J.G. Smith

Ferromagnetism in an intermetallic compound containing palladium, titanium and aluminium

Abstract 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 A. 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.

Investigation of the effect of heat treatment on the magnetism in Pd2MnIn

Abstract An investigation of the effects of heat treatment on the magnetic properties of Pd 2 MnIn is reported. The results are compared to theory in a simplified model employing an RKKY interaction between the Mn atoms.

The discovery of weak metallic ferromagnetism with a high Curie temperature

Abstract A ternary intermetallic compound containing elements which themselves do not order magnetically has been found to have a spontaneous magnetisation. The compound, Pd 2 TiSn, is crystallographically ordered in the L2 1 structure with a lattice parameter of 6.38 A. Magnetisation measurements indicate a ferromagnetically ordered moment per formula unit of σ = 0.005 μ B 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 σ 2 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.

Magnetic phase diagram of Pd2DySn

Abstract Magnetisation and neutron diffraction measurements on Pd 2 DySn reveal that below 9 K a complex magnetic state exists, the details of which depend sensitively on the degree of atomic order. The results are discussed in terms of a crystal field CEF model including both single ion anisotropy and internal field.

The experimental density of states of Pd 4d and Ti 3d in the intermetallic compound

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.

Ultraviolet photoemission studies of the Pd2TiAl Heusler alloy

Abstract The valence band of the ferromagnetic Heusler alloy Pd 2 TiAl 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.

Superweak ferromagnetism in transition metal compounds

Abstract 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.

A photoemission investigation of the valence band electronic structure of and

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.

Magnetic order in ternary intermetallic compounds containing palladium and titanium

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

Magnetisation measurements in U14Au51

Abstract 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.