A. T. Aldred

Structural and magnetic properties of DyFe3 hydrides

Abstract The ternary hydride phases DyFe 3 H x (with x = 1.7, 2.5 and 4.2) all retain the PuNi 3 rhombohedral structure of DyFe 3 , with a maximum volume expansion of 18% for DyFe 3 H 4.2 . All the phases show a preferential expansion parallel to the c 0 axis. From bulk magnetization measurements the DyFe moment compensation temperature is found to decrease linearly, from 545 K for DyFe 3 to 150 K for DyFe 3 H 4.2 , with increasing volume of the hydride phases. The 161 Dy Mossbauer results for the two dysprosium sites in the structure indicate that a slight reduction occurs in the free-ion moment found for DyFe 3 in all the hydride phases. In addition, the 57 Fe Mossbauer data show that the average iron moment for the five inequivalent iron sites increases with hydrogen concentration up to x = 2.5. These trends in the local moments indicate that the variation in the compensation temperature, which is related to the Dy-Fe exchange, is associated with lattice expansion effects due to the presence of hydrogen.

Magnetic properties of the AnFe2 compounds (An = U, Np, Pu, and Am)☆

The magnetic properties of the actinide Laves compounds (cubic C-15 crystal structure) with iron were studied by magnetization, neutron diffraction, and Moessbauer-effect techniques. All the compounds exhibit a spontaneous magnetization. Magnetic moments of 0.06, 1.09, 0.45, and -0.4..mu../sub B/ are associated with the U, Np, Pu, and Am ions, respectively. The corresponding iron moments are 0.6, 1.4, 1.5, and 1.7..mu../sub B/. The ferrimagnetic nature of AmFe/sub 2/ suggests a partial occupancy of the Am/sup 2 +/:f/sup 7/ state, inasmuch as the Am/sup 3 +/:f/sup 6/ state has a nonmagnetic ground state.

Critical magnetic behavior of uranium monosulphide

Abstract A detailed magnetization study has been made on ferromagnetic US near its Curie temperature. The critical exponent values γ, β and δ have been determined, and are close to those found earlier for UTe. The scaling law and then the homogeneous equation of state are exactly satisfied. We also present the tentative results of our analysis of the α exponent, deduced from the heat capacity data of Flotow et al. Our findings are summarized and compared with those previously reported for US and UTe.

Magnetic properties of HfZn2

Abstract HfZn2 is known to be an exchange enhanced paramagnet, with a strongly temperature dependent susceptibility. In a new study, a sample of HfZn2 has been prepared, which is even more strongly enhanced and hence closer to ordering ferromagnetically than found in a previous study. The values of the electronic contribution to the specific heat, the magnetic susceptibility at T = 0, χ(0) and the Stoner exchange enhancement factor S = 1/| N(EF)I−1| have all been found to increase substantially compared to earlier results.

Magnetic properties of the neptunium Laves phases: NpMn2, NpFe2, NpCo2, NpNi2

The magnetic properties of the cubic Laves phases (C 15 structure) NpMn2, NpFe2, NpCo2, and NpNi2 have been studied from 4 to 300 K by means of magnetization, neutron‐diffraction, and nuclear‐gamma‐ray resonance (Mossbauer) measurements. The respective ordering temperatures (and types of ordering) are 18 K (ferro), ∠500 K (ferro), 15 K (antiferro), and 32 K (ferro). Magnetic moments are present on the neptunium atom in all compounds and on the Fe atom in NpFe2. Certain magnetic properties such as the large anisotropy and the relationship between the magnetic moment and the hyperfine field are best interpreted in terms of localized 5f electrons, whereas other properties suggest hybridization between the 5f and 3d electrons.

High‐field susceptibility in ferromagnetic NpOs2

NpOs2 is known to be a ferromagnet with a Curie temperature of 7.5 K. Previous bulk magnetization measurements indicated a field induced magnetization even well below the transition temperature. We have extended this by a measurement of the local high‐field susceptibility, using the Mossbauer effect in 237Np. At 1.6 K, a susceptibility of (1.2±0.2) ×10−2 emu/mole is obtained, in general agreement with the bulk measurement. Such a large susceptibility is best understood by a model of itinerant magnetism, although other properties of the material indicate localized behavior.

