Claudio Aroca

Universidad Politécnica de Madrid | UPM · Institute for Optoelectronic Systems and Microtechnology

The resonant dynamic of a magnetic domain wall in a permalloy microstrip has been investigated using an innovative experimental setup that enables a simultaneous measurement of the ferromagnetic resonance and the magnetoresistance. The resonance frequency associated with the presence of the magnetic domain wall increases linearly with the external...

The fast and in situ measurement of the complex magnetic susceptibility stands a potential geological tool for an enhanced characterization of rocks and comprehension of the geological context of the landing and exploration sites when used on board planetary rovers. The real part of the susceptibility is related to the capability to acquire magneti...

Magnetic Materials characterization usually requires heavy equipment based on electromagnets which limits their use to the laboratory. The volume of the typical samples is small in order to keep a good uniformity of the applied magnetic field in the sample. This kind of equipment is not appropriate for geological measurements in the field, where po...

In this work, we developed a novel approach to the preparation of molecularly imprinted polymer (MIP) coatings directly onto magnetic multicore nanoparticles (MMCs) by using alternating magnetic fields (AMFs) to trigger the polymerization reaction. MIPs were synthetized with rhodamine 123 (R123) as model template molecule, methacrylic acid (MAA) as...

A device named magnetic susceptometer for a complete determination of the magnetic complex susceptibility of materials and minerals has been conceived and manufactured as a complement for the in situ characterization of rocks during high resolution magnetic prospections. In this work a device and its capabilities for susceptibility measurements are...

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, due to its amorphous nature, the study of the interface quality, which is a limitation for the optimization of the soft magnetic...

We report the design, fabrication, and characterization of a new system that combines the performances of two different types of magnetic characterization systems, Alternating Gradient Force Magnetometers (AGFM) and susceptometers. The flexibility of our system is demonstrated by its capability to be used as any of them, AGFM or susceptometer, with...

Several samples of NdFeB and SmCo permanent magnets have been irradiated with gamma rays up to different total irradiation doses until 1Mrad(Si). Magnetic properties of the samples have been measured at different temperatures before and after irradiation. The modifications of the magnetic parameters are presented. From these results it is highlight...

We have designed and fabricated a microelectromechanical device, based on the alternating field gradient concept, to measure surface magnetic field gradient on planets. Its sensitivity is 4 104 T/m, which is appropriate for magnetite outcrops and areas with rocks formed at different stages recording geomagnetic field reversals. We present the resul...

The description of the planetary magnetic anomalies is a difficult task that combines either aeromagnetic or in-situ magnetic field measurements, and further laboratory characterization of the local rocks. In the case of extraterrestrial planets this is a very difficult and costly task. With the objective to develop predictive algorithms prior to i...

The in-situ determination of the Martian magnetic field is one of the most important and ambitious objectives in Mars exploration, because its implications in paleomagnetism, tectonics and mineral determination. To place sensors on Mars is a complicated task, due to the extreme conditions of the planet surface and also because of the relative low...

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 th...

In this work we describe a new fabrication method for magnetostrictive-piezoelectric sensors that improve several characteristics. The mechanical coupling between the ferromagnetic and the piezoelectric has been optimised by means of a mixed method: electrolytic deposition of a copper layer, playing the role of polished interface, and sputtering de...

A system to evaluate nanoparticles efficiency in hyperthermia applications is presented. The method allows a direct measurement of the power dissipated by the nanoparticles through the determination of the first harmonic component of the in quadrature magnetic moment induced by the applied field. The magnetic moment is measured by using an inductio...

In this work, we report the magnetic properties of sputtered Permalloy (Py: Ni80Fe20)/molybdenum (Mo) multilayer thin films. We show that it is possible to maintain a low coercivity and a high permeability in thick sputtered Py films when reducing the out-of-plane component of the anisotropy by inserting thin film spacers of a non-magnetic material...

Se ha estudiado el acoplamiento entre paredes magneticas en peliculas tipo sandwich de permalloy/Cu/permalloy, obtenidas por pulverizacion catodica, de espesores comprendidos entre 2000A/200A/2000A, para evaluar el campo de acoplamiento entre las paredes. Para realizar este estudio se han cortado la muestras de un tamano lo suficientemente pequeno...

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TbxFe1−x thin films deposited by sputtering on Mo were investigated structurally and magnetically. The microstructure consists of TbFe2 nanoparticles embedded in an amorphous matrix, and the Tb content can be correlated with an increase in the volume of these nanoparticles. Similar microstructure and behavior were found when TbFe2 was deposited on...

