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An inverse magnetocaloric effect is studied in Ni 2 Mn 1 + x X 1 − x -type Heusler alloys. Principally known for their shape-memory properties, these alloys also exhibit significant entropy and temperature changes (Δ S and Δ T A d , respectively) under adiabatic conditions when a modest magnetic field is applied. We investigated the impact on magnetocaloric properties of introducing substantial chemical disorder on the X -site (X = Si , Ga , In), of replacing Ni with nonmagnetic Ag, and of replacing a small amount of Mn with Gd. While a reduction in Δ S is observed in the first two cases, we observe a significant enhancement of Δ S when a small amount of Gd is substituted for Mn. A thermodynamic analysis was conducted using magnetization and heat capacity data to estimate adiabatic temperature changes in the range of Δ T A d ≃ − 1 to − 3 K for a 5 T magnetic field. Several alloys characterized in this study exhibit these respectable Δ T A d values near room temperature, making them potentially viable candidates for magnetic refrigeration applications. [ABSTRACT FROM AUTHOR]

A procedure for determining the electrical resistivity of anisotropic materials is presented. It offers several improvements to the well-known Montgomery method. One improvement, in particular, is the ability to obtain the electrical resistivity for all three axes of an orthorhombic crystal analytically, rather than using the iterative approach suggested by Montgomery for the third axis. All necessary equations are derived and their application in determining the tensor components of the electrical resistivity is explained in detail. Measurements on isotropic specimens were executed in order to test the foundations of the method. Measurements on anisotropic samples are compared with measurements obtained by using the standard four-probe method, revealing good agreement. [ABSTRACT FROM AUTHOR]

Microcathodoluminescence (CLS) spectroscopy is used to probe the effect of ionizing radiation on defects inside A1 gate oxide structures. Micron-scale A1-SiO[SUB2]-Si capacitors exposed to 10 keV x-ray irradiation exhibit spatially localized CLS emissions characteristic of multiple deep level traps, including positively charged oxygen-deficient centers and nonbridging oxygen hole centers (NBOHC). Irradiation produces both increases and decreases in their relative emission intensities, depending on spatial location within the oxide. These changes result in a gradient of E′ versus NBOHC defect densities across the oxide thickness between A1 and Si interfaces. These results demonstrate that x-ray irradiation-induced deep level traps can be monitored spatially in metal-oxide-semiconductor gate structures, that x-ray irradiation produces separate increases or decreases in E′ versus NBOHC defect densities, and that these changes vary with position within the oxides. [ABSTRACT FROM AUTHOR]

Both luminescence properties and dissociation kinetics of Mg-H complex for as-grown Mg-doped GaN are simultaneously investigated by low-energy electron-excited nanoluminescence (LEEN) spectroscopy. Ultraviolet luminescence at 3.2-3.3 eV and blue luminescence at 2.8-2.9 eV are observed as predominant LEEN emissions. In-depth profiles of LEEN emission show that the blue luminescence is the predominant emission for highly Mg-doped GaN. Electron-beam exposure less than 50 mC/cm² produces an increase of the ultraviolet luminescence intensity and reduction of the blue luminescence intensity. These characteristics suggest that the blue luminescence is due to a transition from hydrogen-related deep donor to Mg acceptor and that the ultraviolet luminescence is due to transitions from conduction band and/or shallow hydrogen donor to Mg acceptor. We propose a kinetic model for dissociation reactions of Mg-H complex during electron exposure, and the reaction rate is evaluated to be (3.5±0.3)× 10[sup -3] s[sup -1] for electron beams with 3.1× 10[sup -5] A/cm² at 5.0 keV. [ABSTRACT FROM AUTHOR]