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.

A spin transistor which consists of a metallic giant magnetoresistance emitter, a copper base, and a p-n junction was prepared on a Si(100) wafer. The emitter current changes from 1mA at a magnetically parallel state to 0.968mA at a magnetically antiparallel state. At the same states the base currents were 29.3μA and 333nA, respectively, which gave a magnetocurrent ratio of ∼8600% and a transfer ratio of 3×10−2 at room temperature for a common collector configuration. The sensitivity of this spin device is higher than 4000%∕Oe. The memory effect and the high performance make it possible for practical usage. The working principle of this kind of three-terminal spin device can be simply described by circuit theory.

A spin transistor consisting of a metallic pseudo-spin-valve emitter, a copper base, and a p-n junction collector was prepared on a Si(100) wafer. This spin transistor can provide high magnetocurrent output, high magnetocurrent variation, and high transfer ratio. The common collector configuration with an emitter bias of 5.12V at 77K gives a large magnetocurrent variation of more than 95.5μA in the collector, and the change is more than 3400% with a transfer ratio of 2.59×10−3. At room temperature, these changes go down to 98.3μA and 55.3%, respectively, and the transfer ratio rises to 5.98×10−3. The high performance of this spin-valve transistor is due to the use of a p-n junction as an energy barrier to select spin electrons.

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