Magnetic properties of nanostructured systems based on TbFe2

The aim of this work is to study the magnetic properties of annealed [Fe3Ga/TbFe2]n heterostructures grown by sputtering at room temperature. The interest of investigating multilayers comprised of TbFe2 and Fe3Ga is their complementary properties in terms of coercivity and magnetostriction. We have studied the thickness combination which optimizes the magnetic and magnetostrictive properties of the annealed multilayers. The crystallization of the Laves phase upon the thermal treatment in heterostructures with thick TbFe2 layers promotes the increase of the coercivity. This crystallization seems to be prevented by the low mechanical stiffness of the Fe3Ga. [Fe3Ga/TbFe2]n heterostructures show promising characteristics, λ of 340 ppm and a HC of 220 Oe, for the development of new magnetostrictive devices

Local and medium range order influence on the magnetic behavior of sputtered Ga-Rich FeGa thin films

We have investigated the influence of the growth power on the structural properties of Fe100-xGax (x ca. 29) films sputtered in the ballistic regime in the oblique incidence. By means of different structural characterizations, mainly X-ray diffraction and X-ray absorption spectroscopy, we have reached a deeper understanding about the influence of the local and medium range order on the magnetic behavior of Ga-rich FeGa thin films. On the one hand, the increase of the growth power reduces the crystallite size (medium order) that promotes the decrease of the coercive field of the layers. On the other hand, the growth power also determines the local order as it controls the formation of the A2, B2, and D03 structural phases. The increase of the uniaxial in-plane magnetic anisotropy with growth power has been correlated with the enhancement of both Ga pairs and a tetragonal distortion. The results presented in this work give more evidence about the magnetic anisotropy sources in Ga-rich FeGa alloys, and therefore, it helps to understand how to achieve a better control of the magnetic properties in this family of alloys.This work has been financially supported through project MAT2015-66888-C3-3-R (MINECO/FEDER) and RTI2018-097895-B-C43 of the Spanish Ministry of Economy and Competitiveness and through PR26/16-3B-2 of Santander and Universidad Complutense de Madrid. We thank "CAI Difracción de rayos-X" of UCM for the X-ray diffractometry measurements and the "Instituto de Sistemas Optoelectrónicos y Microtecnología" (ISOM) for using its facilities. We also want to thank BM25-Spline, the Spanish CRG at ESRF for providing beamtime

Stripe domains in electrodeposited Ni90Fe10 thin films

Here we have investigated the formation of stripe domains in electrodeposited Ni90Fe10 films, a metallic alloy with relevant magnetoelastic properties. The X-ray diffractometry patterns confirm the deposition of NiFe with an experimental lattice parameter close to the theoretical value. We have analyzed the influence of both magnetic stirring and an applied magnetic field perpendicular to the sample plane on the formation of stripe domains in Ni90Fe10 films. It is observed the characteristic fingerprint of stripe domains, i.e. the transcritical shape in the in-plane hysteresis loops when the electrolyte is not magnetically stirred during electrodeposition. The quality factor reveals a moderate perpendicular magnetic anisotropy which is confirmed by the stripe periodicity inferred by Magnetic Force Microscopy. In particular, stripe domains are only visible by this technique when the sample thickness is well above the theoretical critical thickness for the stripe domains to be formed. Finally, in samples released after being grown in outward bent flexible substrates it has been promoted an induced in-plane magnetoelastic magnetic anisotropy that reduces the perpendicular magnetic anisotropy. The high quality of the samples studied in this work from the magnetoelastic point of view is reflected by the magnetostriction constant of −22 ppm that it has been experimentally inferre

Co-doped (La,Sr)TiO3-d: a high-Curie temperature diluted magnetic system with large spin-polarization

We report on tunneling magnetoresistance (TMR) experiments that demonstrate the existence of a significant spin polarization in Co-doped (La,Sr)TiO3-d (Co-LSTO), a ferromagnetic diluted magnetic oxide system (DMOS) with high Curie temperature. These TMR experiments have been performed on magnetic tunnel junctions associating Co-LSTO and Co electrodes. Extensive structural analysis of Co-LSTO combining high-resolution transmission electron microscopy and Auger electron spectroscopy excluded the presence of Co clusters in the Co-LSTO layer and thus, the measured ferromagnetism and high spin polarization are intrinsic properties of this DMOS. Our results argue for the DMOS approach with complex oxide materials in spintronics

