Van Vleck paramagnetism of the thulium garnet Tm3Al5O12

The magnetic susceptibility of the garnet-type single crystal Tm3Al5O12 exhibits the typical Van Vleck temperature independent paramagnetism below ≈8 K. The temperature dependence of the susceptibility over the range 2.0–300 K has been analyzed on the assumption that the cubic crystal-electric-field dominates the energy level on 3H6 (J=6) ground multiplet for Tm3+ ion having 12-electrons in 4f shell. The ground state of the 3H6is nonmagnetic with Γ2 singlet, avoiding the Kramers doublet. The energy separation between Γ2 and the first excited state Γ(2)5 triplet is evaluated to be 68.0 K. The whole energy interval Δ between Γ2 and the highest state Γ1 in 3H6 is estimated to be 339.5 K

Ferromagnetism and the metal-insulator transition in the thiospinel Cu(Ir1-xCrx)2S4

A thiospinel CuIr2S4 exhibits a temperature-induced metal-insulator (M-I) transition at 230 K with a simultaneous spin-dimerization and charge-ordering transition although a three-dimensional system. On the other hand, CuCr2S4 has the same spinel structure without any structural transformations. CuCr2S4 remains metallic and is ferromagnetic with the Curie temperature TC≃377 K. In order to see the effect of substituting Cr for Ir on the M-I transition, we have carried out a systematic experimental study of electrical and magnetic properties of Cu(Ir1-xCrx)2S4 system. The M-I transition temperature decreases steeply with increasing Cr-composition x and this transition is not detected above x≃0.05. The value of TC decreases with decreasing x from 1.0, then TC disappears below x≃0.20. The ferromagnetic state suggests the non-collinear spin alignment. In the intermediate composition range over x=0.08 to 0.20, the B-site undergoes a local crystal distortion around 180 K, where the energy level t2g splits into lower symmetry. Then the low-spin state within the t2g subspace is realized for Cr3+ ion with s=1/2. The magnetic state of Cr3+ ion indicates a crossover from high temperature s=3/2 to low temperature s=1/2 state around 180 K

Investigation of the hardener with latent and rapid curing based on phenol-amine salts for applications to cyanate ester resins.

We have developed the curing agents that have good storage stability for cyanate ester resins. It should be noted that these agents can be given rapid and efficient curing at low temperatures around 100°C. Even though the nucleophilicity was reduced by a phenol-amine salts consisting of basic aliphatic amines and weakly acidic phenols, the curing reaction with the cyanate ester occurred immediately. It means that the control of the curing reaction with cyanate esters is not easy due to the equilibrium between phenol and amine. In order to overcome this difficultly cyanate esters reactivity, the molecular motions suppression by polymer was applied in addition to the phenol-amine salts. The effect of the suppression for hardeners was studied in terms of the storage stability and reactivity to cyanate esters. It has been found out that PSM-EPEDA composed of ethylenediamine-epoxy adducts and novolac phenolic resin exhibits a large storage stability against cyanate esters by its effective suppression of molecular motions accompanied with efficient and rapid curing around 100°C