We applied a one-dimensional tight-binding model to the study electron transport in a ferromagnetic metal-insulatorferromagnetic metal junction. We included a small external magnetic field perpendicular to the one-dimensional chain as a Zeeman Effect on electron spins. We obtained the transmission and reflection probabilities of an electron across the junction and used them to calculate its tunneling magnetoresistance. We found that the magnetoresistance ratio increases with the insulating gap of the insulator. The variation of the insulator thickness gives an oscillating behavior of the ratio. Our theoretical model predicts the right trend of the magnetoresistance on the thickness, and also indicates that at a certain thickness the maximum magnetoresistance ratio occurs.
