|
|
Trovarelli, O., M. Weiden, R. MullerReisener, M. GomezBerisso, P. Gegenwart, M. Deppe, C. Geibel, J. G. Sereni, and F. Steglich. "Evolution of magnetism and superconductivity in CeCu2(Si1-xGex)(2)." Physical Review B – Condensed Matter and Materials Physics 56, no. 2 (1997): 678–685.
Abstract: We have determined the magnetic phase diagram of CeCu2(Si1-xGex)(2) using specific heat, susceptibility, and resistivity measurements and additional thermal expansion and muon spin resonance experiments. The system evolves continuously from the heavy-fermion state at x = 0 to an antiferromagnetically (AF) ordered state at x = 1, though the magnetic structure undergoes significant modifications. The results strongly suggest that the AF ordering emerges from the A phase of pure CeCu2Si2. The phase diagram can be divided into three regions: Low Ge content (x less than or equal to 0.2) leads to an enhancement of the A phase of pure CeCu2Si2 and to a moderate decrease of the Kondo temperature. Despite this increase of the magnetic character, we could observe superconductivity up to x = 0.1. At large Ge content (x > 0.5) the behavior resembles that of pure CeCu2Ge2. The intermediate region is characterized by the appearance of a second magnetic transition below T-N, which seems to be of first-order type. The appearance of this transition leads to a well-defined critical point at x = 0.3 and suggests the possibility of another critical point at x = 0.5.
|
|
|
|
Weiden, M., R. Hauptmann, W. Richter, C. Geibel, P. Hellmann, M. Koppen, F. Steglich, M. Fischer, P. Lemmens, G. Guntherodt et al. "Magnetic phase diagram of CuGe1-xSixO3." PHYSICAL REVIEW B 55, no. 22 (1997): 15067–15075.
Abstract: The effect of Si doping on the magnetic properties of the spin-Peierls (SP) system CuGeO3 was found to differ strongly between polycrystals (PC's) and single crystals (SC's). In SC's, the SP state is suppressed much mon strongly, whereas the existence region of the antiferromagnetic (AF) state is enhanced. We investigated the origin of this difference by means of magnetic susceptibility, specific heat, thermal expansion, Raman scattering, elastic neutron scattering, and x-ray measurements on CuGe1-xSixO3 samples prepared under different conditions. The partial oxygen pressure and the temperature during the synthesis were found to have a profound influence on the magnetic properties: preparation under reduced oxygen pressure leads to a stabilization of the AF state, whereas heating above the melting point results in a strong decrease of T-SP in Si-doped samples. Therefore, both the AF stabilization and the TSP reduction observed in SC's are not an intrinsic effect of Si doping PC samples, which can be prepared at lower temperatures and more oxidizing conditions, reflect much better the intrinsic properties of CuGe1-xSixO3. We were able to prepare PC samples up to 50 at. % Si and found a continuous decrease of the one-dimensional character of the magnetic properties without pronounced changes in the structure.
|
|
|
|
Trovarelli, O., M. Weiden, R. MullerReisener, M. GomezBerisso, J. G. Sereni, C. Geibel, and F. Steglich. "Development of magnetic order in CeCu2(Si1-xGex)(2)." Physica B: Condensed Matter 223-224, no. 1-4 (1996): 295–298.
Abstract: Measurements of specific heat (C-p), AC and DC susceptibility, and resistivity were carried out on samples of CeCu2(Si1-xGex)(2). The system evolves continuously from the heavy fermion state at x = 0 to an antiferromagnetically (AF) ordered state at x = 1, although the magnetic structure undergoes significant modifications. The results strongly suggest that the AF-ordering emerges from the A-phase of CeCu2Si2. Below the ordering temperature a systematic change in curvature in C-p(T) is observed for x greater than or equal to 0.6, that gets more pronounced with decreasing x, and al x = 0.4 a sharp anomaly is observed suggesting the existence of a critical point for 0.3 < x < 0.5. Below 1 K, a small anomaly is present al some concentrations. The results are compared with those on the Ce(Cu1-xNix)(2)Ge-2 system.
|
|
|
|
Weiden, M., O. Trovarelli, M. Gomez Berisso, R. Muller Reisener, C. Geibel, J. G. Sereni, and F. Steglich. "Low-temperature properties of Ce(Cu1-xPdx)(2)Si-2." Physica B: Condensed Matter 223-224, no. 1-4 (1996): 299–302.
Abstract: We have investigated the composition dependence of the structural and ground state properties in the alloy Ce(Cu1-xPdx)(2)Si-2 by means of lattice parameter, resistivity, susceptibility and specific heat measurements. We observe a highly non-monotonous evolution of the characteristic energy T-K with a strong increase of T-K with x for x < 0.2 and a smooth decrease for x > 0.2. This seems to be related to a change in the evolution of bonding as evidenced by a break in the composition dependence of the lattice parameters at x = 0.2.
|
|