We report on the size, structure and magnetic properties of Ni nanoparticles fabricated with a free-jet sputtering nanoparticle source. It is found how the pressure of the inert gas and the diameter of the source nozzle can control the particle size and coercivity in a wide range. Measurements of the specific magnetic moment of Ni nanoparticles are...

Despite the giant magnetostriction of TbFe2, this material has a very limited popularity in real applications, due to the difficulties for obtaining the Laves phase on thin films. Here we report on the properties of annealed TbFe2 films deposited by sputtering on different substrates and with different buffer materials. We find that the presence of...

In this paper, we give an overview of the research on fluxgate magnetometers carried out in Spain. In particular we focus in the development of the planar-type instruments. We summarize the fabrication processes and signal processing developments as well as their use in complex systems and space.

Inductive coupling-based systems show different problems to work in the presence of metals. The low frequency (LF) systems can work with metals in the surroundings. However, they only can work through metals in some particular circumstances and designs. The different problems arising from metal non-cleaned surroundings have been showed in section 2...

The effect of inserting an ultrathin Gd layer (1-2 nm) in the free layer of a Permalloy-based spin valve has been investigated. In the current in-plane configuration, samples with Gd show a reduced magnetoresistance (MR) value, which tends to zero as Gd gets closer to the nonmagnetic spacer, although good MR values can be sustained when Gd is more...

A new radio frequency identification devices (RFIDs) system operating at very low frequencies (in 1 Hz to 100 kHz range) has been developed and tested. This frequency range has the advantage of the avoiding screening problems that commercial technologies undergo. The new system can operate through thick magnetic shielding layers and in metallic non...

Las aplicaciones que ofrecen las nanopartículas magnéticas basadas en sus interacciones con los campos magnéticos estáticos o variantes en el tiempo, son uno de los principales y más prometedores focos de investigación biomédica en la actualidad. La caracterización magnética de las partículas y de su comportamiento en el interior de materiales biol...

This work reports the magnetic properties of sputtered permalloy (Ni80Fe20) multilayers grown changing the anisotropy direction 90° in successive layers. Magnetic measurements show how the saturating field can be controlled by the thickness ratio between different anisotropy layers and how the coercive field is reduced increasing the number of...

In this work we study the exchange coupling in Permalloy (Py)/gadolinium (Gd) bilayers. The exchange-coupled Py/Gd system is very temperature dependent and moreover the magnetization process in the Py layer is mainly due to domain wall (DW) displacements which are strongly controlled by pinning effects. We propose that this pinning could be caused...

In this work, we experimentally justify that the control of the mechanical stress induced during the deposition of sputtered amorphous magnetostrictive ( Fe ₈₀ Co ₂₀)₈₀ B ₂₀ allows a custom design of its magnetic properties. FeCoB multilayers have been sputtered on thermal oxide Si substrates with differe...

The magnetic and electrical properties of Permalloy∕gadolinium∕Permalloy (Py∕Gd∕Py) trilayers have been studied as a function of temperature by using vibrating sample magnetometer and transport measurements with current in plane configuration. The observed dependence of the magnetic moment with temperature can be explained by a paramagnetic contrib...

The main goal of this work is to generate a method to control the magnetic properties of magnetostrictive metals (anisotropy and coercive field) without affecting the total magnetostriction. Multilayers of amorphous (Fe80Co20)80B20 are sputtered changing alternatively the anisotropy direction of the successive layers. The hysteresis loops show how...

In this study, we report a method to optimize the coercivity keeping the magnetostriction value constant in electrodeposited CoP multilayers for their applications in magnetoelastic magnetic sensors. We have deposited multilayers of two different compositions of CoP (Co0.74P0.26 and Co0.83P0.17) and studied the influence of the thickness of the dif...

In this work we report on the magnetic and electrical properties of Permalloy∕gadolinium∕Permalloy (Py∕Gd∕Py) trilayers at low temperatures. These results are complemented with a structural study and numerical calculations. The Py-Gd coupling field is derived from magnetoresistance measurements in the transverse configuration of the trilayer with a...

A new closed flux stripe domain model is proposed to gain more insight into the magnetic behavior of films with weak perpendicular magnetic anisotropy (PMA). Its main novelty is a new flux-closure pattern in which magnetic flux follows semicircular paths. This approximation has been inspired by the magnetization distribution obtained by some resear...

