Crescimento e caracterização de monocristais das famílias RCuGa3 (R = Ce, Pr, Nd, Gd) e RNiIn4 (R = La, Ce, Pr, Nd) por meio do método de fluxo metálico: estudos estruturais, magnéticos e do campo elétrico cristalino

Abstract

This work presents a systematic experimental study on the synthesis, structural characterization, and investigation of the magnetic properties of single crystals belonging to two families of rare-earth-based intermetallic compounds, RCuGa3 (R = Ce, Pr, Nd, Gd) and RNiIn4 (R = La, Ce, Pr, Nd). The single crystals were grown using the high-flux method, employing gallium (Ga) and indium (In) as solvents for the RCuGa3 and RNiIn4 series, respectively, enabling the growth of samples with high crystalline quality. Structural characterization was performed by X-ray diffraction (XRD), with crystallographic parameters refined using the Rietveld method implemented in the DBWS software, revealing that the RCuGa3 compounds crystallize in a tetragonal structure with space group I4/mmm, whereas the RNiIn4 compounds adopt an orthorhombic YNiAl4-type structure belonging to the Cmcm space group. Complementary scanning electron microscopy (SEM) analyses, particularly for PrNiIn4, confirmed the chemical homogeneity and high structural quality of the crystals, in good agreement with the XRD results. The magnetic properties were investigated through temperature-dependent magnetic susceptibility measurements for both families, and through specific heat (Cp) measurements for the RNiIn4 series, revealing antiferromagnetic behavior at low temperatures, with magnetic transitions characterized by N´eel temperatures (TN ) ranging from 2.2 K to 9.3 K, namely TN ≈ 3 K (Ce), 4.4 K (Pr), 2.2 K (Nd), and 9.3 K (Gd) for the RCuGa3 series, and 2.8 K < TN < 4.2 K for the RNiIn4 series. The analysis of the inverse magnetic susceptibility in the paramagnetic regime, based on the Curie-Weiss model, allowed the determination of the Curie-Weiss temperature (θCW), the experimental effective magnetic moment (µexp), and the magnetic frustration factor (f), revealing a pronounced magnetic anisotropy in the RNiIn4 series, expressed by ratios χeasy/χhard > 1, which is attributed to the significant influence of crystalline electric field (CEF) effects. Similar CEF-related effects were also identified in the RCuGa3 series, particularly for the Ce- and Pr-based compounds, influencing both the values of TN and the deviations observed from the scaling behavior predicted by the De Gennes rule. The specific heat measurements corroborated the magnetically determined transition temperatures and further reinforced the central role of CEF effects in defining the magnetic ground state of these systems, providing, overall, a comprehensive comparative analysis of the correlations between crystal structure, electronic interactions, and magnetic properties in rare-earth intermetallic compounds.