Paul G. Huray

Magnetism of the heavy 5f elements

Abstract Magnetic properties of the trivalent lanthanide ions have been classically used to demonstrate the applicability of L-S coupling and Hunds rule to the 4f element series. An examination of similar behavior for the more spatially extended orbitals of the 5f element series has, until the last few years, been limited to lighter members (actinium through americium). Characterization of magnetic properties of heavier ions (curium, berkelium, californium and einsteinium) has recently led to a comparison with the 4f ion homologues of the actinides and to an extension of the test of L-S coupling to a new region of the periodic table. Investigations of the magnetic properties of heavy element compounds and metals have additionally led to some unexpected results which suggest a rich structure of low temperature magnetic ordering. The increasing degree of spatial localization of the heavy actinide orbitals thereby provides another vehicle for studying the theory of magnetic ordering via the conduction electrons.

Magnetic susceptibility of cerium pnictides

Abstract The magnetic susceptibility of microgram quantities of 248 CmP and 248 CmSb has been determined with the use of a SQUID micromagnetic susceptometer over the temperature range 4.2–340 K and in the applied magnetic field range of 0.45–1600 G. The fcc (NaCl-type) samples yield magnetic transitions at 73 K and 162 K for the phosphide and antimonide, respectively. Together, with published magnetic data for CmN and CmAs, these results indicate spatially extended exchange interactions between the relatively localized 5f electrons of the metallic actinide atoms.

The magnetic susceptibility of 248Cm metal

A SQUID-based micromagnetic susceptometer [1,2] has been used to determine the magnetic susceptibility of 248Cm metal in the temperature range 4.2–320 K and in the applied magnetic field range of 0.45–1400 G. X-ray diffraction indicated that two of the samples of mass 37.2 and 41.2 μg exhibit the dhcp phase and one of mass 152 μg the fcc structure. The nominally dhcp samples exhibit an antiferromagnetic transition at ≈ 65 K. A small second transition near 200 K is observed and influences the high temperature Curie-Weiss fit to the data. For 270 K < T < 307 K and an applied field of 1200 G, x = C/(T + θ), with C = Nμ2/3k and μ = 5.5 μB, θ = −176 K. The fcc sample exhibits a ferrimagnetic transition in the neighborhood of 200 K and at low temperature has a saturated magnetic moment per atom of 0.4 Bohr magnetons in applied fields above 1200 G. At high temperatures three interpretations of the susceptibility may be made. 1. (a) Two regions of Curie-Weiss behavior x = C/(T + θ) with C = Nμ2/3k. For 200 K < T < 300 K, μ = 6.2 μB, θ = −202 K. For 300 K < T < 340 K, μ = 7.7 μB, and θ = −138 K. 2. (b) A modified Curie-Weiss behavior x = x0 + C/(T + θ), with C = Nμ2/3k. Here x0 = 530 × 10−6, μ = 5.36 μB, and θ = −204 K. 3. (c) A ferrimagnetic behavior x = (C1 + C2)T − 2λC1C2T2 − TN2 with Ci = Nμ2i/6k and μi constrained = μ ± 0.4 μB. Here λ = 231 ± 49, μ = 6.13 ± 0.2 μB, and TN = (205 ± 0.6) K.

Magnetism of californium metal

Magnetic susceptibility measurements have been made on samples of californium-249 metal having the dhcp crystal structure. At temperatures between 100 and 340 K and at fields up to 50 kilogauss, the samples exhibit Curie-Weiss behavior. Previous measurements extending only to 1.6 kilogauss gave a magnetic moment per atom of μeff = (10.7±0.2)μB and paramagnetic Weiss temperatures. Θp, in the range of −2 to −16 K for two samples. These values of μeff are in good agreement with the value expected (10.62μB) for a free-ion 5f9 configuration based on an L-S coupling scheme and Hunds rule. In this work extended to higher fields, two additional samples give the values μeff = (9.7 ± 0.2)μB and Θp = −40 K. At low temperatures the samples exhibit an ordered magnetic transition to a state with a saturated moment of 6.1μB/atom when extrapolated to infinitely high field. The low temperature ordered phase exists at temperatures below Tc = (51 ± 2) K as determined from constant magnetization plots.

Anisotropic effects in dilute Pt-Mn: A nuclear orientation study

The paper studies the behaviour of the Mn spin for dilute Mn in Pt as a function of temperature and applied field using the technique of nuclear orientation. In the preferentially oriented cubic polycrystalline foil a preferential nuclear spin ordering axis has been observed in the absence of an applied field. A measure of interaction of the spin with its environment has been obtained which may be modelled by a molecular field with mean value 440 G, and having a distribution in magnitude and direction. The saturation hyperfine field for Mn in Pt was found to be -365+or-15 kG.

The Magnetic Susceptibility of 249Bk Metal

Magnetic susceptibility measurements have been made on a well characterized sample of 249 Bk metal using a SQUID micromagnetic susceptometer1 which has been specifically designed for small volume samples. The sample had ∿12% Cf impurity at the time of measurement and was in the pure dhcp crystal structure. The only previous magnetic measurements on berkelium metal were on samples of mixed crystal structure or with higher concentrations of californium daughter and were made with a mechanical balance susceptometer.2