J. Odin

Remanent magnetization and thermal relaxation in a frustrated spin‐glass: Eu1−xGdxS

The Eu1−xGdxS system evolves from ferromagnetism for small x to antiferromagnetism for x→1. We have studied the remanent magnetization and the thermal relaxation in the concentration range 40%≲x≲58% where a spin‐glass state is observed (1). Both properties are found to decrease exponentially with T ln (t/τo) but with different coefficients (T is the temperature, t the measuring time and τo a characteristic relaxation time). This appears to be a general property of spin glasses at low temperature consistent with a description in terms of two levels systems.

Anomalous magnetic behavior of cerium in Ce2Sn5 and Ce3Sn7, two superstructures of CeSn3

Abstract The two magnetic compounds Ce 2 Sn 5 and Ce 3 Sn 7 have very similar crystallographic structures. They are both superstructures of CeSn 3 with two different cerium sites: one, similar to the cerium site in CeSn 3 , is “non-magnetic” or in intermediate valence state, and the other carries a well-defined moment and dominates the magnetic properties at low temperatures. Although their macroscopic magnetic properties under the effect of an applied field look quite similar, the magnetic structures of the two compounds in zero field are totally different. In fact, Ce 2 Sn 5 presents a modulated structure with moments of maximum value 1.3μ B aligned along a , whereas Ce 3 Sn 7 is an antiferromagnet with moments of only 0.36μ B parallel to c . This difference cannot be attributed to different Crystal Electric Field effects, which, from inelastic neutron spectroscopy measurements, are found to be fairly close in the two compounds. A strong anisotropy of the interionic exchange coupling is evidenced in both compounds from the magnetization curves and neutron data, within a crystal field model. Especially, in Ce 3 Sn 7 , a negative value is found for the c component of the exchange coefficient, leading to strong negative interactions when moments are aligned along c . The effects of hybridization of the cerium 4f-electron with the band electrons play an important role in Ce 2 Sn 5 and Ce 3 Sn 7 . In both compounds, besides the intermediate-valent behavior of cerium in the CeSn 3 -type site, Kondo effects are present on the magnetic cerium site, leading to an extra reduction of the cerium magnetic moments. These hybridization effects are also likely to be at the origin of the anisotropy of the exchange interactions and of the resistivity.

Magnetization and energy relaxations in spin glass AuFe 4 at% below Ting

Abstract We present data on Au Fe 4% showing: a relaxation of the saturated remanent magnetization significative of a wide distribution of barriers; an associated energy relaxation implying that the barriers separate levels of different energies; a time-temperature correlation of these relaxations which implies thermally activated processes.

Influence of cooling rate on the heat capacity and thermal transitions of amorphous polyhexene-1

Abstract Heat capacity measurements have been made on an amorphous polyhexene-1 sample between 20 and 300K, with an adiabatic calorimeter giving a low dispersion on the C p curve (0·2–0·4%). The measured sample was prepared by a new method increasing its thermal diffusivity. The heat capacities were measured for different cooling rates (250 K/h and 0·15 K/h) through the glass transition. This large difference of the cooling rates did not change T g very much (215·5 to 213·5K), but a peak was added to the usual ΔC p at T g . An anomalous behaviour was observed at 80K, which is consistent with an experiment described elsewhere. Around 80K dielectric and mechanical relaxations were found in other experiments. In conclusion, the importance of the glass transition is pointed out, its effect being visible down to the lowest temperatures.

Specific heat of Ce3Al11 and CeAl3 compounds

Abstract Specific heat of the Ce 3 Al 11 compound has been measured to find its properties and connect them to those of the other cerium-aluminum compounds. Two peaks are observed at 3.2 and 6.2 K. Kondo effect and ferromagnetic order coexist between 3.2 and 6.2 K. A modulated phase exists below 3.2 K.

Low-temperature anomalies in the specific heat of heavy-fermion UPt3

High-precision specific-heat measurements (1.3 K < T < 20 K) on UPt3 yield two small, but distinct, anomalies at 6.2 K, where the c/T curves shows a kink, and at 7.3 K, where a small peak is observed. Samples of different origin gave identical results. The possible connection with antiferromagnetic order yielding small moments (TN = 5 K), as recently probed by neutron experiments, is discussed.

Study of the magnetic transitions in Y2BaCuO5 and Y2Cu2O5 by specific heat and Mössbauer measurements

Abstract Magnetic specific heat data on Y 2 BaCuO 5 confirm 3D ordering at T N =15.5 K and the presence of SRO above T N . Mossbauer spectra of 57 Fe doped Y 2 Cu 2 O 5 show the appearance of a hf field below T N ≈12 K; Cu-Fe exchange seems smaller than Cu-Cu exchange.

Coexistence of Intermediate Valence Ce and Ce3+ in the Ce2Sn5 Compound

A large number of intermetallic compounds are reported to exist in the Ce-Sn diagram1. They range from the more dilute Ce compound CeSn3 to the richest one, Ce3Sn. Among these compounds, CeSn3, which crystallizes in the cubic AuCu3 structure, presents a well established intermediate valence state : a high electronic specific heat constant 2,3, a large thermal expansion a very weak magnetic susceptibility, with a broad maximum around 150 K5,6,7, are the main evidences of such a property. Moreover, it has been shown recently8 that the large increase of the susceptibility at low temperature is due partly to the pure CeSn3 phase but also partly to some magnetic defects which are structurally connected with the neighboring phases, mainly Ce2Sn5.

Itinerant ferromagnetism and superconductivity in bct ErRh4B4

The body centered tetragonal ErRh4B4 compound undergoes an itinerant ferromagnetic transition at Tm=21 K characterized by a susceptibility equal to the inverse of the demagnetizing coefficient. The itinerant ferromagnetism does not prevent the simultaneous presence of the superconductivity from 7.7 K down to 0 K. The diamagnetic ac susceptibility can be calculated from the ferromagnetic one. The coexistence of itinerant ferromagnetism and superconductivity among d electrons would be one of the most convincing arguments in favor of ‘‘odd‐parity’’ superconductivity.