Magnetic ripple domain structure in FeGa/MgO thin films

The magnetic domain structure is studied in epitaxial Fe$_{100-x}$Ga$_x$/MgO(001) films with 0 $<$ x $<$ 30 and thicknesses below 60 nm by magnetic force microscopy. For low gallium content, domains with the magnetization lying in the film plane and domain walls separating micrometric areas are observed. Above x $\approx$ 20, the magnetic contrast shows a fine corrugation, ranging from 300 to 900 nm, suggesting a ripple substructure with a periodic oscillation of the magnetization. We discuss the presence of a random magnetic anisotropy contribution, that superimposed to the cubic coherent anisotropy, is able to break the uniform orientation of the magnetization. The origin of that random anisotropy is attributed to several factors: coexistence of crystal phases in the films, inhomogeneous distribution of both internal strain and Ga-Ga next nearest neighbor pairs and interface magnetic anisotropy due to the Fe-O bond.Comment: 9 pages, 3 figure

Propuesta didáctica para la enseñanza de la estimación en 1º de la ESO

El trabajo aborda el tratamiento de la estimación en 1º de ESO. El currículo oficial de matemáticas de Aragón no trata la estimación como un contenido a enseñar. En este trabajo se muestran las deficiencias en los alumnos al no obtener ese aprendizaje. Se plantean diversas razones de ser para motivar al alumnado hacia el aprendizaje de la estimación mediante problemas y debates en el aula. La secuencia didáctica trata sobre la estimación en cálculo y medida. Cronológicamente se encuentra repartida por todo el curso para ser enseñada durante las unidades didácticas de números naturales, proporcionalidad, áreas... También consta de una evaluación escrita en la que se evalúa tanto al alumnado como a la propia secuencia didáctica.<br /

Caracterización y Optimización de Resonadores Superconductores con Aplicaciones en Información Cuántica

El objetivo de este trabajo es utilizar un circuito diseñado por investigadores del ICMA y estudiar su viabilidad como circuito QED al introducir un cristal de qubits de K12GdW30. Posteriormente, se procede a optimizarlo con vistas a conseguir un resonador de alta calidad con acoplo fuerte que pueda sentar las bases para futuras aplicaciones en el ámbito de la información cuántica con espines moleculares

Magnetic and magnetoelastic properties of FeGa epitaxial thin films for low-power Magnetoelectronics

Esta tesis aborda la fabricación y caracterización de películas delgadas de la aleación hierro-galio (FeGa). El interés de esta aleación reside en su alto valor de magnetostricción tetragonal, la cual puede ser 100 veces superior a la del Fe puro. Se han fabricado películas epitaxiales delgadas de FeGa en un rango de 10-50 nm mediante MBE sobre dos tipos de sustratos: MgO y PMN-PT. Estas muestras han sido caracterizadas estructural (RHEED, TEM, XRD, XRR) y magnéticamente (VSM, MOKE, MFM, magnetometría de placa en voladizo).Sobre sustratos MgO se ha estudiado la dependencia magnética y estructural con la temperatura de depósito y contenido de Ga en la aleación. Los resultados indican que al aumentar la temperatura de depósito su superficie se vuelve rugosa. El aumento en contenido de Ga implica la observación de fases cristalinas ordenadas y la aparición de estructuras de dominios magnéticos corrugados atribuibles a una anisotropía magnética aleatoria débil.Además, se han medido a temperatura ambiente los coeficientes magnetoelásticos irreducibles B1 y B2 para aleaciones FeGa y FeGaTb, sin observarse cambios significativos al dopar con Tb. En cambio, para la aleación FeGaCu los valores de dichas tensiones magnetoelásticas disminuyen, debido a la presencia de una fase omega observada mediante TEM.Sobre sustratos ferroeléctricos PMN-PT se han buscado aplicaciones en el campo denominado "Straintronics". Las películas crecidas sobre PMN-PT(011) muestran anisotropía uniaxial, que no varía al aplicar campo eléctrico perpendicular. En cambio, las películas crecidas sobre PMN-PT(001) muestran un giro de anisotropía uniaxial y de la imanación de 90º al aplicar campo eléctrico sin presencia de campo magnético, con un elevado valor del coeficiente magnetoeléctrico inverso de 15 E-6 s/m. Se ha probado con éxito que estas heteroestructuras pueden integrarse en memorias no volátiles.<br /

