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Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1910. / Degree of Bachelor of Science in Mining Engineering determined from "1874-1999 MSM-UMR Alumni Directory". The entire thesis text is included in file. Typescript. Illustrated by author. Title from title screen of thesis/dissertation PDF file (viewed March 5, 2009) Includes bibliographical references (p. 21).

D.Phil. / Spin-density-wave (SDW) effects were studied in diluted Cr-Si and Cr-Ga alloy single cristals. Ga and Si impurities in Cr are respectively from groups 3 and 4 non-magnetic non-transitional elements from the periodic table. Both influence the magnetic behaviour of Cr in a special way. The alloying of Cr with Si and Ga impurities influences the magnetic phase transition temparatures, namely the Néel temparature (Tn) and the transition temparature (T1c) for the incommensurate to commensurate (C) SDW transition, in a very complex way. The magnetic phase diagrams of both Cr-Si and Cr-Ga show a triple phase where the paramegnetic (P), CSDW and ISDW phases co-exist.

The X-band FMR has been employed to investigate the angular variation of resonance Fields of DC sputtered Co-Cr Films with different substrate temperatures. This angular variation has been Fitted with the classical uniaxial anisotropy crystal model and yields the values of 2K₁/M-4πM=-4∼-7 KOe, 4K₂ =-0.8∼0.8 KOe and g-factor = 2.3~2.8. The FMR measurments of the first anisotropy constant are quite different from the counterparts measured with VSM. This discrepancy is interpreted as a result of the formation of two ferromagnetic phases. With this simple model, the substrate temperature dependence of First anisotropy is explained and it is predicted that a lower substrate temperature will improve the Co-Cr Films for their potential application in perpendicular magnetic recording devices. The angular dependence of the FMR linewidth is discussed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Ph.D. / Spin—density—wave (SDW) effects are investigated in four dilute Cr—Ir alloy single crystals. The Ir concentrations in these crystals were chosen to cover all four magnetic phases existing on the magnetic phase diagram of the Cr—Ir system. Thermal expansion, electrical resistivity, elastic constants and ultrasonic attenuation are studied as functions of temperature and alloy concentration. The elastic constants are also studied as a function of applied hydrostatic pressure. The SDW effects in the Cr—Ir system are compared with those in other Cr alloys. The full temperature—concentration and temperature—pressure magnetic phase diagrams of the Cr—Ir system are determined. Existing theories are used to discuss the observations. The following major observations are made: Magnetoelastic interactions in Cr—Ir alloys are very large, resulting in well defined magnetic anomalies in the elastic constants and thermal expansion at all magnetic phase transition temperatures. Elastic constant measurements as a function of temperature appear to be a very sensitive tool to determine the magnetic phase transition temperatures of the Cr—Ir alloy system. Below TN of Cr—Ir alloys, where TN is the transition temperature from the incommensurate transverse spin—density-wave (TISDW) magnetic phase to the paramagnetic phase, elastic constant and thermal expansion measurements show the existence of hysteresis effects, which are probably due to a redistribution of antiferromagnetic domains. These hysteresis effects are the first evidence of such effects in Cr alloys. Spin fluctuation effects are shown to exist to temperatures well above the Neel temperatures of the Cr—Ir alloys. Analyses of the data for electrical resistivity measurements of Cr—Ir alloys show that the fraction of the electron and hole Fermi surface sheets that nests is roughly the same in the ISDW and CSDW (commensurate spin—density—wave) phases, making the resistivity anomaly near the ISDW—CSDW transition temperature very small or non—existing. Measurements of elastic constants as a function of applied pressure at different constant temperatures are shown to be a very powerful tool for an investigation of the interaction of the SDW with the acoustic phonons in dilute Cr—Ir alloys. It is found that the SDW in Cr—Ir alloys couples mainly with the longitudinal—mode acoustic phonons. Coupling to the shear—mode phonons is relatively small. Empirical correspondence is found between the temperature—concentration and temperature— pressure magnetic phase diagrams of the dilute Cr—Ir alloy system by using a linear scaling between pressure and concentration. Existing thermodynamic models fit the experimental results for the elastic constants and magnetovolume of the Cr—Ir alloys well. The main features of the temperature—concentration and temperature—pressure magnetic phase diagrams of the Cr—Ir alloy system are resonably well predicted by existing microscopic theories.

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Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. / Includes bibliographical references. / M.S.