Magnetic and electrical properties of RMn2 compounds, where R=Gd–Tm, have been investigated via SQUID magnetometry, ac-susceptibility, thermal-expansion, electrical-resistivity, and magnetoresistance experiments from 4.2 K to room temperature. All samples with R=Gd, Tb, Dy, Ho, Er, and Tm are found to order ferromagnetically at Tc =109, 54, 35, 24, 15, and 8 K, respectively. The paramagnetic-to-ferromagnetic phase transitions in case of Gd and Tb compounds are of first order, shown as a sharp volume change in the thermal-expansion curve, but the transitions in the cases of other compounds are second order in nature. The first-order transitions are similar in nature to that in the case of YMn2, where the transition is believed to be associated with the collapse of the Mn moment. The transition temperatures in RMn2, where R=Gd–Tm, are in fairly good agreement with the prediction by the de Gennes rule. In GdMn2 and TbMn2, the Mn moment is found to be finite and it appears that Mn and Gd or Tb sublattices order simultaneously, but in the case of RMn2, with R=Dy–Tm, the Mn moment is small. The magnetoresistance at 4.2 K is found to be large and negative, as expected in a localized ferromagnetic metal. In the case of RMn2, for R=Dy–Tm, a T2 dependence is observed in the low-temperature resistivity, consistent with the electron-magnon scattering in a ferromagnet.
