Magnetoresistance anomalies and multiple magnetic transitions in SmMn₂Ge₂

Abstract

The results of magnetoresistance (Δρ/ρ), heat capacity (C), and ac susceptibility (χ) measurements are reported for a polycrystalline specimen of SmMn₂Ge₂. In addition to sharp variations of the order of 3-5% at 110 and 142 K, there are anomalies in the sign and the magnitudes of Δρ/ρ. A finding of considerable interest is that there is a gradual increase of Δρ/ρ from a small negative value at 35 K to a very large value of about 24% at 4.2 K in the presence of a magnetic field of 80 kOe, though apparently there is no corresponding anomaly in the C data. This finding signals the existence of a phase transition below 30 K attributable to magnetic ordering from Sm sublattice, thereby making the origin of the onset of Mn ordering around 110 K a puzzle.