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Thermal stability of optical near field transducers is an important issue for heat-assisted magnetic recording (HAMR), which affects HAMR system lifetime. In this paper, dark-field scattering spectroscopy was used to study the stability of nanometer-scaled Au lollipop transducers that were subjected to thermal annealing. Variation in relative peak intensity and red-shifting in peak position can be observed in scattering spectra for transducer after annealing. Based on the optical characterizations on Au thin films and calculations of Mie scattering by finite-difference time domain simulations, the measured changes in transducer scattering properties can reflect annealing-induced variations in optical properties and dimensional feature size for the Au lollipop transducer. Dark-field scattering spectroscopy can be a promising method to examine HAMR near field transducer thermal stability. [ABSTRACT FROM AUTHOR]

In heat assisted magnetic recording (HAMR), optical near field transducer (NFT) is a key component. Au is currently used as NFT material because of its strong surface plasmon effect. Due to the soft property of Au material, reliability of Au NFT becomes a key issue for realizing HAMR production. In this paper, the possibility of alternative materials, including transition metal nitrides (TMNs) and transparent conducting oxides (TCOs) to replace Au is studied. The results show that all of the listed TMN and TCO materials can meet the mechanical requirements at room temperature in terms of hardness and thermal expansion. An optical model, which includes optical waveguide, NFT and FePt media, is used to simulate NFT performances. The results indicate that the resonant wavelengths for NFT with TCO materials are longer than 1500 nm, which is not suitable for HAMR application. TMN materials are suitable for NFT application at wavelength band of around 800 nm. But the NFT efficiency is very low. ZrN is the best material among TMN materials and the efficiency of ZrN NFT is only 13% of the Au NFT's efficiency. Reducing refractive index (n) and increasing extinction coefficient (k) will both lead to efficiency increase. Increasing k contributes more in the efficiency increase, while reducing n has a relatively low NFT absorption. For materials with the same figure of merit, the NFT with larger k material has higher efficiency. Doping materials to increase the material conduction electron density and growing film with larger size grain may be the way to increase k and reduce n. [ABSTRACT FROM AUTHOR]

In this paper, we present a study on two and a half dimensional (2.5D) perpendicular magnetic recording (PMR) media consisting of dual hard magnetic recording layers (RL) with 1st or top RL1 used for conventional data storage and 2nd or bottom RL2 used for dedicated servo with lower linear densities or DC servo patterns with focus on the writability issue of the bottom servo layer (RL2). We demonstrate experimentally the feasibility to magnetically erase, write, and re-write RL2 by laser assist on a home built heat-assisted-magnetic-recording writing test system. Experimental data (by magnetic force microscopy measurements) show that the signal amplitudes of the pre-recorded magnetic patterns for both RL1 and RL2 decrease at almost the same rate with thermal erasure using scanning laser power (Pw) from 13 mW to 23 mW, clearly indicating equally effective laser heating and close temperature rise for RL1 and RL2 for far field laser heating with laser pulse duration in sub-μs and μs range. This is further verified by theoretical simulations of the thermal distribution and the temperature rise depth profile in dual layer media by laser heating. Simulations indicate very little temperature difference of less than 6K (~1% of maximum temperature rise) between RL1 and RL2 because the main mechanism of temperature rises in RL1 and RL2 is due to the effective thermal conduction from the top layers to lower layers. These experimental and theoretical study results could provide useful understanding and insights into servo writing methods of 2.5D PMR media. [ABSTRACT FROM AUTHOR]

Smaller cross track thermal spot size and larger down track thermal gradient are desired for increasing the density of heat assisted magnetic recording. Both parameters are affected significantly by the thermal energy accumulation and diffusion in the recording media. Pulsed laser heating is one of the ways to reduce the thermal diffusion. In this paper, we describe the benefits from the pulsed laser heating such as the dependences of the cross track thermal width, down track thermal gradient, the required laser pulse/average powers, and the transducer temperature rise on the laser pulse width at different media thermal properties. The results indicate that as the pulse width decreases, the thermal width decreases, the thermal gradient increases, the required pulse power increases and the average power decreases. For shorter pulse heating, the effects of the medium thermal properties on the thermal performances become weaker. This can greatly relax the required thermal properties of the media. The results also show that the pulsed laser heating can effectively reduce the transducer temperature rise and allow the transducer to reach its "dynamically" stable temperature more quickly. [ABSTRACT FROM AUTHOR]

