On the magnetic characteristics of Pr-La and Pr-Y alloys and the nature of elemental praseodymium at low temperatures

Abstract

Magnetic susceptibilities of Pr and Pr-Y alloys are reported for the temperature range 2–300°K and for field strengths ( H) up to 21 kOe. The alloys show deviations from Curie-Weiss behavior and a tendency toward temperature-independent susceptibility similar to that exhibited by elemental Pr. χ at 4.2°K for Pr decreases sharply with alloying; its Weiss constant changes sign with as little as 10 per cent La or Y. χ at 4.2°K is observed to decrease with increasing H above 10 kOe; the decrease is progressively eliminated by alloying with Y or La, and also is not observed at 300°K. The operator equivalent method is used to calculate the energy level structure and associated magnetic moments for cubic and hexagonal Pr +3 ions. Influence of the sixth order term and H is included. Using standard formulae it is possible to account for the χ vs. T behavior for Pr 0.5La 0.5; the overall splittings at the cubic and hexagonal sites are the same as those found by Bleaney for Pr. Extension of the analysis to Pr enables most of its unusual characteristics to be understood. Appearance of spontaneous magnetization is predicted at T c , where T c is calculated to be in the range 24.4 to 32°K, depending on the choice of the molecular field coefficient. This compares favorably with 25°K observed by neutron diffraction techniques. From the analysis it is also clear why (a) the magnetic ordering in Pr is only a weakly cooperative process and (b) order is confined to the hexagonal sites. the new concept of Pr represents a way of harmonizing the two seemingly contradictory models used earlier in describing its low temperature magnetic behavior.