ROCIO RANCHAL - Academia.edu (original) (raw)
Papers by ROCIO RANCHAL
Materials, 2021
The potential use of electrodeposition to synthesize a hybrid magnetostrictive/magnetoelectric la... more The potential use of electrodeposition to synthesize a hybrid magnetostrictive/magnetoelectric layered system is shown in this paper. By appropriately adjusting pH, growth potential, and electrolyte composition, it is possible to achieve thin films in which magnetoelectric oxide GaFeO3 (GFO) is formed in close contact with magnetostrictive metallic FeGa alloy. X-ray diffractometry shows the formation of FeGa as well as GFO and Fe oxides. Electron microscopy observations reveal that GFO mainly segregates in grain boundaries. Samples are ferromagnetic with an isotropic magnetic behavior in the sample plane. Magnetic stripes are observed by magnetic force microscopy and are correlated to Fe3O4. When its segregation is minimal, the absence of stripes can be used to monitor Fe oxide segregation.
![Research paper thumbnail of Synthetic domain walls in [TbFeGa/TbFe]2 multilayers](https://attachments.academia-assets.com/95627249/thumbnails/1.jpg)
](Nanotechnology, 2020
Here we report the possibility of creating synthetic domain walls in nominal [Fe72Ga28/Tb33Fe67]2... more Here we report the possibility of creating synthetic domain walls in nominal [Fe72Ga28/Tb33Fe67]2 multilayers. The magnetization as a function of the temperature reveals the absence of Compensation temperature in the samples which can be understood considering an interdiffusion process that results in the formation of TbFeGa alloys at the nominal FeGa layers. Therefore, samples are actually comprised of TbFeGa and TbFe layers. The hysteresis loops exhibit magnetization steps related to the nucleation of domain walls formed because of the competition between different interactions: i) the antiferromagnetic exchange coupling between the heavy rare earth (Tb) and the transition magnetic metal (Fe) inside each layer, ii) the antiferromagnetic coupling between Tb and Fe at the interfaces, and iii) the Zeeman energy. In good agreement with the experimental values, the nucleation field of the domain walls has been theoretically calculated taking into account the tilt of the magnetization with respect to the sample plane. Our experimental results indicate that by a proper thickness adjustment, it can be tuned both, the value of the nucleation field, and the layer in which this firstly occurs. Experimental values for the exchange bias field have also been calculated.
The Journal of Physical Chemistry C, 2020
![Research paper thumbnail of Investigation of the Out of Plane Component of the Magnetization of [Fe72 Ga28 (x nm)/Tb33 Fe67 (50 nm)]2 Multilayers](https://attachments.academia-assets.com/95627251/thumbnails/1.jpg)
](physica status solidi (a), 2018
In this work the authors present their investigation on sputtered [Fe 72 Ga 28 / Tb 33 Fe 37 ] 2 ... more In this work the authors present their investigation on sputtered [Fe 72 Ga 28 / Tb 33 Fe 37 ] 2 multilayers in which the Tb-Fe thickness is kept fixed (50 nm), whereas the Fe-Ga ranged from 25 to 100 nm. In particular, the authors study the out of plane component of the magnetization by means of vibrating sample magnetometry and magnetic force microscopy. Samples are structurally characterized by X-ray diffractometry and electron microscopy in order to correlate the magnetic characterization with the structural properties. In addition, the authors anneal the samples at 400 C in order to analyze the effect of the thermal treatment on both, structural and magnetic properties. In the as-grown samples, the out of plane component of the magnetization can be related to both, Tb-Fe and Fe-Ga. However, experimental results indicate that annealing reduces this component of the magnetization due to the crystallization of ordered phases in the Fe-Ga layers.
The Journal of Physical Chemistry C, 2016
We have studied the electrodeposition of Bi thin films on two GaAs orientations with different at... more We have studied the electrodeposition of Bi thin films on two GaAs orientations with different atomic arrangement and chemical composition, (110) and (111)B. The electrochemical properties of each substrate have been analyzed by means of cyclic voltammetries and current transients. Then, x-ray diffraction has been used to determine the crystal structure and quality of the Bi films, and atomic force microscopy images have provided information about the surface morphology. Finally, the Bi/GaAs interface has been electrically characterized by means of capacitance-voltage and current-voltage curves. In this study, we have been able to discriminate between the effect of surface chemistry and the arrangement of surface atoms. The former has a direct effect on the reduction process of Bi(III) ions and on the electrical properties of the Bi/GaAs interface, whereas the atoms arrangement at the substrate surface determines the texture and morphology of the Bi films.
