P.G. van Engen

Magneto-optical properties of metallic ferromagnetic materials

Abstract The authors have studied the magneto-optical Kerr rotation in more than 200 metallic systems comprising alloys as well as intermetallic compounds of 3d transition metals. For all these materials the crystal structure, the lattice constants, the room temperature magnetization and the room temperature Kerr rotation at two different wavelengths are specified. For several series of ternary compounds, comprising Heusler alloys Ni2 In-type compounds and Cr23C6 type compounds, we determined the saturation moment at 4.2 K. For a number of representative alloys or compounds a study was also made of the wavelength dependence of the complex polar Kerr effect. The values of the Kerr rotation obtained at 633 nm were compared with the corresponding values of the measured magnetization. Systematic trends were observed and have been used to classify metallic systems into systems where the Kerr rotation will not reach values much in excess of 1° and systems where higher values are likely to be found.

Magnetic and magneto-optical properties of heusler alloys based on aluminium and gallium

Abstract The authors have studied a number of alloys of the type X 2 YZ, where X represents a 3d transition metal (or Cu), Y a second 3d transition metal or one of the elements La, Th, Zr, Hf, Ta, Nb, W or Mo, and Z either Al or Ga. It was found that only a limited number of these combinations leads to the cubic L2 1 Heusler-type compounds. The lattice constants of these compounds were determined. The formation of the Heusler L2 1 -type phase was compared with model predictions. A study to the magnetic properties and the room temperature Kerr rotation of the L2 1 -type Heusler compounds showed that there is hardly any correlation between the Kerr rotation in the ferromagnetic Heusler alloys and the corresponding magnetization. In the Co 2 YAl and Co 2 YGa series the moment per Co atom and the electronegativity difference between Co and the Y component showed a linear dependence.

PtMnSb, a material with very high magneto‐optical Kerr effect

Results are reported of polar magneto‐optical Kerr effect measurements performed at room temperature on the Heusler alloy PtMnSb in the wavelength range 280–2000 nm. The double Kerr rotation has a maximum in excess of 2.5° at 720 nm, which is to our knowledge the highest room‐temperature Kerr rotation reported thus far for any material in the wavelength range under consideration. In order to assess the influence of composition the related materials PdMnSb, NiMnSb, and PtMnSn were also investigated. Here the Kerr effect was considerably lower.

Half-metallic ferromagnets and their magneto-optical properties

We have calculated the electronic structure of PtMnSb in order to explain the very high magneto‐optical Kerr effect (over 2.5° at 720 nm at room‐temperature) of this compound. It is shown that this behavior is related to the unusual electronic properties of PtMnSb: it is a half‐metallic ferromagnet like NiMnSb. The extreme asymmetry in the electronic structure of these compounds—metallic behavior for one spin direction and at the same time semiconducting behavior for the other spin direction—is responsible for the unusual magneto‐optical properties.

Magnetic properties and magneto-optical spectroscopy of Heusler alloys based on transition metals and Sn

Abstract The formation and magnetic properties of Heusler compounds of the general formula X 2 YSn were studied, where X represents a 3d transition metal or Cu and where Y represents a second 3d transition metal or a metal of group IV A, VA and VI A of the periodic table. The lattice constant was determined for all Heusler compounds studied. The Co moment in the Co 2 YSn compounds was not found to scale in a sample manner to the electronegativity difference E φ * between Co and the Y components as was previously observed in the series Co 2 YAl and Co 2 YGa. All compounds of the type Ni 2 YSn were found to be Pauli paramagnetic when Y is non-magnetic metal. Compounds having a Curie temperature above room temperature were investigated by means of magneto-optical polar Kerr-effect spectroscopy. Experimental indications were obtained for charge transfer transitions in the series Co 2 TiSn, Co 2 HfSn.

Magnetic and Crystallographic Properties of Several C1b Type Heusler Compounds

Abstract The compounds NiMnSb and IrMnGa were studied by neutron diffraction. The former compound has the cubic Cl b crystal structure with an ideal site occupancy of the atoms. Below 750 K the compound is ferromagnetically ordered. The magnetic moments are confined to the Mn atoms (4.0μ B /Mn). The compound IrMnGa has a crystal structure related to the C1 b type but characterized by a high atomic disorder. Results of magnetic measurements are presented for NiMnSb, CuMnSb and IrMnGa. The results of these measurements are in accord with the occurrence of high atomic ordering in the first two compounds but point to high atomic disorder in the latter material. Total energies and Mn moments derived from band-structure calculations are presented for three different types of site occupancies in NiMnSb. The lowest total energy as well as the correct value for the Mn moment correspond to the site occupancy found by means of the neutron diffraction.

Magnetic and magneto‐optical properties of amorphous A1−xFex alloys (A = B, Ge, and Sn)

Amorphous alloys of the type A1−xFex, where A represents B, Ge, or Sn, were prepared by two‐source coevaporation in the ranges 0.3⩽x⩽0.9, 0.30⩽x⩽0.65, and 0.45⩽x⩽0.64. The magneto‐optical properties of these alloys were examined by means of the polar Kerr effect. The magnetic properties of the alloys with B and Ge were also studied. The concentration dependence of the Fe moments in the Fe metalloid alloys is analyzed in terms of a model in which due account is taken of the fact that the variation of the heat of alloying in the various iron metalloid alloys entails a variable degree of intrinsic compositional short‐range order.

Optical properties of some half-metallic ferromagnets

The authors report ellipsometry measurements on polycrystalline samples of NiMnSb and PtMnSb at room temperature under ultra-high vacuum conditions. From these measurements the optical constants of the two materials were determined in the energy range 0.5-5.3 eV. The measured optical conductivities are in reasonable agreement with the optical conductivities calculated from the band structures by de Groot (1983). The band gap for the minority-spin direction is clearly observed and can be brought into agreement with the band-structure calculations by consideration of spin-orbit splitting.

Magnetic and magneto-optical properties of amorphous boron-cobalt and silicon-cobalt alloys

Abstract Amorphous alloys of the type B 1−x Co x and Si 1−x Co x were prepared by vapour deposition. Their magnetic properties were determined in the range 4.2 - 300 K. The polar Kerr rotation was measured at two wavelengths ( λ = 633 nm and 830 nm) at room temperature. The magnetic properties of these alloys were compared with amorphous alloys in which Co is combined with Sn, P, Mg, Y, La or Zr. The magnetic properties were analysed in terms of a model in which proper account is taken of possible differences in chemical short-range ordering of the atoms.

Mode degeneracy in magnetic garnet optical waveguides with high Faraday rotation

TE‐TM mode conversion was studied in LPE‐grown garnet films with high Faraday rotation (up to 1800 °/cm at 1.15‐μm wavelength) and positive uniaxial anisotropy. High conversion ratios (80–90%) were found for several modes. The phase matching is satisfactorily explained by the birefringence in the film resulting from the misfit stress.