monte Carlo simulations of isolated transitions. We use a realistic granular medium with HK∼50–80 kOe and a grain size of ...

Experimental Effects of Laser Power on the Writability and Pulse Width in a Heat Assisted Longitudinal Recording System

In this paper the effects of increasing laser power on the writability and pulse width at half max (PW50) were experimentally measured on a longitudinal CoCrPt recording medium in a heat assisted magnetic recording system. The dynamic coercivity, quantified by spin stand measurements, was found to decrease linearly with laser power. Furthermore, it was found that careful optimization of laser power and write current are required to minimize the PW50. By choosing an optimal combination of write current and laser power it was possible to achieve a PW50 with heat assistance that could not otherwise have been reached. The results of this study help to establish the viability of heat assisted magnetic recording technology as a potential solution to density limits set by superparamagnetism.

Areal Density Potential for Non-Stoner-Wohlfarth Media

In composite media switching of magnetization takes place through domain wall reversal, rather than coherent rotation, characteristic of Stoner-Wohlfarth (S-W) media. The angular dependence of coercivity on applied field angle deviates significantly from the S-W astroid. A modified Williams-Comstock formalism is used to show how this angular dependence modifies the effective field gradient, hence the transition length. Analytical expressions are deduced to express the areal density potential of various media designs.