Magnetic force microscopy (MFM) observations have been performed on artificial structures of single-phase Ga0.962Mn0.038N grown by metal organic chemical vapor deposition, showing room-temperature long range magnetic order of Ga0.962Mn0.038N. The MFM results agree well with the theoretical simulation under assumption of uniform magnetization. The ferromagnetism of Ga1−xMnxN is suggested to be closely related to the configuration of Mnn+ and Mn(n+1)+ (n=2,3). This work indicates potential of effectively applying MFM to a variety of weak magnetic epitaxial thin films.
We have investigated the magnetization reversal process of the disk-, ring-, and center dot ring-patterned Ni80Fe20 wires. For the fields applied perpendicular to the wire direction, interesting shape dependent magnetoresistance (MR) ratios were found. The MR ratios were varied from 0.8%, 0.65%, and 0.4% at room temperature and 1.7%, 1.5%, and 1.1% at 10 K for the disk-, ring-, and center dot ring-patterned wires. For the same wires, the switching field is reduced from −170, −110, and −90 Oe at room temperature to −140, −70, and −20 Oe at 10 K. These results were due to the shape anisotropy and domain-wall motion. The anisotropy MR (AMR) ratios measured at 10 K of the disk-, ring-, and center dot ring-patterned wires were 1.9±0.1%, 1.7±0.1%, and 1.3±0.1%, respectively, it is almost even the same (1.1±0.1%) at room temperature. We have observed that the center dot reduces the MR ratio and increases magnetic saturation field of the nanosize Ni80Fe20 wires.
High-speed laser photography was used in two measurements on the radial expansion dynamics of unichiral, S = 1 magnetic bubbles during and after the application of large 20-, 40-, and 57-Oe expansion pulses. The bubble diameter was photographed at varying intervals after the beginning of a 120-ns pulse and the chirality change resulting from the application of pulses of widths from 17.5 to 120 ns measured. Plots of the probability of chirality change versus pulse width were used to infer the rate of rotation of the magnetization within the wall. Results are compared with the one space dimensional Schryer-Walker model. The features of high-speed initial motion followed by a slower uniform average velocity agree between the model and the data, but the large transients predicted when the pulse leaves the bubble in the unstable Néel wall state were never observed. It is necessary to increase the Gilbert damping parameter a by fourfold in order to get quantitative agreement between the model and the diameter data. The rotation rate of the model and the data agree for the 57-Oe pulse but a fourfold a increase is required at the lower amplitudes.
Advances in real-time magnetic force microscopy (MFM) permit us to directly observe the domain structures under magnetic field, which enable us to understand magnetic phenomena in nanostructure with controlled shapes. Magnetoresistance change is a complementary way to understand the magnetization reversal process, e.g., domain wall formation and annihilation. Using systematic pattern design, we arrange Permalloy octagons in chains to study the associated domain configurations inferred from real-time MFM and MR loop.
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