The magnetoimpedance effect was employed to study magnetotunneling junction (MTJ) with the structure of Ru(5nm)∕Cu(10nm)∕Ru(5nm)∕IrMn(10nm)∕CoFeB(4nm)∕Al(1.2nm)-oxide∕CoFeB(4nm)∕Ru(5nm). A huge change of more than ±17000% was observed in the imaginary part of the impedance between the magnetically parallel and antiparallel states of the MTJ. The inverse behavior of the magnetoimpedance (MI) loop occurs beyond 21.1MHz; however, the normal MI at low frequency and the inverse MI at high frequency exhibit the same magnetization reversal as checked by the Kerr effect. The reversal in MI was due to the dominance of magnetocapacitance at high frequency.

Articles you may be interested inSpin-valve transistors with high magnetocurrent and 40 μA output currentThe magnetoimpedance ͑MZ͒ effect of the pseudo-spin-valve transistor ͑PSVT͒ was investigated at room temperature in the frequency ranged from 100 Hz to 15 MHz. The PSVT can be regarded as a complex combination of resistors, inductors, and capacitors, while the impedance ͑Z͒ consists of a real part, the resistance ͑R͒, and an imaginary part, the reactance ͑X͒. Besides, all these components exhibit magnetic hysteresis. It is due to the frequency dependent behavior that R does not reach a minimum at the resonant frequency ͑f r ͒. The frequency dependences of MZ and MX ratios cross zero at f x = 6.5 MHz and at f r = 3.65 MHz, respectively. The shape of magnetoreactance ͑MX͒ loop is reverse to the magnetoresistance ͑MR͒ loop; furthermore, MX ratio changes sign from negative at f Ͻ f r to positive at f Ͼ f r . The MZ loop also reverses shape and sign after crossing f x . For instance, the MZ loop with a ratio of 0.077% at 6 MHz switches to −0.086% and −0.125% at 7 and 8 MHz, respectively.

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The resistance bistability and the switching effect has been systematically studied in nickel oxide films with variable oxygen concentrations. Both the switching bias voltage and the resistance ratio of RESET to SET were found to be strongly concentration dependent. Meanwhile, the electrical characteristics can be exactly examined by an Schottky emission. By means of mathematical fitting, the resistance bistability seems to be related to the alternating of dielectric constant and the barrier height. Furthermore, the room temperature cycle endurance with a distinguishable operation window was found to exceed 800. This indicates that the nickel oxide has the potential to be a promising material on resistance random access memory.

The crystallization structure and thickness of PtMn layer in a magnetic tunnel junction system are important factors to improve its exchange bias effect. This study shows that the PtMn layer could be changed from a FCC (111) structure to a FCT (111) structure after annealing above 270 °C. The minimum thickness of PtMn layer is found to be 10 nm for exchange coupling effect to be occurred in our MTJ system. The magnetic exchange effect between PtMn and SAF layers is near 4,300 Oe. Annealing temperatures can be higher than 400 °C for samples without patterning; however, temperature at 275 °C is too high for samples after patterning. This may be due to the breakdown of edges of the patterned samples as well as the complicated environments around the patterned samples.