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The temperature dependences of DC and AC magnetisation, electrical resistivity and magnetoresistivity of TbCu4Ag and DyCu4Ag are reported. In contrast to previous studies which indicate TbCu4Ag to be a simple antiferromagnet and DyCu4Ag to be a ferromagnet, our study indicates a more complicated behaviour for these materials. We observe three magnetic transitions for TbCu4Ag, viz. at TC=20 K, T1=11 K and T2=2.5 K. At temperatures T⩽ 10 K the magnetic isotherms show metamagnetic behaviour, while for T1⩽T⩽TC our results suggest canted antiferromagnetism. For DyCu4Ag magnetic transitions are observed at TC=19 K and in the vicinity of 5 K. Also for this material there is evidence suggesting a canted antiferromagnetic spin structure.

Electrical resistivity results of Ce ( Pt 1 - x Ni x ) Ga and CePt ( Ga 1 - y Al y ) alloys show features at low temperature indicating antiferromagnetic ordering and Kondo behaviour. The variation of Neel temperature with alloy composition is interpreted in terms of a Doniach diagram and the possible existence of a quantum critical point is indicated. Magnetoresistance data are presented and analysed in terms of the Schlottmann formalism.

We have analyzed the temperature dependence of the ac susceptibility, χ ac ( T ), of UCu x Ge y samples (0.800 ≤ x , y ≤ 1.00) applying various frequencies and magnetic field strengths up to 1 T. This was done in order to verify the reentrant ferromagnetic behaviour of UCu x Ge and the antiferromagnetic behaviour of UCuGe y previously observed by dc susceptibility experiments. Our χ ac results are discussed on the basis of existing theories.

Bulk magnetization measurements and elastic neutron scattering have been used to determine the critical exponents β, γ and δ for single-crystal USe. The magnetization behavior in the ferromagnetic region is significantly influenced by anisotropy. An anomalously low value of β = 0.246±0.010 is observed and this is discussed in terms of an axial next-nearest-neighbor Ising model.

Magnetic susceptibility X(T), electrical resistivity ρ(T) and magnetoresistivity of CePt 2 (Si 1-x Ge x ) 2 alloys (0 ≤ x < 1) are reported. For X(T) of these, the Curie-Weiss relationship is followed with effective moments in close agreement with μ eff = 2.54 μ B expected for Ce 3+ . A maximum in ρ(T) is observed at a temperature T max ∼ T K ∼ exp(-1/|JN(E F )|). From the decrease in T max with increasing x it is deduced that |JN(E F )| x=0 = 0.11 ± 0.02.

Magnetoresistivity (MR) isotherm measurements of CeCu 5 In 0.6 Al 0.4 and CeCu 5 In 0.6 Ga 0.4 alloys down to low temperatures in fields up to 8 T are presented. A negative MR and single-ion Kondo-like behavior is observed at all temperatures. The results are analyzed on the basis of calculations by Andrei and Schlottmann for the Bethe-ansatz solution in the context of the Coqblin-Schrieffer model. The analyses yield Kondo temperatures of T K = 10 ± 2 K and 20 ± 2 K and effective moments for the Kondo ion of μ K = 0.062 ± 0.006 μ B and 0.107 ± 0.008 μ B , respectively, for the CeCu 5 In 0.6 Al 0.4 and CeCu 5 In 0.6 Ga 0.4 alloys. The scaling of the data with the Bethe-ansatz formulation of the single-ion MR is presented.

Previous studies of Ce 8 Pd 24 M compounds are extended to magnetic susceptibility and electrical resistivity measurements for a series of Ce 8 Pd 24 M x alloys (0.1⩽ x ⩽2, M=Al, Ga, Ge). A rich variety of behaviours is observed by varying x , viz. intermediate valence, coherent and incoherent Kondo, antiferromagnetic ordering and spin-glass characteristics.

The results of measurements of the electrical resistivity ( ρ ), specific heat ( C ), and magnetic susceptibility ( χ ) are reported for compounds near the ferromagnetic transition in the CePd 1− x Ni x system. The magnetoresistance is large and positive at low temperatures. The zero-field non-Fermi-liquid characteristics of ρ ( T ) and of C ( T ) are shown to be modified in an applied field.

The zero-field resistivity of Ce x La 1− x Pd 2 Al 3 alloys (0.1⩽ x ⩽0.4) is of single-ion character and for 1.4⩽ T ⩽4 K it follows a non-Fermi-liquid ρ 4f = ρ 0 − bT dependence. Application of a field results in a breakdown of single-ion behaviour and in maxima occurring in isofield resistivity curves. Magnetoresistivity data for T ⩾13 K follow the single-ion Schlottmann description and leads to a Kondo temperature T K =23(1) K .

Negative magnetoresistance is observed for Ce x Nd 1− x Cu 6 ( x = 0.85, 0.6, 0.4) at low temperatures and analysed following calculations by Andrei and Schlottmann for the Bethe-ansatz solution of the Coqblin-Schrieffer Hamiltonian.

