Various types of thin-film dc gradiometer SQUIDs with integrated pickup loops were investigated. The SQUIDs were prepared on a 5 mm × 10 mm chip in the well developed Nb-NbO x -Pb/Au/In technology. It was shown that the SQUIDs work in an unshielded environment. Our best SQUIDs have a field gradient sensitivity better then 30 fT cm −1 Hz −1/2 . All gradiometers have some response to a homogeneous field, i.e., a parasitic area. The effective pickup area, the field gradient sensitivity, and the components of the parasitic area for the field perpendicular and parallel to the gradiometer plane were measured for all types of gradiometer. The calculations of flux coupling efficiency are compared with experimental results. The origins of parasitic area are discussed. A further reduction of external disturbances was achieved by using an electronic second-order gradiometer. Examples of magnetocardiographic measurement in a physical laboratory without any shielding with first and second-order gradiometers are shown.

The ideal resistance‐ratios of tungsten single crystals are studied over the temperature range of liquid‐helium, hydrogen, and neon. The crystals have residual‐resistance ratios R0/R(273) between 3 and 67 × 10−6. Between 1.4 and 4.2 °K the temperature dependence of the ideal resistance ratio is influenced considerably by the sample diameter. Within this range, for the purest sample, the mean free path of the current carriers is found to be larger than the sample diameter. Above 14 °K, all samples have the same ideal resistance ratio, and between 19 and 27 °K, this ratio is represented very well by the Bloch‐Grüneisen formula ri ∼ T5.

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The electrical resistivity of iron is measured between 2 and 30 K. The results can be extremely well explained by fitting the data to a simple two-current model including electron-magnon, electron-phonon, and electron-impurity scattering. Below 10 K large deviations from Matthiessen's rule are observed arising from the two-current character of the conduction.Der elektrische Widerstand von Eisen wird im Bereich von 2 bis 30 K gemessen. Die Ergebnisse konnen auDerordentlich gut durch Anpassung der Daten an ein einfaches Zwei-Strom-Modell, das Elektron-Magnon-, Elektron-Phonon-und Elektron-Storstellen-Streuung beriicksichtigt, erklart werden. Unterhalb von 10 K werden groSe Abweichungen von der Matthiessen-Regel, die aus dem Zwei-Strom-Charakter der Leitung resultieren, beobachtet.

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