Abstract
Equi-atomic FeRh is a very interesting material as it undergoes a magnetostructural transition from an antiferromagnetic (AF) to a ferromagnetic (FM) phase between 75–105 °C. Its ability to present phase co-existence separated by domain walls (DWs) above room temperature provides immense potential for exploitation of their DW motion in spintronic devices. To be able to effectively control the DWs associated with AF/FM coexistence in FeRh thin films we must fully understand the magnetostructural transition and thermomagnetic behaviour of DWs at a localised scale. Here we present a transmission electron microscopy investigation of the transition in planar FeRh thin-film samples by combining differential phase contrast (DPC) magnetic imaging with in situ heating. We perform quantitative measurements from individual DWs as a function of temperature, showing that FeRh on NiAl exhibits thermomagnetic behaviour consistent with the transition from AF to FM. DPC imaging of an FeRh sample with HF-etched substrate reveals a state of AF/FM co-existence and shows the transition from AF to FM regions proceeds via nucleation of small vortex structures, which then grow by combining with newly nucleated vortex states into larger complex magnetic domains, until it is in a fully-FM state.
Highlights
Equiatomic iron-rhodium (Fe48Rh52 to Fe56Rh44) has attracted considerable attention due to its magnetostructural transition from its antiferromagnetic (AF) to ferromagnetic (FM) phase[1]
This combined in situ transmission electron microscopy (TEM) and differential phase contrast imaging (DPC) imaging study has provided a visual and quantitative investigation of the magnetostructural transition in planar FeRh thin films, prepared via focused ion beam (FIB) methods or HF-etching
selected area electron diffraction (SAED) patterns from planar TEM lamellae of samples 1–3 further reinforced the evidence for the epitaxial growth of single crystalline FeRh, whilst their corresponding thickness profiles from energy-loss spectroscopy (EELS) analysis revealed all samples were electron transparent
Summary
Equiatomic iron-rhodium (Fe48Rh52 to Fe56Rh44) has attracted considerable attention due to its magnetostructural transition from its antiferromagnetic (AF) to ferromagnetic (FM) phase[1]. The magnetostructural transition has been followed in situ through scanning electron microscopy with polarisation analysis (SEMPA) and suggested that the interfacial ferromagnetism coexisting with the AF phase inside the film is an intrinsic property of the FeRh (001) surface[9] These techniques are often limited to a spatial resolution of ~20–30 nm in typical cases[10,11] and ~5 nm for SEMPA in specialised SEM instruments[12], as well as being restricted in penetration depth to a few nm[10,13]. Comparison is made between the integrity of the planar FeRh TEM samples prepared via different methods and the ability to perform quantitative measurements of magnetic induction from DWs using DPC imaging, as a function of temperature. We show the evolution of magnetic domains and the subsequent AF/FM phase co-existence in a FeRh film during in situ heating, and mechanisms of the AF to FM phase transition are proposed
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