Tunable magnetic transition and reversible magnetocaloric effects at room temperature in transition-metal-oxyfluorides CrO2−xFx

We report the tuning of magnetic transition and associated reversible magnetocaloric effect in CrO2−xFx by manipulating the doping levels. At x = 0.12, the magnetic transition occurs at room temperature, with magnetic-entropy changes of around 4 J kg−1 K−1 and relative cooling power of 388 J kg−1 at magnetic-field changes from 0 to 50 kOe. The reversibility is verified by negligible thermal and magnetic hysteresis, as well as the positive slope at Arrott plots. The complete phase diagram for electronic and magnetic states is drawn for CrO2−xFx. This work indicates CrO1.88F0.12 is a promising candidate for room temperature magnetic refrigeration because of the nature of second-order transition and abundance of elements involved.