Specific heat of Gd4Co3.

The specific heat (C(T)) of Gd4Co3 was measured in the temperature range 2-300 K and its magnetic contribution (C(m)(T)) was determined using a new method that fits the electronic specific heat coefficient (γ) and the Debye temperature (θ(D)) by constraining the resulting magnetic entropy (S(m)(T)) to saturate at temperatures far above the Curie temperature (T(C)). C(m)(T) exhibits a low-temperature bump originating from thermal excitation of gapped spin waves, which is responsible for pronounced peaks, at ≈35 K, in both C(m)/T and the temperature derivative of the magnetic contribution to electrical resistivity (dρ(m)/dT). Apart from in the vicinity of T(C), an excellent global correlation was found between C(m)/T and dρ(m)/dT. Our results provide strong support for the consistency of the new method proposed for the determination of C(m)(T) and rule out any major role of short-range order on Gd moments or d-electron spin fluctuation effects in the paramagnetic phase. A comparative analysis with other methods used in similar compounds points to the need for a better evaluation of C(m)(T) in such compounds, especially in the magnetically ordered phase, where a deficient evaluation of C(m)/T has a larger impact on the S(m)(T) curve.

Electronic band effects on the spin disorder resistivity of Gd(4)(Co(1-x)Cu(x))(3) compounds.

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.