Low-Temperature Magnetoresistance in Magnesium and Aluminum Containing Small Concentrations of Manganese or Iron

Magnetoresistance measurements in magnetic fileds up to 21 kOe have been made on Mg-Mn, Mg-Cd, Mg-Al, Al-Mn, and Al-Fe alloys in the temperature region of liquid helium. Magnesium alloys containing more than 0.1-at.% Mn which exhibit a resistance maximum and minimum in zero filed, show a negative magnetoresistance, whereas the more dilute samples (0.001-0.1 at. % Mn) show a positive magnetoresistance, the magnitude of which decreases with decreasing temperature. The magnesium alloys containing non-transition element impurities, as well as the aluminum alloys containing transition metal impurities, are found to obey Kohler\u27s rule. From an analysis of these data it is found that the magnetoresistivity of a dilute alloy of magnesium containing manganese, can be considered as the sum of a normal positive magnetoresistivity (obeying Kohler\u27s rule) and an anomalous term which is negative in sign, does not obey Kohler\u27s rule and is presumably due to a magnetic scattering of the conduction electrons. Using values of thes s-d exchange integral and the Coulomb scattering integral derived from an analysis of the zero-field resistivity permits an explanation of the magnetoresistivity based on Kasuya\u27s theory, at temperatures near the Neel point

Role of s-d Exchange Interactions in Dilute Alloys Exhibiting Both Low-Temperature Resistance Anomalies and Superconductivity

Measurements of the magnetic susceptibility of some dilute Zn-Mn alloys are reported in the temperature range where this alloy system is known to exhibit low-temperature resistance anomalies. All of the alloys studied obey a Curie law with the most concentrated alloy (0.43-at. % Mn) exhibiting deviations in the neighborhood of 6°K. The Curie constant indicates that manganese when dissolved in zinc has a spin value of 3/2 which is temperature-independent between 5 and 273°K. Calculations of the exchange integral J from the magnetic properties of dilute Zn-Mn alloys have been made from the Neel temperature, the magnetoresistivity as a function of field strength and the suppression of the superconducting critical temperature based on theoretical equations which assume a scalar s-d interaction between the paramagnetic ions and conduction electrons. All of the derived values of J lie in the range of (1.4±0.2) ×10^ erg which would lead one to conclude that the magnetic interaction giving rise to these various effects is of the same nature. A graphical method for separating the resistance minimum from the total resistivity, in the presence of a resistance maximum produced by magnetic ordering in the Zn-Mn system, is presented

Magnetotransport of CeRhIn5

We report measurements of the temperature-dependent anisotropic resistivity and in-plane magnetoresistance on single crystals of the tetragonal heavy-fermion antiferromagnet (TN = 3.8 K) CeRhIn5. The measurements are reported in the temperature range 1.4 K to 300 K and in magnetic fields to 18 tesla. The resistivity is moderately anisotropic, with a room-temperature c-axis to in-plane resistivity ratio rho_c/rho_a(300 K) = 1.7. rho(T) measurements on the non-magnetic analog LaRhIn5 indicate that the anisotropy in the CeRhIn5 resistivity stems predominately from anisotropy in Kondo-derived magnetic scattering. In the magnetically ordered regime an applied field H reduces TN only slightly due to the small ordered moment (0.37mu_B) and magnetic anisotropy. The magnetoresistance (MR) below TN is positive and varies linearly with H. In the paramagnetic state a positive MR is present below 7.5 K, while a high-field negative contribution is evident at higher temperatures. The positive contribution decreases in magnitude with increasing temperature. Above 40 K the positive contribution is no longer observable, and the MR is negative. The low-T positive MR results from interactions with the Kondo-coherent state, while the high-T negative MR stems from single-impurity effects. The H and T-dependent magnetotransport reflects the magnetic anisotropy and Kondo interactions at play in CeRhIn5.Comment: submitted to Physical Review

Using clickers in a large business class: examining use behavior and satisfaction

YesAs more and more institutions are integrating new technologies (e.g., audience response systems such as clickers) into their teaching and learning systems, it is becoming increasingly necessary to have a detailed understanding of the underlying mechanisms of these advanced technologies and their outcomes on student learning perceptions. We proposed a conceptual model based on the technology acceptance model to understand students’ use behavior and satisfaction with clickers. The valid response from 138 second-year business students of Digital Marketing module taught in a British university, where clickers are extensively used in the teaching and learning process, made the basis for data analysis. The results provided a strong support for the proposed model with a reasonably adequate variance (i.e., adjusted R2) of 67% on behavioral intentions and sufficiently high variance on use behavior (i.e., 86%) and user satisfaction (i.e., 89%)

LOW TEMPERATURE MAGNETORESISTANCE AND ELECTRON SPIN RESONANCE IN Ge-Mn-Te

Nous avons mesuré, à basse température, la magnétorésistance, la magnétisation et l'absorption E. S. R. pour un alliage Ge-Te (0,9 at. % Mn) ayant une concentration de porteurs négatifs de 9 x 1020/cc. Il y a corrélation entre la composante négative de la magnétorésistance et le carré de la magnétisation. Cette caractéristique identifie un métal ferromagnétique, à une température inférieure, à la température de Curie. La valeur de saturation de la composante négative de la magnétorésistance augmente pour une diminution de température et peut être reliée à l'intensité du signal E. S. R. pour le même composé.Low temperature measurements of the magnetoresistance, magnetization and E. S. R. absorption are reported for a sample of Ge-Te with a hole concentration of 9 x 1020/cc and containing 0.9 at. % Mn. The magnetoresistance exhibits a negative component which correlates with the square of the experimentally measured magnetization. This behaviour is characteristic of a ferromagnetic metal below the Curie temperature. The saturation value of the negative component of the magnetoresistance increases with decreasing temperature and can be correlated with the E. S. R. line intensity on the same sample