lucas perez - Academia.edu (original) (raw)

Papers by lucas perez

ACS Applied Materials & Interfaces, 2016

The magnetic properties of CoP electrodeposited alloys can be easily controlled by layering the a... more The magnetic properties of CoP electrodeposited alloys can be easily controlled by layering the alloys and modulating the P content of the different layers by using pulse plating in the electrodeposition process. However, because of its amorphous nature, the study of the interface quality, which is a limitation for the optimization of the soft magnetic properties of these alloys, becomes a complex task. In this work, we use Rutherford backscattering spectroscopy (RBS) to determine that electrodeposited Co0.74P0.26/Co0.83P0.17 amorphous multilayers with layers down to 20 nm-thick are composed by well-defined layers with interfacial roughness below 3 nm. We have also determined, using magnetostriction measurements, that 4 nm is the lower limitation for the layer thickness. Below this thickness, the layers are mixed and the magnetic behavior of the multilayered films is similar to that shown by single layers, thus going from in-plane to out-of-plane magnetic anisotropy. Therefore, these results establish the range in which the magnetic properties of these alloys can be controlled by layering.

Phys. Chem. Chem. Phys., 2016

The capability of synthesizing Fe-based antiferromagnetic metal alloys would fuel the use of elec... more The capability of synthesizing Fe-based antiferromagnetic metal alloys would fuel the use of electrodeposition in the design of new magnetic devices such as high-aspect-ratio spin valves or new nanostructured hard magnetic composites. Here we report the synthesis of high quality antiferromagnetic FeMn alloys electrodeposited from chloride-based electrolytes. We have found that in order to grow homogeneous FeMn films it is necessary to incorporate a large concentration of NH4Cl as an additive in the electrolyte. The study of the structure and magnetic properties shows that films with composition close to Fe50Mn50 are homogeneous antiferromagnetic alloys. We have established a parameter window for the synthesis of FeMn alloys that show antiferromagnetism at room temperature.

Topics in Applied Physics, 2010

Chapter 10 High-Temperature Ferromagnetism in the Super-Dilute Magnetic SemiconductorGaN:Gd O. Br... more Chapter 10 High-Temperature Ferromagnetism in the Super-Dilute Magnetic SemiconductorGaN:Gd O. Brandt, S. Dhar, L. Pérez, V. Sapega ... Sect. 10.3 presents the basic structural and magnetic properties of GaN:Gd, and Sect. 10.4 discusses the phenomenological model ...

Physical Review B

We present a systematic study of growth, structural, and magnetic characterization of GaN:Gd laye... more We present a systematic study of growth, structural, and magnetic characterization of GaN:Gd layers grown directly on 6H-SiC(0001) substrates by reactive molecular-beam epitaxy with a Gd concentration ranging from 7×1015 to 2×1019cm-3 . The structural properties of these layers are found to be identical to those of undoped GaN layers. However, the magnetic characterization reveals an unprecedented effect. The average value of the magnetic moment per Gd atom is found to be as high as 4000μB as compared to its atomic moment of 8μB . Such a colossal magnetic moment can be explained in terms of a long range spin polarization of the GaN matrix by the Gd atoms which is reflected by the circular polarization of magnetophotoluminescence measurements. Moreover, the material system is found to exhibit ferromagnetism well above room temperature in the entire concentration range under investigation. We propose a phenomenological model to understand the macroscopic behavior of the system. Our st...

A new contactless system that can work at ultralow frequencies (

Sensors and Actuators B Chemical

Electrochimica Acta, 2015

ABSTRACT Bismuth ultra-thin films grown on n-GaAs electrodes via electrodeposition are porous due... more ABSTRACT Bismuth ultra-thin films grown on n-GaAs electrodes via electrodeposition are porous due to a blockade of the electrode surface caused by adsorbed hydrogen when using acidic electrolytes. In this study, we discuss the existence of two sources of hydrogen adsorption and we propose different routes to unblock the n-GaAs surface in order to improve Bi films compactness. Firstly, we demonstrate that increasing the electrolyte temperature provides compact yet polycrystalline Bi films. Cyclic voltammetry scans indicate that this low crystal quality might be a result of the incorporation of Bi hydroxides within the Bi film as a result of the temperature increase. Secondly, we have illuminated the semiconductor surface to take advantage of photogenerated holes. These photocarriers oxidize the adsorbed hydrogen unblocking the surface, but also create pits at the substrate surface that degrade the Bi/GaAs interface and prevent an epitaxial growth. Finally, we show that performing a cyclic voltammetry scan before electrodeposition enables the growth of compact Bi ultra-thin films of high crystallinity on semiconductor substrates with a doping level low enough to perform transport measurements.

