Hong-Guang Piao

Ratchet effect of the domain wall by asymmetric magnetostatic potentials

We investigate a ratchet effect of magnetic domain wall motion in a ferromagnetic nanowire under AC magnetic fields using micromagnetic simulation. The ratchet effect for a transverse domain wall is achieved using an asymmetric magnetic potential generated by stray fields from non-contact trapezoidal ferromagnetic stubs near the straight nanowire. The ratchet phenomenon has been examined with various combinations of amplitude and frequency of the driving AC field. Interestingly, we find that the domain wall propagates along a preferential direction by the diode-like ratchet effect under AC field. The propagation of the domain wall strongly depends on the profile of the asymmetrical magnetic potentials and the driving AC field characteristics.

Ratchet Effect of Domain Wall Motion by GHz AC Magnetic Field in Asymmetric Sawtooth-Shaped Ferromagnetic Nanowires

We have investigated a ratchet effect of magnetic domain wall in asymmetric sawtooth-shaped ferromagnetic nanowires under high frequency AC magnetic fields by means of micromagnetic simulation. The ratchet phenomenon has been intensively examined during the domain wall propagation with variation of the asymmetric sawtooth geometry of nanowires as well as variation of the AC external field frequency/strength. Very interestingly, it has been found that there is a strong correlation between the spatial frequency of asymmetrical notches and the effective driving frequency/strength of AC external fields. It is demonstrated that number of notches swept by domain wall ratchet motion per each half-cycle of the driving frequency is controlled under a GHz AC driving field.

Enhanced low field magnetoresistance in germanium and silicon-diode combined device at room temperature

We report on a large (∼200%), room-temperature, small field (20 mT) magnetoresistance effect in germanium and silicon-diode combined device. This enhanced magnetoresistance is attributed to geometry of germanium and nonlinear electro-transport characteristic of silicon-diode. A two-dimensional finite element model is built to simulate the experimental results. Our work may pave a way to develop low field magnetoresistance devices from germanium and silicon.

Enhanced linear magnetoresistance of germanium at room temperature due to surface imperfection

We report an enhanced linear magnetoresistance in germanium at room temperature. The magnetic-field dependence shows no saturation at magnetic fields (B) up to 4 T and the magnetoresistance sensitivity at low fields (B < 0.4 T) can reach ∼8 T−1. It is found that this magnetoresistance effect is ascribed to surface imperfection, which cannot only increase the recombination rate but also enhance the inhomogeneity. Our work may be attractive to the magnetic-field sensing industry and make germanium-based magnetoelectronics further developed.

Programmable Logic Based on Large Magnetoresistance of Germanium

We find extremely large low-magnetic-field magnetoresistance (~350% at 0.2 T and ~180% at 0.1 T) in germanium at room temperature and the magnetoresistance is highly sensitive to the surface roughness. This unique magnetoelectric property is applied to fabricate logic architecture which could perform basic Boolean logic including AND, OR, NOR and NAND. Our logic device may pave the way for a high performance microprocessor and may make the germanium family more advanced.