arXiv subjects

Sakura Pascarelli

Publications and source records attributed to Sakura Pascarelli.

3 recordsLinked to original sources

arXiv2019

Magnetic response of FeRh to static and dynamic disorder

Changes of the magnetic and crystal structure on the microscopic scale in 40 nm FeRh thin films have been applied to investigate the phenomena of a disorder induced ferromagnetism at room temperature initiated through light ion-irradiation with fluences up to 0.125 Ne$^+$/nm$^{-2}$. Magnetometry shows an increase of magnetic ordering at low temperatures and a decrease of the transition temperature combined with a broadening of the hysteresis with rising ion fluence. $^{57}$Fe Mössbauer spectroscopy reveals the occurrence of an additional magnetic contributions with an hyperfine splitting of 27.2 T - identical to that of ferromagnetic B2-FeRh. The appearance of an anti-site Fe-contribution can be assumed to be lower than 0.6 Fe-at%, indicating that no change of the chemical composition is evident. The investigation of the local structure shows an increase of the static mean square relative displacement determined by X-ray absorption fine structure spectroscopy, while an increase of the defect-concentration has been determined by positron annihilation spectroscopy. From the changes of the microscopic magnetic structure a similarity between the temperature induced and the structural disorder induced ferromagnetic phase can be observed. These findings emphasize the relationship between magnetic ordering and the microscopic defect structure in FeRh.

cond-mat.mtrl-sci↗

arXiv2016

Local Structure and Spin Transition in Fe2O3 Hematite at High-Pressure

The pressure evolution of the local structure of Fe2O3 hematite has been determined for the first time by extended x-ray absorption fine structure up to 79 GPa. The comparison to the different high-pressure forms proposed in the literature suggests that the orthorhombic structure with space group Aba2 is the most probable. The crossover from Fe high-spin to low-spin states with pressure increase has been monitored from the pre-edge region of the Fe K-edge absorption spectra. The "simultaneous" comparison with the local structural changes allows us to definitively conclude that it is the electronic transition that drives the structural transition and not viceversa.

cond-mat.mtrl-sci↗

arXiv2004

XMCD under pressure at the Fe K edge on the energy dispersive beamline of the ESRF

The present paper demonstrates the feasibility of X-ray Absorption Spectroscopy (XAS) and X-ray Magnetic Circular Dichroism (XMCD) at high pressure at the Fe-K edge on the ID24 energy dispersive beamline of the ESRF. In 3d transition metals, performing experiments at the hard X-ray K-edge rather than at the magnetically interesting soft X-ray L-edges represents, the only way to access the high pressure regime obtainable with Diamond Anvil Cells. The simultaneous availability of a local structure (XAS) and of a magnetic (XMCD) probe on the sample in identical thermodynamical conditions is essential to study correlations between local structural and magnetic properties. We briefly summarize the state of the art theoretical understanding of K-edge XMCD data, then illustrate the setup of beamline ID24 for high pressure XMCD experiments and underline the conditions required to perform measurements at the K-edges of 3d transition metals. Finally, we present two examples of recent high pressure results at the Fe-K edge in pure Fe and Fe3O4 powder.

physics.ins-det↗