Antony Ajan

Electrically conductive (Mg0.2Ti0.8)O underlayer to grow FePt-based perpendicular recording media on glass substrates

We have explored a new electrically conductive underlayer material to grow (001) textured L10-FePt films on glass substrates for potential application in ultrahigh density magnetic recording media. We found (Mg0.2Ti0.8)O (MTO) polycrystalline film grows with a strong (001) texture on Cr buffer layer, which induces strong (001) texture of L10-FePt polycrystalline and granular films. Strong perpendicular anisotropy of 3.8 × 107 erg/cm3 and coercivity of 15 kOe of a FePt-C film has been demonstrated using the MTO underlayer on glass substrates.

SPUTTER DEPOSITED STRONTIUM FERRITE FILMS WITH C-AXIS ORIENTED NORMAL TO THE FILM PLANE

M‐type strontium ferrite films were deposited by radio‐frequency (rf) sputtering on fused quartz substrates kept at ambient temperatures. The as‐deposited films were amorphous. They crystallized on annealing at a temperature of 800 °C or higher. The films deposited at low rf power and low oxygen to argon ratio showed c‐axis orientation normal to the film plane. The magnetic properties of these films were studied using vibrating sample magnetometer, polar Kerr rotation, and torque magnetometer. The perpendicular M‐H loops for c‐axis oriented films were nearly rectangular with coercivity of the order of 3 kOe.

Measurement of FePt thermal properties relevant to heat-assisted magnetic recording

Heat-assisted magnetic recording (HAMR) is the likely successor of the conventional perpendicular magnetic recording. Due to its high anisotropy, graded L10 ordered FePt is widely used as a HAMR recording layer. Electrically insulating MgO under-layer is essential for growing FePt in HAMR media. Experimentally, we observe very low thermal conductivity of FePt and significant thermal boundary resistance between FePt and MgO, whose magnitudes affect the HAMR thermal gradient. Realistic granular FePt media has >30% segregation, and, experimentally, we observe that FePt thermal properties are affected by segregation. We utilized time domain thermo-reflectance (TDTR) technique for studying FePt thermal conductivity and boundary resistance in realistic HAMR media stack. 1D finite element heat transport model was used for fitting experimental TDTR data and extracting thermal conductivities and related thermal boundary resistances. We found best fit thermal conductivity value for non-segregated FePt is as low as ...

Synthetic ferrimagnetic media: effects of thermally assisted writing

Thermally assisted writing on high-coercivity synthetic ferrimagnetic media (SFM) was demonstrated using a conventional spin stand equipped with an optical head for commercial magnetooptical drives. The laser light (/spl lambda/ = 685 nm) was focused through a glass substrate onto a recording layer. The optical spot size was 1.1 /spl mu/m and a commercial magnetic head had a writer width of /spl sim/0.25 /spl mu/m. The recording properties were measured as a function of the writing current (I/sub w/) and the laser power (P/sub w/). For the thermally stable medium with H/sub c/ = 6 kOe, a laser irradiation with an optimum power significantly improved the overwrite performance and the signal-to-noise ratio (SNR) values. The SNR values were improved by optimizing P/sub w/ over a wide writing current range. The improvements with the assist were found in both the signal and the noise. The media with a large dynamic coercivity value or with thick magnetic layers clearly showed the advantages with thermal assist.

Oriented strontium ferrite films sputtered onto Si(111)

Abstract Recently we have shown that M-type Sr ferrite films (SrM) can be sputter deposited on fused amorphous quartz substrates with c -axis normal to the film plane [1]. In the present study we show that the c -axis orientation of SrM on Si(111) can be tailored to vary from in plane to normal to the film plane by changing the deposition parameters.

Ferromagnetic resonance spectra in Co/Nb multilayers with large Co thickness

The perpendicular ferromagnetic resonance spectra for four Co/ Nb multilayered films have been studied. Three of these multilayers had the same thickness of Co (210 A) with Nb layer thicknesses varying between 18 and 135 A. The fourth film was a trilayer sandwich film. A multimode spectrum was observed for all the films. The results indicated that the Co films are magnetically coupled even when the Nb film thickness was 135 A. A new approach to understand the multimode ferromagnetic resonance in magnetic/nonmagnetic multilayer thin film structures was worked out. In this approach, the equation of motion is solved in the magnetic layers, which are assumed to be coupled through a boundary condition. The theoretical calculations gave a good agreement with the experimentally observed field positions when it was assumed that the magnetic properties of the top and the bottom Co layers are slightly different from the intermediate ones.

Magnetic and Mössbauer studies of amorphous Fe72−xYxHo8B20 alloys

Abstract We have carried out magnetic and Mossbauer studies of amorphous Fe 72− x Y x Ho 8 B 20 alloys. The Fe moment decreases with the addition of Y and a magnetic compensation occurs at 4 K for x = 16. The temperature and field dependences of the magnetization have been interpreted using the mean field theory and Chudnovskys model, respectively. These analyses yield some interesting parameters such as the random anisotropy, the exchange interactions J Fe−Fe , J Fe−Ho , etc. The Mossbauer studies show that the average hyperfine field decreases linearly with the addition of Y, in accordance with the decrease in the Fe moment.

Conversion electron Mossbauer studies on strontium ferrite films with in-plane and perpendicular anisotropies

Hexagonal strontium ferrite thin films with in-plane and perpendicular magnetic anisotropies have been studied using conversion electron Mossbauer spectroscopy. The hyperfine parameters of the films were found to be similar to the one obtained for bulk strontium ferrite. However, the intensity ratios of the first and second lines of the Mossbauer spectra were found to be different for films deposited at different rf powers. This indicated a change in the anisotropy of the deposited film. The resultant change in the magnetization direction and crystallization texture was compared to other measurements.

FMR studies of diffusion on ferromagnetically coupled Co/Zr systems

Summary form only given. Ferromagnetic resonance is a useful tool to study interlayer exchange coupling of multilayers. However, the ferromagnetic resonance (FMR) spectrum becomes complicated when the thickness of the magnetic layer and the number of bilayers are large. We recently developed a model using Hoffmann boundary conditions to explain the resonance spectra in such cases. In this report, we study the multimode resonance observed in (t/sub Co//t/sub Zr/)/sup 8/ multilayers, in as deposited and thermally treated conditions and demonstrate that this model can be used to obtain quantitative values of the interface roughness (or mixing).