C. E. Olsen

Magnetic Properties of DyAl2 and NdAl2

The magnetic properties of two dialuminides, DyAl2 and NdAl2, have been investigated by neutron diffraction and susceptibility measurements. Both compounds show Curie‐Weiss behavior in the paramagnetic region and are basically ferromagnetic below Curie temperatures of 62°K and 65°K, respectively. At low temperatures, the compound NdAl2 is a pure ferromagnet, whereas DyAl2 is almost completely ferromagnetic, but has the additional property of a weak antiferromagnetic ordering. The susceptibility measurements show an effective moment per molecule of 9.7±0.1 and 3.1±0.05 μB for DyAl2 and NdAl2, respectively. The neutron diffraction data show a rare‐earth‐ordered saturation moment of 9.1±0.4 and 2.5±0.1 μB on the Dy and Nd atom sites, respectively. The Al atom sites exhibit no measureable moment within the limits of experimental detection (0.5 μB). Both compounds show a temperature‐dependent magnetic ordering process which obeys a Brillouin function. The experimental magnetic form factor for both the Dy3+ and...

Magnetic Properties of PrAl2 and ErAl2

The magnetic properties of PrAl2 and ErAl2 have been investigated by neutron‐diffraction and susceptibility measurements on powder samples of the above compounds. The susceptibility data show that both compounds obey the Curie‐Weiss law; the effective moment per molecule in the paramagnetic region is 3.5±0.05 μB for PrAl2 and 9.2±0.1 μB for ErAl2. The neutron‐diffraction measurements confirm that these compounds are ferromagnetically ordered below a Curie temperature of 34°K for PrAl2 and 14°K for ErAl2; the respective saturated ordered moments at the rare earth atom sites are 2.94±0.05 μB and 8.3±0.3 μB. The magnetic form factor data from the ErAl2 coherent magnetic reflections are in good agreement with similar data obtained by other investigators on an Er single crystal. The magnetic scattering intensity of the (111) reflection from PrAl2 was measured just below the Curie temperature TC in order to determine the long‐range magnetic‐order temperature dependence. The results show that the spontaneous mag...

Magnetic Structure of DyAg

Neutron‐diffraction measurements on the intermetallic compound DyAg show that this material is antiferromagnetic below a Neel temperature, TN, of 51°±1°K; this magnetic structure is in agreement with previous susceptibility data. The measured ordered moment on the Dy atom sites is 9.8±0.5 μB which is essentially the full moment to be expected from the free Dy3+ ion. The observed antiferromagnetic structure is in disagreement with predictions derived from the Ruderman—Kittel—Yosida indirect exchange interaction. Molecular field calculations based on TN show that the exchange energy, |Jex|/k, is in the range from 1.5° to 2.2°K.

A spectrometer for inelastic scattering using neutrons from 1 eV to 186 eV

Abstract A Filtered Beam Spectrometer (FBS) has been developed at the spallation neutron source at the Los Alamos National Laboratory. It has been demonstrated that this spectrometer can measure inelastic neutron scattering using neutrons from 1 eV to 186 eV. In the FBS, a filter having a strong and narrow resonance is used to define the energy of neutrons before (or after) scattering and time of flight is used to measure the energy after (or before) scattering. In this paper, the FBS is described and examples of data are given.

Magnetic Properties of Uranium Digermanide

Investigations on the magnetic properties of actinide element intermetallic compounds has disclosed that UGe2 and PuGe2 are ferromagnetic with magnetic moments greater than 0.803 and 0.144 Bohr magneton per molecule respectively at 4°K. Electrical resistivity measurements on UGe2 indicate an interaction of the conduction electrons with the local spin which produces ferromagnetism. Also the electrical resistivity of USi2, which is not ferromagnetic, was measured for comparison.

Comparison of Self‐Irradiation Effects in Alpha Plutonium Enriched and Unenriched in 238Pu

Self‐damage accumulation at 22.5°K has been studied in alpha plutonium enriched and unenriched in 238Pu. The enriched specimen was held at this low temperature for a period equivalent to about 14 000 h in terms of damage accumulated in the unenriched specimen. The resistivity of the enriched specimen increased to a maximum of 141.5 μΩ‐cm and then decreased gradually with additional time. The increase has been attributed to self‐irradiation damage consisting of interstitials and vacancies, and the decrease is discussed in terms of possible effects due to phase transformation, internal stresses, magnetic ordering, impurities, and clustering of defects. Annealing behavior differed widely in the two plutonium specimens studied and this is also discussed.

Anomalous paramagnetic‐state μSR in spin‐glass AgMn

Muon spin rotation (μSR) experiments have been carried out in the paramagnetic state (T≳Tg) of a dilute AgMn spin glass, to probe internal field distributions during the onset of impurity‐spin freezing. μ+ resonance frequencies and depolarization rates were measured in a 1.6 at.% Mn sample in transverse fields between 0.15 and 5 kOe for temperatures up to ∼3Tg. The depolarization rate Λ increased well above the value Λd expected in the absence of impurity‐spin exchange coupling as Tg was approached from above. The largest relative increase of Λ was obtained for lowest fields. The average precession frequency was constant to within 0.2% down to 1.1Tg. The data scale roughly with T/Tg and H/Tg when compared to recent μSR studies of CuMn. Although a case has been made for attributing this anomamous increase in Λ to dynamic broadening (spin‐lattice relaxation), evidence exists which argues that static inhomogeneity in the muon hyperfine field is the origin of Λ. If this is the case, the absence of muon enviro...

Magnetic Properties of PrAl2

Neutron diffraction powder patterns have confirmed that the compound PrAl2 undergoes a magnetic transition to a ferromagnetic structure at a Curie temperature of 38°K. The ordered moment at saturation on the Pr atom sites is 2.94±0.05 μB which is close to the full moment of 3.2 μB expected for the free Pr+3 ion. No detectable moment is observed for Al. The present results for the total moment per molecule are in satisfactory agreement with previous magnetization measurements. The shape of the magnetic form factor for the Pr3+ ion was determined over the range from (sinθ)/λ=0.1 A−1 to 0.5 A−1 and is in good agreement with calculated values.

Magnetic Properties of Plutonium Hydride and Deuteride

Magnetic investigations on plutonium hydride (PuH2.74) and deuteride (PuD2.74) have shown these compounds to be either ferromagnetic, like the corresponding uranium compounds, or ferrimagnetic. The Curie temperatures of plutonium hydride and deuteride are the same, within experimental error, and are 107°K. The magnetic moment for the hydride and deuteride are greater than 0.24 and 0.13 Bohr magnetons per mole of compound, respectively, at 76°K. In addition the cubic plutonium oxide PuO1.62 was found to be either ferro‐ or ferrimagnetic with a magnetic moment greater than 0.16 Bohr magnetons per mole of plutonium at 4°K and a Curie temperature of 96.7°K.

Magnetic susceptibility of pure plutonium metal above 300 K

Abstract The magnetic susceptibility of two samples of plutonium, one highly oriented and the other randomly oriented, were measured on heating between 300 and 850 K. The susceptibilities of the alpha, beta, gamma, delta, delta-prime, and epsilon phases were determined as a function of temperature. Principal magnetic axes and the magnetic anisotropy with respect to these axes were determined for the alpha, beta, gamma, and the delta phases.