Synthesis and characterization of Cobalt-Platinum thin films

Co-based alloy thin films have attracted a lot of interest, due to their excellent magnetic properties, that is essential in the field of magnetic recording media. Alloying Co with metals like Pt changes some of its intrinsic magnetic properties such as increasing the magnetocrystalline anisotropy constants of the alloy. Co-Pt thin films and multilayers are more suitable for ultra high-density magnetic recording media because they have high-magnetic anisotropy, chemical stability, excellent coercivity and resistance to corrosion. In the present study, Co-Pt alloy and Pt/Co multilayered films were deposited on Si substrate using dual electron beam co-evaporation. The Co-Pt alloy thin films are vacuum-sealed and annealed for 2 hours at 300°C and 400°C to study the annealing effects on structural and magnetic properties. All the films were characterized using scanning and transmission electron microscopy, electron microprobe, and profilometry. In Co-Pt alloy films, Co and Pt were present in the atomic ratio of 3:1. A mixture of hexagonal close packed and face centered cubic structure Co3Pt was present in both as-deposited and annealed films. The magnetic measurements were conducted at 300°K and 10°K in both perpendicular and parallel orientations in physical property measurement system (PPMS) and magnetic property measurement system (MPMS). The results from analytical and characterization techniques showed the addition of Pt to Co increased the coercivity of the films. Annealing enhanced the grain size and coercivity of the as-deposited Co3Pt film. However, the presence of ε-Co decreased the coercivity of the Co-Pt film annealed at 400°C. Asymmetry in the hysterisis loops was observed for all films at 10°K. The antiferromagnetic CoO and ferromagnetic Co and Co3Pt undergo exchange coupling at the interface and give rise to exchange anisotropy leading to the shift in the hysterisis loop. This property of the Co-Pt alloy thin film system may find its application in the magnetic sensor systems, like spin valve and magnetoresistance devices

Designing rare-earth free permanent magnets in Heusler alloys via interstitial doping

Based on high-throughput density functional theory calculations, we investigated the effects of light interstitial H, B, C, and N atoms on the magnetic properties of cubic Heusler alloys, with the aim to design new rare-earth free permanent magnets. It is observed that the interstitial atoms induce significant tetragonal distortions, leading to 32 candidates with large ($>$ 0.4 MJ/m$^3$) uniaxial magneto-crystalline anisotropy energies (MAEs) and 10 cases with large in-plane MAEs. Detailed analysis following the the perturbation theory and chemical bonding reveals the strong MAE originates from the local crystalline distortions and thus the changes of the chemical bonding around the interstitials. This provides a valuable way to tailor the MAEs to obtain competitive permanent magnets, filling the gap between high performance Sm-Co/Nd-Fe-B and widely used ferrite/AlNiCo materials.Comment: 4 gigure

Effects of AG on structural and magnetic properties of FePt thin films

Ph.DDOCTOR OF PHILOSOPH

Preparation and Characterization of Sputtered SmCo5 Thin Films for Magnetic Recording Media

Ph.DDOCTOR OF PHILOSOPH