Anomalous critical behavior and localized ferromagnetism of the half‐metallic double perovskite Sr 2 CrReO 6

Abstract Double perovskites such as Sr 2 CrReO 6 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 Sr 2 CrReO 6 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 ( β = 1.115 and γ = 2.224) are quite different from any traditional universality class. The abnormal critical behavior implies that at the quantum critical point, Sr 2 CrReO 6 exists a strong competition among several magnetic interactions. By analyzing their effective critical exponents, we show that the double perovskite Sr 2 CrReO 6 is really an ordered and homogeneous ferromagnet. With the help of Takahashi's theory, the nature of ferromagnetism in Sr 2 CrReO 6 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.