Spin valve sensors are one of the most used magnetic field sensors, in particular in relation wit... more Spin valve sensors are one of the most used magnetic field sensors, in particular in relation with spintronics applications. A spin-valve is a multilayered structure with a thin non-magnetic spacer layer sandwiched between two ferromagnetic layers, which have different coercivities. This can be achieved by pinning one of the layers to an antiferromagnetic layer, leaving the other magnetic layer free to rotate. The magnetization alignment of the ferromagnetic layers can be changed from antiparallel (high resistance state) to parallel (low resistance state) depending on the external applied magnetic field. These structures have the advantage of high magnetoresistance signals and high sensitivities at lower fields [1]. The difficulty of electrodepositing antiferromagnetic materials has limited the introduction of electrodeposition in the field of spintronics. Some efforts have been done to synthesized multi-layered spin-valves, replacing the antiferromagnetic materials by artificial or...

Diamond and Related Materials, 2015

Electrochimica Acta, 2014

ABSTRACT In this work we have studied the electrochemical behaviour of the BiO+/n-GaAs interface ... more ABSTRACT In this work we have studied the electrochemical behaviour of the BiO+/n-GaAs interface using an acidic solution. We present several experimental evidences of a surface blockade that inhibits the reduction of BiO+ ions on the substrate surface. This leads to poor quality Bi thin films with a high porosity. After the analysis of our experimental results, we propose that the blocking effect is produced by a layer of adsorbed hydrogen that passivates the substrate surface. Due to the covalent nature of the As-H bond, the adsorbed hydrogen remains at the surface until the applied potential is high enough to promote the hydrogen evolution.

Sensors and Actuators A: Physical, 2004

Sensors and Actuators B: Chemical, 2010

CrystEngComm, 2014

ABSTRACT We report a comparison of the magnetic properties of Fe53Co47 grown with DC and Pulsed D... more ABSTRACT We report a comparison of the magnetic properties of Fe53Co47 grown with DC and Pulsed DC (PDC) sputtering sources. While no remarkable differences concerning structure and composition are found, films grown by PDC reduce their coercivity in several times that in samples grown by DC sources under similar conditions. In addition, PDC films exhibit hard axis rocking effects and a better defined anisotropy axis. By means of EXAFS we have measured the atomic distances of the FeCo matrix and bcc-Co clusters. We show that the small changes within the FeCo matrix are directly related with the coercivity reduction. The tuning of these properties by simply choosing source or power open a simple path to tailor the magnetic properties.

MRS Proceedings, 2002

ABSTRACT Thin films and arrays of lines of magnetic CoNiFe alloy have been produced by electrodep... more ABSTRACT Thin films and arrays of lines of magnetic CoNiFe alloy have been produced by electrodeposition. A magnetic field was applied during the electrodeposition process in order to induce a magnetic anisotropy in the sample. The dependence of the magnetic properties and the magnetic domain structures on the thickness of the films is reported.. In addition to this, the magnetic properties and the domain structure of a thin film and an array of lines, with the same thickness and deposited in the same conditions, have been compared. An increase in the coercivity of the array of lines has been shown.

The Journal of Physical Chemistry C, 2008

ABSTRACT Bismuth is a semimetal with unusual transport properties, such as long mean free path an... more ABSTRACT Bismuth is a semimetal with unusual transport properties, such as long mean free path and large magnetoresistance (MR) effect. Here we report on the influence of deposition potential, Bi(III) concentration, and thickness on the microstructure and morphology of bismuth thin films. Polycrystalline bismuth films were deposited on gold from bismuth nitrate solution. The texture of the films is strongly dependent on deposition potential and Bi(III) concentration, but only weakly dependent on film thickness. The film morphology is strongly dependent on deposition potential and on film thickness. The magnetoresistance (MR) of the as-deposited films was highly dependent film morphology and grain size. Understanding the structure−property relationships is an important first step in optimizing the transport properties of as-deposited films and patterned features.

Solid State Communications, 2009