Browsing by Author "Long, Jerome R."

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    The aperiodically dampened loudspeaker system
    Short, George Elliott III (Virginia Tech, 1988-07-15)
    The theory of the aperiodically damped loudspeaker system is derived and investigated in both the time and frequency domains. The advantages of the aperiodic configuration over sealed box loudspeaker systems are discussed. The aperiodically damped loudspeaker system is described by the parameters used for sealed box loudspeaker systems, with some additions. A real system is constructed which takes full advantage of aperiodic configuration, and its performance is compared with a sealed box system of the same dimensions. Complete derivations of the theory for both the sealed box and aperiodically damped systems are included, as well as methods for measuring all required parameters.
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    Curie temperature of PdFe films
    Long, Jerome R.; Mattozzi, Raymond W. (American Institute of Physics, 1984)
    Ferromagnetic ordering of giant moments formed by dilute Fe in Pd host bulk alloys has been the subject of many investigations, but thin films have had little attention. Thin films exhibit evidence of a spin glass phase not observed in the bulk and a crossover from three_dimensional to two_ dimensional ferromagnetic ordering. The range of ferromagnetic ordering for PdFe is long compared to that of pure Fe, so that the crossover to two_dimensional behavior should occur in relatively thick films. A study of the effect in pure Fe would require uniform films of a few tens of angstroms. The crossover is manifested by a depression of the Curie temperature, which is expected to vary as a critical exponent of the thickness. Using a mutual inductance technique with SQUID detection, the temperature dependences of the spontaneous magnetization and the acsusceptibility were measured for some sputtered films with approximately 8% Fe. As expected, the Curie temperature decreased as the film thickness decreased. Unlike Fe, the Curie temperature of PdFe is dependent upon microstructure, and the microstructure of a film may have a systematic thickness variation that could result in a false crossover effect. The extent to which a model sensitive shift exponent can be extracted from the results is discussed.
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    Magnetic tricritical behavior of ethylammonium tetrachlorocuprate
    Long, Jerome R.; Haines, Donald N.; Drumheller, John E. (American Institute of Physics, 1988-04-15)
    In order to investigate the prediction by Tuthill that a tricritical point may exist in the phase diagram of spin_flop antiferromagnets with intermediate anisotropy, an experimental reexamination of the phase diagram of the quasi_two_dimensional system (C2H5NH3)2CuCl4 was performed. Measurements were made of the differential magnetic susceptibility,d M/d H, vs dc field and temperature in the (10 K, 100 Oe) region of the proposed tricritical point. A low amplitude, low frequency, ac biphase SQUID susceptometer was used. The sample was a single crystal with field along the antiferromagnetic easy (orthorhombic a_axis) direction. The data show some evidence of the existence of at least one tricritical point, but the results are not definitive.
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    Phase transitions in thin iron-palladium films
    Mattozzi, Raymond William (Virginia Polytechnic Institute and State University, 1982)
    Sputtered thin films have the capability of producing a very random distribution of alloying elements within a host element. This study demonstrates the ability of the SQUID (Superconducting Quantum Undulating Interference Device) to measure the Curie temperature of thin films of Pd(1-x)Fe(x). The Curie temperatures of these films were found to be significantly less than bulk samples having the same iron concentration. The Curie temperature, furthermore, showed a systematic shift to higher values as the thickness of the film increased. Magnetic structure below the Curie temperature is revealed in magnetization and a.c. susceptibility curves for x=. 078. For other samples susceptibility data exhibited more sensitivity than magnetization in revealing magnetic detail below the Curie temperature. We attribute some of this magnetic detail to cluster glass behavior.
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    Resistivity and galvanomagnetic coefficients of iron group metallic glasses with chromium substitutions
    Long, Jerome R.; Hadjipanayis, George C.; Sellmyer, David J. (American Institute of Physics, 1982)
    Magnetic field and temperature dependences of the electrical resistivities and Hall resistivities were measured for the metallic glass ferromagnets Fe13Ni60Cr5Si10B12, Fe37Ni36Cr5Si10B12, Fe81B13.5Si3.5C2, and Fe5Co75Si15B5. Resistance minima and magnetoresistivity of the FeNiCr glasses have been found to be consistent with a modified Kondo model of low temperature scattering. The Hall resistivities are positive and large. The spontaneous Hall coefficients of the FeNiCr glasses are in good agreement with previous magnetization measurements on the same glasses.