Baoxi Xu

Thermal issues and their effects on heat-assisted magnetic recording system (invited)

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. Th...

Relationship Between Near Field Optical Transducer Laser Absorption and Its Efficiency

Heat-assisted magnetic recording (HAMR) has shown its promising application for recording density beyond 1 Tb/in2 . However, the reliability/lifetime of the near field optical transducer is a big challenge. The temperature rise of the transducer is one of the reasons that lead to its failure. In this paper, the laser absorption of the transducer is investigated compared with the transducer efficiency (high efficiency is one of the main targets in the transducer design). The results show that with a fix medium and fix transducer material, high efficiency is always accompanied by high laser absorption which could be 10-25%. High efficiency and low absorption can be obtained by optimizing the medium properties and using transducer material with low refractive index. With the built HAMR head model, the transducer temperature rise is evaluated. The results show that the transducer temperature increase depends on the absorbed power, its size, and the space between the transducer and magnetic pole. The space affects the transducer temperature rise more seriously in large transducer size. Big size is preferable for the transducer to reduce its temperature increase.

Lubrication for Heat-Assisted Magnetic Recording Media

A novel lubricant with good thermal stability (Td=328degC) is developed for the application of heat-assisted magnetic recording (HAMR) media to achieve the areal density of 1 Tb/in2 and beyond. Compared to currently-used commercial lubricants, the newly developed lubricant film can resist the laser irradiation without damage while Z-dol film is completely depleted under the same experimental conditions. Frictional coefficient and dewetting behavior are also superior to the candidate for HAMR media protection

HAMR media design in optical and thermal respects

Heat-assisted magnetic recording media is critical in high density recording. Except medias magnetic property, its thermal property plays a very important factor. In this paper, combining medias optical property, its thermal property is studied. Its design in optical and thermal respects is discussed.In a heat-assisted magnetic recording (HAMR) system, the thermal performances of recording medium are very critical for recording density because the track density and bit density are dominated by thermal spot size in the cross-track direction and temperature gradient in the down-track direction. The optical intensity and its distribution generated by the near field optical transducer serve as a heat source to heat the medium. Therefore, the medium optical response to the transducer is also very important for the mediums thermal response. In this paper, based on the structure required by the magnetic performance, the effects of the medium structures on its optical and thermal performances are studied. The results show that a thinner interlayer (MgO layer) is beneficial to the mediums performance. However, the seed layer (NiTa layer) deteriorates the performance seriously. Small in-plane thermal conductivity (good isolation) of the granular recording layer is also very important for the thermal performance of the medium. However, the out-plane thermal conductivity is not very critical in certain ranges.

Dynamic Thermal Responses of Heat-Assisted Magnetic Recording Head in Data Writing Process

In the data writing process of heat-assisted magnetic recording (HAMR), due to the existence of servo sectors in the magnetic recording media, the laser power has to be “off” when the near field optical transducer passes over the servo sectors so as to protect the servo sector from being erased. In this paper, HAMR head dynamic thermal responses to the laser source heating and transducer absorption in the data writing process are studied. The results show that the dynamic temperature response times of the laser source and air-bearing surface are around 1 s. The transducer temperature can almost follow the transducer heating change (caused by absorption) because of its very fast temperature response which is around 2 μs. However, the transducer protrusion response time to the transducer absorption is 2 ~ 3 ms. Owing to the long response times of the slider temperature to the laser source heating and the transducer protrusion to its laser absorption, the fly height changes caused by the slider temperature increase and the transducer protrusion may be compensated with the thermal fly height control technology.

Thermal effects of heated magnetic disk on the slider in heat-assisted magnetic recording

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 2000rpm rotation speed. A higher temperature case is also discussed.

Optical property study of FePt-C nanocomposite thin film for heat-assisted magnetic recording.

Optical properties of the FePt-C nanocomposite thin film that was synthesized by sputtering with MgO/NiTa underlayer on glass substrate have been determined by an approach combining spectroscopic ellipsometry and transmission over the wavelength range of 380 - 1700 nm. It was observed that the refractive index is larger than the extinction coefficient, indicating that free electron absorption is not the dominant optical transition in the FePt-C thin film. Compared with FePt thin film, the FePt-C thin film has smaller optical constants, which lead to better optical performance including smaller optical spot on recording media and higher transducer efficiency for heat assisted magnetic recording.

Thermal Effects in Heat Assisted Bit Patterned Media Recording

It is a big challenge to achieve recording density of 10 Tb/in2 for magnetic recording. Two promising technologies have been proposed for achieving density beyond 1 Tb/in2: heat assisted magnetic recording and bit patterned media. Owing to limitation of minimum media grain size or requirement of higher writing magnetic field, the densities of both technologies are still limited at below 5 Tb/in2. There is a need for new technology to push the density towards 5 Tb/in2 and beyond. Heat assisted bit patterned media recording is a good candidate to achieve this target. In this paper, thermal effects on bit patterned media at densities from 5 to 10 Tb/in2 are studied by numerical simulations. The results show that the media with soft under layer has bit mark vertical expansion of around 0.15 nm at 5 Tb/in2, which may cause recording performance change in the case of less than 3 nm space between magnetic write pole and recording layer. In order to obtain less than 1 ns cooling speed, a pulse heating method is proposed. With this method, the cooling speed gets tremendous improvement at BAR = 1 . Media with large BAR has worse thermal performances.

Thermal effect on slider flight height in heat assisted magnetic recording

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 0.2nm 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.

Field enhancement of nano-sized metal aperture with and without surrounding corrugations through resonant surface plasmons

The different behaviors of the surface plasmons along the in-plane surface of silver sheet and along the side wall of bare aperture inside the same sheet are analyzed, and their respect roles to the final field enhancement are discussed as well. The short pitch surface plasmons resonance along the side wall of the aperture is regarded as the origin of the thickness dependence of the field enhancement at the exit side of the aperture. Several solutions such as corrugation incident plane, protrusion design at the exit side to realize maximized field enhancement at the exit side of aperture are proposed. Furthermore, the step and non-step nano-sized silver apertures surrounded with circular surface corrugation structures were compared in detail. It was proved that if the 40 nm sized step aperture with circular grating the near-field intensity can reach up to around 1000 times enhancement factor at the immediate exit and around 400 times enhancement even if at the plane of 10 nm away from exit of aperture.