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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]

Films of L11-type CoPt/NiFe exchange springs were grown with different NiFe (Permalloy) layer thickness (tNiFe=0-10 nm). X-ray diffraction analysis reveals that the characteristic peak position of NiFe(111) is not affected by the CoPt-layer-confirming the absence of any inter-diffusion between the CoPt and NiFe layers. Magnetic studies indicate that the magnetization orientation of NiFe layer can be tuned through varying tNiFe and the perpendicular magnetic anisotropy of L11-type CoPt/NiFe films cannot sustain for tNiFe larger than 3.0 nm due to the existence of exchange interaction at the interface of L11-CoPt and NiFe layers. Magnetic force microscopy analysis on the as-grown samples shows the changes in morphology from maze-like domains with good contrast to hazy domains when tNiFe≥3.0 nm. The three-dimensional micro-magnetic simulation results demonstrate that the magnetization orientation in NiFe layer is not uniform, which continuously increases from the interface to the top of NiFe layer. Furthermore, the tilt angle of the topmost NiFe layers can be changed over a very wide range from a small number to about 75° by varying tNiFe from 1 to 10 nm. It is worth noting that there is an abrupt change in the magnetization direction at the interface, for all the tNiFe investigated. The results of present study demonstrate that the tunable tilted exchange springs can be realized with L11-type CoPt/NiFe bilayers for future applications in three-axis magnetic sensors or advanced spintronic devices demanding inclined magnetic anisotropy. [ABSTRACT FROM AUTHOR]

We report a study of magnetization reversal process on a tall magnetic nano-ring with a wall height-to-thickness ratio of up to 21. Samples in a hexagonal lattice pattern of ring array with an outer/inner diameter of 300/260 nm and a ring height of 420 nm are fabricated using electron beam lithography in conjunction with an ion beam etching technique. A longitudinal magneto-optical Kerr effect (MOKE) measurement reveals that meta-stable states exist during the magnetization reversal process. In particular, the exact magnetization configurations at the top end of the nano-ring are illustrated using magnetic force microscopy (MFM) that is facilitated with a photoresist etch-back technique. Most interestingly, MFM images of two sets of head-to-head (H2H)/tail-to-tail (T2T) domain walls are captured during the magnetization reversal process. It is believed that the domain walls formation and evolution processes at the top end of the nano-ring are mediated by the anti-symmetrical distribution of the vortex domain wall on the tubular sidewalls. Simulation results using Object Oriented Micromagnetic Framework confirm the MOKE hysteresis loop and MFM imaging. [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]

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]