In this paper, the real time thermal effect of the heat assisted magnetic recording (HAMR) on the slider flying height is investigated with HAMR spin stand. In the experiment, a modulated laser beam is used to heat the media and the slider vibration is measured with laser Doppler vibrometer. The slider vibrations at different laser modulation frequencies and different laser powers are investigated and near 0.2 nm flying height change is observed. Analysis shows that the main reason to cause the flying height change results from the disk surface thermal distortion caused by thermal expansion. [ABSTRACT FROM AUTHOR]

In this paper, the real time thermal effect of the heat-assisted magnetic recording (HAMR) on the slider is investigated with the HAMR platform. The net temperature rises of the slider caused by laser absorption and heat radiation of the locally heated recording magnetic disk are studied by monitoring the calibrated read sensor resistances in different rotation speeds. The maximum slider temperature increase of about 3.5 °C caused by the locally heated recording disk is obtained when the media net temperature increase is 85 °C at 2000 rpm rotation speed. A higher temperature case is also discussed. [ABSTRACT FROM AUTHOR]

The TbFeCo magneto-optical media with the coercivity of bigger than 1.0 kOe are used for the investigation of ultrafast heating and magnetic switching with the weak external magnetic field. It has been found that the laser-induced active region becomes larger with an external magnetic field because the boundary of the active region is magnetized with the assistance of the external field during the ultrafast heating. According to this physical phenomenon, the so called 'mark expansion method' has been proposed for visual observation of ultrafast switching marks. Using this method, the ultrafast magnetic switching in TbFeCo media has been studied using 40 fs laser pulse with linear polarization. The result shows that the ultrafast magnetic switching can be implemented by the laser pulse with assistance of the weak external field of about 0.7 kOe. Further studies show that the area percentage of the magnetic mark expansion relative to its thermal mark decreases with the increasing of the laser pulse energy. There exists the threshold pulse energy that the active region is fully magnetized. The theoretical analysis of electron, spin, and lattice temperatures has been conducted to the active region of the media where the maximum spin temperature is close to the Curie temperature of the media. The result indicates that the media become active at 4.137 ps and the ultrafast heating plays a key role for the ultrafast magnetic switching. The weak external magnetic field provides sufficient driving force to control the magnetization direction in the media. [ABSTRACT FROM AUTHOR]

Compared to the conventional magnetic recording, the big difference in the heat-assisted magnetic recording (HAMR) is the introduction of the thermal energy. It is necessary to study the thermal effects on the HAMR system which includes the head, the media, the head and disk interface (HDI) and data recording and reproducing performance. In this paper, the key thermal issues in the HAMR system and their effects on the recording performances are analyzed and discussed. In the HAMR head, the heat sources are analyzed, and their effects on the temperature increase of the HAMR head are studied. The thermal profile of the media generated by the near field transducer is a determinant for achieving high density. Based on the measured thermal parameters of the medium materials, the thermal profiles of the medium at different medium parameters are studied. The results indicate that the boundary thermal resistance and the insulation of the grains are very important factors for obtaining small thermal spot sizes. The recording performances at a variety of temperatures are analyzed by the simulation of a micro-magnetic modeling. In the HDI, one of the key challenges is if the lubricant film can suffer the dynamic high temperature working environment. The lubricant thermal response for the dynamic high temperature working environment is characterized. [ABSTRACT FROM AUTHOR]

The TbFeCo magneto-optical media with the coercivity of bigger than 1 kOe are used for the investigation of ultrafast magnetic switching and thermal demagnetization. The magnetic marks induced by 25 fs laser pulses with circular polarization have been observed. The thermal demagnetization spots are measured based on their digital images for the estimation of laser fluence. Based on the experimental parameters, a theoretical calculation for estimation of the maximum applicable effective magnetic field is conducted, where the 25 fs laser pulses with wavelength of 800 nm, NA of 0.6 and circular polarization is applied. The results show that, with the maximum applicable laser fluence, the effective magnetic field on the outer boundary of the laser spot defined by 1/e electrical field amplitude is about 0.52 kOe. It implies that the spin flips can be implemented by a small effective magnetic field, which can be explained with the analysis of spin temperature. [ABSTRACT FROM AUTHOR]