Giant magneto-electric coupling in 100 nm thick Co capped by ZnO nanorods

Magnetoelectric Coupling at the Ni/Hf0.5Zr0.5O2 Interface

Composite multiferroics containing ferroelectric and ferromagnetic components often have much larger magnetoelectric coupling compared to their single-phase counterparts. Doped or alloyed HfO₂-based ferroelectrics may serve as a promising component in composite multiferroic structures potentially feasible for technological applications. Recently, a strong charge-mediated magnetoelectric coupling at the Ni/HfO₂ interface has been predicted using density functional theory calculations. Here, we report on the experimental evidence of such magnetoelectric coupling at the Ni/Hf_0.5Zr_0.5O₂(HZO) interface. Using a combination of operando XAS/XMCD and HAXPES/MCDAD techniques, we probe element-selectively the local magnetic properties at the Ni/HZO interface in functional Au/Co/Ni/HZO/W capacitors and demonstrate clear evidence of the ferroelectric polarization effect on the magnetic response of a nanometer-thick Ni marker layer. The observed magnetoelectric effect and the electronic band lineup of the Ni/HZO interface are interpreted based on the results of our theoretical modeling. It elucidates the critical role of an ultrathin NiO interlayer, which controls the sign of the magnetoelectric effect as well as provides a realistic band offset at the Ni/HZO interface, in agreement with the experiment. Our results hold promise for the use of ferroelectric HfO₂-based composite multiferroics for the design of multifunctional devices compatible with modern semiconductor technology.

An integrated ultra-high vacuum apparatus for growth and in situ characterization of complex materials

Here, we present an integrated ultra-high vacuum apparatus-named MBE-Cluster -dedicated to the growth and in situ structural, spectroscopic, and magnetic characterization of complex materials. Molecular Beam Epitaxy (MBE) growth of metal oxides, e.g., manganites, and deposition of the patterned metallic layers can be fabricated and in situ characterized by reflection high-energy electron diffraction, low-energy electron diffraction, Auger electron spectroscopy, x-ray photoemission spectroscopy, and azimuthal longitudinal magneto-optic Kerr effect. The temperature can be controlled in the range from 5 K to 580 K, with the possibility of application of magnetic fields H up to ±7 kOe and electric fields E for voltages up to ±500 V. The MBE-Cluster operates for in-house research as well as user facility in combination with the APE beamlines at Sincrotrone-Trieste and the high harmonic generator facility for time-resolved spectroscopy.

Optical radiation stability of ZnO hollow particles

Zinc oxide has multifunctional physical properties depending on its microstructure and morphology. Herein, we reported the in situ investigations of the radiation stability of ZnO particles with hollow, ball, star and flower shapes under electron and proton irradiation. 100 keV protons with a fluence of 5 × 10¹⁵ cm^-2 and 50 keV electrons with fluence ranging from 0.5 to 7 × 10¹⁶ cm^-2 are employed to investigate the radiation stability of nanostructured ZnO particles. In situ reflectance, X-ray photoelectron spectra and photoluminescence were characterized in the irradiation environment to avoid the effects of the atmospheric environment on radiation induced defects. The experimental results reveal that, compared to the other shapes, the hollow structure with the best radiation stability due to the hollow structure facilitates the decrease of the accumulation of radiation defects. This study clearly demonstrates the promise of ZnO hollow particles as a plasmonic nanostructure for achieving high radiation stability, and they could be easily employed to serve as the radiation stability pigment for coatings.

MOKE setup exploiting a nematic liquid crystal modulator

Here we report on the magneto-optical Kerr effect employing a nematic liquid crystal (LC) device as an optical modulator. This device allows performing intensity, phase, and polarization modulated measurements with a huge signal-to-noise ratio when compared to those obtained by means of an opto-mechanical chopper and a photo-elastic modulator. The results demonstrate that the optimal performance is achieved modulating the polarization state of the incident light by means of the LCs.

Low-field giant magneto-ionic response in polymer-based nanocomposites

The future of magnetoelectric (ME) materials is closely linked to the optimization of the ME response on nanocomposites or to the introduction of new effects to achieve higher ME performance from low magnetic fields. Here, we report a P(VDF-TrFE)/[C4mim][FeCl4] nanocomposite with a magneto-ionic response that produces giant magnetoelectric coefficients up to ≈10 V cm-1 Oe-1. This response comprises a magnetically triggered ionic/charge movement within the porous structure of the polymer, being this a novel phenomenon never experimentally observed or explored in magnetoelectric composites. This work successfully demonstrates the concept of exploring magnetic ionic liquids, such as [C4mim][FeCl4], in polymer-based magnetoelectric nanocomposites, suitable for low-field magnetic sensing devices. Such nanocomposites have remarkable potential for applications, not only because they exhibit a high ME response with scalable production and with good reproducibility but also because this coupling between magnetic order and electric order via ionic effects can lead to additional novel effects.