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The current induced magnetization reversals on the free layer of patterned spin valve ellipse have been investigated using differential magnetoresistance (MR) measurements, in which various direct currents were superimposed to 14 μA alternating current for the MR measurements. Conventional field scanned MR minor loops and subminor loops were measured under different scan ranges of magnetic field to verify the existing metastable states. The magnetization transitions between metastable states were realized in the dc scanned MR loop, in which the resistance levels were identified in accordance with the field scanned MR loop. This phenomenon is believed to be associated with the domain wall motion pushed by the direct current. [ABSTRACT FROM AUTHOR]

Controllable remanent states have been studied on the microstructured magnetic tunnel junction (MTJ) rings through magnetoresistance measurements. These rings were designed accordingly with an outer/inner diameter of 2/1 and 1/0.5 µm to reveal two and one metastable states, respectively, during the magnetization reversal process on the free layer. The distinct magnetoresistance levels based on the tunneling magnetoresistance effect are associated with the relative alignment of magnetization of free layer and pinned layer. As a result, four and three controllable remanent magnetic states on the free layer were manipulated by ramping external magnetic fields, applied in the biasing direction, with various field ranges, giving rise to four and three stable mangetoresistance values at zero field. These results may provide a great potential in magnetic multibit memory applications using ring-shaped cells. [ABSTRACT FROM AUTHOR]

Microstructured magnetic tunnel junction rings have been fabricated by a top-down technique combining electron beam lithography and ion milling process. Four-terminal magnetoresistance measurements and magnetic force microscopy were used to successfully explore a four-transition process within the free layer throughout the magnetization reversal. Various magnetization configurations were identified to be the onion state, vortex-pair state, vortex state, vortex-core state, and reverse onion state. In addition, the various durations of each magnetic state observed in the magnetoresistance curve can be utilized for the study of a coupling effect between the pinned layer and the free layer. [ABSTRACT FROM AUTHOR]

In this study, the exchange coupling properties of submicron patterned MnIr/CoFe bilayers with strong exchange coupling strength were investigated. The large area of 2.5 mm\,\times\,2.5 mm of submicron sized bilayer rings were fabricated by electron beam lithography and ion-milling processes. The clear variations of normalized magnetic hysteresis loops of patterned films are the degradation of pinned CoFe at the MnIr/CoFe interfaces and the decrease of exchange bias field, comparing with sheet film. After post-field-annealing treatment, only the exchange field was improved. A magnetic tunnel junction ring with outer diameter/linewidth of 2/0.5 \mum was constructed as well to further certify the speculations. The magnetoresistance loops of as-fabricated and post-field annealed MTJ ring revealed that the slightly improved magnetoresistance ratio and exchange field. These results were attributed to the rearrangement of distorted spins at the sample edges. However, in comparison with sheet film, the great degradation of magnetoresistance ratio of patterned device, without respect to as-fabricated or post-field annealed, was not retrieved, revealing that the futility of post-field-annealing treatment to the pinning portion of CoFe layer. [ABSTRACT FROM AUTHOR]

Microstructured magnetic tunnel junction ring with outer/inner diameter of 2/1 μm has been fabricated to investigate the angular dependence of magnetoresistance during magnetization reversal process. The minor loop of magnetoresistive curve reveals four distinct resistance levels associated with four magnetization configurations within the free layer throughout the magnetization reversal. The magnetoresistance decreases with increasing angle between applied external field and biasing direction, which is resulted from the relative alignment of total magnetization of pinned and free layer. An extra feature appeared in the minor loop when the external field is transverse to the biasing direction; this can be attributed to a vortex-pair formation/annihilation in the free layer. Furthermore, a series of schemes of magnetic configurations of pinned and free layers are illustrated to explain the routes of minor loops. [ABSTRACT FROM AUTHOR]