Thickness-Dependent Magnetic Properties in Double-Perovskite Sr ₂ FeReO ₆ Films

The search for magnetic materials with high spin polarization and Curie temperature well above room temperature is a key issue in the field of magnetoresistive sensors and spintronic devices. Due to the flexible combination of cations at the A and B sites, double perovskites exhibit various crystal structures, rich electronic properties, and abundant magnetic structures and have promising potential applications in those areas. In this work, we systematically investigate the thickness-dependent magnetic and electrical transport properties of Sr2FeReO6 films. A crossover from nonmagnetic to ferrimagnetic behavior occurs at a critical thickness of ∼4 nm. With increasing Sr2FeReO6 thickness, the saturation magnetization and coercive field increase gradually, while the Curie temperature rises sharply at ∼4 nm and then saturates slowly. In addition, a giant anisotropic magnetoresistance has been observed with the applied magnetic field rotating along the xz (α scan), yz (β scan), and xy (γ scan) planes. The anisotropic magnetoresistance maximum in α and β scans appears when the magnetic field points along the in-plane direction, irrespective of the direction of current flow, which is attributed to crystalline anisotropic magnetoresistance. The 4-fold symmetry in γ scan anisotropic magnetoresistance mainly originates from the magnetocrystalline anisotropy. These observations provide a sound basis for the applications of double perovskites in spintronics devices such as spin field-effect transistors and magnetic tunnel junctions. The systematic understanding of thickness-dependent magnetic and electrical properties is crucial for the scaling and interface engineering of such nanoscale devices.