Magnetic reversal dynamics of NiFe-based artificial spin ice: Effect of Nb layer in normal and superconducting state

Abstract

Square arrays of artificial spin ice (ASI) constituting weakly interacting NiFe nano-islands, with length ∼312 nm, width ∼125 nm, thickness ∼20 nm, and lattice constant ∼570 nm, were fabricated on Nb thin film and on thermally grown 300 nm SiO2 on silicon. Detailed investigations of magnetic force microscopy (MFM) at room temperature, and magnetization M(H) loops and relaxation of remanent magnetization (Mr) at various temperatures were carried out in two in-plane field geometries, namely, parallel (“P”-parallel to the square lattice) and diagonal (“D”- 45° to the square lattice). The magnetic response of the ASI samples shows striking difference for insulating (SiO2), metallic (Nb, T > 6.6 K) and superconducting (Nb, T < 6.6 K) bases, and the field geometry. For instance, with the Nb base in the normal metallic state (T > 6.6 K), (1) in “P” geometry the M(H) loops are found to be more “S” shaped in comparison with that for SiO2 base; (2) the ratio of magnetic vertex population of Type II to Type III vertices extracted from MFM studies in “P”(“D”) geometry is ∼1:1.1(1.2:1) that changed for the SiO2 base to ∼2.1:1 (4: 1). However, the NiFe-ASI on both metallic Nb and SiO2 bases exhibit a highly athermal decay of magnetization, and the % change in Mr in about two hours at T = 10 K (300 K) lies in a range of ∼1.07–1.80 (0.25–0.62). With Nb base in superconducting state (T < 6.6 K), the M(H) loops not only look radically different from those with SiO2 and metallic Nb as bases but also show significant difference in “P” and “D” geometries. These results are discussed in terms of inter-island magnetostatic energy as influenced by field geometry, presence of metallic Nb base and competing vortex pinning energy of superconducting Nb base.

Emergent Magnetic Monopole and Dipole Screening by Proximity Effect With Noble Metal

“…In the hysteresis curve of Figure 2a, it is possible to observe reasonable coercivity decrease and vanishing of steps related to magnetostatic traps from nanomagnets defects when aluminum layer is present. Similar results were reported using vibrating sample magnetometry technique for ASI in contact with normal metal and superconductor 35 . Most pronounced effect can be noticed in the monopole density evolution curve of Figure 2b, with smaller Figure 1.…”

Emergent magnetic monopole and dipole screening by proximity effect with noble metal

“…In the hysteresis curve of Figure 2a, it is possible to observe reasonable coercivity decrease and vanishing of steps related to magnetostatic traps from nanomagnets defects when aluminum layer is present. Similar results were reported using vibrating sample magnetometry technique for ASI in contact with normal metal and superconductor [36].…”

Influence of cutoff dipole interaction radius and dilution on phase transition in kagome artificial spin ice

“…The main distinctive feature of artificial spin ice from spin ice is that due to its mesoscopic scale and two-dimensionality, both the state of each island and the state of the system as a whole can be investigated using contemporary technologies. The modern development of experimental approaches allows observing static magnetic states of the systems using MFM [3,4,5,6,7], it is even possible to observe dynamic magnetic states in real time with X-PEEM [8] and XMCD-PEEM [9,10,11,12] methods. Gartside et al in recent work [13] showed the "topological defect-driven magnetic writing" method with which one can set the direction of magnetization for each macrospin in the array of artificial spin ice.…”