Crystal structure and local ordering in epitaxial Fe100−x_{100-x}Gax_x/MgO(001) films

In this work we present a study of the structural properties of Fe$_{100-x}$ Ga$_x$ grown by Molecular Beam Epitaxy on Mg0(100). We combine long range and local/chemically selective X-ray probes (X-ray Diffraction and X-ray absorption spectroscopy) together with real space imaging by means of Transmission Electron Microscopy and surface sensitive $in situ$ Reflected High Energy Electron Diffraction. For substrate temperature $T_s$ below 400 $^o$C we obtain $bcc$ films while, for $x \approx$ 24 and $T_s \geq$ 400$^o$C the nucleation of the $fcc$ phase is observed. For both systems a Ga anticlustering or local range ordering phenomenon appears. The Ga/Fe composition in the first and second coordination shells of the $bcc$ films is different from that expected for a random Ga distribution and is close to a D0$_3$-like ordered phase, leading to a minimization of the number of Ga-Ga pairs. On the other side, a true long-range D0$_3$ phase is not observed indicating that atomic ordering only occurs at a local scale. Overall, the epitaxial growth procedure presented in this work, first, avoids the formation of a long range ordered D0$_3$ phase, which is known to be detrimental magnetostrictive properties, and second, demonstrates the possibility of growing $fcc$ films at temperatures much smaller than those required to obtain bulk $fcc$ samples.Comment: 21 pages, 7 figure

Caracterización y optimización de resonadores superconductores con aplicaciones en información cuántica

Trabajo Fin de Grado realizado en el ICMA(CSIC-Universidad de Zaragoza) y Departamento Física Materia Condensada, Universidad de Zaragoza.El objetivo de este trabajo es utilizar un circuito diseñado por investigadores del ICMA y estudiar su viabilidad como circuito QED al introducir un cristal de qubits de K12GdW30. Posteriormente, se procede a optimizarlo con vistas a conseguir un resonador de alta calidad con acoplo fuerte que pueda sentar las bases para futuras aplicaciones en el ámbito de la información cuántica con espines moleculares.Peer Reviewe

Strain-mediated giant magnetoelectric coupling in a crystalline multiferroic heterostructure

Multiferroic heterostructures based on the strain-mediated mechanism present ultralow heat dissipation and large magnetoelectric coupling coefficient, two conditions that require endless improvement for the design of fast nonvolatile random access memories with reduced power consumption. This work shows that a structure consisting of a [Pb(Mg1/3Nb2/3)O3]0.7-[PbTiO3]0.3 (001) substrate on which a crystalline FeGa(001)/MgO(001) bilayer is deposited exhibits a giant magnetoelectric coupling coefficient of order 15 × 10–6 s m–1 at room temperature. That result is a 2-fold increment over the previous highest value. The spatial orientation of the magnetization vector in the epitaxial FeGa film is switched 90° with the application of electric field. The symmetry of the magnetic anisotropy is studied by the angular dependence of the remanent magnetization, demonstrating that poling the sample generates a switchable uniaxial magnetoelastic anisotropy in the film that overcomes the native low 4-fold magnetocrystalline anisotropy energy. Magnetic force microscopy shows that the switch of the easy axis activates the displacement of domain walls and the domain structures remain stable after that point. This result highlights the interest in single-crystalline structures including materials with large magnetoelastic coupling and small magnetocrystalline anisotropy for low-energy-consuming spintronic applications.This work was supported by Spanish MICINN (Grant MAT2015-66726-R), and Aragón Government (Grant E10-17D) and Fondo Social Europeo. A.B. acknowledges funding from Ministry of Science and Innovation for the PhD contract BES-2016-076482.Peer reviewe