Journal of Physics D: Applied Physics, 2015
ABSTRACT We have investigated the magnetic behavior of Fe1 − xGax (15 ≤ x ≤ 22 at.%) thin films g... more ABSTRACT We have investigated the magnetic behavior of Fe1 − xGax (15 ≤ x ≤ 22 at.%) thin films grown by electrodeposition. The samples exhibit a <1 1 0 > texture although a rather small diffraction peak related to the (1 0 0) phase can also be observed. The layers do not present perpendicular magnetic anisotropy but magnetic hysteresis loops and magnetic force microscopy evidence a significant out-of-plane component for the magnetization. This component seems to increase for Ga contents around the 19 at.% value at which these alloys present a peak for the magnetostriction constant in the [1 0 0] direction. In this composition range, we have also observed an enhancement of the period of the magnetic structures. The experimental results indicate that the origin of the domain configuration is the presence of clusters with a (1 0 0) structural phase. The out-of-plane component of the magnetization seems to arise because of the compression of these nanoaggregates.
Electrochimica Acta, 2015
Bismuth ultra-thin films grown on n-GaAs electrodes via electrodeposition are porous due to a blo... more 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...
Nanotechnology, 2002
The influence of magnetic anisotropy on magnetoresistance has been studied in magnetic-non-magnet... more 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 magnetoresistance (GMR). Appropriate magnetic anisotropy configurations allow GMR without antiferromagnetic coupling between the magnetic layers. Sandwiches of permalloy-copper-permalloy
Electrochimica Acta, 2014
In this work we have studied the electrochemical behaviour of the BiO + /n-GaAs interface using a... more 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 AsH bond, the adsorbed hydrogen remains at the surface until the applied potential is high enough to promote the hydrogen evolution.
Review of Scientific Instruments, 2015
We report the design, fabrication, and characterization of a new system that combines the perform... more 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, without any modification in the experimental setup because of the electronics we have developed. Our system has a limit of sensitivity lower than 5 × 10 −7 emu. Moreover, its main advantage is demonstrated by the possibility of measuring small quantities of materials under DC or AC magnetic fields that cannot properly be measured with a commercial vibrating sample magnetometers or AGFM.
Physical Review B, 2012
We explore the influence of Fe content on the interfacial magnetic properties of Ni 1−x Fe x (50Å... more We explore the influence of Fe content on the interfacial magnetic properties of Ni 1−x Fe x (50Å)/Fe (tÅ)/ Gd(50Å)/Fe (tÅ)/Ni 1−x Fe x (50Å) (x = 0.2 and 0.6, and t = 0 and 10Å) multilayers by means of element-specific x-ray magnetic circular dichroism measurements at Gd M 5 and (Ni, Fe) L 2,3 absorption edges, superconducting quantum interference device magnetometry, and specular reflectivity measurements. Increasing Fe content in the Ni-Fe layer enhances the Gd ordering temperature in the interfacial regions. Addition of a 1-nm Fe spacer results in the largest enhancement in Gd ordering temperature in both interior and interfacial Gd regions, even for high Ni content in the Ni-Fe layer. This indicates that the Fe spacers act as effective barriers (albeit imperfect) in reducing Gd-Ni contact interactions responsible for limiting the interfacial Gd magnetic ordering temperature to values larger than bulk Gd, but significantly lower than observed at Fe/Gd interfaces.
Physical Review B, 2012
The atomic environments of Fe and Co involved in the magnetostriction effect in FeCoB alloys have... more 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.
physica status solidi (a), 2006
Py/Gd/Py trilayers (Py : Fe 20 Ni 80) have been electrical and magnetically characterized as a fu... more Py/Gd/Py trilayers (Py : Fe 20 Ni 80) 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 exchange coupling has been obtained in these samples where the Ni concentration in the Gd layer is almost null.
New Journal of Physics, 2008
In this work we study the exchange coupling in Permalloy (Py)/gadolinium (Gd) bilayers. The excha... more 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 by magnetostatic and exchange interactions between Py DWs and the magnetostrictive Gd layer. These effects mask the antiferromagnetic coupling between layers and, depending on temperature and Py thicknesses, apparent ferromagnetic coupling occurs. The study has been performed in the 80-300 K temperature range for different Py layer thicknesses and different Py induced anisotropies. Contents 1. Introduction 2 2. Experimental 3 3. Results and discussion 5 4. Conclusions 9 Acknowledgments 9 References 10
Journal of Applied Physics, 2011
In this work, we report the magnetic properties of sputtered Permalloy (Py: Ni 80 Fe 20)/molybden... more In this work, we report the magnetic properties of sputtered Permalloy (Py: Ni 80 Fe 20)/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 like Mo. For these kind of multilayers, we have found coercivities which are close to those for single layer films with no out-of-plane anisotropy. The coercivity is also dependent on the number of layers exhibiting a minimum value when each single Py layer has a thickness close to the transition thickness between Neel and Bloch domain walls. V
Journal of Applied Physics, 2006
ABSTRACT In this work we report on the magnetic and electrical properties of Permalloy∕gadolinium... more ABSTRACT 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 Permalloy thickness lower than its exchange correlation length. The coupling field obtained was low, likely due to the presence of low Curie temperature Gd1−xNix alloys at the Py∕Gd interfaces.
