A superconducting point contact is used to determine the spin polarization at the Fermi energy of several metals. Because the process of supercurrent conversion at a superconductor-metal interface (Andreev reflection) is limited by the minority spin population near the Fermi surface, the differential conductance of the point contact can reveal the spin polarization of the metal. This technique has been applied to a variety of metals where the spin polarization ranges from 35 to 90 percent: Ni0.8Fe0.2, Ni, Co, Fe, NiMnSb, La0.7Sr0.3MnO3, and CrO2.

We have developed a simple method to measure the transport spin polarization of ferromagnetic materials. This technique relies on the fact that the Andreev reflection process at the interface between a superconductive and normal is influenced by the spin polarization P of the normal metal. In a very short time we have been able to measure the spin polarization of several metals: NixFe1−x, Ni, Co, Fe, NiMnSb, La0.7Sr0.3MnO3, and CrO2, whose spin polarization ranges from 35% to 90%. Our results compare well with other methods for measuring P.

Direct measurement of the conduction electron spin polarization ͑P͒ in epitaxial NiMnSb was performed to test the prediction of half metallicity in this material. Spin-polarized tunneling in NiMnSb/Al 2 O 3 /Al junctions showed P of 28%, contrary to the predicted value of 100%. Magnetoresistance measurements in NiMnSb/Al 2 O 3 /Ni 80 Fe 20 junctions concurred with this result. The discrepancy between theory and experiment is discussed. Also, the latter junctions show four nonvolatile remanent states due to the NiMnSb magnetocrystalline anisotropy, which has potential as four-level logic elements.

No abstract

No abstract

Ferromagnet-insulator-ferromagnet tunnel junctions with one NiMnSb electrode were studied to test the 100% conduction electron spin polarization predicted from band structure calculations performed on this compound. This phenomenon, known as half-metallic ferromagnetism (HMF), should result in significantly larger junction magnetoresistance (JMR) than in junctions using only conventional ferromagnetic materials such as Ni, Co, and Fe alloys which show JMR of up to 32%. Analysis by x-ray diffraction, Rutherford back scattering, SQUID, AFM, and STM confirm that the NiMnSb has the desired physical properties. A maximum JMR of 8.1% was observed in NiMnSb/Al2O3/Ni0.8Fe0.2 junctions at 77 K and 5.7% for NiMnSb/Al2O3/Co0.5Fe0.5. Maximum JMR for these two types of junctions at room temperature was 2.4% and 3.7%, respectively. The JMR observed is much lower than that expected for an HMF-I-FM junction. This could be due to scattering of the spins at the FM-I interfaces resulting from surface degradation of the NiMnSb, since the film growth requires deposition at elevated temperatures of >400 °C.

We demonstrate a Monte Carlo algorithm for efficiently simulating ferrofluids. By identifying particle clusters and evolving them as single units, we reduce correlation times by more than two orders of magnitude. This method enables accurate calculations of ferrofluid thermodynamics in the limit of strong magnetic coupling that would be impossible by conventional means. We apply the method to study magnetic anisotropy in dilute thin films. ͓S1063-651X͑99͒05702-5͔

The diagonal component xx and off-diagonal component xy of the complex dielectric tensor for the ferromagnetic compound NiMnSb are determined using ex situ spectroscopic ellipsometry and magneto-optic analysis over the spectral range from 0.7 to 6.2 eV. The effects of the overcoat on the raw data are removed by the analysis. First, the complex xx of thin-film NiMnSb were determined by ex situ spectroscopic ellipsometry; then xy was determined by analyzing Kerr rotation and ellipticity data using the determined xy data. Lorentz oscillators were used to model peaks seen in the xx spectra. The diagonal dielectric component xx is dominated by free-carrier effects below 1.15 eV, and dominated by interband transitions above 2.0 eV. The center energies of the Lorentz oscillators are consistent with the calculated band structure and minority-spin optical conductivity of NiMnSb. Joint density of states and optical conductivity calculated from xx (2) data with free-carrier effects removed shows onset energies at ϳ0.6 and ϳ0.2 eV, respectively. From a study of the xx and xy spectra, the Kerr rotation peak at lower energy is determined to be due to combined contributions from: ͑1͒ a crossover between the free-carrier effect and interband transitions, and ͑2͒ transitions involving spin-orbit coupling. The high-Kerr rotation peaks at higher energies result exclusively from transitions involving spin-orbit coupling. ͓S0163-1829͑99͒13615-4͔