Magnetic interactions in equi-atomic rare-earth intermetallic alloys RScGe(R = Ce,Pr, Nd and Gd) studied by time differential perturbed angular correlation spectroscopy andab initio calculations

Abstract

Applying the time differential perturbed angular correlation (TDPAC)technique we have measured electric and magnetic hyperfine fields of the111Cd impurity in equi-atomic rare-earth intermetallic alloys RScGe(R = Ce,Pr and Gd) showing antiferro- and ferromagnetism with unusually high ordering temperatures.The Cd nuclei occupying the Sc site show high magnetic hyperfine fields with saturation valuesBhf(0) = 21 kG, 45 kG and 189 kG in CeScGe, PrScGe and GdScGe, respectively. By comparing the resultswith the hyperfine field data of Cd in rare-earth metals and estimations from the RKKY model,we find evidence for the presence of additional spin density at the probe nucleus, possibly dueto spin polarization of Sc d band electrons. The principal electric field gradient componentVzz in CeScGe, PrScGe and GdScGe has been determined to be5.3 × 1021 V m−2,5.5 × 1021 V m−2 and 5.6 × 1021 V m−2, respectively. Supplementing the experimental measurements, we have carriedout ab initio calculations for pure and Cd-doped RScGe compounds withR = Ce, Pr, Nd and Gd using the full potential linearized augmented plane wave(FLAPW) method based on density functional theory (DFT). From the totalenergies calculated with and without spin polarization we find ferrimagnetic groundstates for CeScGe and PrScGe while NdScGe and GdScGe are ferromagnetic.In addition, we find a sizable magnetic moment at the Sc site, increasing from≈0.10 μB inCeScGe to ≈0.3 μB in GdScGe, confirming the spin polarization of Sc d band electrons. The calculated electricfield gradient and magnetic hyperfine fields of the Cd impurity closely agree with theexperimental values. We believe spin polarization of Sc 3d band electrons, stronglyhybridized with spin polarized 5d band electrons of the rare-earth, enables a long rangeRuderman–Kittel–Kasuya–Yosida (RKKY) interaction between RE 4f momentswhich in turn leads to high magnetic ordering temperatures in RScGe compounds.