Unveiling the different physical origins of magnetic anisotropy and magnetoelasticity in Ga-Rich FeGa thin films

The aim of this work is to clarify how in-plane magnetic anisotropy and magnetoelasticity depend on the thickness of Ga-rich FeGa layers. Samples with an Fe72Ga28 composition were grown by sputtering in the ballistic regime in oblique incidence. Although for these growth conditions uniaxial magnetic anisotropy could be expected, in-plane anisotropy is only present when the sample thickness is above 100 nm. By means of differential X-ray absorption spectroscopy, we have determined the influence of both Ga pairs and tetragonal cell distortion on the evolution of the magnetic anisotropy with the increase of FeGa thickness. On the other hand, we have used the cantilever beam technique with capacitive detection to also determine the evolution of the magnetoelastic parameters with the thickness increase. In this case, experimental results can be understood considering the grain distribution. Therefore, the different physical origins for anisotropy and magnetoelasticity open up the possibility to independently tune these two characteristics in Ga-rich FeGa films.This work has been financially supported through the projects MAT2015-66888-C3-3-R and MAT2015-66726-R (MINECO/FEDER) of the Spanish Ministry of Economy and Competitiveness, RTI2018-097895-B-C43 of the Spanish Ministry of Science, Innovation, and Universities, and Gobierno de Aragón (Grant E10-17D) and Fondo Social Europeo. A.M.-N. is thankful for the contract from Universidad Complutense and Comunidad de Madrid “Atracción de Talento” program 2018-T1/IND-10360, and A.B. thanks MINECO for the Ph.D. grant BES-2016-076482.Peer reviewe

Domain structures in Fe100-xGax/MgO(001) films

Resumen del trabajo presentado al 9th Joint European Magnetic Symposia (JEMS), celebrado en Mainz (Alemania) del 3 al 7 de septiembre de 2018.In this work we present the magnetic domain structures of Fe100-xGax/MgO(001)(x 16 a fine stripe-like structure is observed. The stripe phase is explained considering a perpendicular anisotropy Ku with a value comparable and lower than the shape anisotropy coefficient Ksh. Hysteresis loops performed along the film normal indicate that Ku/Ksh is around 0.4 (x > 16), a value for which the observation of the stripe phase is expected. The magnetoelastic (ME) anisotropy energy term favors in-plane magnetization due to the signs of residual strain and ME stress coefficient. The presence of next-nearest-neighbor Ga pairs in Fe100-xGax alloys has been addressed as source for the cubic anisotropy constant K1 while in epitaxial films a preferential asymmetry in the formation of these Ga-Ga pairs, along the out-of-plane direction, can result in large Ku and explain the stripe structure observed for x > 16. It appears that small variations of the Ga-Ga pair distribution in a body, although undetected by local probes techniques, such as EXAFS, could introduce strong magnetic anisotropy in that specimen.Peer Reviewe

Magnetic ripple domain structure in FeGa/MgO thin films

The magnetic domain structure is studied in epitaxial /MgO(0 0 1) films with 0 < x < 30 and thicknesses below 60 nm by magnetic force microscopy. For low gallium content, domains with the magnetization lying in the film plane and domain walls separating micrometric areas are observed. Above x ≈ 20, the magnetic contrast shows a fine corrugation, ranging from 300 to 900 nm, suggesting a ripple substructure with a periodic oscillation of the magnetization. We discuss the presence of a random magnetic anisotropy contribution, that superimposed to the cubic coherent anisotropy, is able to break the uniform orientation of the magnetization. The origin of that random anisotropy is attributed to several factors: coexistence of crystal phases in the films, inhomogeneous distribution of both internal strain and Ga–Ga next nearest neighbor pairs and interface magnetic anisotropy due to the Fe–O bond.This work has been supported by Spanish MICINN (Grant No. MAT2015-66726-R) and Gobierno de Aragón (Grant E10-17D) and Fondo Social Europeo. AB thanks MINECO for the Ph. D. grant BES-2016-076482.Peer reviewe