Preserving Metamagnetism in Self-Assembled FeRh Nanomagnets

Abstract

Preparing and exploiting phase-change materials in the nanoscale form is an ongoing challenge for advanced material research. A common lasting obstacle is preserving the desired functionality present in the bulk form. Here, we present self-assembly routes of metamagnetic FeRh nanoislands with tunable sizes and shapes. While the phase transition between antiferromagnetic and ferromagnetic orders is largely suppressed in nanoislands formed on oxide substrates via thermodynamic nucleation, we find that nanomagnet arrays formed through solid-state dewetting keep their metamagnetic character. This behavior is strongly dependent on the resulting crystal faceting of the nanoislands, which is characteristic of each assembly route. Comparing the calculated surface energies for each magnetic phase of the nanoislands reveals that metamagnetism can be suppressed or allowed by specific geometrical configurations of the facets. Furthermore, we find that spatial confinement leads to very pronounced supercooling and the absence of phase separation in the nanoislands. Finally, the supported nanomagnets are chemically etched away from the substrates to inspect the phase transition properties of self-standing nanoparticles. We demonstrate that solid-state dewetting is a feasible and scalable way to obtain supported and free-standing FeRh nanomagnets with preserved metamagnetism.

Magnetic-field-controlled growth of magnetoelastic phase domains in FeRh

“…We interpret the presence of these defects as solid-state dewetting centers that are formed during post-growth annealing of the samples. The film-to-substrate mismatch in surface energy and mass transport during annealing promote the formation of holes around impurities or stacking faults, leading to partial or advanced dewetting scenarios of the film [53,54]. In our case, the grooves are about 50 nm deep (figure 3(d)) and do not reach all the way down to the substrate.…”

“…The observed steps in reflectivity are consistently larger during cooling than heating, an observation that agrees well with the more prominent elongation of AF domains in the cooling cycle (figure 2(b)). A number of works on FeRh have already pointed out that this effect can be ascribed to the different kinetics of the transition during heating and cooling, where phase separation is more prominent in the latter [52], and can lead to remarkable supercooling behavior in nanoscale confined FeRh systems [13,53].…”

Finite size effects on the metamagnetic phase transition in a thick B2 FeRh nanocluster film

“…Despite a lot of studies on thin films with low defect density 19,20,24,25 , the study of single B2 FeRh nanomagnets is rather rare. Some publications emphasized the strong interplay between crystal faceting, surface configuration, morphology and magnetic state in FeRh nanoparticles from DFT calculations and experimental studies [26][27][28] . By preparing FeRh nanocrystallites using low energy cluster beam deposition (LECBD) diluted in an amorphous carbon matrix, we demonstrated the persistence of the F order down to 3 K for sizeselected clusters in B2 phase less than 10 nm in diameter [29][30][31] .…”