Role of Surface Roughness on Resistive Switching and Diode Effect in DC Sputtered CoTb/Cu/CoTb Spin Valve Films

The spin valve structure, where two magnetic layers are separated by a nonmagnetic insertion layer, has attracted considerable attention due to its use in applications such as spintronics and magnetoresistive random-access memory (MRAM) devices. In such a structure, the surface roughness plays an important role in tuning the magnetic and transport properties of thin films, especially in ultrathin films. The current work aims to investigate the effect of the surface roughness of a CoTb/Cu/CoTb spin valve on its transport properties. DC magnetron sputtering was used to fabricate thin films of Ta(3 nm)/Co_1−xTb_x (20 nm)/Cu(5 nm)/Co_1−xTb_x(20 nm)/Ta(3 nm), where x = 0.10, 0.15, 0.18, and 0.33, on a silicon substrate under two condition, i.e., as-deposited and by post-annealing (in situ) the original films for 60 min at 300°C. The surface roughness of the films was examined using a 3D profilometer, and the results revealed that the average surface roughness (S_a) and line roughness (R_a) of the deposited thin films varied in the range of 0.58 nm to 1.40 nm with increasing Tb content. The current–voltage (I–V) curve measurement indicated that the Co_1−xTb_x/Cu/Co_1−xTb_x/Ta thin films show hysteresis behavior. The I–V curve of the deposited thin films shows diode-like I–V characteristics with high breakdown voltage. The variation is discussed in relation to changes in surface roughness.