Eddy Current Determination of the Effects of Cyclic Strain and Temperature on the Magnetoresistivity of Pure Aluminum

Abstract

An important characteristic of pure metals for use in low temperature conductor applications is the behavior of the material in the presence of a high magnetic field. Using the eddy current decay method, the magnetoresistivity of 99.99% and 99.999% aluminum is examined at temperatures of 4.2, 20, and 27.2 Kelvin and at fields of 0 to 7 Tesla. The effects of cyclic strain are also closely examined Comparisons of magnetoresistivity behavior of materials at different temperatures and with different defect concentrations, although with similar zero field resistivities, are made. The results show that magnetoresistivity is strongly dependent on the zero field resistivity. Furthermore, the effects of temperature are small, but noticeable, and the effects of strain and impurities on magnetoresistivity are apparently similar in nature. For materials with RR (ρ_rt/ρ_temp) values of 400 or more, resistivity increases linearly at fields above 1 to 2 T. The onset of this linear behavior occurs at lower fields when the zero field resistivity of the material is lower, regardless of the test temperature, strain level, etc. In the range of variables covered, materials with a lower zero field resistivity always have a lower in-field resistivity for similar applied fields. The results also show that the measurement of transverse magnetoresistivity in situations where values of H*RR are greater than several thousand tesla may be unacceptable if the eddy current decay method is used; an anomalous voltagetime record is generated by the eddy current pickup coil.