Effect of Grain Boundaries on the Electrical Resistivity of High-Purity Iron at 4.2°K

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Abstract
Electrical resistivity (ρ) of samples with different grain sizes, made from iron of three different purities (containing a maximum of 34, 79, and 2150 atomic ppm impurities, respectively), has been studied at 4.2°K in the presence of applied longitudinal magnetic fields up to 60 kOe. It has been found that the resistivity is influenced not only by impurities and magnetic domain arrangements but also by the grain‐boundary area per unit volume. The ratio R=ρ(300.0°K)/ρmin (4.2°K) varies from 2875 to 528 for the interfacial grain area range of 0 (single crystal) to 7.0 mm−1 in the highest purity iron. (ρmin is the minimum in the resistivity measured as a function of the applied field at 4.2°K.) Due consideration of these large magnetic and grain‐boundary effects discloses a clearer correlation between R and purity.