Mahendra Pakala

Head and Media Challenges for 3 Tb/in Microwave-Assisted Magnetic Recording

A specific design for microwave assisted magnetic recording (MAMR) at about 3 Tb/in2 (0.47 Tb/cm2 or 4.7 Pb/m2) is discussed in detail to highlight the challenges of MAMR and to contrast its requirements with conventional perpendicular magnetic recording (PMR). In particular, it has been determined that MAMR-optimized media should have: higher damping than todays PMR media upon which ferromagnetic resonance measurements are reported, very low intergranular exchange coupling, and somewhat stronger layer to layer exchange coupling. It was found that with exchange-coupled composite type media (i.e., graded anisotropy with controlled exchange), a spin torque oscillator in the write gap of a wider shielded pole cannot adequately define the written track at high track density. Adequate lateral field gradient, however, is achieved by modifying the pole tip geometry. Other details of this conceptual design are also discussed.

Influence of Boron Diffusion on Transport and Magnetic Properties in CoFeB/MgO/CoFeB Magnetic Tunnel Junction

Influence of boron concentration in CoFeB on the transport properties of CoFeB (B 20% and B 16%)/MgO/CoFeB magnetic tunnel junction (MTJ) was investigated. Boron distribution was studied by using X-ray photoelectron spectroscopy (XPS). High-resolution transmission electron microscope was utilized for analysis of the texture and interface quality. The MTJ with the boron diluted CoFeB (B 16%) pinned layer shows 10% higher MR than the CoFeB (B 20%). HRTEM shows that the MgO/CoFeB interface for the sample with diluted CoFeB layer has a better epitaxial MgO/CoFeB growth. Higher boron concentration in the as-deposited CoFeB stays high after annealing but boron content in the MgO increases as well. These results suggest that that MR improvement is directly related to the distribution of the boron in CoFeB/MgO/CoFeB MTJs after annealing.

Effect of Substrate and Surface Conditioning on Magnetic Properties and Texture of CoPt Hard Bias Films

Effect of growth surface on CoPt hard bias film performance has been systematically studied using different substrates and substrate surface conditioning. Films deposited on four different types of substrates show different levels of crystallographic quality and magnetic performance. Among them, the films deposited on Al2O3-coated substrates are the best, up to 400 Oe higher in coercivity and 0.05 higher in remnant squareness. Proper substrate surface conditioning by ion-beam depositions has been found to be effective in improving inplace c-axis orientation; hence, magnetic properties of CoPt hard bias films. In addition, the deposition of a thin amorphous Al2O3 film on substrates prior to the hard bias film deposition helps to promote nearly 100% inplane c-axis crystallographic orientation.