Crossover from low-dimensional to three-dimensional ferromagnetism in alloys

The hexagonal material CePdSb exhibits low-dimensional ferromagnetism with (Formula presented) while isostructural CePtSb shows normal three-dimensional ferromagnetism with (Formula presented) To understand the low-dimensional ferromagnetic ordering of CePdSb we have investigated (Formula presented) alloys, using ac susceptibility, heat capacity, thermal expansion, and zero-field spin-echo NMR measurements. The ac susceptibility shows that the (Formula presented) of the Pd-rich alloys is higher than that expected from a linear extrapolation of the Pt-rich alloys. The heat capacity shows a smooth crossover from the anomalous (Formula presented) to normal (Formula presented) ferromagnetic behavior with increasing Pt concentration. Thermal expansion results agree with the heat-capacity data for the alloys that are either Pd rich (Formula presented) or Pt rich (Formula presented) However, the thermal expansion shows anomalous behavior for the alloys (Formula presented) and 0.6, in the composition range where the heat capacity exhibits the crossover behavior. From the heat capacity and ac susceptibility measurements a phase diagram, temperature vs x, for (Formula presented) alloys has been proposed. Low power zero-field Sb spin-echo NMR studies show well-defined quadrupole split NMR spectra in both CePdSb and CePtSb, confirming the ferromagnetic ground state. Only a very broad NMR signal has been observed in the substituted alloys of (Formula presented) because of the differences between the quadrupole splitting of CePtSb and CePdSb. The internal field at the Sb nucleus at low temperatures for CePtSb(CePdSb) is +2.3 T (+2.8 T) and the quadrupole splitting 8.5 and 5.1 MHz (3.8 and 2.3 MHz) for (Formula presented) and (Formula presented) respectively.