Journal of Applied Physics, 2007
The magnetic and electrical properties of Permalloy/gadolinium/Permalloy (Py/Gd/Py) trilayers hav... more 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 contribution. Electrical measurements show that this contribution is originated by the formation of Gd1-xNix alloys at the Py/Gd interfaces because of the Ni diffusion. Despite the Ni diffusion, we find no evidence of amorphization from either the Py layer or the Py/Gd interfaces. We also obtain the Curie temperature of the Gd1-xNix alloys by the position of inflexion points in the resistance versus temperature curve.
Journal of Applied Physics, 2010
ABSTRACT Despite the giant magnetostriction of TbFe2, this material has a very limited popularity... more ABSTRACT 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 the highly magnetostrictive Laves phase is not necessarily related to crystallinity of the substrate. Strikingly we find a correlation between the degree of TbFe2 crystallization and the rigidity of the substrate or the buffer layer underneath the TbFe2. This opens the possibility of easy manufacturing of devices based on TbFe2 layers.
Journal of Alloys and Compounds, 2014
We report the magnetic anisotropy and domain configuration of cosputtered TbFeGa alloys. The laye... more We report the magnetic anisotropy and domain configuration of cosputtered TbFeGa alloys. The layers were deposited from two targets with compositions TbFe 2 and Fe 3 Ga, respectively. The structural and magnetic properties do not only depend on the composition but also on the growth conditions. Alloys with the same composition but deposited using a DC or a pulsed power source in the TbFe 2 target exhibit a different magnetic anisotropy. The perpendicular magnetic anisotropy, the size and topology of domain patterns can be tailored by changing the evaporation parameters of TbFe 2. The width of the stripe domain increases from 235 to 835 nm when using the DC source in the TbFe 2. We correlate this effect with Tb enrichment of the Tb x Fe! x phases present in the samples.
Materials, 2021
The potential use of electrodeposition to synthesize a hybrid magnetostrictive/magnetoelectric la... more The potential use of electrodeposition to synthesize a hybrid magnetostrictive/magnetoelectric layered system is shown in this paper. By appropriately adjusting pH, growth potential, and electrolyte composition, it is possible to achieve thin films in which magnetoelectric oxide GaFeO3 (GFO) is formed in close contact with magnetostrictive metallic FeGa alloy. X-ray diffractometry shows the formation of FeGa as well as GFO and Fe oxides. Electron microscopy observations reveal that GFO mainly segregates in grain boundaries. Samples are ferromagnetic with an isotropic magnetic behavior in the sample plane. Magnetic stripes are observed by magnetic force microscopy and are correlated to Fe3O4. When its segregation is minimal, the absence of stripes can be used to monitor Fe oxide segregation.
Nanotechnology, 2020
Here we report the possibility of creating synthetic domain walls in nominal [Fe72Ga28/Tb33Fe67]2... more Here we report the possibility of creating synthetic domain walls in nominal [Fe72Ga28/Tb33Fe67]2 multilayers. The magnetization as a function of the temperature reveals the absence of Compensation temperature in the samples which can be understood considering an interdiffusion process that results in the formation of TbFeGa alloys at the nominal FeGa layers. Therefore, samples are actually comprised of TbFeGa and TbFe layers. The hysteresis loops exhibit magnetization steps related to the nucleation of domain walls formed because of the competition between different interactions: i) the antiferromagnetic exchange coupling between the heavy rare earth (Tb) and the transition magnetic metal (Fe) inside each layer, ii) the antiferromagnetic coupling between Tb and Fe at the interfaces, and iii) the Zeeman energy. In good agreement with the experimental values, the nucleation field of the domain walls has been theoretically calculated taking into account the tilt of the magnetization with respect to the sample plane. Our experimental results indicate that by a proper thickness adjustment, it can be tuned both, the value of the nucleation field, and the layer in which this firstly occurs. Experimental values for the exchange bias field have also been calculated.
