Zuoyi Li

Investigations of LRE-HRE-TM thin films for hybrid recording

Light rare earth-heavy rare earth-transition metal (LRE-HRE-TM) thin films are a kind of important recording media. A lot of researches have been carried out on the LRE-HRE-TM thin films to improve its properties for data storage application and fruitful results have been achieved. This report gives a glance on the evolution of the research on LRE-HRE-TM recording media. At the same time, combined with the hybrid recording technology, some experimental results obtained on LRE-HRE-TM recording media are discussed, which suggest the promising prospect of the LRE-HRE-TM media in hybrid recording application.

Advanced hybrid recording media

Combining the advantages of hard-disk magnetic recording and magneto-optical recording, hybrid recording is regarded as promising candidate for extremely-high density recording technology beyond Tera bits/in2. To obtain such high areal density, hybrid recording media are required to have high coercivity and large remanent magnetization at room temperature, the desired temperature dependence of coercivity and magnetization, as well as very short thermal response time. Currently, the researches on the hybrid recording media mainly involve the magnetic hard-disk polycrystalline recording media and the magneto-optical amorphous media. This report presents the latest progresses in the researches on these two kinds of media for hybrid recording.

Temperature dependence of magnetic and magneto-optical properties in Sm(Tb,Dy)FeCo thin films

The temperature dependence of the amorphous Sm(Tb,Dy)FeCo quaternary alloys films was investigated using the mean-field model in combination with genetic algorithm. It is shown that when the light rare earth element Sm was substituted for the heavy rare earth element Tb or Dy, the compensation temperature (TCOMP) decreases, Curie temperature (TC) remains unchanged and the saturation magnetization (Ms) at room temperature increases. Experimental data show good agreement with the calculated results.

Optical and Electric and Structural Properties of Ti1-xAlxN Thin Films

A sequence of Ti1-xAlxN films has been prepared by rf reactive magnetron sputtering. The optical and electric properties versus aluminum content x have been studied. Values suitable for magneto-optic protective layers have been achieved in Ti1-xAlxN thin films with aluminum content x > 0.75. X-ray diffraction results show that Ti1-xAlxN thin films in this study are a bcc structure up to x = 0.75, further increase in the aluminum content gives a wurtzite structure. All of the results show that the optical and electric properties of Ti1-xAlxN films might be related to the crystal structure.

Mathematical analysis of temperature distribution in hybrid recording film using AFM tip writing

In this paper, a heat transfer model has been developed and employs method of Green function (heat source method) to calculate the temperature distribution in the magnetic film by using ATM tip transferring heat. The results indicate that the temperature in a magnetic film is relative to the diameter of the tip and the power of the laser pulse. Specifically, the power of laser pulse has a critical point threshold in hybrid recording by using this method.

The influence of porous alumina underlayer on structure and magnetization reverals of hybrid recording media

A self-ordered hexagonal array of nanopores has been fabricated by anodizing a thin film of Al on glass and subsequently the magnetic properties of TbFeCo on this templates were studied. We carried out anodic oxidation of a sputtered Al film at the anodic voltage in the range of 10-30 V and temperature in the range of 5-40 degrees C, and found that the density of the nanohole arrays increased with the decrease in anodization voltage and temperature. On the other hand, hole diameter decreased with the decrease in anodic voltage and temperature . Then TbFeCo was deposited onto this porous array by sputtering with a thickness of around 90 nm and subsequently was overcoated with 10 nm SiN for the protection from surface oxidation. The TbFeCo deposited on this porous layer shows complete perpendicular anisotropy and the AAO template can promot the growth of the microcolumnar structure in TbFeCo films. The coercivity increased with the decrease of hole diameter. The coercivity of the TbFeCo deposited on the porous array with a mean hole diameter of around 15 nm is 5.6 kOe and larger than that on bare glass, but the squareness ratio gets poorer than that on bare glass. Experience and simulation indicate that the magnetization reversal mode follows the Stoner-Wohlfarth .

A minimax optimization approach to fabrication of CoCrPt thin film

The minimax optimization method is applied broadly to industrial design, agricultural test, automation, economy and so on. In the field of magnetic recording, we utilize it in determining optimal fabricating conditions of recording thin film media. In the procedure of thin film fabrication, the coercivity, the remenance- hickness product and the squareness ratio of magnetic thin film are considered as multiple-objective functions of these parameters: element composition, atmosphere pressure, substrate temperature, post-annealing temperature and thin film thickness. The optimal fabricating conditions and high performance of CoCrPt thin film are obtained using the minimax optimization based on a series of experiments and data. The coercivity of CoCrPt thin film is up to 3523Oe; the remenance-thickness product is up to 1.75 memu/cm2; and the squareness ratio is up to 0.83. The results show that the minimax optimization method can improve the fabricating conditions of recording thin film and is helpful for a short path of achieved high performance of CoCrPt thin film.

Preparation and properties of (Sm,Nd)(Tb,Dy)Co thin film with perpendicular anisotropy

The (Sm,Nd)(Tb,Dy)Co thin Film had been prepared with spf-430H r.f.-magnetron sputtering system. The effects of heavy rare earth Tb, Dy substituted by light rare earth Sm, Nd on the magnetic and magneto-optical properties have been investigated. With the increasing of light rare earth Sm, Nd composition, the saturation magnetization Ms, the reflectivity R and the Kerr rotation angle θk are increased, while the coercivity (Hc) is decreased distinctly. This can be explained with the ferri-magnetic structure of RE-TM alloy. Mr/Hc Ratio is increased with the increasing of Sm composition in SmTbCo and SmDyCo. The influence of composition and sputtering conditions on perpendicular anisotropy films are reported in detail.

Magnetic and magneto-optic properties of TbCo/Cr thin films

The magnetic and magneto-optic properties of TbCo/Cr thin films were studied. A comparison of the MO properties was made between TbCo thin films with and without Cr underlayer. It was found that Cr underlayer helps to increase the Kerr rotation angle and to enhance the coercivities of TbCo thin films. The effects of the thickness of Cr underlayer and the gas pressure during Cr underlayer preparation on the magnetic and magneto-optic properties of TbCo layers were investigated, as well as the temperature dependence of these properties of TbCo/Cr thin films.

Analysis of fatigue characteristic of sm-substituted DyFeCo magneto-optical films

The fatigue characteristic of the amorphous Sm-substituted DyFeCo magneto-optical alloy films fabricated by R.F. magnetron sputtering method were investigated by accelerated pulse training method under the condition of magnetic field modulation plus laser pulse irradiation. The evaluation of fatigue characteristic is determined from the static magneto-optical signal readout level after several writing/erasing repetitions compared with initial level. The experimental dependence of fatigue characteristics is in good agreement with the model based on the JMA equation. Furthermore, the Avrami factor can be derived from the model. Experimental results show that it is very effective in studying the writing/erasing ability of magneto-optical films employed the method of combined the accelerated pulse training with the JMA equation and Sm-substituted HRE-TM alloys can act as a practical medium for MO storage at short wavelength.