Intrinsic spin-valve-type magnetoresistance (SVMR) behavior recently observed in Sr 2 FeMoO 6 (SFMO) is proposed to originate from the 'magnetic hardness' of the insulating grain boundary. It suggests the potential for tuning the SVMR by manipulating the magnetoresistance peak position of the grain boundary with a suitable magnetic material. In this paper, CoFe 2 O 4 /Sr 2 FeMoO 6 (CFO(x)/SFMO(100%): x = 0%-30%) composites were specifically designed by introducing the hard magnetic insulator CFO into the grain boundary of SFMO. Insulating CFO can increase the grain boundary strength (macroscopic resistivity), resulting in an enhanced low-field magnetoresistance (LFMR) of ~1.6 times with respect to the maternal SFMO. The magnetic coercivity (H C ) of the CFO/SFMO grain material shows a complete enhancement which is dependent on the CFO content (x) and is due to the high magnetic anisotropy of the CFO. Vastly different from the H C response is the coercive field variance of the magnetoresistance (H C (MR)), which exhibits a complex correlation with the CFO content (x). Regardless of how much the H C (MR) changes, the SVMR behavior is still maintained because of a larger H C (MR) than that of H C when x 18%. However, almost comparable values of H C (MR) and H C are observed when x increases up to 30%, where the SVMR property is greatly destroyed. In addition, the ferromagnetic transition temperature T C values of all the samples show no obvious dependence on the CFO content (x). These interesting observations indicate that the CFO content (x) not only significantly optimizes the LFMR but it also effectively tunes the SVMR behavior. Our work may encourage further investigation of SVMR behavior in SFMO and other similar systems.

Both the band filling effect and Fe/Mo disorder have a close correlation with the physical properties of the double perovskite Ca 2 FeMoO 6 . Two series of Ca 2 FeMoO 6 and Nd 0.3 Ca 1.7 FeMoO 6 ceramics sintered at (1050 ∘ C, 1200 ∘ C, and 1300 ∘ C) were specially designed to comparatively investigate the band-filling effect and Fe/Mo disorder on the physical properties of Ca 2 FeMoO 6 . The x-ray diffraction indicates that Fe/Mo disorder is sensitive to the sintering temperature. The magnetization behavior is mainly controlled by the Fe/Mo disorder not by the band filling effect, manifested by a close correlation of saturated magnetization (M s ) with the Fe/Mo disorder. Interestingly, magnetoresistance (MR) property of the same composition is dominantly contributed by the grain boundary strength, which can be expressed by the macroscopic resistivity values. However, the band filling effect caused by the Nd-substitution can decrease the spin polarization, and thus suppress the MR performance fundamentally. Contrary to the MR response, the Curie temperature (T C ) shows an obvious optimization due to the band filling effect, which increases the carrier density near the Fermi level responsible for the ferromagnetic coupling interaction strengthen. Maybe, our work can provoke further research interests into the correlation of the band-filling effects and Fe/Mo disorder with the physical properties of other Fe/Mo-based double perovskites.