The Journal of Physical Chemistry C, 2020
physica status solidi (a), 2018
In this work the authors present their investigation on sputtered [Fe 72 Ga 28 / Tb 33 Fe 37 ] 2 ... more In this work the authors present their investigation on sputtered [Fe 72 Ga 28 / Tb 33 Fe 37 ] 2 multilayers in which the Tb-Fe thickness is kept fixed (50 nm), whereas the Fe-Ga ranged from 25 to 100 nm. In particular, the authors study the out of plane component of the magnetization by means of vibrating sample magnetometry and magnetic force microscopy. Samples are structurally characterized by X-ray diffractometry and electron microscopy in order to correlate the magnetic characterization with the structural properties. In addition, the authors anneal the samples at 400 C in order to analyze the effect of the thermal treatment on both, structural and magnetic properties. In the as-grown samples, the out of plane component of the magnetization can be related to both, Tb-Fe and Fe-Ga. However, experimental results indicate that annealing reduces this component of the magnetization due to the crystallization of ordered phases in the Fe-Ga layers.
The Journal of Physical Chemistry C, 2016
We have studied the electrodeposition of Bi thin films on two GaAs orientations with different at... more We have studied the electrodeposition of Bi thin films on two GaAs orientations with different atomic arrangement and chemical composition, (110) and (111)B. The electrochemical properties of each substrate have been analyzed by means of cyclic voltammetries and current transients. Then, x-ray diffraction has been used to determine the crystal structure and quality of the Bi films, and atomic force microscopy images have provided information about the surface morphology. Finally, the Bi/GaAs interface has been electrically characterized by means of capacitance-voltage and current-voltage curves. In this study, we have been able to discriminate between the effect of surface chemistry and the arrangement of surface atoms. The former has a direct effect on the reduction process of Bi(III) ions and on the electrical properties of the Bi/GaAs interface, whereas the atoms arrangement at the substrate surface determines the texture and morphology of the Bi films.
Journal of Physics D: Applied Physics, 2015
ABSTRACT We have investigated the magnetic behavior of Fe1 − xGax (15 ≤ x ≤ 22 at.%) thin films g... more ABSTRACT We have investigated the magnetic behavior of Fe1 − xGax (15 ≤ x ≤ 22 at.%) thin films grown by electrodeposition. The samples exhibit a <1 1 0 > texture although a rather small diffraction peak related to the (1 0 0) phase can also be observed. The layers do not present perpendicular magnetic anisotropy but magnetic hysteresis loops and magnetic force microscopy evidence a significant out-of-plane component for the magnetization. This component seems to increase for Ga contents around the 19 at.% value at which these alloys present a peak for the magnetostriction constant in the [1 0 0] direction. In this composition range, we have also observed an enhancement of the period of the magnetic structures. The experimental results indicate that the origin of the domain configuration is the presence of clusters with a (1 0 0) structural phase. The out-of-plane component of the magnetization seems to arise because of the compression of these nanoaggregates.
Electrochimica Acta, 2015
Bismuth ultra-thin films grown on n-GaAs electrodes via electrodeposition are porous due to a blo... more 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...
Nanotechnology, 2002
The influence of magnetic anisotropy on magnetoresistance has been studied in magnetic-non-magnet... more 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 magnetoresistance (GMR). Appropriate magnetic anisotropy configurations allow GMR without antiferromagnetic coupling between the magnetic layers. Sandwiches of permalloy-copper-permalloy
Electrochimica Acta, 2014
In this work we have studied the electrochemical behaviour of the BiO + /n-GaAs interface using a... more 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 AsH bond, the adsorbed hydrogen remains at the surface until the applied potential is high enough to promote the hydrogen evolution.
Review of Scientific Instruments, 2015
We report the design, fabrication, and characterization of a new system that combines the perform... more 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, without any modification in the experimental setup because of the electronics we have developed. Our system has a limit of sensitivity lower than 5 × 10 −7 emu. Moreover, its main advantage is demonstrated by the possibility of measuring small quantities of materials under DC or AC magnetic fields that cannot properly be measured with a commercial vibrating sample magnetometers or AGFM.
