Exchange bias effects in Fe nanoparticles embedded in an antiferromagnetic Cr2O3 matrix

Powders consisting of ferromagnetic (FM) Fe nanoparticles, of about 7 nm in size, embedded in an antiferromagnetic (AFM) Cr2O3 matrix have been obtained by high-temperature reduction under a hydrogen atmosphere of a mixed Cr–Fe oxide. This FM–AFM system exhibits exchange bias effects, i.e. a loop shift (HE) and coercivity enhancement (ΔHC), when field-cooled through the N´eel temperature, TN, of Cr2O3. The exchange bias properties were measured as a function of temperature. HE and ΔHC are found to vanish at about TN(Cr2O3), indicating a good quality AFM matrix. Hence, high-temperature reduction of mixed oxides is demonstrated to be a suitable technique to develop new types of FM–AFM exchange-biased nanoparticles, from which novel applications of this phenomenon may be developed

Baixem de les tarimes i connectem: recerca en història medieval i innovació docent

We would like to introduce our group of research, [CONTRA TAEDIUM], created by professionals from different fields, that have contributed in this article. Our purpose is to expose our reflections based on our own experiences, not only in research, but also in teaching. We propose new forms of writing history in order to understand the dairy life of the women and men of the past, from birth to death. We would like to point out that interacting all types of sources is essential to understand our history. But, what really makes sense is to bring our students in the historical methodology and involve them in their education. Moreover, it is necessary to design new teaching materials using the new technologies, although it requires team-work and a great, but satisfying, effor

Spontaneous formation of spiral-like patterns with distinct periodic physical properties by confined electrodeposition of Co-In disks

Spatio-temporal patterns are ubiquitous in different areas of materials science and biological systems. However, typically the motifs in these types of systems present a random distribution with many possible different structures. Herein, we demonstrate that controlled spatio-temporal patterns, with reproducible spiral-like shapes, can be obtained by electrodeposition of Co-In alloys inside a confined circular geometry (i.e., in disks commensurate with the typical size of the spatio-temporal features). These patterns are mainly of compositional nature, i.e., with virtually no topographic features. Interestingly, the local changes in composition lead to a periodic modulation of the physical (electric, magnetic and mechanical) properties. Namely, the Co-rich areas show higher saturation magnetization and electrical conductivity and are mechanically harder than the In-rich ones. Thus, this work reveals that confined electrodeposition of this binary system constitutes an effective procedure to attain template-free magnetic, electric and mechanical surface patterning with specific and reproducible shapes

Preparación y caracterización de aleaciones basadas en FeCoNbBSiCu

Se prepararon aleaciones de composición Fe 73-x Co x Nb 6 B 11 Si 10 (x = 35 at.%) y Fe 72-x Co x Nb 6 B 11 Si 10 Cu 1 (x = 35 , 30 y 40 at.%) por la técnica del melt spinning . Se estudió la influencia del Co en la temperaura de Curie y en la estabilidad térmica del material amorfo obtenido, en función de las variaciones de (Fe-Co) manteniendo constante la suma de las proporciones de estos elementos (72 at.%) y los demás elementos de la aleación. Se realizó este estudio mediante la técnica de termogravimetría magnética y la técnica de calorimetría diferencial de barrido. El aumento de contenido de Co provocó un aumento en la temperatura de Curie del material amorfo y en las temperaturas de los picos de cristalización del material, para las muestras con mayor contenido de Co variando las proporciones de (Fe-Co) en 12 y 8 at.%. Sin embargo, cuando el contenido de Co es mayor que 35 at.%, no se observó ningún cambio en la temperatura de Curie del material. Con el aumento de contenido de Co se estabiliza térmicamente el material amorfo

Impact of magnetization easy-axis distributions on the ferromagnet-antiferromagnet exchange-coupling estimation

It is frequently reported that different measurement techniques may yield distinct values for the exchange anisotropy, being the difference of up to one order of magnitude on comparing magnetization loop with ac susceptibility measurements. We show, by both model calculations and a straight-forward experiment, that at least part of this difference could be attributed to big errors in the evaluation of the ferromagnet/ antiferromagnet exchange coupling strengths obtained by means of ac magnetic susceptibility and dc magnetometry measurements which are caused by neglecting the easy-axis distributions or underestimating the uniaxial anisotropy of the ferromagnetic material

Discrimination between coupling and anisotropy fields in exchange-biased bilayers

In the framework of models that assume planar domain wall formed at the antiferromagnetic part of the interface of exchange-biased bilayers, one cannot distinguish between the cases of high or low ratios between the coupling and the antiferromagnet’s anisotropy fields by using hysteresis loop measurement, ferromagnetic resonance, anisotropic magnetoresistance, or ac susceptibility techniques applied on one and the same sample. The analysis of the experimental data obtained on a series of FeMn/Co films indicated that once the biasing is established the variation in the coercivity with the FeMn layer thickness could be essential for solving this problem. If the coercivity decreases with the thickness then the interlayer exchange coupling is the parameter that varies while the domain-wall energy of the antiferromagnet remains practically constant

Discrimination between coupling and anisotropy fields in exchange-biased bilayers

In the framework of models that assume planar domain wall formed at the antiferromagnetic part of the interface of exchange-biased bilayers, one cannot distinguish between the cases of high or low ratios between the coupling and the antiferromagnet’s anisotropy fields by using hysteresis loop measurement, ferromagnetic resonance, anisotropic magnetoresistance, or ac susceptibility techniques applied on one and the same sample. The analysis of the experimental data obtained on a series of FeMn/Co films indicated that once the biasing is established the variation in the coercivity with the FeMn layer thickness could be essential for solving this problem. If the coercivity decreases with the thickness then the interlayer exchange coupling is the parameter that varies while the domain-wall energy of the antiferromagnet remains practically constant

Impact of magnetization easy-axis distributions on the ferromagnet-antiferromagnet exchange-coupling estimation

It is frequently reported that different measurement techniques may yield distinct values for the exchange anisotropy, being the difference of up to one order of magnitude on comparing magnetization loop with ac susceptibility measurements. We show, by both model calculations and a straight-forward experiment, that at least part of this difference could be attributed to big errors in the evaluation of the ferromagnet/ antiferromagnet exchange coupling strengths obtained by means of ac magnetic susceptibility and dc magnetometry measurements which are caused by neglecting the easy-axis distributions or underestimating the uniaxial anisotropy of the ferromagnetic material