Spin-polarized low energy electrons from a GaAs source were used to probe magnetized nickel(111) surface. Intensity curves as well as spin-orbit and exchange induced polarization asymmetries were obtained for the $(00)-20\sp\circ, (00)-30\sp\circ,$ $(00)-45\sp\circ, (10)$ and $(-10)$ beams. Comparison with a preliminary theoretical study yields no quantitative information on the magnetic moment per surface atom.

Electron capture spectroscopy (ECS) measures the surface electron spin polarization (ESP) by passing a deuteron ion beam very close to and grazing an atomically flat sample. Polarized electrons that are captured polarize the deuterons by the hyperfine interaction. The polarization of the deuterons is measured by the asymmetry of scattered alpha particles resulting from the nuclear reaction D(T,n)$\alpha$. On the proposed, half-metallic, half-semiconducting, ferromagnetic material, NiMnSb, electron capture spectroscopy measures a surface electron spin polarization (ESP) of +13%, establishing unambiguously that long-range, surface ferromagnetic order exists for this ternary alloy.

There has been a considerable amount of investigation, both theoretical and experimental, of how spin systems behave in magnetic resonance when the applied dc field and the rf oscillating field have comparable amplitudes. A technique called Double Electron Muon Resonance has recently been applied to fused quartz at low frequency enabling us to see directly how the spin precesses in perpendicular dc and rf magnetic fields of comparable strength. The precessional frequency spectra are in excellent agreement with predictions by numerical integration of the equations describing spin precession. Among the effects observed have been harmonic responses, Bloch-Siegert shifts and multi-quantum transitions.

By the use of holographic storage techniques, the conductivity of iron doped lithium niobate has been investigated. The results indicate that the conductivity of the material immediately after hologram formation is much greater than previously suspected. This increased conductivity is shown to be a direct result of the multivalent properties of the iron dopant molecules, and the underlying theory necessary to account for the effect is presented, this theory being an elaboration of the bulk photovoltaic theory of von der Linde and Glass.

Muon-containing defects in insulators and in semiconductors have been studied for several years using the muon spin rotation ((mu)SR) technique. Double electron muon resonance (DEMUR) is an extension to the more common technique. This new double resonance technique can be used to observe EPR transitions of these muonic defects that are not directly observable in normal (mu)SR. This experimental technique has been applied successfully to muonium in quartz. A general theory of the response of two strongly coupled spin 1/2 particles to an intense rf magnetic field, when particularized to muonium in quartz, is found to describe the experimental results in detail.

A source of electron spin polarized He*(2('3)S) metastable atoms is described that provides a thermal energy beam with a flux up to 8 x 10('12) metastables/sec/sterad at a polarization P(,z) (TURN) 50%. The polarization is created by optical pumping and can be simply reversed or modulated without changing the beam trajectory or flux. The source is housed in a system of three differentially pumped vacuum chambers which allows the beam to be used for surface experiments in an ultra high vacuum environment. The polarization is measured with a Stern-Gerlach type analyzer which also serves as a useful diagnostic of beam composition and verifies the purity of the 2('3)S beam. The beam is demonstrated not to contain any significant admixture of 2('1)S metastables, ions, fast neutrals, or photons. Unless care is exercised, however, it is possible to produce a beam of energetic ground state helium which is of much greater intensity than the metastable beam. The conditions under which this occurs are described. A brief overview of metastable deexcitation spectroscopy (MDS) is given and a proposed first experiment involving the investigation of surface magnetism of Ni(110) and the necessary apparatus for this experiment are described.

A two-step matrix formulation is used to analyze the intermediate-coupling problem for an orbital doublet coupled to one doubly-degenerate vibrational mode (a Jahn-Teller doublet). First the linear-coupling problem is formulated in terms of a basis that reduces the effective Hamiltonian to blocks of tridiagonal matrices. The eigenfunctions for the lower states from this first step are then used as a new basis when including nonlinear-coupling and anharmonic terms. The energies are computed and the final eigenfunctions are used to compute reduction factors and polarizability matrix elements among many of the lower-energy states. Linear coupling, nonlinear coupling and anharmonicity are varied independently over a wide range. Even though these calculations are accurate (being equivalent to diagonalizing a matrix of order up to 16,000) and cover the intermediate-coupling region, there are no important deviations from theories using strong-coupling approximations for the lowest energy states which are important in experiment.

The first PLEED measurements of an ordered two component system (Cu(,3)Au(001)) are reported. Using this data an attempt is made to determine the long range order parameter as a function of the crystal temperature. A polarized electron source with an electron spin polarization of 27% and delivering a current of 0.3(mu)A to the crystal surface is described in the first section. This source uses photoemission from negative electron affinity GaAs(001) to produce an electron beam whose polarization can be easily modulated without changing other characteristics of the beam by changing the helicity of the photoemission light. Once operational, the source is used in an attempt to determine the long range order parameter of the (001) face of Cu(,3)Au. Polarization vs. Energy (P-V) curves were taken at room temperature at a number of angles ((theta)) to obtain usable P-V curves for theoretical modeling. Next, P-V curves were measured for the 00 beam at 13 degrees and the 01 beam at normal incidence as a function of temperature. As the crystal was heated through the order-disorder tranition temperature no large change in the P-V curves was noted.

A new method, described herein, has been developed for probing magnetic and other spin-dependent surface properties. The technique utilizes a He 2 ('3)S(,1) beam in which a plurality of atoms is in one m(,J) level. This electron spin polarized beam has been used to probe the surface magnetic properties of a clean and adsorbate-covered Ni (110) crystal. The electrons ejected from the sample when the metastables deexcite depend upon metastable polarization and sample magnetization. By examining the ejected electrons, the sample magnetization has been measured as a function of electron energy, crystal temperature, and adsorbate (CO) coverage. The results demonstrate that He 2 ('3)S(,1) metastables constitute a method for probing surface magnetism with unparalleled surface specificity. In addition to discussing the physics of the metastable/surface interaction and the results obtained, the theoretical background and a perspective of surface spectroscopies are provided in sections on magnetism and other surface spectroscopies.

Muon spin relaxation ((mu)SR) has been used to study the magnetic ordering in PdMn and AgMn dilute alloys representing disordered ferromagnetism, reentrant ferromagnetism, and spin glass order. A theory of static linewidths for both transverse applied field and zero applied field (mu)SR is described for all types of spin order. The temperature dependence of the static linewidth in the spin glass and ferromagnetic phases is consistent with both a mean field theory of disordered magnetism and an inhomogeneous percolation model. Linewidths in paramagnetic AgMn privde the first direct observation of a conduction electron mediated RKKY component to the muon-local moment interaction. In PdMn, muons are excluded from occupying octahedral interstitial sites directly adjacent to Mn impurities. A theory relating muon spin-lattice relaxation to impurity spin correlation times in the paramagnetic and ordered phases is described. All types of magnetic ordering show a rapid slowing down of impurity spin fluctuations just above the ordering temperature. Muon spin-lattice relaxation in both the ferromagnetic and spin glass state is expected to be insensitive to both long wavelength spin waves and to higher frequency localized spin wave-like excitations. The observed spin glass state relaxation is consistent with a phenomenological theory of low-frequency barrier mode excitations.