Review/Synthèse: Triangular antiferromagnets

Misfit layer compounds : Structures and physical properties

The charge-ordering states with lattice distortions of a halogen-bridged binuclear-metal mixed-valence complex (called MMX chain), Pt2(dta)4I (dta = CH3CS2-), have been investigated by transport, magnetic, and optical measurements. This complex is a binuclear unit-assembled conductor containing metal−metal bonds. It exhibits metallic conduction above room temperature, representing the first example of a metallic halogen-bridged one-dimensional transition-metal complex. Below 300 K it shows semiconducting behavior, which is considered to be of the Mott−Hubbard type due to electron correlation. The metal−semiconductor transition at 300 K (= TM-S) is derived from a valence transition of Pt from an averaged-valence state of 2.5+ to a trapped-valence state of 2+ and 3+. The charge-ordering modes are considered to be −IPt2+−Pt3+−IPt2+−Pt3+−IPt2+−Pt3+−IPt2+−Pt3+−I for the semiconducting phase below TM-S and −I−Pt2.5+−Pt2.5+−I−Pt2.5+−Pt2.5+−I−Pt2.5+−Pt2.5+−I−Pt2.5+−Pt2.5+−I− for the metallic phase above TM-S. 129...

Charge Ordering with Lattice Distortions in a Conductive MMX-Chain Complex, Pt2(dta)4I (dta = CH3CS2-)

We describe a systematic study of the hydrothermal synthesis of rare-earth orthochromites, RCrO3 (R = La, Pr, Sm, Gd, Dy, Ho, Yb, and Lu) and YCrO3. All nine of these materials can be prepared in a single step by hydrothermal treatment of an amorphous mixed-metal hydroxide at temperatures above 300 °C upon heating around 24 h, with no post-synthesis annealing needed. The as-made materials are highly crystalline powders with submicrometer particle size. In the case of LaCrO3 the addition of solution additives to the hydrothermal synthesis allows some modification of crystallite form of the material, and in the presence of sodium dodecylsulfate nanocrystalline powders are produced. Profile refinement of powder X-ray diffraction (XRD) data show that each of the RCrO3 materials adopts an orthorhombic distorted (Pbmn) perovskite structure. Detailed, magnetization studies as a function of temperature reveal the high quality of the specimens, with low temperature antiferromagnetic behavior seen by direct current...

Direct Hydrothermal Synthesis and Physical Properties of Rare-Earth and Yttrium Orthochromite Perovskites

Over the past two decades, fiber laser technologies have matured to such an extent that they have captured a large portion of the commercial laser marketplace. Yet, there still is a seemingly unquenchable thirst for ever greater optical power to levels where certain deleterious light-matter interactions that limit continued power scaling become significant. In the past decade or so, the industry has focused mainly on waveguide engineering to overcome many of these hurdles. However, there is an emerging body of work emphasizing the enabling role of the material. In an effort to underpin these developments, this paper reviews the relevance of the material in high power fiber laser technologies. As the durable material-of-choice for the application, the discussion will mainly be limited to silicate host glasses. The discussion presented herein follows an outward path, starting with the trivalent rare earth ions and their spectroscopic properties. The ion then is placed into a host, whose impact on the spectroscopy is reviewed. Finally, adverse interactions between the laser lightwave and the host are discussed, and novel composition glass fiber design and fabrication methodologies are presented. With deference to the symbiosis required between material and waveguide engineering in active fiber development, this review will emphasize the former. Specifically, where appropriate, materials-based paths to the enhancement of laser performance will be underscored.

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Materials for optical fiber lasers: A review

The intervalence charge-transfer absorption spectra in the mixed-valence complexes [Pt(en) 2 ][PtI 2 (en) 2 ](SO 4 ) 2 ·6H 2 O and [Au x Pt 1- x I(en) 2 ]SO 4 ·3H 2 O ( x =0.03) have been investigated at 4.2 K. In these complexes, below the charge-transfer absorption edge, a weak absorption band ( A -band) has been observed for the light polarized parallel to the chain axis. When these complexes were irradiated with the light in the region of the charge-transfer transition from Pt II to Pt IV , the absorption coefficient of the A -band increased remarkably, which implies that the A -band is a photo-induced absorption band. The photo-induced effect for the A -band in [Au x Pt 1- x I(en) 2 ]SO 4 ·3H 2 O ( x =0.03) is more intense than that in [Pt(en) 2 ][PtI 2 (en) 2 ](SO 4 ) 2 ·6H 2 O. The A -band suggests the existence of new excitations such as a soliton-like excitation in the electronic state of the platinum chains.