Mössbauer and magnetization measurements in FeCr solid solutions

Mossbauer effect and magnetization measurements have been obtained for Fe‐Cr alloys having Cr concentrations c=0.20, 0.25, and 0.30. The magnetically split Mossbauer spectra have been analyzed by the procedure of Window1 to give the probability distribution of hyperfine fields P(H) as a function of temperature and concentration. This distribution is closely approximated by two Gaussians: one centered near H=0 and the other at a value of H1 which is concentration and temperature dependent. The halfwidths ΔH of these Gaussians are independent of temperature and concentration. Both H1 and the zero field magnetization are proportional to (T−Tc)1/2 with Tc=160±3 K and 255±3 K for c=0.25 and 0.30, respectively. For c=0.20, H1 goes to zero at Tc=60±3 K. The magnetization for this sample is strongly field‐dependent and the spontaneous magnetization difficult to obtain. These results are in general agreement with a suggestion of Shull and Beck2 that the Fe‐Cr solid solutions are mictomagnets for 0.09?c≡0.23 and ar...

Magnetic Properties of Antiferromagnetic NpP

Neptunium phosphide has the NaCl‐type structure with a lattice parameter of a = 5.610 A. The compound orders antiferromagnetically at 120°K. Between 120 and 74°K, the magnetic moments are arranged in a longitudinal sinusoidal modulation with the spin direction parallel to the cube axis, and with a constant repeat distance of 2.78±0.08 unit cells. Below 74°K the spin structure becomes commensurate with the lattice, having a repeat of 3 unit cells, and higher‐order harmonics in the neutron pattern indicate a tendency towards forming a square 3+, 3− wave. At 4.2°K, however, the process is incomplete, the two neptunium magnetic moments being 2.4 and 1.8 μg. The Mossbauer spectra at 4.2°K can be explained by assuming two different hyperfine fields of 3690±40 kOe and 4210±40 kOe at the Np site, with an occupation ratio of two to one. This interpretation is in agreement with the neutron results. Magnetization and resistivity measurements both indicate transitions at 120°K (TN), and 74°K. The resistivity falls sh...

Magnetic Properties of NpAl3

We have studied the magnetic properties of NpAl3 by means of magnetization and Mossbauer‐effect measurements between 4 and 300°K. This compound, which has the AuCu3‐type structure with a lattice parameter of a = 4.260 A, orders ferromagnetically at 62.5 ± 0.5°K. The magnetization cannot be saturated by an applied field of 13.5 kOe at 4°K. However, the 237Np magnetic hyperfine field of 2630 kOe measured at 4.2°K indicates an Np magnetic moment of ∼1.2 μB. Although the magnetic susceptibility above Tc deviates strongly from Curie‐Weiss behavior, the temperature dependence can be reasonably well reproduced theoretically if it is assumed that the neptunium ion has a +4 charge (5f3) and is situated in a cubic crystal field of 12 negatively charged ligands.

Magnetic Properties of

We have studied the magnetic properties of NpAl3 by means of magnetization and Mossbauer‐effect measurements between 4 and 300°K. This compound, which has the AuCu3‐type structure with a lattice parameter of a = 4.260 A, orders ferromagnetically at 62.5 ± 0.5°K. The magnetization cannot be saturated by an applied field of 13.5 kOe at 4°K. However, the 237Np magnetic hyperfine field of 2630 kOe measured at 4.2°K indicates an Np magnetic moment of ∼1.2 μB. Although the magnetic susceptibility above Tc deviates strongly from Curie‐Weiss behavior, the temperature dependence can be reasonably well reproduced theoretically if it is assumed that the neptunium ion has a +4 charge (5f3) and is situated in a cubic crystal field of 12 negatively charged ligands.