Nanoscale structural characterization of manganite thin films integrated to silicon correlated with their magnetic and electric properties

A detailed nanoscale structural characterization was performed on high-quality La0.66Sr0.33MnO3 (LSMO) thin films of different thicknesses and deposited by pulsed laser deposition onto buffered Si (100) substrates. A multilayered structure built of Y0.13Zr0.87O2 (YSZ) and CeO2 layers was used as buffer in order to optimize the manganite films growth. The stacking of the different layers, their morpholohy, composition and strains were analysed using different experimental techniques. In-situ characterization of the films, performed with reflection high-energy electron diffraction, revealed their epitaxial growth and smooth surfaces. High-resolution transmission electron microscopy (HR-TEM) images showed sharp interfaces between the constituents lattices and combined with energy-dispersive X-ray analysis allowed us to determine that there was no ion interdifussion across them. The Fourier-Fast-Transform of the HR-TEM images was used to resolve the epitaxy relationship between the layers, resulting in [100] LSMO (001) // [110] CeO2 (001) // [110] YSZ (001) // [110] Si (001). The LSMO thin films were found to be ferromagnetic and metallic at low temperature regardless their thickness. The effect of strains and defects was only detected in films thinner than 15 nm and put in evidence by X-ray diffraction patterns and correlated with magnetic and electrical parameters.Comment: 14 pages, 8 figure

Tuning the interfacial charge, orbital, and spin polarization properties in La0.67Sr0.33MnO3/La1-xSrxMnO3 bilayers

The possibility of controlling the interfacial properties of artificial oxide heterostructures is still attracting researchers in the field of materials engineering. Here, we used surface sensitive techniques and high-resolution transmission electron microscopy to investigate the evolution of the surface spin-polarization and lattice strains across the interfaces between La0.66Sr0.33MnO3 thin films and low-doped manganites as capping layers. We have been able to fine tune the interfacial spin-polarization by changing the capping layer thickness and composition. The spin-polarization was found to be the highest at a critical capping thickness that depends on the Sr doping. We explain the non-trivial magnetic profile by the combined effect of two mechanisms: On the one hand, the extra carriers supplied by the low-doped manganites that tend to compensate the overdoped interface, favouring locally a ferromagnetic double-exchange coupling. On the other hand, the evolution from a tensile-strained structure of the inner layers to a compressed structure at the surface that changes gradually the orbital occupation and hybridization of the 3d-Mn orbitals, being detrimental for the spin polarization. The finding of an intrinsic spin-polarization at the A-site cation observed in x-ray magnetic circular dichroism (XMCD) measurements also reveals the existence of a complex magnetic configuration at the interface, different from the magnetic phases observed at the inner layers

Nanoscale magnetic and charge anisotropies at manganite interfaces

Strong correlated manganites are still under intense research owing to their complex phase diagrams in terms of Sr-doping and their sensitivity to intrinsic and extrinsic structural deformations. Here, we performed X-ray absorption spectroscopy measurements of manganite bilayers to explore the effects that a local Sr-doping gradient produce on the charge and antiferromagnetic anisotropies. In order to gradually tune the Sr-doping level along the axis perpendicular to the samples we have grown a series of bilayers with different thicknesses of low-doped manganites (from 0 nm to 6 nm) deposited over a La0.7Sr0.3MnO3 metallic layer. This strategy permitted us to resolve with high accuracy the thickness region where the charge and spin anisotropies vary and the critical thickness tc over which the out of plane orbital asymmetry does not have any further modifications. We found that the antiferromagnetic spin axis points preferentially out of the sample plane regardless the capping layer thickness. However, it tilts partially into the sample plane far from this critical thickness, owing to the combined contributions of the external structural strain and electron doping. Furthermore, we found that the doping level of the capping layer strongly affects the critical thickness, giving clear evidence of the influence exerted by the electron doping on the orbital and magnetic configurations. These anisotropic changes induce subtle modifications on the domain reorientation of La0.7Sr0.3MnO3, as evidenced from the magnetic hysteresis cycles

Magnetic and electrical properties of single-phase multiferroic (1-x)Pb(Zr0.52Ti0.48)O3–xPb(Fe0.5Nb0.5)O3 thin films prepared by sol-gel route

Single-phase multiferroic (1-x)Pb(Zr0.52Ti0.48)O3-xPb(Fe0.5Nb0.5)O3 (0≤x≤0.5) thin films were synthesized by sol-gel route and characterized to understand their structural, electrical, and magnetic properties. The films were thermally treated by conventional furnace (CFA) and rapid thermal annealing (RTA). A pyrochlore-free perovskite phase is stabilized only by RTA in samples with high Fe3+/Nb5+ content. The films displayed excellent dielectric and ferroelectric properties in the whole concentration range, with saturated hysteresis loops and remanent polarization values of ∼15μC/cm2. Films with x>0.3 showed ferromagnetic behavior at room temperature. Consequently, the multiferroic behavior in the films occurs in a different concentration range than that observed in bulk ceramics. The origin of the weak ferromagnetism is discussed.The authors thank Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) for financial support. M.G.S thanks support from CIUNR and L.B.S from FONCYT PICT2014-1047. We also acknowledge the financial support of H2020-MSCA-RISE-2020 MELON Grant No. 872631 and the access to TEM equipment at LMA- University of Zaragoza to perform TEM studies.Peer reviewe

FMR and thermal spin pumping enhanced by perpendicular anisotropy in YIG/Pt bilayers

Resumen del póster presentado al Joint European Magnetic Symposia (JEMS), celebrado en Warsaw (Poland) del 24 al 29 de julio de 2022.N

Magnetization reversal modes and coercive field dependence on perpendicular magnetic anisotropy in FePt thin films

The competition between shape and perpendicular magnetic anisotropies in magnetic thin films gives rise to unusual magnetic behaviors. In ferromagnetic thin films, the presence of an out-of-plane component of the magnetic anisotropy may induce a transition from planar to stripe-like magnetic domains above a critical thickness, tc. In this article, we present a detailed study of the magnetization switching mechanism in FePt thin films, where this phenomenon is observed. Using micromagnetic simulations and experiments, we found that below tc the reversal mechanism is well described by the two-phase model while above this thickness the magnetization within each stripe reverses by coherent rotation. We also analyzed the out-of-plane component of the magnetic anisotropy and its temperature dependence, probing that substrate-induced strains are responsible for the abnormal coercive field behavior observed for FePt films with t > tc.Authors thanks the financial support of FONCYT PICT 0867-2016, PICT 02781-2019 and the European Commission through the Horizon H2020 funding by H2020-MSCA-RISE-2016–Project No. 734187 –SPICOLOST. Beamtime was Granted on the XRD2 beamline by the LNLS. C G acknowledges the financial support received by ANID FONDECYT/REGULAR 1201102, ANID PIA/APOYO AFB180002 and ANID FONDEQUIP EQM140161.Peer reviewe