“…The enhanced low-field magnetoresistance (LFMR) is generally thought to be extrinsic in nature and ascribed to the spin-polarized tunneling of conduction electrons through grain boundaries as proposed by Hwang et al [9]. These secondary insulators include Co 3 O 4 [10], glass [11], MgO [12], CuO [13], V 2 O 5 [14], ZrO 2 [15], Fe 2 O 3 [16], NiO [17], PMMA [18] and CuMn 2 O 4 [19]. These results suggest that the insulating boundary or the barrier layer is important to enhance the MR effect.…”