Abstract
We have studied experimentally the states formed in artificial square ice nanomagnet systems following demagnetisation in a rotating in-plane applied magnetic field that reduces to zero in a manner that is linear in time. The final states are found to be controlled via the system's lattice constant, which determines the strength of the magnetostatic interactions between the elements, as well as the field ramping rate. We understand these effects as a requirement that the system undergoes a sufficiently large number of active rotations within the critical field window in which elements may be reversed, such that the interactions are allowed to locally exert their influence if the ground state is to be approached. On the other hand, if quenched disorder is too strong when compared to the interaction strength, any close approach to the ground state is impossible. These results show that it is not necessary for there to be any ac component to the field amplitude that is applied to the system during demagnetisation, which is the method almost exclusively employed in field protocols reported to date. Furthermore, by optimising the parameters of our linear demagnetisation protocol, the largest field-generated ground state domains yet reported are found.
Highlights
Artificial spin ices are patterned nanomagnet arrays designed to act as analogs of bulk geometrically frustrated materials [1, 2]
MAGNETIC STATES vs. LATTICE CONSTANT Figure 3 shows a series of magnetic force microscopy (MFM) images of states prepared for r = 6 Oe/s, with a shown in each case
Whilst field-driven demagnetization is not as effective at larger a, we have shown here that the field ramping rate is crucial, which determines how many active rotations a system undergoes whilst the applied field lies within a critical dynamical window
Summary
Artificial spin ices are patterned nanomagnet arrays designed to act as analogs of bulk geometrically frustrated materials [1, 2] They realize two-dimensional (2D) Ising and vertex ice models [3,4,5], in which each single domain element forms an anisotropic macrospin which can be directly imaged via magnetic microscopy. As they are built via nanolithography and thin film deposition, it is possible to engineer system parameters such as lattice geometry [6], inter-elemental dipolar coupling strength [2, 3], moment switching behavior [7], and (to an extent) quenched disorder (QD) [3, 8]. The repeatable experimental access of well-defined states is of its own interest and is further complementary to numerous current studies, e.g., of ferromagnetic resonance in nanopatterned magnetic structures [18,19,20] and numerical simulations of ordering processes [21,22,23,24,25]
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