Photo-Induced Absorption Band in One-Dimensional Halogen-Bridged Mixed-Valence Platinum Complex: [Pt(en)2][PtI2(en)2](SO4)2·6H2O and its Au-Doped Complex: [AuxPt1-xI(en)2]SO4·3H2O

Raman scattering and infrared reflection spectra of misfit layer compounds MNbS3 (M=Sn, Pb, La, Ce) have been measured to study the interlayer interaction and the charge transfer from the MS layer to the NbS2 layer. Analysis of the Raman spectra indicates that the interlayer interaction is considerably stronger for the La and Ce compounds than for the Sn and Pb compounds, which may be related to the difference in the amount of the charge transfer.

https://iopscience.iop.org/article/10.7567/JJAPS.32S3.581/pdf

Raman and Infrared Spectra of Misfit Layer Compounds MNbS3 (M=Sn, Pb, La, Ce)

The magnetic susceptibilities and magnetizations of incommensurate layer compounds (CeS) 1.2 NbS 2 and (CeS) 0.6 NbS 2 are reported. The magnetic susceptibilities in the paramagnetic region of the above two compounds are analyzed taking account of the crystal field acting on Ce 3+ and the molecular field. The crystal field splitting of 2 F 5/2 multiplet (Ce 3+ ) is estimated at ca. 500 K. The large splitting suggests that the screening of the crystal field by conduction electrons is weak in the CeS layer. The compound (CeS) 1.2 NbS 2 orders antiferromagnetically near 3 K accompanied by a weak-ferromagnetic moment, while a magnetic ordering with a spontaneous magnetization is observed near 3 K in (CeS) 0.6 NbS 2 . Both the two compounds display a metamagnetic transition at 2.3 kOe ( T =2.0 K). Possible magnetic structures are discussed in terms of ferromagnetic CeS layers.

Magnetic Properties of Incommensurate Layer Compounds, (CeS)1.2NbS2 and (CeS)0.6NbS2

Synthesis, transport and magnetic properties of a new ternary system Ce-Ta-S have been investigated. (CeS) 0.6 TaS 2 and (CeS) 1.2 TaS 2 order antiferromagnetically with Neel temperatures of 2.3 K and 2.7 K, respectively. In the former compound, a diverging anomaly in the susceptibility at T N , a small spontaneous magnetization below T N and a magnetic phase transition at 2.5 kOe are observed. From these results, (CeS) 0.6 TaS 2 is supposed to be a quasi-2D antiferromagnet with a weak ferromagnetism composed of ferromagnetic layers. The fractional superconductivity is observed with the magnetic ordering. Ce 4 f electrons are well localized and the correlation between Ce 4 f and conduction electrons is weak in these compounds.

Magnetic and Transport Properties of Ce-Ta-S Ternary System

Incommensurate layer compounds (RES) x NbS 2 are a new class of the intercalation compounds of NbS 2 ; the x =1.2 and the x =0.6 compound have a stage-1 and a stage-2 structure, respectively. The results of the resistivity and the Seebeck coefficient measurements for several of them and the Pauli paramagnetic susceptibility of (LaS) 1.2 NbS 2 are well interpreted with the rigid-band model by incorporating a large charge transfer from the intercalate RES layer to the host NbS 2 layer. Large residual resistivities of the compounds are discussed in terms of the structural incommensurability. A logarithmic temperature dependence of the resistivity observed for the stage-2 compounds below ∼20 K is discussed in relation with the carrier localization. A fractional superconductivity has been observed for most of the samples below 2∼6 K and its model based on the peculiar structure is proposed.

Norimichi Kojima

Papers

Photo-Induced Absorption Band in One-Dimensional Halogen-Bridged Mixed-Valence Platinum Complex: [Pt(en)2][PtI2(en)2](SO4)2·6H2O and its Au-Doped Complex: [AuxPt1-xI(en)2]SO4·3H2O

Raman and Infrared Spectra of Misfit Layer Compounds MNbS3 (M=Sn, Pb, La, Ce)

Magnetic Properties of Incommensurate Layer Compounds, (CeS)1.2NbS2 and (CeS)0.6NbS2

Magnetic and Transport Properties of Ce-Ta-S Ternary System

Electrical Transport Properties of Incommensurate Layer Compounds (RES)xNbS2 (RE=Rare-Earth Metals; x=1.2, 0.6)