Emission Mössbauer spectrometer from ILmenau (eMIL): An update & TDPAC measurements in Bismuth Ferrite

by Alice Kern, Danylo Kviatkovskyi

Tuesday 14 Nov 2023, 16:00 → 17:00 Europe/Zurich

26/1-022 (CERN)

Emission Mössbauer spectrometer from ILmenau (eMIL): An update

The advanced emission Mössbauer spectrometer, eMiL (Emission Mössbauer from Ilmenau) was built for the emission Mössbauer (eMS) collaboration at ISOLDE/CERN. The set-up is based on the emission geometry and combines on-line and off-line isotope implantation used to measure hyperfine interactions in solids. Using radioactive Mössbauer probes that are ion-implanted to the sample by the GLM setup, eMiL has multiple advantages over the more common transmission or electron conversion setups. The versatility of the set-up is epitomized through five different lids: rotation, magnetic, powder, hot and cold lid, which can be easily interchanged. Within the scope of my CERN Summer Student Programme, I joined the Solid State Physics (SSP) Group at ISOLDE. During this time at CERN I prepared the set-up for Beam Time. Furthermore, I was able to participate in eMiL’s first successful run during beam time this year, which marks the first beam time for the Mössbauer collaboration since 2018. During this beamtime it was proven that the set-up is easy to handle while providing the flexibility needed by the eMS collaboration.

TDPAC measurements in Bismuth Ferrite

Over the past decades, multiferroic materials have attracted increasing attention due to their potential for various practical applications in technology. Multiferroic materials demonstrate more than one of the main properties of ferrous in one phase, which include ferromagnetism, ferroelectricity and ferroelasticity. In the group of materials that demonstrate these characteristics, BiFeO3 (BFO) is currently the most interesting and most studied, as both its Néel and Curie temperatures are well above room temperature (TN ≈ 370 oC and TC ≈ 820 oC).
That is why in the report we present a study local magnetoelectric effect at
Bi site in multiferroic bismuth ferrite (BiFeO3 or BFO) by using time differential perturbed angular correlation (TDPAC) spectroscopy. The main approach is to use the 111mCd (111Cd) probe as a tracer ion for the investigation of the Bi site. The TDPAC measurements were carried out at various temperatures (15 – 500 oC) after thermal treatment at 800 oC in air for 20 minutes. The resulting TDPAC spectra show the absence of magnetoelectric coupling at the site of the bismuth ion in antiferromagnetic BFO below the Néel temperature. This key investigation experimentally confirms the anti-parallel alignment of iron-spins in BFO in anti-ferromagnetic (AF) phase. The experimental results agree well with calculations based on TDPAC theory. The substitutional Bi site location of the 111mCd (111Cd) probe is confirmed using ab-initio DFT simulations.