Chan-Gyu Lee

Aging effects on microstructure and GMR in Au-Co and Au-Co-X (X=Cu,Ni,Fe) bulk alloys

Aging effects on the microstructure and the GMR in Au-Co and Au-Co-X (X=Fe,Ni,Cu) bulk granular alloys have been investigated. TEM observation shows that Co particles are of plate-like type and grow with the aging time. The optimum size for the maximum MR ratio is a length of about 10 nm and a thickness of 0.6 nm. In Au-Co-X (X=Cu,Ni,Fe) bulk alloys, it was confirmed that the maximum value of the MR ratio is about 3.5% at 10 kOe for Au/sub 80/Co/sub 15/Fe/sub 5/ bulk alloy aged at 300/spl deg/C for 1 hr.

Fabrication of Cr-Al based multilayer spin valve with anti-corrosion and thermal stability

The magnetic properties, thermal stability and anti-corrosion properties of Cr/sub 86/Al/sub 14/ multilayer spin valves have been studied. CrAl spin valves are more thermally stable than FeMn, and the inserted Co layer prevents the CrAl spin valves from becoming poor for the magnetic properties. It was also confirmed that there were no changes of H/sub ex/ and MR ratio for CrAl. While H/sub ex/ and MR ratio for FeMn spin valve were lost 15 days later in corrosion resistance test under 35/spl deg/C with 90% humidity conditions.

Detection and determination of solute carbon in grain interior to correlate with the overall carbon content and grain size in ultra-low-carbon steel.

In this study, every effort was exerted to determine and accumulate data to correlate microstructural and compositional elements in ultra-low-carbon (ULC) steels to variation of carbon content (12-44 ppm), manganese (0.18-0.36%), and sulfur (0.0066-0.001%). Quantitative analysis of the ULC steel using optical microscope, scanning electron microscope, transmission electron microscope, and three-dimensional atom probe revealed the decrease of grain size and dislocation density with the increase of carbon contents and/or increase of the final delivery temperature. For a given carbon content, the grain interior carbon concentration increases as the grain size increases.

The Structure and Magnetic Properties of CoNbZr-Sm2O3 Granular Films

In this study, granular films were prepared by reactive RF magnetron sputtering. The film was deposited on Si (100) substrates. The magnetic properties (coercivity) were measured by a vibrating sample magnetometer (VSM). The electrical resistivity (p) of the thin film was determined by means of a four-point probe method. The film structures were investigated by X-ray diffractometry (XRD) and transmission electron microscopy (TEM).

Cobalt Effects on the Structure, Electrical and Magnetic Properties of La0.7Ca0.3Mn1-xCoxO3(x=0-0.05) Manganite Oxide

Manganite La_0.7Ca_0.3MnO₃, one of the CMR materials, is an insulator with a perovskite crystal structure and can be composed with various chemical compositions. When dope it with transition metal ions (TM = Fe, Co, Ni etc.), we obtain a LaCaMn_1-xTM_xO₃ system that shows a very large magnetoresistance. In the present paper, we report the structure, the magnetic and the electrical properties of Co-doped La_0.7Ca_0.3Mn_1-xCo_xO₃ CMR system. Sintering reactions proceeded rapidly in the order of La_0.7Ca_0.3MnO₃ > La_0.7Ca_0.3Mn_0.99Co_0.01O₃ > La_0.7Ca_0.3Mn_0.97Co_0.03O₃ > La_0.7Ca_0.3Mn_0.95Co_0.05O₃. It is assumed that cobalt may interrupt the sintering reaction of mangannite. Magnetic and electrical properties were evaluated with densified pellet. From M-T curve, we determined the Curie temperature, where the magnetization value decreases abruptly. Curie temperature were examined by superconducting quantum interference device (SQUID). Curie temperatures of 250K for La_0.7Ca_0.3MnO₃, 290K for La_0.7Ca_0.3Mn_0.99Co_0.01O₃, 280K for La_0.7Ca_0.3Mn_0.97Co_0.03O₃ and 260K for La_0.7Ca_0.3Mn_0.95Co_0.05O₃ were obtained. With very small amount of co-dopping, transition metal dominates overall property. However, the amount of cobalt increases, the Curie temperature decreases. It is considered that the decrement of magnetic order by decreasing of Mn3+ and lattice distortion. Temperature-dependent resistivity was measured by physical property measurement system (PPMS) between 0 and 300K at a magnetic field of 10 kOe. In case of un-substituted pellet, maximum MR ratio and metal semiconductor transition temperature appears at 200K. MR ratio tends to increase with temperature up to Curie temperature and shows the maximum values around Curie temperature. In addition, La_0.7Ca_0.3Mn_0.99Co_0.01O₃ shows the highest MR ratio because it shows the highest Curie temperature.

