Electronic structure theory of surface, interface and thin-film magnetism

Pd-Ni alloys are of special interest as a system where a critical composition for the paramagnetic to ferromagnetic transition exists. Interpretation of the magnetization as a function of the field, temperature and concentration for this system is not quite straightforward and previous measurements have not examined the low field behaviour in detail. New data on this system have been obtained and careful analysis with the help of Arrott plots yield Curie temperatures T0 which extrapolate to the same value for the critical concentration as that found previously from the resistivity measurements. Existing susceptibility results for some paramagnetic Pd-Ni alloys appear to conform with this value for the critical concentration and in particular the specific heat data, where disagreement has been cited previously, are reanalysed and shown to be in agreement also with the authors value of 2.3+or-0.05 at% Ni.

https://iopscience.iop.org/article/10.1088/0305-4608/7/11/020/pdf

Critical concentration for the onset of ferromagnetism in Pd-Ni alloys

Magnetism and spatial order in transition metal alloys: Experimental and theoretical aspects

The authors have studied the high field susceptibility of nickel-platinum alloys in fields up to 150 kOe, at temperatures between 4.2 and 300K. The high field susceptibility is analysed in the ferromagnetic and paramagnetic range by means of Arrott plots and Landau coefficients. The paramagnetic initial susceptibility follows a Curie-Weiss law, with a Curie constant independent of nickel concentration. The results are compared with those obtained for palladium-nickel alloys. The experimental data are discussed in the framework of recent theories on itinerant ferromagnetism.

https://iopscience.iop.org/article/10.1088/0305-4608/4/8/021/pdf

Itinerant ferromagnetism and susceptibility of nickel-platinum alloys

Transition metal surfaces are important technologically as good catalysts. Interfaces and superlattices of magnetic transition metals also hold the promise of new device applications. The properties of surfaces and interfaces are determined by the local band structure which is directly related to the magnetisation density. One of the fundamental problems of surface magnetism is, therefore, to determine the ground-state surface perturbation to the magnetisation density. After a somewhat turbulent history, the ground-state surface problem is now well understood. The current status of the theory and detailed results for Fe and Ni surfaces are reviewed in the first part of the article. Experimental methods for magnetic surfaces are also discussed, with particular emphasis on the interpretation of data for Fe and Ni, which is still in some cases controversial. The other two central questions addressed in this review concern the nature of magnetic excitations at surfaces and the way the magnetisation disorders near a surface at finite temperatures.

Magnetism at transition metal surfaces

Neutron-scattering experiments show evidence of long-range magnetic polarization of the palladium matrix in dilute ferromagnetic Pd(Ni) alloys. The measured cross sections, for alloys containing up to 4.7 at.% nickel, are interpreted in terms of a model in which the concentration of ferromagnetically aligned giant moments is less than the concentration of nickel atoms.

Giant Moments in Pd(Ni) Alloys near the Critical Composition

Measurements have been made at 4.2°K of the elastic diffuse scattering of 4.8 A neutrons from ferromagnetic Pd(Ni) alloys containing 3.0, 3.4, 4.7, and 6.3 at.% Ni. The magnetic cross sections, measured with scattering vectors ranging from 0.17 to 1.1 A−1, are all strongly peaked towards the forward direction. The range of polarization of the palladium matrix around a nickel atom deduced from the measurements is independent of nickel concentration up to 4.7 at.% Ni, and is larger than that obtained by Holden and Low1 for dilute Pd(Fe) and Pd(Co) alloys. The cross section per nickel atom extrapolated to the forward direction increases with increasing nickel concentration up to 4.7 at.% Ni, and then drops sharply. For the most dilute alloys the extrapolated forward cross sections are about a factor of 2 less than those calculated from a general expression due to Marshall and Balcar,2 and it is concluded that the effective concentration of aligned polarization distributions is less than the true concentration of nickel atoms. The mean moment of the nickel atom and the matrix polarization per nickel atom were calculated from the measured cross sections and are independent of concentration for the three most dilute alloys, with values of 0.9±0.2 μB and 3.7±1.4 μB respectively.

M. W. Stringfellow

Papers

Giant Moments in Pd(Ni) Alloys near the Critical Composition

Magnetic Moment Distribution in Dilute Alloys of Nickel in Palladium