Using an MTJ with positive tunneling magnetoresistance (TMR) as an example for illustration. If the magnetization directions of the reference layer and free layer are in a parallel orientation, the MTJ is in a low-resistance state (P-state). If the magnetization directions of the reference layer and free layer are in an anti-parallel orientation, the MTJ is in a high-resistance state (AP-state). The insertion of the first NLR device 310 increases I_p, decrease I_ap, and thereby increases a difference of I_ap and I_p, and thus increase TMR. The first NLR device 310 provides a first resistance (r_nlr) when the low-resistance state P-state is read and a second resistance (R_nlr) greater than the first resistance (r_nlr) when the high-resistance state AP-state is read. Thus, the difference between I_p and I_ap is increased. The effective TMR becomes: (R_AP?R_P)+(R_nlr?r_nlr)}/(R_Path+R_P+R_MOS+r_SD). The insertion of the first NLR device 310 also provides more margin to design the reference memory cell 100′. The reference resistor R_ref would be in a range between R_AP+R_nlr and R_P+r_nlr, instead of in a smaller range between R_AP and R_P. The reference memory cell 100′ has a reference resistance greater than a sum of the first resistance (R_P) of the MTJ memory cell 100 and the first resistance (r_nlr) of the first NLR device 310 and smaller than a sum of the second resistance (RAP) of the MTJ memory cell 100 and the second resistance (R_nlr) of the first NLR device 310.