Field-tuned quantum tunneling in a supramolecule dimer [Mn4]2[Mn_4]_2

Field-tuned quantum tunneling in two single-molecule magnets coupled antiferromagnetically and formed a supramolecule dimer is studied. We obtain step-like magnetization curves by means of the numerically exact solution of the time-dependent Schr\H{o}dinger equation. The steps in magnetization curves show the phenomenon of quantum resonant tunneling quantitatively. The effects of the sweeping rate of applied field is discussed. These results obtained from quantum dynamical evolution well agree with the recent experiment[W.Wernsdorfer et al. Nature 416(2002)406].Comment: 11 pages, 4 figures, 2 tables. Submited to Phys. Rev.

Current-driven spring-like oscillatory motion of coupled vortex walls in a two-nanostripe system

In a two closely spaced nanostripes system, the coupled vortex wall undergoes a spring-like oscillatory motion (SOM) when current is applied to both nanostripes in opposite directions. The SOM may vanish, when the current density is larger than a critical value. The critical current density for destroying the SOM decreases as the interstripe spacing increases. However, as the perpendicular anisotropy of the system increases, the critical current density firstly decreases and then increases. Two competitive effects of the perpendicular anisotropy on the SOM are shown. Moreover, diagrams of without oscillation, spring behavior and motionless phases upon the current and the interstripe spacing (or the perpendicular anisotropy) are given

Manipulation of multiple 360o domain wall structures and its current-driven motion in a magnetic nanostripe

Dynamics of multiple transverse walls (TWs) in a magnetic nanostripe is studied by micromagnetic simulations. It shows that, when TWs are arranged in a stripe with same orientation, they will attract each other and finally annihilate. However, when adjacent TWs are arranged with opposite orientation, a metastable complex wall can be formed, e.g., two TWs lead to 360o wall. For three or more TWs, the formed complex wall includes a number of 360o substructures, which is called multiple 360o structure (M360S) here. The M360S itself may be used to store multiple logical data since each 360o substructure can act as logical ”0” or ”1”. On the other hand, the M360S may behave like single TW under an applied current, namely, the M360S can be driven steadily by current like that of single TW. A parity effect of the number of 360o substructures on the critical current for the annihilation is found. Namely, when the number is odd or even, the critical current increase or decrease with the increasing of the number, respectively. The parity effect is relevant to the out-of-plane magnetic moment of the M360S