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This work investigates the variations of the infrared transmission spectra of yttrium-hydride films YH[sub x] during the hydrogen loading process for the frequency range 500-4000 cm-1. The results indicate that the transmittance slightly decreases in the dihydride phase, followed by a significant increase in the trihydride phase. In addition, the carrier concentration decreases, whereas the carrier relaxation time increases with hydrogen content. The hydrogen vibration modes at interstitial sites are completely screened in the dihydride phase. The screening effect decreases as the system goes through the metal-insulator transition. Moreover, the screening effect can be continuously tuned by simply varying the hydrogen content in the yttrium-hydride system. Analysis indicates that the absorption intensity of the vibration mode depends on the carrier concentration. This effect can be used as a diagnostic tool for estimating the carrier concentration and hydrogen content i! n rare-earth hydrides. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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]

A series of hysteresis loops with off-axial external magnetic fields have been measured to identify magnetization reversal properties as well as coupling effects in magnetic tunnel junctions (MTJs). MTJ films, consisting of a synthetic artificial antiferromagnetic pinned layer of CoFeB/Ru/CoFe/IrMn, were patterned into an elliptical cell array with sizes of 200 × 300 nm and 500 × 750 nm. The hysteresis loops were measured using a vibrating sample magnetometer with various directions of the external magnetic field; the angle θ between the external magnetic field (Hvector E) and the biasing field of the pinned layer (Hvector B) was varied from 0° to 90°. The two significant coupling effects, ascribed to exchange bias between CoFe/IrMn and Ruderman-Kittel-Kasuya-Yosida-like coupling in CoFeB/Ru/CoFe, can be observed in these hysteresis loops. The angular dependence of the hysteresis loops is employed to characterize the variation of these coupling effects in extended and patterned MTJ films. [ABSTRACT FROM AUTHOR]

Presents information on photoluminescence and photominescence excitation spectroscopy which is from triple barrier resonant tunneling structures. Purpose of the spectroscopic techniques; Details on the charging behavior; Evidence for negatively charged exciton formation in the first quantum well.

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]