The effect of reduced lateral dimension on the magnetic behavior of long microstrips with weak perpendicular magnetic anisotropy has been studied. The hysteresis loops of the surface and the whole volume of microstrips and large films have been recorded by magneto-optic Kerr effect magnetometry and vibrating sample magnetometry. Also, the magnetic...

In this paper we present an analytical model for describing the sensitivity of a toroidal fluxgate sensor. The model is based on a simplified schematics for the hysteresis loop of the fluxgate core that only includes the coercivity, the saturation field and the saturation magnetization. In spite of this simplicity, the model has been successfully u...

Py/Gd/Py trilayers (Py:Fe20Ni80) have been electrical and magnetically characterized as a function of the temperature. Results show a weak Py-Gd exchange coupling probably due to the Ni interdiffusion into the Gd layer. These results have been compared with magnetic measurements in Py/Gd double bilayers ([Py/Gd/Mo](2)). An enhancement of the Py-Gd...

We have studied the influence of the growth conditions on the structural characteristics of sputtered Py(Fe20Ni80)/ Gd/Py(Fe20Ni80) thin films. Auger electron spectroscopy reveals the existence of Ni in the Gd layer. The Ni concentration profile appears asymmetric with a higher concentration close to the top Py layer. This asymmetrical Ni concentra...

CoP alloys have been electrodeposited at room temperature from electrolytes with different pH values and their magnetic properties have been studied. Cracks and fractures appear when using stiff substrates, showing that high internal stresses, due to hydrogen evolution, are involved in the electrodeposition process. Samples electrodeposited onto fl...

This paper describes an optical cantilever-based system for the measurement of the magnetoelastic coupling of magnetostrictive thin films. The system is calibrated to evaluate the magnetoelastic coupling with no dependence on the Young modulus of the substrate. It has been applied to the measurement of the magnetoelastic coupling of a (Fe80Co20)80B...

In this paper we report a study of the magnetostatic coupling of square dot films and strips of films of Permalloy/Copper/Permalloy (200/20/200 nm). Results show a good magnetostatic coupling which leads to a monodomain structure in the case of square dots as it is observed from hysteresis loops. These monodomain structures appear to be stable for...

A new magnetic sensor with a great sensitivity and simplicity is presented. This device is based on the magnetostatic repulsion force between induced magnetic poles. The force of repulsion between a set of two magnetic plates magnetized by an applied field is measured by using one of them as a cantilever. The measurement of the cantilever bending a...

A new planar fluxgate is presented. The primary coil consists on a spiral grown on a ferrite disc in order to increase the magnetic field produced by the driving current and also to compensate for superimposed external magnetic fields. Two metallic spirals in opposite phase have been mounted over this coil as the secondary winding. They detect the...

We have combined the printed circuit board (PCB) technology with the electrodeposition of amorphous ferromagnetic Co–P alloys to produce a new 2D fluxgate sensor. The fabrication procedure avoids the use of glue to integrate the core in the device, which improves its performance and makes the production process more reproducible. Choosing properly...

A new contactless system that can work at ultralow frequencies (<100kHz, 2kHz used) has been developed. At this frequencies the screening problems of the current technologies are avoided. It is characterized by the use of a tunable magnetic sensor; concretely, a fluxgate with a double demodulation technique, as detection module. The main difference...

By using a combination of sputtering, photolithography, and electrochemical deposition techniques spiral coils with good performances have been grown (low resistance, high number of turns/cm …). This can be used as exciting coils of a magnetic sensor or as a part of a planar inductor.

The magneto-impedance effect has been studied in Permalloy (3μm)/Cu (1μm)/Permalloy (3μm) sandwiches of different shapes obtained by sputtering. Results show the importance of sensor geometry in the magneto-impedance ratio. Values of magneto-impedance ratio measured at a frequency of 80MHz vary between 25% and 140% depending on the sensor shape.

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 additio...

The increasing density in recording media has augmented the interest in magnetic structures with dimensions in the range of nanometers. One of the interesting nanoscale devices for these kind of applications are the square magnetic nanodots. However a very large integration of this structures in a 2D array leads to interactions between different do...

A new generation of hybrid magnetic sensors is presented. These sensors inherit the principles of the piezoelectric–magnetostrictive sensors improving some of their deficiencies by using a stripe actuator instead of a single piezo ceramic. The hysteresis of these sensors has almost been reduced to zero in magnetic sensors using amorphous ribbons an...

