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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]

This report investigates the current-induced switching of exchange bias without an external magnetic field in nano-scaled magnetic tunnel junction (MTJ) cells. An MTJ stack film was patterned into an ellipse with dimensions of 120 nm × 270 nm by using standard electron beam lithography in combination with ion beam etching. A spin-polarized current pulse with a duration of 100 ns was used to switch the exchange bias direction of the synthetic antiferromagnetic (SAF) pinned layer. It is worth noting that the MTJ cell was initialized in a high resistance state before applying the current pulse. For the application of both positive and negative current pulses, the resistance can be switched from the high (antiparallel) state to the low (parallel) one at 2.95 and -2.80 mA, respectively. After the current-induced switching, it was found that the magnetoresistance curve is reversed relative to the one before the current-induced switching. Predominantly, this behavior is independent of the polarity of the current pulse. As a result, it is shown that the exchange bias in the SAF pinned layer changes its direction with a sufficient supply of current pulse. [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]

A 3-pole gradient-damping wiggler (GDW) was developed for the ALPHA storage ring at Indiana University. The GDW is effective in modifying the momentum-compaction factor and the damping partition number in the ALPHA storage ring. The yokes of GDW are made by lamination of silicon steel sheets (50CS1300) with a thickness 0.5 mm. Glue (3M 2216) is used to paste the lamination sheets together to create a block using a punch fixture. The C-shape structure and the pole profile of the damping wigglers are cut from the silicon-steel blocks with the wire-cutting machine. One middle pole and two outer poles are assembled on the same girder as the set of GDW. The oblique of pole profile of middle and outer poles is different to obtain the same polarity of gradient field. The magnet gaps of the middle and outer poles are 40 and 35.87 mm; respectively to obtain the same dipole field strength. The field strengths of dipole and gradient-field of the middle (outer) pole are 0.67 T (-0.67 T) and 1.273 T/m (1.273 T/m), by keeping the integral ratio of (dB/dx)/B=1.9\ m^-1 constant. The three combined functions of the dipole magnet can be charged in 1 Hz with a single power supply. There are trim coils on the three poles to adjust the first and second integral fields to zero. The good field region of the middle and outer poles along the transverse x-axis (\DeltaB/B=0.1\%) are \pm50 and \pm40 mm respectively. After fabrication of one set GDW magnet, a Hall probe measurement system was used to measure the magnetic field to verify the design and construction performance of the magnet. [ABSTRACT FROM PUBLISHER]

This paper presents the design of magnets for the storage ring of the 3-GeV Taiwan Photon Source project. Detailed calculations of the field were performed according to a three-dimensional model, and the magnetic geometry was determined in transverse and longitudinal planes to conform to highly precise magnetic fields. The final tolerances of the pole profiles of the magnets within 20 \mum were manufactured and measured in all prototype magnets. The characteristics of the magnetic fields were measured with Hall-probe and rotating-coil systems to verify the quality of the magnetic fields. The centers of the magnets will be aligned on the girder with precisely machined rails within 20 \mum, and the magnets have no provision for shimming on the girder. The features of the main field and homogeneity of these magnets are described and analysed to reveal the satisfactory magnetic performance. [ABSTRACT FROM PUBLISHER]

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]