Structural and magnetic properties of CrPt 3 ( 111 ) films grownon WSe 2 ( 0001 )

We report on the growth-induced properties of 30 Å thick CrPt 3 ( 111 ) deposits on surfaces of WSe 2 ( 0001 ) with a van der Waals interaction. Assemblies of (111)-oriented fcc grains are obtained with average lateral sizes ranging from 5 to 15 nm for growth temperatures increasing from 50°C to 550°C. The grains develop a partial L 1 2 -type chemical long-range order starting at a deposition temperature as low as 50°C, much lower than reported for films grown on other suitable substrate surfaces. An ordering parameter of about 0.3 was found over a wide temperature range between 200°C and 550°C, for a deposition rate of 0.1 Å/s. Lowering the deposition rate by a factor of 5 results in a higher ordering parameter of about 0.4. Above 400°C, ordering is accompanied by a pronounced segregation of Se atoms toward the free surface, forming a ( 4 × 4 ) superstructure. All samples exhibit superparamagnetic behavior with blocking temperatures that scale with the activation volume of the ferrimagnetic grains. This work shows the importance of substrate choice in reducing the ordering temperature of thin CrPt 3 films, an effect that might also occur in other alloy systems.