In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), en...

Compound Copper Chalcogenide Nanocrystals

Co1−xPtx alloys with Pt contents in the range 0.45≤x≤0.9 show sizable perpendicular magnetic anisotropy, 100% perpendicular remanence and coercivities in the range 160 kA/m. Thin films of this material are grown by electron beam evaporation onto fused silica or Si, at substrate temperatures between 150 and 350 °C. Spectroscopic investigations of the polar Kerr rotation show a significant enhancement of the Pt related UV peak. A comparison of the static signal levels R×(θk2+ek2)1/2 of Co/Pt multilayers and alloys shows an overall 50% enhancement in the case of alloys. Curie temperatures around 200 °C are observed for Co∼22Pt∼78 compositions. These properties, together with the potentially high chemical stability and ease of manufacturing make Co1−xPtx alloys very attractive materials for short wavelength magneto‐optic recording.

Magnetic and magneto‐optical properties of cobalt‐platinum alloys with perpendicular magnetic anisotropy

Relationship between Kerr effect and perpendicular magnetic anisotropy in Co1−xPtx and Co1−xPdx alloys

A comprehensive study of magnetic, optical, and magnetooptical properties was carried out for single crystals of the spinel-type A Cr 2 X 4 ( A =Mn, Fe, Co, Cu, Zn, and Cd; X =O, S, and Se). The optical reflectivity measurements for 0.1–30 eV revealed a wide variation in electronic structures on a large energy scale between oxides ( X =O) and chalcogenides ( X =S and Se). For A =Fe and Co, we observed the intra-atomic d – d transitions of A 2+ ions with a tetrahedral coordination, and successfully deduced the crystal field splitting Δ E , the Racah parameter B , and the spin–orbit coupling constant ζ by analysis based on the ligand field theory. A comparison of these optical parameters between oxides and chalcogenides indicated the strong covalency effect in the chalcogenides. In A =Cu, the insulator–metal transition between X =O and Se was clearly demonstrated by optical conductivity spectra. Magnetic properties were discussed in relation to electronic structures. A compound with a small optical gap is t...

Magnetic, Optical, and Magnetooptical Properties of Spinel-Type ACr2X4 (A=Mn, Fe, Co, Cu, Zn, Cd; X=O, S, Se)

Spectroscopy of multilayers for magneto-optic storage

The magneto‐optical polar Kerr effect has been measured on CuCr2Se4 single crystals between 0.55 and 5.0 eV. The single Kerr ellipticity eK reaches −1.19° at 0.96 eV which is (besides PtMnSb with θK=−1.27° at 1.72 eV) the highest value ever observed at room temperature. The figure of merit R1/2(θ2K + e2K)1/2 has a maximum value of 0.84° at 0.88 eV which is as high as in PtMnSb (0.83° at 1.57 eV). This large magneto‐optical Kerr effect is due to the steep plasma edge observed in the reflectivity R. First experiments show that the photon energy at which the plasma edge occurs can be shifted by suitable substitutions in CuCr2Se4.

Large room‐temperature magneto‐optical Kerr effect in CuCr2Se4

Magneto-optical properties of UCo5

Large room-temperature magneto-optical Kerr effect in CuCr2Se4−xBrx (x = 0 and 0.3)

The optical reflectivity between 0.03 and 12.0 eV and the magnetooptical polar Kerr effect between 0.6 and 4.8 eV have been measured on a polycrystalline sample of UFe/sub 10/Si/sub 2/. A maximum Kerr rotation of -0.55 degrees at 0.75 eV, a value comparable to the maximum Kerr rotation of pure Fe, was observed. This Kerr rotation is one of the strongest ever found in a noncubic Fe compound. It is concluded that this material is a candidate for magnetooptical recording. >

W. Reim

Papers

Spectroscopy of multilayers for magneto-optic storage

Large room‐temperature magneto‐optical Kerr effect in CuCr2Se4

Magneto-optical properties of UCo5

Large room-temperature magneto-optical Kerr effect in CuCr2Se4−xBrx (x = 0 and 0.3)

Magneto-optical Kerr effect of UFe/sub 10/Si/sub 2/