An experimental determination has been made of the magnetic fields necessary to induce the superconducting transition in microscopic tin filaments called "whiskers." For temperatures near the zero-field transition temperature, T c , the results are unambiguous, and in this region the critical fields are significantly higher than those of a bulk superconductor. At lower temperatures the critical field curve splits into two parts, the upper curve giving the field for destruction of superconductivity and the lower curve the field for restoration. The temperature dependence of the critical field is compared with the predictions of the London and Ginsburg-Landau theories of superconductivity. It is found that the London theory is inadequate to describe the data over the whole useful range, whereas the Ginsburg-Landau theory provides a satisfactory fit. The disappearance of hysteresis occurs at a temperature for which 2.0

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A study has been made of the low-temperature magnetic behavior of gold-based solid solutions containing transition metals in dilute concentration. Of particular interest are Au-Cr, Au-Mn, and Au-Fe, for which solid solutions of higher concentration have been found by other workers to undergo antiferromagnetic (Cr) and ferromagnetic (Mn and Fe) transitions. The present results show that for alloys of about 1 at.% there occur low-temperature magnetic transitions which are similar for all three solutes. The main features of the transitions, as in dilute Cu-Mn alloys, are a susceptibility maximum and, below the temperature of the maximum, a saturable remanent magnetic moment which increases with decreasing temperature in a characteristic manner. The temperature of the maximum increases nearly in proportion to concentration and also depends on the identity of the solute, being about 12, 4, and 8°K/at.%, respectively, for Cr, Mn, and Fe. In the case of Au-V and Au-Co alloys susceptibility maxima and remanent magnetization were absent. INTRODUCTIONT HE purpose of this article is to report results on the low-temperature magnetic behavior of dilute binary Au-based solid solutions containing transition metals. Because of the relatively wide solubility range in such systems they present an unusual opportunity for the study of dilution effects. Previous work on dilute Au-Cr, 1 Au-Mn, 2 and Au-Fe 3-5 alloys has demonstrated high-temperature paramagnetism, evident mainly from the Curie-Weiss law of temperature dependence of the magnetic susceptibility. The effective atomic moments deduced from this law are generally comparable in magnitude with those of the free atom. In addition, predictions from the paramagnetic Curie temperature 6 P concerning the magnetic transitions in the more concentrated alloys are fairly satisfactory. Thus Au-Cr alloys between 21.4 and 29.2 at. % Cr with large nega-TABLE I. Solute resistivities. Alloy

LETTERS TO THE EDITORfour atoms in the unit cell and thus assigning two of Wallace's diagonal matrix elements a different value than the other two. The discontinuity of the density of state at the band edge is proportional to the difference (H n -H22) and if this is large enough (greater than 271) the bands need not touch at alL It should be mentioned that asymmetry in the energy contours is a necessary feature to explain the sizeable negative Hall coefficient. 3 The purpose of the present note is to point out that the effect of including next-nearest neighbors (in the basal plane) is to introduce an asymmetry in the density of states in the same qualitative fashion as above. Nextnearest neighbors in the plane are easily taken into consideration and, in fact, Wallace 2 has already done so, although he neglects such terms when calculating the density of states. From reference 2, the energy of a state k, including nearest and next-nearest neighbors in the plane and nearest neighbors out of the plane, is;Here K X y 2 =K x 2 +fCy 2 , where K==k-k(corner), e is measured from the band edge, and 70, 70', and 71 are the resonance integrals involving coplanar nearest and nextnearest and interplanar nearest neighbors, respectively. The only effect of including 7