En Yang

L10 FePt-oxide columnar perpendicular media with high coercivity and small grain size

Perpendicular L10 ordered FePt-oxide two-phase thin films with an average grain size of ∼7nm were prepared by alternate sputtering of FePt and oxide at 475°C. Very uniform and well-isolated columnar grains were obtained with coercivity as high as 7kOe. It is found that the texture of thin films depends greatly on the thickness of FePt; SiO2 works better than MgO as the amorphous oxide, which provides for magnetic isolation of the FePt grains. The coercivity of the films rises with increasing grain size and thinner alternately sputtered single layers. Reducing the grain size to ∼2.9nm produces granular grains with a coercivity of 3.5kOe.

Optimization of Ta thickness for perpendicular magnetic tunnel junction applications in the MgO-FeCoB-Ta system

The impact of Ta thickness on magnetic anisotropy and interlayer magnetic coupling is evaluated for the Ta-FeCoB-MgO thin film system commonly used in magnetic tunnel junctions. It is shown that there exists a window of Ta thickness where strong magnetic coupling of FeCoB with another magnetic layer is achievable through Ta while still maintaining properties required for use in a perpendicular magnetic tunnel junction. We also expand on existing knowledge about the role of annealing temperature, film composition, and seedlayer sequence on magnetic anisotropy in Ta/FeCoB/MgO tri-layers of varying FeCoB thickness.

Correction of Order Parameter Calculations for FePt Perpendicular Thin Films

The order parameter of FePt thin films plays an essential role in determining such diverse materials properties as magneto-crystalline anisotropy, magnetic coercivity and magnetic recording density. Typically, the order parameter for a bulk material is obtained by measuring the X-ray integrated intensity ratio of a super lattice peak to a fundamental peak and comparing this ratio to a theoretical value which has been calculated for a fully ordered sample. In this work, we present an analysis of the order parameter calculation in FePt L10 thin films taking into account the geometric features of the X-ray diffractometer, the crystallographic texture of FePt films, and the finite thickness of the films. The theoretical ratio of the (001) super lattice peak of FePt and the (002) fundamental peak of FePt is calculated as a function of the full width half maximum (FWHM) diffraction peaks from film and thickness for FePt thin films with perpendicular texture. A reliable order parameter calculation equation for Fe50Pt50 fiber textured perpendicular recording media is established.

Columnar grain growth of FePt(L10) thin films

An experimental approach for obtaining perpendicular FePt-SiOx thin films with a large height to diameter ratio FePt(L10) columnar grains is presented in this work. The microstructure for FePt-SiOx composite thin films as a function of oxide volume fraction, substrate temperature, and film thickness is studied by plan view and cross section TEM. The relations between processing, microstructure, epitaxial texture, and magnetic properties are discussed. By tuning the thickness of the magnetic layer and the volume fraction of oxide in the film at a sputtering temperature of 410 °C, a 16 nm thick perpendicular FePt film with ∼8 nm diameter of FePt grains was obtained. The height to diameter ratio of the FePt grains was as large as 2. Ordering at lower temperature can be achieved by introducing a Ag sacrificial layer.

STRUCTURE AND MAGNETIC PROPERTIES OF L10-FEPT THIN FILMS ON TIN/RUAL UNDERLAYERS

Highly ordered L10 FePt-oxide thin films with small grains were prepared by using a RuAl layer as a grain size defining seed layer along with a TiN barrier layer. Different HAMR (Heat Assisted Magnetic Recording) favorable underlayers were studied to encourage perpendicular texture and preferred microstructure. It was found that the epitaxial and small grain growth from the RuAl/TiN underlayer results in small and uniform grains in the FePt layer with perpendicular texture. By introducing the grain size defining underlayers, the FePt grain size can be reduced from 30 to 6 nm with the same volume fraction (9%) of SiO2 in the film, excellent perpendicular texture, and very high order parameter at 520 °C.

Multiple oxide content media for columnar grain growth in L10 FePt thin films

An approach to enhance the height-to-diameter ratio of FePt grains in heat-assisted magnetic recording media is proposed. The FePt-SiOx thin films are deposited with a decrease of the SiOx percentage along the film growth direction. When bi-layer and tri-layer media are sputtered at 410 °C, we observe discontinuities in the FePt grains at interfaces between layers, which lead to poor epitaxial growth. Due to increased atomic diffusion, the bi-layer media sputtered at 450 °C is shown to (1) grow into continuous columnar grains with similar size as single-layer media but much higher aspect ratio, (2) have better L10 ordering and larger coercivity.

Increased Perpendicular TMR in FeCoB/MgO/FeCoB Magnetic Tunnel Junctions by Seedlayer Modifications

By modifying the seedlayer in perpendicular FeCoB/MgO/FeCoB magnetic tunnel junctions (MTJs), we observe an increase in maximum tunneling magnetoresistance (TMR) from 65% up to 138%. Its found that decreasing the Ta deposition rate in Ta/Ru/Ta underlayers allows for greater annealing temperatures (up to 350 ) while still maintaining a perpendicular easy axis. An improvement is also seen at a lower temperature where both seedlayers maintain a perpendicular FeCoB easy axis indicating that the increase in TMR is not solely related to annealing at a higher temperature.

Naturally Oxidized FeCo as a Magnetic Coupling Layer for Electrically Isolated Read/Write Paths in mLogic

Recently, a nonvolatile, low power circuit scheme based on current-induced domain wall motion and perpendicular magnetic tunnel junctions known as mLogic has been proposed that requires electrically isolated, magnetically coupled read and write paths. Here, we suggest naturally oxidized FeCo for the magnetic coupling layer. Relevant properties of the FeCo-oxide were evaluated by a preliminary investigation of [FeCo/FeCo-Oxide]N artificial superlattices. It is found that FeCo thin films form an insulating 11 Å passivating oxide layer with a magnetization of 500 emu/cc. Experimental measurements show that FeCo-oxide can couple two perpendicular FeCoB layers with a coupling strength greater than 0.35 ergs/cm2.

Buffer Layers for Highly Ordered L1

In this work, we present an experimental technique for obtaining highly ordered L10 FePt-oxide thin film media at moderate deposition temperatures. In most previous studies, a FePt-Oxide layer is directly deposited on a (001) textured MgO layer. By introducing a buffer layer in between the FePt-oxide layer and the MgO underlayer, we are able to substantially enhance the L10 ordering of the FePt-oxide layer while lowering the deposition temperature to 400 . The buffer layer also yields a significantly enhanced (001) texture of the formed L10 FePt structure. With the order parameter near unity, the coercivity of the resulting granular L10 FePt-oxide film exceeds 20 kOe with an average grain size about 8 nm. With the buffer layer technique, 18kOe coercivity has also been achieved for L10 FePt-oxide film at a grain size of about 4.5 nm. In this work, the detailed material composition choice of the buffer layers and the corresponding results are presented.

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We present an experimental approach for obtaining highly ordered L10 FePt-oxide thin film media with small grains by using a RuAl layer as a grain size defining underlayer. In most previous studies, the FePt grain size was controlled by tuning the oxide volume fraction of the film. By introducing the RuAl grain size defining layer, 6 nm of FePt grains can be obtained at 520°C with 9% SiO2 in the film. A 5 nm thin barrier layer was introduced between FePt and RuAl to prevent the inter-diffusion between RuAl and FePt. The influence of different barrier layers was studied. With a thin Ag sacrificial layer inserted between the barrier layer and the FePt magnetic layer, a smaller grain size can be achieved, the ordering temperature was lowered, and the (001) texture of FePt was enhanced.