Magnetic Proximity Effect

The penetration depth of the spin polarization of a magnetic metal (Fe, Ni, or Cr) into a nonmagnetic metal or alloy with a high exchange-enhanced spin susceptibility (Pd and Ni0.58{Rh}0.42$) was studied by use of the superconducting proximity effect. Pb-Pd-(Fe or Cr) and Pb-${Ni}0.58Rh0.42-Ni sandwiches as well as Pb-Mo-Cr were prepared by the getter-evaporating and getter-sputtering techniques at 77^∘{}K and their transition temperatures were measured without warming up. Since the magnetic penetration depth is very small, the Mo sandwiches were used to rule out the possibility of pinholes through the nonmagnetic metal. Also, the Mo sandwiches permit the evaluation of the superconducting proximity effect in the Pd sandwiches, since molybdenum has a low spin susceptibility, but at the same time the penetration of superconducting pairs is approximately the same in Mo and Pd. The ranges of polarization of Fe and Cr into Pd were found to be approximately 20±{}10 {}, and the range is possibly less for Ni into Ni0.58{Rh}0.42$. Finally, ${Ni}₃$Ga-Pb sandwiches (${Ni}₃$Ga was chosen because of its very high spin susceptibility) had transition temperatures consistent with ${Ni}₃$Ga being a normal nonmagnetic compound, from which it is concluded that if spin fluctuations are present in ${Ni}₃$Ga, they do not lead to appreciable spin depairing.