GMR and magnetodynamics of MnIr spin valves depending on growth order of FM and AFM layers

The influence of spin valve layers on its main properties was investigated. Giant magnetoresistance and domain structures of two types of spin valves, Si/5 nm Ta/3 nm Co/2.5 nm Cu/3 nm Co/ 10 nm Ir/sub 20/Mn/sub 80//5 nm Ta top spin valve (TSV) and Si/5 nm Ta/3 nm/10 nm Ir/sub 20/Mn/sub 80// Co/2.5 nm Cu/3 nm Co/5 nm Ta bottom spin valve (BSV), were studied experimentally. The samples were fabricated by dc magnetron sputter deposition on Si substrates. The magnetic properties (magnetic anisotropy, magnetization reversal, magnetic structure) and magnetoresistance of the spin valves were measured using vibrating sample magnetometer and four-point probe respectively.

Effect of boron addition on the ordering process in the FePt thin film

The (MgO)/sub 20 nm//(FePt-B)/sub 10 nm//(MgO)/sub 20 nm/ films were prepared on Si(111) substrates in a RF magnetron sputtering system under an argon gas pressure of 5 mTorr. The boron chips were uniformly placed on the FePt target. Annealing was performed in the vacuum chamber of 2/spl times/10/sup -7/ Torr at the temperature of 25/spl sim/600/spl deg/C for 1 hr. The magnetic properties of the film were examined by a digital measurement system vibrating sample magnetometer (DMSVSM) in the maximum field of 26 kOe. The crystal structure and the lattice parameters were determined by the X-ray diffractometry with symmetric /spl theta/-2/spl theta/ scan. The lattice parameters, a and c, were accurately evaluated by Cohens method using the Nelson-Reily function.

Study of Surface Alloying of TiC, TiB 2 and VC with Carbon Steel Using High Energy Electron Beam Irradiation

Surface alloying using TiC, and VC ceramic particles on carbon steel has been performed using high voltage electron beam. Each type of ceramic particles was mixed with flux of Al and in 1 to 4 ratio. The microstructures of the surface alloyed layers consisted of melted region, interface region. heat affected region and the unaffected matrix. The surface layer of the TiC surface alloyed had a cubed primary and a eutectic type of TiC. in surface layer of surface alloyed were incompletely melted with particles as observed before the alloying. On the surface layer of the VC surface alloyed, very well defined cell structure was observed with VC on the cell boundary. In addition, ~50 nm in diameter VC particles in high density were ubiquitous in the matrix. Those fine VC particles prominently improved the hardness and wear resistance of the surface layer of the VC surface alloyed.

Antiferromagnetic Cr-Ga layers with a high Neel temperature for biasing spin valves

The magnetic properties, anti-corrosion properties and thermal stability of Cr/sub 93/Ga/sub 7/ bilayers and multilayer spin valves have been investigated. In corrosion resistance tests under 35/spl deg/C with 90% humidity conditions, the MR ratio for Cr/sub 93/Ga/sub 7/, did not change, while the MR ratio for FeMn spin valve was lost after 15 days, CrGa/FeCo/Cu/FeCo spin valves were determined to be more thermally stable than CrGa/NiFe/Cu/NiFe and FeMn/NiFe/Cu/NiFe spin valves.

Aging treatment effects on microstructure and GMR in Au-Co and Au-Co-X(X=Cu,Ni,Fe) bulk alloys

Bulk granular alloys in t y p e s of NM-TR(NM : non-magneuc metals, TR : Fe, Co. Ni and their alloys) aUoys with nano-structure3 magnetic mipiki tes would open UP the pmpect of new applications as a GMR motor semom at high magnetic field. Furthermore, such bulk granular alloys have ?.om merits for ease of fabrication. Recently, it has been re~lted that G M R is obtained in the process of phase barnuon in the bullis and Liquid-quenched ribbons 11-31, However, the influences of the microstruchre obtained by heat-treatment and allaying elements an GMR have not bfcn d i m s & Ln detail yet. In the present, we have studied the effect of the rnicmsmctum and alloying elements such as Cu, Ni and Fe in Au-CO bulk alloys.