R. A. Butera

Magnetic properties of RCo2 Ge2 compounds (R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y)

The magnetic properties of the RCo2 Ge2 compounds with R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y have been investigated. It was found that the compounds for which R=La, Ce, Sm, Er, Tm, Yb, and Y exhibit paramagnetic behavior down to 4.2 °K with ErCo2Ge2 and TmCo2Ge2 probably ordering at lower temperatures. The compounds for which R=Gd, Tb, Dy, and Ho order antiferromagnetically. PrCo2Ge2 and NdCo2Ge2 show an unusual magnetic behavior. PrCo2Ge2 exhibits a susceptibility which decreases from 4.2 °K, then rises to a peak at 27.5 °K. NdCo2Ge2 has two peaks in the susceptibility‐vs‐temperature curve at 13.5 and 27.5 °K. The Neel points for the heavy rare‐earth compounds follow the de Gennes function, and the equation χM = χ0,M + CM/T−θ is used to interpret the susceptabilities in the paramagnetic region. χM is the molar susceptibility; χ0,M is a temperature independent contribution to the susceptibility; CM is the Curie constant; T is the temperature and θ is the Weiss constant.

Electronic specific heat and high field magnetization studies on the Y6(Fe1−xMnx)23 system☆

Abstract Magnetizations at applied fields up to 120 kOe and electronic specific heats have been determined for ternaries represented by the formula Y 6 (Fe 1− x Mn x ) 23 . The Curie temperature and ordered magnetic moment of Y6Mn 23 and Y 6 Fe 23 decrease sharply when these materials are formed into solid solutions, being minimal in the vicinity of the equimolal solution. To test whether the reduction is a band effect electronic specific heats were measured; they are maximal where T c and the moment are minimal, indicating unimportance of band effects. Curie-Weiss behavior is exhibited at low fields, suggesting rather localized d -electrons. The nearest neighbor distances are such as to lead to antiferromagnetic Mn-Mn interactions. Y 6 Mn 23 is taken to be ferrimagnetic whereas Y 6 Fe 23 appears to be ferromagnetic. While the magnetic structure of the ternaries is yet to be fully clarified, it is clear that antiferromagnetic exchange is enhanced when either binary is formed into a ternary. It also appears that the Mn-Fe coupling is antiferromagnetic in the ternaries.

Magnetic properties of RT3−x′Nix compounds (R=Dy or Ho and T′=Fe or Co)

The effect of varying electron concentration on the magnetic ordering in the ternary intermetallic compounds DyCo3−xNix, DyFe3−xNix, HoCo3−xNix, HoFe3−xNix, with 0<x<3, has been investigated by saturation magnetization studies. The results show a filling of the Co and Fe bands and also a polarization of the 3d band of nickel. In the case of the Co compounds an additional contribution from the induced moment on cobalt by the rare‐earth exchange field is found to be important.

Mössbauer and crystallographic study of DyFe3−x Nix compounds

Mossbauer and crystallographic investigations were carried out on DyFe3−x Nix compounds crystallizing in the PuNi3 type of structure. The hyperfine field observed at the iron sites shows a maximum at x =0.75. The 12‐line spectrum observed at room temperature corresponding to the two different kinds of iron in the structure collapsed into a single six‐line pattern at 4.2 K. Lattice parameter c shows a rapid decrease when x is increased beyond 2.0, but no such behavior was found in the a lattice parameter. The results of the x‐ray and Mossbauer data are explained in terms of site preference and nonlocalized transition‐metal moments, respectively.

