B.R. Coles

Effects of alloying on Ce heavy fermion compounds

Abstract We report on the electrical resistivity and magnetic susceptibility measurements which have been made to investigate the effects of substitution on the Cu sites in CeCu6 and on the Al sites in CeAl3. These results are compared with effects of alloying on the Ce sites in both materials.

Enhanced moments, resistivity minima and spin-glass character in Gd-doped UAl2

Abstract Susceptibility and resistivity measurements have been made on U1-xGdxAl2 Laves phase alloys with x up to 0.3. For x⩾0.1 susceptibility maxima are found with field cooling effects that suggest spin-glass formation, while the resistivities show minima at temperatures rather higher than those of the susceptibility maxima. Higher temperature Curie-Weiss plots give effective moments significantly larger than 7.9μB of Gd3+. This behaviour is rather similar to that of Pt-Mn alloys and suggests a strong coupling of the Gd 4f moments to spin fluctuations in UAl2.

Onset of ferromagnetism in UCo2-UFe2 alloys

Abstract Results are presented of a study of U(Co1-xFex)2 alloys by susceptibility and resistivity measurements. The critical value of x for ferromagnetism is 0.61. Alloys with smaller x show no local moment or spin glass behaviour.

Conditions for ferromagnetism in cobalt intermetallic compounds

Abstract Attention is drawn to the remarkable contrast between XCo2 and XFe2 Laves phases, none of the Co ones being magnetically ordered when X is non-magnetic. For the Y-Co intermetallic compounds and for superconductive Zr2Co and ferromagnetic Co2TiAl specific heat data are presented. In the light of the low λ value for Y9Co7 both its superconductive and magnetic character are ascribed to structural peculiarities. For other materials the roles of electron transfer and atomic spacing in governing the appearance of ferromagnetism are discussed.

The effects of light and heavy rare-earth elements on magnetic ordering in Sm

Abstract The effect of 5% of Pr, Nd, Gd and Tb on the magnetic ordering temperatures of Sm has been examined by susceptibility and resistivity measurements. Neither transition correlates with the average de Gennes factor. The data for the as cast Gd and Tb alloys reveal the presence of the dhcp structure.

Magnetic ordering in the dhcp, Sm and hcp structures of the Pr-Y alloys

Abstract Measurements of electrical resistivity, low field ac susceptibility and higher field susceptibility have been used to study magnetic ordering in the Pr-Y system, and the magnetic behaviour has been correlated with X-ray diffraction indications of crystal structure. Susceptibility peaks have been observed for all three phases but the magnitudes and concentration dependences of the peak temperatures are distinctly different. In the phase with the Sm structure the peak temperature increases with decreasing Pr content. The effects of field cooling and the behaviour of the resitivity have been used to provide evidence about the character of the magnetic ordering.

ac susceptibility and electrical resistivity of Nd single crystals

Abstract As a contribution to our knowledge of the magnetic phase diagram of Nd measurements have been made of the ac susceptibility, of the effects on it of supersposed dc fields and changes in frequency, and of the electrical resistivity for different directions in single crystals. Only small effects are seen near the upper ordering temperature at 20 K, but a susceptibility maximum is found in all specimens near 8.3 K. Shoulders of various types are seen at lower temperatures. The dc field has its greatest effect on the 20 and 7.1 K shoulders. The c -axis resistivity data show an antiferromagnetic type anomaly at 20 K. In some specimens susceptibility effects are found near 30 K and are probably due to the presence of some fcc material.

Transformation effects, stacking faults and magnetism in the light rare earths

Abstract Speculations about the existence, origin, long-period ordering and implications for magnetism of stacking faults in light rare earth metals and alloys are presented. Some fragmentary evidence for stacking fault effects is indicated.

Low temperature behaviour and spin fluctuations in UPt3 alloys

Abstract Measurements have been made on the effect of Pu substitution on U sites in UPt 3 on the specific heat, and of the resistivity and susceptibility of ThPt 3 alloys containing small substitutions of U on the Th sites. In the latter system the aim was to look for typical dilute Kondo behaviour.

Magnetic hysteresis above the curie temperature in imperfect weak ferromagnets

Abstract In the intermetallic compound Y 9 Co 7 the hysteresis and magnetic remanence at 4.2 K decrease with increasing metallurgical quality, but still persist even in single-phase samples which are non-ferromagnetic by Arrott plot criteria down to ≈ 3 K; at lower temperatures they become superconducting. Evidence is produced for some type of spin-glass freezing above 8 K. An as-cast Pd-0.3% Co alloy shows related behaviour which is removed by annealing. The conditions for spin-glass freezing before long-range ferromagnetism sets in are discussed and other possible candidates for this behaviour are examined.