Amorphous soft magnetic CoP electrolytic multilayers have been obtained with a controlled surface magnetic anisotropy. The surface magnetization easy direction can be continuously altered from an initial perpendicular position to a final arrangement within the longitudinal plane. This continuous change of magnetization direction is controlled durin...

The influence of magnetic anisotropy on magnetoresistance has been studied in magnetic-non-magnetic-magnetic sandwiches. A numerical model has been developed considering different anisotropies in each magnetic layer and different exchange couplings between them. Both contributions to the magnetoresistance are evaluated; anisotropic and giant magnet...

The structure of magnetization in magnetic square dots is studied in the range of tens of nanometer by means of micromagnetic simulations. Two magnetic configurations are found, diagonal and vortex structures for thin films, flower and vortex for magnetic nanocubes and a hybrid flower in bulk and vortex near the surfaces for dots with thicknesses l...

In this paper, we present a hybrid piezoelectric–magnetostrictive two-axis magnetometer in which the strains induced by the piezoelectric element in the magnetostrictive one produces a macroscopic bending of the sensor. With such a vibration, perpendicular anisotropy constants of the order of 780N/m2 are induced in the magnetostrictive element, who...

Electrodeposited CoNiFe alloys have been produced under potential and current control conditions. It was found that composition, crystalline structure and magnetic properties are the same irrespective of which plating control is used. Magnetic anisotropy is present in the softest samples. A study of the dependence of magnetic properties and domain...

The Ellwood representation (B- mu H, H) of magnetic loops in the Rayleigh region does not give enough information to study the magnetic properties in weak fields. The authors propose an additional representation (B, H-B/ mu ) which allows information on coercivity to be obtained. Magnetic and electrical compensation methods for obtaining both repre...

A system for the measurement of the Fourier components of low-level electrical signal is presented. The system has been applied to the measurement of the harmonics of the dynamic hysteresis loop of an amorphous material, finding a good correlation between the hysteresis loop obtained by conventional methods and the one reconstructed from the harmon...

This paper presents the results obtained with a prototype of a magnetostrictive-piezoelectric magnetic sensor where the ferromagnetic material has been grown by sputtering over the piezoelectric support where a copper layer has been previously deposited and electrolitically polished. In this way, the coupling between the piezoelectric and the ferro...

A new working configuration for magnetostrictive-piezoelectric magnetic sensors is presented. In this configuration, the excitation is caused using an electrical current flowing through the ferromagnetic sample and the induced signal is sensed in the piezoelectric support as an electrical voltage. This new idea allows a magnetic field detection wit...

Multilayer films composed of Co_x P_(1-x) ferromagnetic layers with different composition (0.74 < x < 0.86) have been obtained by varying the electrolytic current during the deposition process. These samples exhibit planar anisotropy, high permeability and a very low coercive force (~5 A/m). The magnetic properties of these samples have been compar...

A highly sensitive method of detecting vibrations of a cantilever in atomic-force microscopy has been introduced as a detector in an alternating-gradient field magnetometer. Use of light is the success of this system as it is compatible with vacuum systems and closed-flux cryostals. The optical signal is electronically conditioned easily. Experimen...

: We have studied the effect of the homogeneity of hydrogen distribution on magnetic properties of hydrogen charged amorphous samples (Metglass 2826MB: Fe40Ni40Mo4B18). The results suggest that, in high magnetostrictive samples, the induced internal stresses and hence the magnetic anisotropy are related to the hydrogen distribution and not to the...

CoP amorphous samples, electrodeposited on copper wires and exhibiting a longitudinal magnetic anisotropy, show a spontaneous Matteucci effect once the substrate has been subjected to torque. This induces an easy axis to allow for magnetization to occur, breaking away from its original longitudinal direction. The magnetic domain structures, as obse...

In this work we describe a new fabrication method for magnetostrictive-piezoelectric sensors that improve several characteristics. The mechanical coupling between the ferromagnetic and the piezoelectric has been optimised by means of a mixed method: electrolytic deposition of a copper layer, playing the role of polished interface, and sputtering de...

We have studied, by means of numerical simulation, the structure of domain walls in permalloy thin film monolayers and sandwiches consisting of two permalloy layers separated by a Cu interlayer. The calculated transition thicknesses between Bloch and Néel domain walls increase notably for the sandwiches with respect to monolayers. The structures ob...

