J. Dumas

Magnetic properties of (Ti1-xVx2O3 powders

Abstract The magnetic susceptibility of (Ti1-xVx2O3 powders with 0 ⪕ x ⪕ 0.12 has been measured over the temperature range 4.2–300 K. The data show a Curie-Weiss behaviour between 20 and 150 K. As x is increased, the effective magnetic moment per V atom first decreases from 3.8 to 1.8 μB shows a steep increase for x = 0.02 and reaches a limit of 1.8 μB. These results are discussed in connection with a theoretical model proposed by Van Zandt, involving a narrow V impurity band.

Weak magnetism in the two dimensional purple bronze K0.9Mo6O17

Abstract Magnetoresistance, magnetization and 57 Fe Mossbauer studies in K 0.9 Mo 6 O 17 single crystals are reported. A large and positive magnetoresistance, sigmoidal magnetization curves and a quadrupole splitting of the Mossbauer spectrum are found at low temperatures. The results are discussed in relation with the onset of a charge density wave below 120 K.

Lattice parameters variation with temperature of Ti2O3 and (Ti0.98V0.02)2O3 from single crystal X-ray data

Abstract The lattice parameters of Ti2O3 and (Ti0.98V0.02)2O3 have been measured as a function of temperature (24–670°C for Ti2O3 and 24–440°C for V-doped Ti2O3) from single crystal X-ray data. The high temperatures were attained by blowing hot argon directly on the crystal mounted on an automatic Philips diffractometer. This experimental set-up gives standard deviations which are at least 10 times better than those of the previous measurements and allows to keep Ti2O3 as such well above the transition. The variations of a, c, c a (hexagonal axes) for pure Ti2O3 are in agreement with the previous results. On the contrary we did not observe any transition in the unit cell volume. The V-doping seems to attenuate the transition which is visible only on the a vs T curve

CDW depinning in the blue bronze: A study bby current pulse measurements, proton channeling, electron paramagnetic resonance

Abstract CDW depinning in the blue bronze has been investigated using three techniques: voltage response to current pulses, proton channeling and electron paramagnetic resonance. The voltage response involves four distinct regimes as the amplitude of the pulse increases. The backscattering yield of protons increases when the applied dc voltage exceeds the threshold value for depinning. An asymmetry of the EPR spectra at low temperatures is found as the threshold is approached from below. These results indicate that CDW structural defects play a predominant role in the depinning process.

CDW nonlinear transport in the organic systems (Per)2M(mnt)2

Abstract Nonlinear electrical conductivity measurements in the Charge Density Wave (CDW) state of the quasi-one- dimensional conductors (Per) 2 M(mnt) 2 , with Mue5fbAu, Pt and Co, are reported. Broad band and narrow band noise measurements provide, for the first time in an organic based molecular system, clear evidence for coherent CDW motion as the origin of the non-linear transport in these compounds. Studies of the transient response to current pulses show variable degree in the rigidity of the CDW, some samples presenting a delayed switching behaviour. These results are discussed within the current models for CDW nonlinear transport.

From the spin glass to the antiferromagnetic regime in (Ti1-xVx)2O3

(Ti1-xVx)2O3 single crystals with 0.10 <x<0.50 are shown to be mictomagnetic with a peak in the initial susceptibility at a temperature TB and remanent magnetizations for T < TB. For x 0.50, susceptibility and electrical resistibility and electrical resistivity data give experimental evidence for an antiferromagnetic metallic phase.

A simple thermodynamical model for the conductive transition in Sm1−xNdxSe

Abstract We report here a simple thermodynamical model based on the existence of two kinds of ions Nd 2+ , Nd 3+ , and which can account for the anomalous behaviour of resistivity ϱ ( x ) versus composition x of the alloy Sm 1− x Nd x Se (where SmSe ( x = 0) is semiconducting and NdSe ( x = 1) is metallic). In this model, a critical value of x is found around which the drop in resistivity occurs and good agreement with the experimental curve ϱ ( x ) is also obtained.

Electron paramagnetic resonance in Fe3O2BO3

Abstract We report an EPR study of the Fe oxyborate Fe 3 O 2 BO 3 which shows charge ordering below 220xa0K, an antiferromagnetic transition at 112xa0K and weak ferromagnetism below 70xa0K. A single broad line ascribed to Fe 2+ ions is observed in the temperature range 10–300xa0K with no anomalies at 112 and 70xa0K. However, for 120 T

Electron paramagnetic resonance study of the warwickites Mg1+xTi1−xBO4

Abstract We have performed EPR measurements between 10 K and 300 K at 9.4 GHz on crystals of the warwickites Mg1−xTi1−xBO4. These compounds belong to the family of quasi-one dimensional disordered magnetic systems. The warwickites are characterized by the presence of ribbons along the c axis where the metallic ions are randomly located. The EPR spectra consist of two lines attributed to Ti3+ paramagnetic centers. A narrowing of the linewidths is observed upon increasing the temperature. A large change in the relative amplitudes of the lines is observed as a function of temperature. We suggest that the observed behaviour reflects intra and inter-ribbons interactions between Ti3+ ( S = 1 2 ) ions. A hopping mechanism is proposed for the line narrowing.

Depinning of the charge density wave in pure and non-stoichiometric blue bronzes A0.30MoO3 (A=K, Rb)

Abstract We report the observation of non-linear voltage response to unipolar current pulses in pure A0.30MoO3 (A=K, Rb) and non-stoichiometric Rb0.28MoO3 blue bronzes near threshold for depinning of the charge density wave. In both types of samples, the transient response waveforms involve overshoot at the leading edge and a tail at the trailing edge of the pulse whose time decays obey stretched exponential laws exp-(t/τ)β (O