Magnetic precursor effects, electrical and magnetoresistance anomalies, and heat-capacity behavior of Gd alloys

The electrical resistivity ({ρ}), magnetoresistance (Δρ/ρ), heat capacity $(C),$ and magnetization $(M)$ behavior in a number of Gd alloys are reported. Particular attention is paid to the {ρ} and Δρ/ρ behavior at temperatures just above respective long-range magnetic ordering temperatures (T₀). In some compounds, e.g., GdNi₂Sn₂ and GdPt₂Ge₂, there is an enhancement of {ρ} prior to long-range magnetic order over a wide temperature range which can be highlighted by the suppression of {ρ} caused by the application of a magnetic field. However, such features are absent in many other Gd compounds, e.g., GdCu₂Ge₂,GdAg₂Si₂,GdAu₂Si₂,GdPd₂Ge₂, and GdCo₂Si₂. Attempts to relate these features to magnetic precursor effects in C are made. We observe interesting features in the C data, like shoulders and additional transitions in the magnetically ordered state and peak values of C at T₀ varying from one compound to the other. The implications of these observations are discussed. In addition, various Δρ/ρ anomalies, including large positive values at low temperatures in some cases, and the sensitivity of magnetoresistance to field-induced magnetic transitions in comparison with the isothermal M data, are also brought out.