Mixing effects of light and heavy rare earths in the Laves phasecompounds Nd1−xHRxCo2 (HR = Gd,Tb)

Abstract

The mixing effects of light and heavy rare earths in cubic Laves phasecompounds Nd1−xHRxCo2 (HR = Gd,Tb)have been investigated by means of x-ray powder diffraction and magneticmeasurements. In Nd1−xTbxCo2, the saturationmoment MSexhibits an anomaly and could be ascribed to an abrupt jump of theCo moment at a critical concentration xc ≈ 0.33,whereas, in Nd1−xGdxCo2,MSdoes not show such an anomaly and a relatively simplemagnetic behaviour is observed at xc ≈ 0.43.The different behaviours of these two systems can be understood by consideringthe structural distortion of a cubic unit cell at low temperature. Afield-induced metamagnetic transition from weak ferrimagnetism to strongferrimagnetism is observed in both systems. This can be interpreted bythe evolution of magnetization with the help of percolation theory. Thecompensation points are observed in both systems, which are well explainedwithin the two-sublattice model. A double peak of the AC susceptibilityobserved in Nd1−xTbxCo2 nearx0 ≈ 0.19does not necessarily mean the occurrence of a first-order phasetransition. The observed second-order magnetic phase transition nearx0can be well described by Landau theory of the phase transition.