Magnetic reversal in nanoscopic ferromagnetic rings

Abstract

We present a theory of magnetization reversal due to thermal fluctuations in thin submicron-scale rings composed of soft magnetic materials. The magnetization in such geometries is more stable against reversal than that in thin needles and other geometries, where sharp ends or edges can initiate nucleation of a reversed state. The 2D ring geometry also allows us to evaluate the effects of nonlocal magnetostatic forces. We find a 'phase transition', which should be experimentally observable, between an Arrhenius and a non-Arrhenius activation regime as magnetic field is varied in a ring of fixed size.

Fluctuations, classical activation, quantum tunneling, and phase transitions

“…The constant τ 0 in (40) indicates the translational symmetry in imaginary time arising from the periodic boundary conditions, and corresponds to a zero mode as described in Sec. III.…”

Energy barriers for bit-encoding states based on 360° domain walls in ultrathin ferromagnetic nanorings

“…It has been realized that switching between the two vortex directions may present difficulties due to high current densities that may be required. [5][6][7]10,11 At the same time, while vortices are always energetically preferred, in ultrathin ferromagnetic nanorings, they coexist with the long-lived metastable magnetization configurations, such as the onion and the twisted states, which belong to a different topological class. 7,12,13 Persistence of these configurations is due to the fact that by topological reasons the magnetization is required to go out of plane in order for a transition to the vortex state to occur.…”

“…[1][2][3][4][5][6][7][8][9] In the simplest device concept, one bit of information is encoded by the polarity of the vortex state in a ring. It has been realized that switching between the two vortex directions may present difficulties due to high current densities that may be required.…”

Determination of the exchange constant ofTb0.3Dy0.7Fe2by broadband ferromagnetic resonance spectroscopy

“…This includes static properties such as saturation magnetization, anisotropy field(s) and quasi-static magnetoelastic coupling coefficients, along with dynamic properties including Gilbert damping, the spectroscopic g –factor and the exchange stiffness. The last parameter is particularly important as it determines the most energetically favorable magnetic configurations in nanoscale magnetic objects, for example in nanorings 23,24 and nanopillars. 25 With regards to the magnetic transition metals (Ni, Fe and Co) and their alloys, these properties have been studied extensively; however, their rare earth counterparts have only just begun to be critically examined, especially as it pertains to their dynamic properties.…”