Unusual electrical resistivity anomalies of thulium thin films at low temperatures

Abstract

High precision electrical resistance measurements were performed in the temperature range from 4.2 K up to room temperature on a pure thulium bulk sample with a high residual resistivity ratio, RRR=146, and on thulium thin films in the thickness interval from 25 to 115 nm. The observed size-effect of the electrical resistivity is in accordance with theory and it is without resistivity vs. thickness anomalies. The typical “hump-backed” anomaly in the resistivity vs. temperature dependence was observed for the Tm bulk sample near the Néel temperature. In contrast, unexpected resistivity vs. temperature anomalies were observed for thulium thin films in the low temperature region below ∼60 K and near ∼170 K. A crystal structure study using X-ray diffraction revealed that these thin films were single phase with the Tm hcp crystal structure and with preferential orientation of crystallites.