The antiferromagnetic structure of the intermetallic compound has been determined from neutron polarimetric measurements and refined by combining these data with integrated intensity measurements. The structure was found to be non-collinear with the U moments confined to the a - b plane. The moments of U atoms in each of the two sets of sixfold sites are arranged hexagonally with rotations of between them and the two sets are rotated with respect to one another by . The third (twofold) set of U atoms has no ordered moment. These conclusions are in disagreement with a previous determination of the structure from powder data which gave a collinear structure with moments parallel to the c axis. Magnetization measurements made on single crystals in the temperature range 300 - 2 K can be understood in terms of a transition to a non-collinear easy plane antiferromagnetic structure stable below 22 K. Polarized neutron measurements have been used to determine the contribution of each of the U sites to the susceptibility between 22 and 2 K. These show that of the two sixfold U sites, that with the smaller ordered moment contributes more than half of the total susceptibility. The twofold site, which is characterized by a small U - U separation, makes the smallest contribution.

The valence bands of the intermetallic compounds and have been investigated by ultraviolet photoemission utilizing synchrotron radiation. The valence bands of both alloys have a width of 7 - 8 eV with a prominent peak at a binding energy of 2.6 eV and a shoulder extending to the Fermi edge. Measurements obtained at the Pd 4d Cooper minimum and at the Ti 3p threshold indicate that the feature at 2.6 eV is largely composed of contributions from Pd 4d states, whereas the Ti 3d states contribute most strongly immediately below the Fermi level. Experimental photoemission spectra show good agreement with theoretical calculations.

Photoemission measurements have been made of the intermetallic compound utilizing synchrotron radiation in the energy range 40 - 180 eV. The valence band extends to a binding energy of 7 eV. Measurements made at the Cooper minimum for Pd 4d indicate that the highest density of states for Ti 3d is at the Fermi edge and that it decreases towards higher energy. Using this density of states and correcting for the photoemission cross-sections with energy, it has been possible to determine the density of states for Pd 4d which also contributes to the Fermi level. Resonance photoemission measurements are consistent with this conclusion and also indicate that the Pd 4d band is not completely full.

In previous polarized neutron inelastic scattering experiments on Fe - Ni alloys [1] a `forbidden' mode was found at the Invar composition. This mode has the same dispersion as the transverse acoustic phonon, but was observed in longitudinal scans in which the momentum transfer was along the () direction. The origin of this mode, which seems to be confined to the Invar composition, is not yet understood. This paper reports the results of an inelastic neutron scattering experiment using high-energy incident neutrons in which the mode has been found, and the wavevector dependence of its energy measured, in the first Brillouin zone. The intensity of the mode is greater in the first zone than in that centred on (200) and since the phonon cross section is minimized at small wavevectors it was concluded that the mechanism giving rise to the excitation is predominantly magnetic in origin. This conclusion receives support from the decrease in intensity of the mode with increasing temperature. On the basis of these results it is postulated that the `forbidden' mode arises from a dynamic modulation of the magnetic moments associated with the compressive strain in the phonon excitations rather than from magnetovibrational scattering. These results together with the earlier polarized neutron measurements, indicating a frequency-dependent moment, are able to account for the anomalous thermal variation of the magnetization.

Magnetisation and susceptibility measurements on intermetallic compounds based on the Heusler composition Pd(2)TiZ where Z is Al, In or Sn are reported.

The valence band of the ferromagnetic Heusler alloy Pd2TiAl has been investigated using synchrotron radiation ultraviolet photoemission spectroscopy. By use of the Cooper minimum for palladium it was found that the Fermi level of the material is dominated by titanium 3d electrons.

A ternary intermetallic compound containing elements which themselves do not order magnetically has been found to have a spontaneous magnetisation. The compound, Pd2TiSn, is crystallographically ordered in the L21 structure with a lattice parameter of 6.38 Å. Magnetisation measurements indicate a ferromagnetically ordered moment per formula unit of σ = 0.005μB which essentially does not change with temperature over the range of 2 to 300 K. Over this temperature range, magnetic hysteresis was observed, confirming the existence of a ferromagnetic state. Arrott plots reveal that the isotherms in the high field region are characterised by straight lines which, over the temperature range investigated, converge approximately to a single point on the σ2 axis. Such behaviour can be accounted for if the coefficients in the free energy expansion giving rise to Arrott plots have a similar temperature dependence. A description of these observations is given in terms of a band model.

Single-crystal magnetisation measurements are reported for the intermetallic compound U14Au51. Two magnetic phase transitions are identified at low temperatures. The results are compared with measurements carried out on powder samples.

Superweak ferromagnetism in transition metal compounds is characterised by the combination of unusually large transition temperatures and small magnetic moments. Using a simple microscopic model it is argued that superweak ferromagnetism is more general phenomenon which characterises the magnetic behaviour of transition metal compounds with the lighter transition elements.

An investigation of the effects of heat treatment on the magnetic properties of Pd2MnIn is reported. The results are compared to theory in a simplified model employing an RKKY interaction between the Mn atoms.

Ferromagnetism has been observed in a ternary intermetallic compound whose constituent elements themselves do not order magnetically. The compound formed at the stoichiometric composition Pd2TiAl has the cubic Heusler L21 structure and a lattice parameter of 6.322 Å. Magnetisation measurements made between 2 and 300 K and in applied fields of up to 5 T indicated a ferromagnetically ordered state. On the basis of these measurements, the saturation magnetic moment per Pd2TiAl formula unit was determined to be (0.21 ± 0.005)μB. Furthermore, the spontaneous magnetisation only decreases by approximately 3% between 2 and 300 K. If a Brillouin variation of the magnetisation is assumed, then a Curie temperature must be at least 900 K. The observed decrease in the magnetisation follows very closely a T2 dependence expected for Stoner behaviour. However, since the spontaneous moment is roughly half that of nickel and the Curie temperature is nearly that of iron, the compound does not fall into the category of a weak itinerant ferromagnet. A model based on a band structure description is put forward to account for the observations.