CoP multilayers grown over Cu wires exhibit magnetoimpedance phenomenon. The change in the real part of the measured voltage is VR = [V(H = 0 Oe)-V(Hmax)]/V(Hmax) ≈ 3300%(Irms = 500 mA, 90 kHz); the maximum dVR/dH, is 1280%/Oe at HDC = 1.2 Oe. These quantities are enhanced if the wire is subjected to an angular deformation by means of a torque appl...

Fe20Ni80 single layers and Fe20Ni80/Cu/Fe20Ni80 thin films were grown by using a magnetron sputtering system in order to study the domain wall structures in both kinds of samples. The magnetostatic coupling energy between the domain walls in the sandwich structures has been obtained. When there is no coupling, these structures exhibit Cross—Tie dom...

The irreversible effect produced by hydrogen charging on the magnetic properties, at low magnetic field, of high magnetostrictive amorphous ribbons has been studied. The experimental measurements show irreversible effects on the propagation field in as-cast samples and very low effect in annealed samples. These results have been explained by the fo...

CoP multilayers grown over Cu wires exhibit magnetoimpedance phenomenon. The change in the real part of the measured voltage is VR = [V(H = 00e)-V(Hmax)]/V(Hmax) ~ 3300%(Irms = 500 mA, 90 kHz); the maximum dVa/dH, is 1280%/Oe at HDC = 1.20e. These quantities are enhanced if the wire is subjected to an angular deformation by means of a torque applie...

In this paper, we present a method to avoid hysteresis in magnetostrictive-piezoelectric sensors. It is based on the application of an alternating magnetic field of a frequency different than the piezoelectric exciting frequency that supplies enough energy to overcome any domain wall pinning. The signal is filtered with a notch filter synchronized...

Ferromagnetic amorphous ribbons with an helical anisotropy, that show bistable magnetization processes in which the magnetization in the center and in both surfaces are coupled, have been recently reported. These special magnetization processes make these kind of samples suitable for their use as sensor cores of magnetometers based on "demagnetizin...

Exact analytic expressions for magnetostatic energy calculations in arrays of ferromagnetic prisms are presented. They apply to two-dimensional (2-D) and three-dimensional (3-D) arrays of variable length prisms with uniform magnetization inside each prism. This permits the study of irregular magnetic structures allowing also a variable grid where t...

Amorphous ribbons with helical induced anisotropy show outstanding properties such as their capability to be magnetized through a single Barkhausen jump. This phenomenon is due to the helical anisotropy distribution induced in the samples by current annealing. The anisotropy direction rotates 180° continuously from one surface of the ribbon to the...

Negative magnetostrictive amorphous ribbons have been annealed by means of short current pulses. The temperature of the ribbons was determined by magnetic measurements and by using a thermocouple attached to the samples for temperatures below the Curie point. To estimate the temperature above the Curie point, we have used the local intensity of the...

Positive and negative magnetostrictive amorphous ribbons have been locally current annealed under local stress to induce different anisotropies, which have been studied by observing the magnetic domains. The results are explained using a theoretical model based on the assumption that the sample behaves like a membrane. Complementary information is...

Magnetic domain-wall patterns in magnetostatically coupled bilayers separated by a non-magnetic interlayer have been studied for different anisotropy configurations. A numerical treatment is presented for the case of a parallel anisotropy axis between magnetic layers for samples with thicknesses of 1000Åfor the magnetic layers and 100Åfor the inter...

CoP electrolytic monolayers and multilayers were grown over copper wires using a constant or pulsed electrical current density, exhibiting radial or planar anisotropy, respectively. Over the surface of a monolayer, multilayers of different thicknesses were deposited. The surface radial anisotropy evolves to a planar one as the overlayer thicknesses...

Magnetization processes with large Barkhausen jumps can be obtained in low-magnetostrictive amorphous ribbons with helical induced anisotropy. In this work, we have made a study of the induction of such anisotropies showing that in as-cast samples stronger anisotropies can be induced than in samples pre-annealed above the Curie temperature. The kin...

CoP electrolytic monolayers and multilayers were grown over copper wires using a constant or pulsed electrical current density, exhibiting radial or planar anisotropy, respectively. Over the surface of a monolayer, multilayers of different thicknesses were deposited. The surface radial anisotropy evolves to a planar one as the overlayer thicknesses...

The objective of this work was to obtain CoP amorphous metallic multilayers with controlled magnetic anisotropy. Samples, formed by a single layer, with perpendicular anisotropy have been obtained by electrodeposition. Over the sample surface a multilayer with in plane magnetic anisotropy was grown. A study on the evolution of this anisotropy, whic...