Spin-dependent Momentum Density Research Articles

Magnetic Compton scattering study of the magnetocaloric materialGd7Pd3

The spin-dependent momentum density ofGd7Pd3 was probed by the magnetic Compton scattering technique with ellipticallypolarized synchrotron radiation. A contribution to the spin moment from Pd 4delectrons was observed, at 2 and 280 K, alongside a large Gd 4f moment and asmaller Gd 5d moment. The total spin moment, at 2 K, was determined as50.8 ± 0.7 μB (f.u.)−1. The Gd 4f contribution to the spin moment was determined as43.4 ± 1.8 μB (f.u.)−1, the Gd 5dmoment as 4.4 ± 0.7 μB (f.u.)−1 and the Pd 4d spin moment contribution as2.9 ± 1.1 μB (f.u.)−1, where f.u. represents a formula unit. At 280 K the total spin moment was27.3 ± 0.9 μB (f.u.)−1 with individual contributions determined as a Gd 4f spin moment of23.8 ± 1.1 μB (f.u.)−1, a Gd 5d contributionof 2.2 ± 0.5 μB (f.u.)−1 and a Pd 5dspin moment of 1.2 ± 0.6 μB (f.u.)−1.

Spin dependent momentum density and Fermi surface of ferromagnetic Ni obtained by positron annihilation experiments

AbstractThe cover picture of this issue, taken from [1], shows a cross section of the Fermi surface in the basal plane of nickel. The measurements were carried out using 2D angular correlation of annihilation radiation (ACAR) experiments. The intersecting plane is normal to the c‐axis, passing through the Γ and X points. The light regions correspond to a high electron momentum density. The Fermi surface is presented as two hole surfaces around the Γ point and two electron surfaces around the X point.

Spin dependent momentum density and Fermi surface of ferromagnetic Ni obtained by positron annihilation experiments

AbstractThe spin‐dependent momentum density and Fermi surface of ferromagnetic Ni have been obtained through positron annihilation experiments. The measurements were carried out through 2D angular correlation of annihilation radiation (ACAR) using longitudinally polarized positrons. The magnetic field direction was reversed in order to study the effect of the spin‐dependent positron–electron momentum space density on the Fermi surface of Ni. The results showed that ferromagnetic Ni had different Fermi surfaces for the majority‐spin and minority‐spin states. The differences due to the spin‐states were studied in the momentum space and in the wave vector space. In general, the experimental results showed good agreement with previous theoretical calculations. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spin density in Gd studied by magnetic Compton scattering

The spin-dependent momentum density of single-crystal ferromagnetic gadolinium was probed by the magnetic Compton profile technique. Comparison with electronic structure calculations indicate that the local spin-density approximation is adequate for describing the magnetic Compton profiles. Furthermore, the linear combination of muffin-tin orbitals prescription compared favourably with a full-potential method. We find that testing theory against the experimental density of states is problematic. Our calculations also indicate that the spin density is sensitive to the treatment of the 5p electrons.

Spin density in ferromagnetic nickel: a magnetic Compton scattering study

The magnetic Compton profiles (MCPs) measured in the [100], [110], [111] and [112] directions in single-crystal nickel with an incident photon beam of energy 224 keV are presented and discussed. The momentum resolution achieved, of 0.43 atomic units, improves on previous studies by almost a factor of two, and facilitates the interpretation of the MCPs in terms of the underlying spin-dependent momentum densities. Calculations have been performed using the linear muffin-tin orbital method, within both the local spin-density approximation (LSDA) and the generalized gradient approximation (GGA). Comparison with experiment reveals the limitations of the LSDA at low momentum, where the GGA is better able to reproduce the contribution of the s- and p-like electrons. All of the calculations overestimate the moment associated with the d-like electrons, for momenta corresponding to the first Brillouin zone. We also confirm the existence of the so-called Umklapp shoulders, which derive from the Fermi surface topology.

Magnetic Compton profile of nickel

Spin-dependent momentum densities in ferromagnetic nickel have been calculated by using the self-consistent spin-polarized linear combination of Gaussian orbitals (LCGO) method. The resulting magnetic Compton profiles have been compared with the recently measured experimental profiles reported by Timms et al. (1990). The LCGO magnetic profile along (111) direction disagrees with the experimental profile near the origin (pz=0), in that the central dip seen in the experimental profile is not reproduced, a feature shared by APW profile. It is argued that the overestimation of the profiles near the origin is mainly due to electron-electron correlation effects inadequately treated in the local-density approximation.

Positron-annihilation study of the half-metallic ferromagnet NiMnSb: Theory.

Calculations of the electronic structure, the Fermi surface, and the momentum density of annihilation photon pairs are presented in preparation for an experimental study of the half-metallic ferromagnet NiMnSb with the aid of the two-dimensional angular correlation of annihilation radiation technique. The band structure obtained is in good agreement with former calculations and consists of a metallic majority-spin and a semiconducting minority-spin band. The majority-spin Fermi surface consists of three \ensuremath{\Gamma}-centered hole sheets, two of which have necks at L. The different nature of the bands is clearly reflected in the spin-dependent momentum densities. From these densities a magnetic difference effect in the angular correlation can be derived which should be clearly observable with polarized positrons.

Spin polarized positron annihilation in nickel

The two photon angular correlation of the positron annihilation radiation (ACPAR) has been studied in nickel, using polarized positrons and two-dimensional detectors (2-D). The relative spin dependent momentum density distribution in the (110) plane obtained from the measurements in two opposite directions of the magnetic field is compared with that obtained from a ferromagnetic LMTO band structure calculation.