Internal Friction in the Tantalum‐Hydrogen System

Internal friction in a series of Ta‐H alloys has been measured over the temperature range −190° to +250°C. Six peaks were observed at mean temperatures of −170°, −83°, 1°, 36°, 54°, and 210°C. The peaks occurring at −170°, −83°, and 1°C are found only in the samples containing greater than 33.3 at. % hydrogen. Both the −83° and the 1°C peaks have an amplitude dependence on the hydrogen concentration, suggesting that they are caused by stress‐induced ordering of hydrogen in Ta2H. The 36° and 54°C peaks are compared with heat capacity data obtained by Saba, Wallace, Sandmo, and Craig and are assigned to the long and short range order of hydrogen in the Ta2H phase. Consideration is given to the effect of hydrogenation on the stress‐induced ordering of interstitial oxygen and the activation energy of the stress‐induced ordering of interstitial hydrogen. This consideration gives rise to the suggestion of both tetrahedral and octahedral locations for the hydrogen atoms in excess of 33.3 at. %.

Heat capacity and thermodynamic functions of theRFe2 compounds (R =Gd, Tb, Dy, Ho, Er, Tm, Lu) over the temperature region 8 to 300 K

Abstract Experimental heat capacity data for the Laves phase R Fe 2 intermetallic compounds ( R =Gd, Tb, Dy, Ho, Er, Tm, and Lu) have been determined over the temperature range 8 to 300 K. The error in these data is thought to be less than 1%. Smoothed heat capacity values and the thermodynamic functions, ( H ° T − H ° 0 ) and S ° T , are reported throughout the temperature range for the R Fe 2 series. In addition, ( G ° 298 − H ° 0 ) at 298 K is reported for all the R Fe 2 compounds. These data were analyzed and it was shown that the maxima in the thermodynamic functions near HoFe 2 are due to the magnetic contribution of the lanthanide element. The lattice contribution to the entropy at 300 K was estimated, and from this quantity the Debye temperature was calculated to be about 300 K, which is in good agreement with the low-temperature heat capacity. Furthermore, this analysis indicates that the apparent electronic specific heat constants, γ′, for TbFe 2 , DyFe 2 , and HoFe 2 , reported earlier, are in error.

Magnetic properties of DyFe3−xCox and HoFe3−xCox*

Abstract Magnetic moments, Curie and compensation temperatures were measured for DyFe 3−x Co x and HoFe 3−x Co x compounds. The variation of transition metal moment has been explained on the basis of the rigid band model.

Heat capacity studies of RFe2 intermetallic compounds over the temperature region 1.5–10 K (R=Gd, Tb, Dy, Ho, Er, Tm and Lu)

The heat capacities of the RFe2 intermetallic compounds (R=Gd, Tb, Dy, Ho, Er, Tm, and Lu) have been measured over the temperature region 1.5–10 K. Values for the apparent electronic heat capacity coefficients have been determined and exhibit a cusp‐like behavior as the R atom is changed across the rare earth series going from Gd to Lu. The maximum is found to occur for HoFe2.

Heat capacity studies of RFe2 intermetallic compounds (R=Ho, Er, and Lu)

Rare earth intermetallic compounds possess crystal field interactions which can be observed as contributions to the heat capacity. This paper reports the results of heat capacity studies of several RFe2 compounds (R=Ho, Er, and Lu). The crystal field contributions to the heat capacities for the Ho and Er ions, determined from the heat capacity data obtained for HoFe2 and ErFe2, have been used in determining the crystal field parameters for these rare earth ions. In our case, for Er3+, B40=1.937×10−3 K and B60 =−1.195×10−5 K; and for Ho3+, B40=−9.40×10−4 K and B60=5.10×10−6 K. These parameters are discussed and compared to those obtained by neutron diffraction and spin reorientation studies.

Hydrogen diffusion and hydride formation at the metal–hydride interface

Synchrotron radiation photoemission has been used to examine interface reaction of overlayers of V and Ca deposited onto clean surfaces of the bulk hydride YH2 and the deuteride NbD0.75. Changes in the hydrogen‐induced bonding bands and the d bands near EF and variations in the intensities of the substrate core level emission as a function of metal coverage indicate that hydrogen diffuses from the substrate into the overlayer. The results are discussed in terms of the mechanism for hydride formation.