D. C. Chen

Bio: D. C. Chen is an academic researcher from National Chiao Tung University. The author has contributed to research in topics: Magnetoresistance & Domain wall (magnetism). The author has an hindex of 4, co-authored 13 publications receiving 39 citations. Previous affiliations of D. C. Chen include Academia Sinica.

Demonstration of edge roughness effect on the magnetization reversal of spin valve submicron wires

Abstract: We prepared submicron wide trilayer spin valve wires designed with periodic “spikes” as artificial roughness. The height and the pitch of the spikes were varied systematically. No obvious dependence was found between the roughness and the domain wall velocity when the spikes were smaller than a threshold of 30 nm for NiFe. The average velocity was slowed down when the height of the spikes were larger than the threshold. In-plane transverse magnetic fields help to reduce the critical current density for current induced domain-wall motion. Our results could be attributed to the space modulation of the local magnetization.

Variation of magnetization reversal in pseudo-spin-valve elliptical rings

Abstract: We studied nanoscale elliptical ring shaped NiFe/Cu/NiFe trilayer pseudo-spin-valve structures. The magnetization reversal processes showed simultaneous-reversal single-step transition or double-step transition involving flux closure states. For various aspect ratios (short axis to long axis) and linewidths, transition between single-step and double-step magnetization reversals was measured to form a phase diagram. When the linewidth was reduced, edge roughness became important. Simulations of the magnetization reversal behavior agreed qualitatively with our results.

Magnetic switching and reversal process in a tip ring structure

Abstract: Patterned Permalloy submicron-size structures have been fabricated by e-beam lithography in the shape of a ring with a tip. A tip was intentionally added into the ring as a geometrical defect to interrupt the continuity of the magnetization, which aligns along the ring, in order to pin the domain wall. Magnetic switching and reversal process have been measured by the magnetoresistance measurement. The switching field about 260 Oe was obtained. At the remanent state, there was a 0.21% difference in the magnetoresistance between the angles of 90° and 0° that was equivalent to the domain wall magnetoresistance. By applying an external field, the domain wall moved along the ring under a lower field (100 Oe), which is smaller than the switching field. A drop (0.24%) in the resistance between the angle of 70°–120° has been observed that means the domain wall was moving into the voltage measuring region during the rotation.

Structure and magnetic properties of Co grown on yttria-stabilized cubic zirconia substrates

Abstract: Cobalt films have been grown on yttria-stabilized cubic zirconia (YSZ) (100) and (110) substrates by molecular beam epitaxy. Both hcp(0001) and fcc(111) twin structures and fcc(110) films have been successfully fabricated on the YSZ(100) and (110), respectively. For the Co on YSZ(100) case, the Co films possess either hcp(0001) or fcc(111) crystals with in-plane 30° rotation. For the Co on YSZ(110) case, the structural relationship is YSZ(110)[100] ‖ Co(110)[1–10]. All the films display an isotropiclike magnetic anisotropy with the coercivity increasing abruptly above its martensitic transition temperature. The coercivity decreases with increasing the thickness of Co films from 100 A to 500 A; and increases as the deposited temperature above 500 °C. Co films grown on YSZ(100) are in favor of the layer by layer growth, and Co films grown on YSZ(110) are in favor of the island growth.

Spin-polarised currents and magnetic domain walls

Abstract: Electrical currents flowing in ferromagnetic materials are spin-polarised as a result of the spin-dependent band structure. When the spatial direction of the polarisation changes, in a domain structure, the electrons must somehow accommodate the necessary change in direction of their spin angular momentum as they pass through the wall. Reflection, scattering, or a transfer of angular momentum onto the lattice are all possible outcomes, depending on the circumstances. This gives rise to a variety of different physical effects, most importantly a contribution to the electrical resistance caused by the wall, and a motion of the wall driven by the spin-polarised current. Historical and recent research on these topics is reviewed. Contents PAGE 1. Introduction5862. Spin-polarised current587 2.1. Tunnelling current spin polarisation589 2.2. Ballistic current spin polarisation592 2.3. Diffusive current spin polarisation5933. Magnetic Domain Walls598 3.1. Basics of domain walls598 3.1.1. Domain wall thickness and...

The stochastic nature of the domain wall motion along high perpendicular anisotropy strips with surface roughness

Abstract: The domain wall dynamics along thin ferromagnetic strips with high perpendicular magnetocrystalline anisotropy driven by either magnetic fields or spin-polarized currents is theoretically analyzed by means of full micromagnetic simulations and a one-dimensional model, including both surface roughness and thermal effects. At finite temperature, the results show a field dependence of the domain wall velocity in good qualitative agreement with available experimental measurements, indicating a low field, low velocity creep regime, and a high field, linear regime separated by a smeared depinning region. Similar behaviors were also observed under applied currents. In the low current creep regime the velocity-current characteristic does not depend significantly on the non-adiabaticity. At high currents, where the domain wall velocity becomes insensitive to surface pinning, the domain wall shows a precessional behavior even when the non-adiabatic parameter is equal to the Gilbert damping. These analyses confirm the relevance of both thermal fluctuations and surface roughness for the domain wall dynamics, and that complete micromagnetic modeling and one-dimensional studies taking into account these effects are required to interpret the experimental measurements in order to get a better understanding of the origin, the role and the magnitude of the non-adiabaticity.

Magnetic Vortex Core Observation in Circular Dots of Permalloy (SOLID STATE CHEMISTRY-Artificial Lattice Allolys)

Abstract: Spin structures of nanoscale magnetic dots are the subject of increasing scientific effort, as the confinement of spins imposed by the geometrical restrictions makes these structures comparable to some internal characteristic length scales of the magnet. For a vortex (a ferromagnetic dot with a curling magnetic structure), a spot of perpendicular magnetization has been theoretically predicted to exist at the center of the vortex. Experimental evidence for this magnetization spot is provided by magnetic force microscopy imaging of circular dots of permalloy (Ni(80)Fe(20)) 0.3 to 1 micrometer in diameter and 50 nanometers thick.

Nanopatterning of a thin ferromagnetic CoFe film by focused-ion-beam irradiation

Abstract: High-resolution magnetic patterning of a thin CoFe layer has been performed by irradiation using a focused-ion-beam system. Features <50nm wide were formed reproducibly. The irradiated pattern comprised sets of alternating 3.0- and 1.0-μm-long magnetic wires, 100 nm wide. During magnetization reversal, the longer wires reversed at a lower field resulting in the formation of an ordered array of domains with density 10μm−1 supporting antiparallel magnetization. The ability to create domains at predefined locations is important both for fundamental studies and technological applications.