Full oxide heterostructure combining a high-Tc diluted ferromagnet with a high-mobility conductor

We report on the growth of heterostructures composed of layers of the high-Curie temperature ferromagnet Co-doped (La,Sr)TiO3 (Co-LSTO) with high-mobility SrTiO3 (STO) substrates processed at low oxygen pressure. While perpendicular spin-dependent transport measurements in STO//Co-LSTO/LAO/Co tunnel junctions demonstrate the existence of a large spin polarization in Co-LSTO, planar magnetotransport experiments on STO//Co-LSTO samples evidence electronic mobilities as high as 10000 cm2/Vs at T = 10 K. At high enough applied fields and low enough temperatures (H < 60 kOe, T < 4 K) Shubnikov-de Haas oscillations are also observed. We present an extensive analysis of these quantum oscillations and relate them with the electronic properties of STO, for which we find large scattering rates up to ~ 10 ps. Thus, this work opens up the possibility to inject a spin-polarized current from a high-Curie temperature diluted oxide into an isostructural system with high-mobility and a large spin diffusion length.Comment: to appear in Phys. Rev.

Stripe domains in electrodeposited Ni90Fe10 thin films

Here we have investigated the formation of stripe domains in electrodeposited Ni90Fe10 films, a metallic alloy with relevant magnetoelastic properties. The X-ray diffractometry patterns confirm the deposition of NiFe with an experimental lattice parameter close to the theoretical value. We have analyzed the influence of both magnetic stirring and an applied magnetic field perpendicular to the sample plane on the formation of stripe domains in Ni90Fe10 films. It is observed the characteristic fingerprint of stripe domains, i.e. the transcritical shape in the in-plane hysteresis loops when the electrolyte is not magnetically stirred during electrodeposition. The quality factor reveals a moderate perpendicular magnetic anisotropy which is confirmed by the stripe periodicity inferred by Magnetic Force Microscopy. In particular, stripe domains are only visible by this technique when the sample thickness is well above the theoretical critical thickness for the stripe domains to be formed. Finally, in samples released after being grown in outward bent flexible substrates it has been promoted an induced in-plane magnetoelastic magnetic anisotropy that reduces the perpendicular magnetic anisotropy. The high quality of the samples studied in this work from the magnetoelastic point of view is reflected by the magnetostriction constant of-22 ppm that it has been experimentally inferred

Determination of the magnetostrictive atomic enviroments in FeCoB alloys

The atomic environments of Fe and Co involved in the magnetostriction effect in FeCoB alloys have been identified by differential extended x-ray fine structure (DiffEXAFS) spectroscopy. The study, done in amorphous and polycrystalline FeCoB films, demonstrates that the alloys are heterogeneous and that boron plays a crucial role in the origin of their magnetostrictive properties. The analysis of DiffEXAFS in the polycrystalline and amorphous alloys indicates that boron activates magnetostriction when entering as an impurity into octahedral interstitial sites of the Fe bcc lattice, causing its tetragonal distortion. Magnetostriction would be explained then by the relative change in volume when the tetragonal axis of the site is reoriented under an externally applied magnetic field. The experiment demonstrates the extreme sensitivity of DiffEXAFS to characterize magnetostrictive environments that are undetectable in their related EXAFS spectra

Correlation between local structure and magnetic behavior in co-sputtered Tb_xFe_(73)Ga_(27-x) (7 ≤ x ≤11) thin films

We report on the evolution of the microstructure of Tb-Fe-Ga films deposited by co-sputtering from Tb_(33)Fe_(67) and Fe_(72)Ga_(28) targets. The sputtering power was fixed (90 W) in the Fe_(72)Ga_(28) whereas it was increased from 50 to 90 W in the Tb_(33)Fe_(67) target resulting on Tb_xFe_(73)Ga_(27-x) layers with 7 ≤ x ≤ 11. The local structure was determined by means of x-ray absorption fine structure spectroscopy at Fe-K, Ga-K and Tb-L_(3) edges. The increase of Tb in the alloy promotes the phase segregation that produces a larger amount of the TbFe_2 structural phase. The structural results have been correlated with the magnetic characterization that shows the enhancement of the out-of-plane component of the magnetization