Physical Review B, 2012
We explore the influence of Fe content on the interfacial magnetic properties of Ni 1−x Fe x (50Å... more We explore the influence of Fe content on the interfacial magnetic properties of Ni 1−x Fe x (50Å)/Fe (tÅ)/ Gd(50Å)/Fe (tÅ)/Ni 1−x Fe x (50Å) (x = 0.2 and 0.6, and t = 0 and 10Å) multilayers by means of element-specific x-ray magnetic circular dichroism measurements at Gd M 5 and (Ni, Fe) L 2,3 absorption edges, superconducting quantum interference device magnetometry, and specular reflectivity measurements. Increasing Fe content in the Ni-Fe layer enhances the Gd ordering temperature in the interfacial regions. Addition of a 1-nm Fe spacer results in the largest enhancement in Gd ordering temperature in both interior and interfacial Gd regions, even for high Ni content in the Ni-Fe layer. This indicates that the Fe spacers act as effective barriers (albeit imperfect) in reducing Gd-Ni contact interactions responsible for limiting the interfacial Gd magnetic ordering temperature to values larger than bulk Gd, but significantly lower than observed at Fe/Gd interfaces.
Physical Review B, 2012
The atomic environments of Fe and Co involved in the magnetostriction effect in FeCoB alloys have... more 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.
physica status solidi (a), 2006
Py/Gd/Py trilayers (Py : Fe 20 Ni 80) have been electrical and magnetically characterized as a fu... more Py/Gd/Py trilayers (Py : Fe 20 Ni 80) 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 exchange coupling has been obtained in these samples where the Ni concentration in the Gd layer is almost null.
New Journal of Physics, 2008
In this work we study the exchange coupling in Permalloy (Py)/gadolinium (Gd) bilayers. The excha... more 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 by magnetostatic and exchange interactions between Py DWs and the magnetostrictive Gd layer. These effects mask the antiferromagnetic coupling between layers and, depending on temperature and Py thicknesses, apparent ferromagnetic coupling occurs. The study has been performed in the 80-300 K temperature range for different Py layer thicknesses and different Py induced anisotropies. Contents 1. Introduction 2 2. Experimental 3 3. Results and discussion 5 4. Conclusions 9 Acknowledgments 9 References 10
Journal of Applied Physics, 2011
In this work, we report the magnetic properties of sputtered Permalloy (Py: Ni 80 Fe 20)/molybden... more In this work, we report the magnetic properties of sputtered Permalloy (Py: Ni 80 Fe 20)/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 like Mo. For these kind of multilayers, we have found coercivities which are close to those for single layer films with no out-of-plane anisotropy. The coercivity is also dependent on the number of layers exhibiting a minimum value when each single Py layer has a thickness close to the transition thickness between Neel and Bloch domain walls. V
Journal of Applied Physics, 2006
ABSTRACT In this work we report on the magnetic and electrical properties of Permalloy∕gadolinium... more ABSTRACT 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 Permalloy thickness lower than its exchange correlation length. The coupling field obtained was low, likely due to the presence of low Curie temperature Gd1−xNix alloys at the Py∕Gd interfaces.
Journal of Applied Physics, 2007
The magnetic and electrical properties of Permalloy/gadolinium/Permalloy (Py/Gd/Py) trilayers hav... more 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 contribution. Electrical measurements show that this contribution is originated by the formation of Gd1-xNix alloys at the Py/Gd interfaces because of the Ni diffusion. Despite the Ni diffusion, we find no evidence of amorphization from either the Py layer or the Py/Gd interfaces. We also obtain the Curie temperature of the Gd1-xNix alloys by the position of inflexion points in the resistance versus temperature curve.
Journal of Applied Physics, 2010
ABSTRACT Despite the giant magnetostriction of TbFe2, this material has a very limited popularity... more ABSTRACT 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 the highly magnetostrictive Laves phase is not necessarily related to crystallinity of the substrate. Strikingly we find a correlation between the degree of TbFe2 crystallization and the rigidity of the substrate or the buffer layer underneath the TbFe2. This opens the possibility of easy manufacturing of devices based on TbFe2 layers.
Journal of Alloys and Compounds, 2014
We report the magnetic anisotropy and domain configuration of cosputtered TbFeGa alloys. The laye... more We report the magnetic anisotropy and domain configuration of cosputtered TbFeGa alloys. The layers were deposited from two targets with compositions TbFe 2 and Fe 3 Ga, respectively. The structural and magnetic properties do not only depend on the composition but also on the growth conditions. Alloys with the same composition but deposited using a DC or a pulsed power source in the TbFe 2 target exhibit a different magnetic anisotropy. The perpendicular magnetic anisotropy, the size and topology of domain patterns can be tailored by changing the evaporation parameters of TbFe 2. The width of the stripe domain increases from 235 to 835 nm when using the DC source in the TbFe 2. We correlate this effect with Tb enrichment of the Tb x Fe! x phases present in the samples.