Effect of FePd alloy composition on the dynamics of artificial spin ice

Abstract

Artificial spin ices (ASI) are arrays of single domain nano-magnetic islands, arranged in geometries that give rise to frustrated magnetostatic interactions. It is possible to reach their ground state via thermal annealing. We have made square ASI using different FePd alloys to vary the magnetization via co-sputtering. From a polarized state the samples were incrementally heated and we measured the vertex population as a function of temperature using magnetic force microscopy. For the higher magnetization FePd sample, we report an onset of dynamics at T = 493 K, with a rapid collapse into >90% ground state vertices. In contrast, the low magnetization sample started to fluctuate at lower temperatures, T = 393 K and over a wider temperature range but only reached a maximum of 25% of ground state vertices. These results indicate that the interaction strength, dynamic temperature range and pathways can be finely tuned using a simple co-sputtering process. In addition we have compared our experimental values of the blocking temperature to those predicted using the simple Néel-Brown two-state model and find a large discrepancy which we attribute to activation volumes much smaller than the island volume.

A comparative study of the influence of the deposition technique (electrodeposition versus sputtering) on the properties of nanostructured Fe70Pd30 films

“…Iron-palladium alloys arise great attention from the technological viewpoint as they show a unique and very interesting combination of mechanical and magnetic properties. As a result, they find uses in magnetic recording media [1][2][3], as microactuators and microsensors [4,5] or in spintronics [6]. In particular, the Fe 70 Pd 30 (at.%) alloy shows the so-called ferromagnetic shape memory effect, related to the occurrence of a martensitic-to-austenitic phase transition [7,8].…”

Understanding thermal annealing of artificial spin ice

“…Certain artificial spin ice geometries have well-defined collective magnetic ground states, such as the square lattice 1 , while others have intrinsically disordered and complex ground states, such as the Shakti lattice [3][4][5] . These low-energy collective states have sparked considerable interest in attempting to realize the lowest energy state of different artificial spin ice lattices [6][7][8][9][10] . One successful approach to collective energy minimization involves annealing the arrays by heating them to temperatures near or above the Curie temperature (T C ) of the ferromagnetic material 11,12 .…”

Magnetization Dynamics of weakly Interacting sub-100 nm Square Artificial Spin Ices

“…However, they did not observe an inverse correlation of the average T B with the interaction strength. However, in those ASIs the activation volumes were much smaller than the nanoelement volumes, which is an effect previously reported in ASIs with larger nanoelements 30 . This means that the nanoelements are able to reverse at much lower temperatures than those expected for the full nanoelement volume barrier.…”

“…The string and domain regime formation in thermally active ASIs was first shown by Farhan et al 24 for strongly interacting arrays. More recent work comprised the study of both strongly interacting square ASIs, showing similar results, and weakly interacting ones where vertical string propagations occur 30 . Both cases present 1-D thermal excitations which happen in the initial part of the relaxation process or, compared to the present work, at lower temperatures.…”

“…These systems include thermal annealing processes taking place during fabrication 20 , and systems where the anisotropy barrier of the nanomagnets has been tuned to be in a thermally accessible regime by judicious choice of a magnetic material with a lowered Curie temperature (T C ) 21,22 and by carefully heating the sample above its blocking temperature (T B ) 23 . These reports were shortly followed by studies of thermally fluctuating ASIs which have been imaged via PEEM [24][25][26][27] and TXM 28,29 in real time in a variety of geometries, and recently via MFM imaging of the intermediate thermally stable states after a temperature quenching process 30 . Nonetheless, it has only been very recently that experiments where a phase transition from the superparamagnetic regime ( > > T T T C B ) to the ASI regime have been demonstrated.…”