D.C. Johnston

Multiple phase transitions in rare earth tetraborides at low temperature

Abstract We report the temperature dependence of the magnetic susceptibility of single crystals of PrB 4 , GdB 4 , TbB 4 , HoB 4 and TmB 4 , both parallel and perpendicular to the tetragonal c-axis. We also present low temperature resistance measurements on crytals of GdB 4 through TmB 4 . Two magnetic phase transitions are found for TbB 4 , DyB 4 , HoB 4 and TmB 4 . For the latter two compounds, the lower transitions appear to be first order. For HoB 4 , we have measured the low temperature specific heat. The lower transition in TbB 4 and HoB 4 is rapidly depressed upon dilution with YB 4 .

Influence of charge density wave fluctuations on the magnetic susceptibility of the quasi one-dimensional conductor (TaSe4)2I

Abstract The results of magnetic susceptibility (χ) measurements from 4 K to 430 K are reported for the quasi one-dimensional (1-D) conductor (TaSe 4 ) 2 I. The long range charge density wave (CDW) transition at T c = 265 K is manifested in the data via a small (20%) slope change in χ(T). By comparison with the 1973 theoretical prediction of Lee, Rice and Anderson for χ(T) of isolated 1-D chains, CDW amplitude fluctuations are found to be responsible for the strong continuing increase of χ observed above T c . Comparison with χ(T) previously reported for the quasi 1-D conductors o-TaS 3 and K 0.3 MoO 3 reveals the universal behavior of χ(T) above T c for these compounds.

Intercalation of organometallic compounds into layered transition metal oxyhalides

Abstract The syntheses of the new intercalate compounds FeOCl[(EtMe 4 Cp) 2 Fe] 0.16 , VOCl(CoCp 2 ) 0.16 , and TiOCl(CoCp 2 ) 0.16 are reported. Their structures are found by X-ray powder diffraction to be qualitatively the same as those of the previously reported complexes FeOCl(CoCp 2 ) 0.16 and FeOCl(FeCp 2 ) 0.16 . Results of 57 Fe Mossbauer and magnetic susceptibility studies on the latter two compounds are reported, and shown to be consistent with electron transfer from the metallocene to the host upon intercalation.

Ambient temperature phase relations in the system ifNa13(H2O)yTaS2 (0<-y<-2)

A gravimetric study of the ambient temperature phase relations is reported for the system Na13(H2O)yTaS2 (0<-y<-2). Five different phases were found, at y ≈ 0, 23, 0.8, 1.5 and 2.0; those with y ≈ 0.8 and 1.5 have not been previously reported. These results are discussed with respect to previous work on the Nax(H2O)yTaS2 and similar systems.

Observation of new cointercalation compounds in the system Na0.33(H2O)yTaS2 (0 ⩽ y ⩽ 2) from powder X-ray diffraction measurements

A powder X-ray diffraction study of the occurrence of hydrate phases in the system Na0.33(H2O)y,TaS2 (0 ⩽ y ⩽ 2) at ambient temperature is reported. Two new phases were found at y ≈ 0.8 and y ≈ 1.5 in addition to those previously reported at y ≈ 0.67 and y ≈ 1.8. Structural models for these phases are discussed.

Magnetic susceptibility and band structure of intercalation compounds of 2H-TaS2

Abstract A universal correlation is reported between the magnetic susceptibility of the TaS 2 layers at 300 K and the population (1 to 2 e - /TaS 2 ) of the TaS 2 conduction d-band in intercalation compounds of 2H-TaS 2 . From this curve, the variation in the density of states at the Fermi level D(E F ) with E F was derived; good agreement with the variation predicted by band structure calculations for 2H-TaS 2 was found.

Observation of the antiferromagnetic transition in the linear chain compound KFeS2 by magnetic susceptibility and heat capacity measurements

Abstract Magnetic susceptibility (ξ) measurements and the first heat capacity measurements on KFeS2 are reported. The data were obtained on a specially purified sample over the temperature ranges 10–360 K and 225–296 K, respectively. Both measurements revealed small but distinct singularities at the Neel temperature TN≈253 K; extensive short range ordering above TN was also evident from these data. The present work shows that the intrinsic ξ(T) of KFeS2 was largely masked by that from magnetic impurities in previous ξ studies of this compound.

The role of boron in the superconductivity of ternary RT4B4 compounds

Abstract A large and abrupt composition-induced change in the superconducting critical temperature has been reported in seven R(Rh1−xTx)4B4 systems (R = Y, rare earth; T = Ru, Ir). Additional related data are presented. Based on crystallographic data of Yvon and Gruttner, this phenomenon is proposed to arise from an abrupt composition-induced redistribution of electron density between the boron and transition metal sublattices. Several experimental tests of this model are suggested.

Synthesis and study of multiple cationic salts of hexamethoxytriphenylene (HMTP)

Abstract 2,3,6,7,10,11-Hexamethoxytriphenylene (HMTP) is known to exhibit multiple reversible oxidation states. We report on the synthesis and the physical properties of stable monocation, dication, and alloy salts between HMTP and ClO 4 − . The monocation salt, HMTP-ClO 4 , is a half-filled band, quasi one-dimensional semiconductor with a possible spin-Peierls transition at 240K. The dication is also found to be a semiconductor.

Superconductivity and magnetism of Mx(H2O)yTaS2 layered cointercalation compounds

Abstract Magnetization measurements between 1 K and 300 K are reported for the layered cointercalation compounds Mx(H2O)yTaS2 (y = 0, 2; M x = Na 1 3 ), Mn 1 6 , Y 1 9 , La 1 9 , Gd 1 9 . Superconductivity was observed for each compound with y = 2. Removal of the water results in a large increase in the magnetic interactions between the magnetic ions in the Mn 1 6 (H 2 O) y TaS 2 and Gd 1 9 (H 2 O) y TaS 2 systems, with Mn 1 6 TaS 2 exhibiting a ferromagnetic transition near 40 K, replacing the superconducting transition found in Mn 1 6 (H 2 O) 2 TaS 2 below 3 K.