Resistivity, magnetoresistivity and susceptibility are reported for UCu 5 − x Pd x . A linear temperature dependence of the resistivity and a logarithmic divergence of the susceptibility are observed at low temperatures.

We present an experimental study of the tetragonal heavy-fermion materials CeT 2 Sn 2 (T  Ni, Cu), CeNi 2 Sb 2 and CeCu 1.3 Sb 2 . Their large low-temperature specific heat partly results from a small crystalline electric field splitting, which decreases in the CeT 2 X 2 (X  Si, Ge, Sn, Sb) series with increasing size of the X-atom.

Results of neutron diffraction measurements on single-crystal U 3 As 4 are reported. The exponent β describing critical scaling of the spontaneous magnetization close to the ferromagnetic phase transition is determined to have a value of β = 0.49, which is close to the mean-field model value.

The elastic constant C 33 and attenuation α 33 of Ho measured in b -axis directed applied fields indicate marked anomalies which correlated with the temperature extent of the lock-in at wave vector τ = 5 18 c ∗ as observed with neutron diffraction. A phase diagram is presented.

Thermal strains for both b and c axes are reported for a hep Ho0.67Tb0.33 single crystal between 300 and 4 K. indicating the effect of both helical and ferromagnetic ordering.

The magnetic field dependence of the shear ultrasonic properties c 44 and α 44 in applied fields along principal axes of a high purity holmium single crystal are reported for temperatures in the proximity of the 98 K zero field anomalies.

Magnetization isotherms measured with the field along the b -axis of a Ho 0.67 Tb 0.33 single-crystal indicate the transition from the helical to a ferromagnetic configuration at a critical field H c . The temperature dependence of H c is given and hysteresis between the results of increasing and decreasing fields indicated.

Neutron scattering has revealed that the magnetic response in many actinide rock-salt structure compounds forms a broad continuum that extends to frequencies much higher than kT 0 , where T 0 is the ordering temperature. In ferromagnetic uranium sulphide the continuum extends to 17 THz. Consistent with evidence from resonant photoemission, the neutron inelastic scattering and moment suppression suggest the presence of f-d fluctuations that are a function of interatomic spacing. Thus for compounds with large lattice constants such as UTe and USb the characteristic frequency of the f-d spin fluctuations decreases so as to allow collective spin-wave excitations to appear.

The broad peak and jumps that occur in the isofield magnetization curves of US single crystals when these are heated after first being thermally demagnetized by cooling from above T c to low temperatures, are investigated. The jumps (two for the [110] direction, one for the [111] direction and none for the [001] direction) are correlated with the same behaviour in the initial magnetization curves and interpreted as due to the nucleation and growth of 70, 109 and 180° domains. The crystals also exhibit a high coercivity (∼ 1000 Oe) and remanent magnetization of up to 92% along the [001] direction at 4 K. This enabled us to study the peak and step behaviour also by premagnetization experiments.

Neutron measurements of the order parameter near the planar helical ↔ paramagnetic transition of dysprosium and terbium are reported. For Dy a critical exponent β = 0.39 (+0.04, -0.02) is obtained in agreement with the expectation from a renormalization group calculation of β − 0.39 for a n = 4-component model. For Tb, due to factors discussed in the text, no definitive conclusions about the value of β can be made.

The temperature and field dependences of the magnitization of ferromagnetic single crystal US along its easy 〈111〉 axis and hard 〈110〉 and 〈100〉 axes are reported. A considerable anisotropy is observed. The behaviour near the Curie temperature is described in terms of the Belov method of thermodynamic coefficients, as well as in terms of critical exponents. The temperature dependence of the spontaneous magnetization is investigated.

It is shown for ferromagnetic US that an extremely large anisotropy restrains magnetic moments to 〈111〉 easy axes, resulting in a near cos θ angular dependence of the magnetization away from the 〈111〉 axes. This is further confirmed by torque measurements, which in addition show large hysteresis effects upon rotation through the hard axes. It is illustrated through torque and magnetization measurements that a near stable domain configuration can be established by field rotation through decreasing angular amplitude around a hard 〈001〉 direction. The anisotropy constant K 1 ( T ) is estimated by computing the small angle through which the magnetization deviates from the 〈111〉 axes when a field is applied along the [001] direction.

A localized model has been developed for the ferromagnetic uranium chalcogenides that describes their static and dynamic magnetic properties. The model describes the Curie-Weiss temperature, the effective paramagnetic moment, the ordered moment, the low temperature structural distortion and the temperature dependence of the C 44 elastic constant, as well as the dynamical susceptibility.

A simultaneous measurement of the sublattice magnetization of helical ordered Dy with neutrons and of the C 11 , C 33 and C 44 elastic constants, indicate a Neel temperature of (177.3±0.2) K. This value is not noticeably changed by repeated cycling of the specimen through T N , in contrast to a previous observation of a large change in T N for a Dy crystal (Palmer and Greenough, 1976).