We have carried out a systematic magnetic relaxation study, measured after applying and switching off a 5 T magnetic field to polycrystalline samples of La 0.5 Ca 0. The above measurements suggested that the general temperature dependence of the LTLRR and the underlying physics were mainly independent of the particular charge ordering system considered. All relaxation curves could be fitted using a logarithmic law at long times. This slow relaxation was attributed to the coexistence of ferromagnetic and antiferromagnetic interactions between Mn ions, which produced a distribution of energy barriers.
We reported a systematic change in the average magnetic relaxation rate, after the application and removal of a 5 T magnetic field, in a polycrystalline sample of La 0.5 Ca 0.5 MnO 3 . Magnetic relaxation measurements and magnetization versus field curves were taken from 10 K to 160 K. The long time behavior of the relaxation curves was approximately logarithmic in all cases.Charge ordering compounds have a large variation of resistivity and magnetization as a function of temperature and magnetic field 1,2 .A representative example, La 0.5 Ca 0.5 MnO 3 has a paramagnetic-ferromagnetic transition around 265 K and a ferromagnetic-antiferromagnetic (FM-AFM) phase transition at 160 K 3 . Accompanying the FM-AFM transition there is also a charge disordered to a charge ordered phase transition 3 .Polycrystalline samples of La 0.5 Ca 0.5 MnO 3 were prepared by the solid-state method described elsewhere 4 . X-ray diffraction measurements pointed out high quality samples. Magnetization measurements were done with a standard MPMS-5S SQUID magnetometer. The relaxation measuring procedure was the following: first, the sample was heated to 400 K in zero magnetic field; second, the remanent magnetic field in the solenoid of the SQUID magnetometer was set to zero; third, the sample was cooled down to the working temperature
We present a study of the spin disorder resistivity ([Formula: see text]) and the electronic specific heat coefficient (γ) in Gd(4)(Co(1-x)Cu(x))(3) compounds, with x = 0.00, 0.05, 0.10, 0.20 and 0.30. The experimental results show a strongly nonlinear dependence of [Formula: see text] on the average de Gennes factor (G(av)) which, in similar intermetallic compounds, is usually attributed to the existence of spin fluctuations on the Co 3d bands. Values of γ were found around 110 mJ mol(-1) K(-2) for the Gd(4)(Co(1-x)Cu(x))(3) compounds, much larger than 38.4 mJ mol(-1) K(-2) found for the isostructural nonmagnetic Y(4)Co(3) compound. Using a novel type of analysis we show that the ratio [Formula: see text] follows a well-defined linear dependence on G(av), which is expected when appropriate dependencies with the effective electron mass are taken into account. This indicates that band structure effects, rather than spin fluctuations, could be the main cause for the strong electron scattering and γ enhancement observed in the Gd(4)(Co(1-x)Cu(x))(3) compounds. A discussion on relevant features of magnetization and electrical resistivity data, for the same series of compounds, is also presented.
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