Anomalous critical behavior and localized ferromagnetism of the half-metallic double perovskite Sr₂CrReO₆

Double perovskites such as Sr2CrReO6 attract great scientific attention owing to their high Curie temperatures (T-C >= 550 K) as well as large magnetoresistances. However, both the specific physical mechanism of high T-C and magnetic ground state in Sr2CrReO6 remain ill-defined. In order to clarify and understand these issues, we studied its critical phase transition characteristics using critical behavior analysis. We found that the obtained critical exponents (beta = 1.115 and gamma = 2.224) are quite different from any traditional universality class. The abnormal critical behavior implies that at the quantum critical point, Sr2CrReO6 exists a strong competition among several magnetic interactions. By analyzing their effective critical exponents, we show that the double perovskite Sr2CrReO6 is really an ordered and homogeneous ferromagnet. With the help of Takahashi's theory, the nature of ferromagnetism in Sr2CrReO6 is confirmed to be localized instead of itinerant. The results of this research will provide new insights into the origins of high T-C as well as the magnetic ground state in this double perovskite.