181 research outputs found
An insight into the role of magnetic anisotropies in the behavior of thin films and arrays of nanoparticles
No full textIn this thesis work we discussed the properties of magnetic materials derived by the reduction of at least one of the spatial dimensions under the micrometer scale: in particular we analyzed the origin of some magnetic behaviors in magnetic nanostructures like thin films and arrays of nanodots.
One of the important properties which is strongly affected by the size reduction and in which is contained most of the physical description of a magnetic system is the anisotropy energy term: a direction-dependent parameter which strongly contributes to the determination of the equilibrium state and magnetic behavior. We described various nanostructured systems concentrating prevalently on thin films and arrays of interacting nanoparticles and for each system the origin and the physical implications of magnetic anisotropy is discussed.
In thin magnetic films, two types of magnetic anisotropies are presented: Perpendicular Magnetic Anisotropy which has a crystalline origin and competes with the shape anisotropy of the thin film producing a singular type of magnetic domains called “stripes” and the Rotatable Anisotropy (the easy magnetic direction is not fixed but could be rotated by means of an external magnetic field). We tried to give a better explanation and modeling of the Rotatable Anisotropy, making a parallelism between the static and dynamic experimental evidences.
We performed also a description of the interaction of magnetic dots in arrays with different symmetry and with finite dimensions. In particular we discovered a peculiar space-dependent behavior that we called “Global Configurational Anisotropy”, that has a strong importance when the dimension of the array becomes comparable with the dimension of the nanoparticles
Magnetic properties of sputtered Tb-Fe-Ga ternary compounds
No full textThe investigation on materials systems with perpendicular magnetic anisotropy (PMA) receives a large interest because of their applications in magnetic storage or in spintronic devices. Tb-Fe alloys were investigated because of their pretty large out-of-plane anisotropy constant. Recently, there have appeared reports about the influence of small amounts of Tb (< 1 at.%) in the magnetostriction of Fe-Ga alloys [1-3]. In other group of studies, the interest is the magnetic anisotropy of Tb-Fe-Ga compounds with a much higher Tb content [4-6].
We have studied how to control the magnetic properties of 250 nm thick Tb-Fe-Ga layers. Samples were cosputtered from two targets (TbFe2 and Fe3Ga) on glass substrates capped with a Mo layer. Two series of samples have been obtained depending on the power source (DC or pulsed) used in each target.
Regardless of the power source used in the targets, we have found PMA in the Tb10Fe77Ga13 layers and an in-plane magnetic anisotropy for the Tb9Fe75Ga16. The Tb10Fe76Ga14 alloy has a magnetic anisotropy that depends on the power source. There is a clear PMA when using the DC power source in the TbFe2 target, whereas it changes to a weak PMA when using it in the Fe3Ga target. We have also found rotatable magnetic anisotropy in some samples. This means that the orientation of the magnetic domains depends on the direction of a previous applied magnetic field. This behavior can be used as a method for the determination of frauds produced by magnetic fields in devices such as water meters or hard disks [7].
References
[1] T. Ma et al, Appl. Phys. Lett. 106, 112401 (2015).
[2] W. Wu et al, Appl. Phys. Lett. 103, 262403 (2013).
[3] L. Jiang et al, Appl. Phys. Lett. 102, 222409 (2013).
[4] R. Ranchal et al, J. Alloys Compnd. 582, 839 (2014).
[5] R. Ranchal and V. Gutiérrez-Díez, Thin Solid Films, 534, 557 (2013).
[6] R. Ranchal et al, J. Alloys Compnd. 667, 262 (2016).
[7] R. Ranchal, S. Fin, and D. Bisero. Spanish Patent, P201500492
Magnetic microstructures in electrodeposited Fe(1 −x)Gax thin films (15 ≤x≤ 22 at.%)
No full textWe have investigated the magnetic behavior of Fe(1 − x)Gax (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
Rotation of stripe domains in a sputter deposited Tb-Fe-Ga thin film
No full text©2017 Elsevier B.V. All rights reserved.
The authors thank M.G. Pini for valuable discussions. This work has been financially supported through the projects FIRB2010 RBFR10E61T ‘NANOREST’ of the Italian Ministry of Education, University and Research and MAT2015-66888-C3-3-R of the Spanish Ministry of Economy and Competitiveness (MINECO)The interest in Tb-Fe-Ga alloys, prepared by techniques compatible with technological processes, has been increasing in the last years, due to their high magnetostriction combined with their potential application in spintronic devices. In this letter, we report the domain configurations of a Tb10Fe76Ga14 thin film grown by co sputtering deposition. The film exhibits a weak perpendicular magnetic anisotropy (PMA) and the presence of discontinuous stripe domains. The application of an external field in the film plane, perpendicular to the stripe direction, induces the rotation of the stripes and the alignment of their axis with the field. This property of the material has been observed in the range of applied fields 0-70 mT, above which PMA disappears and stripe annihilation occurs.Ministerio de Economía y Competitividad (MINECO)Italian Ministry of Education, University and ResearchDepto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu
Evolution of the structural and magnetic properties of sputtered Tb_xFe_73Ga_27-x (7 at.% ≤ x ≤ 11 at.%) thin films upon the increase of Tb content.
No full text© 2016 Elsevier.
We thank ‘CAI Difracción de rayos-X’ of UCM for the x-ray diffractometry measurements. This work has been financially supported through the projects PRIN 2010ECA8P3 ‘DyNanoMag’ and FIRB2010 RBFR10E61T ‘NANOREST’ of the Italian Ministry of Education, University and Research and project of the Universidad Complutense de Madrid ‘Ayudas para Grupos de Investigación GR3/14’.Tb_xFe_73Ga_27-x (7 at.% ≤ x ≤ 11 at.%) ternary alloys have been obtained by cosputtering from Tb_33Fe_67 and Fe_72Ga_28 targets. In contrast with other Tb-Fe-Ga compounds that consist of just one structural phase, the diffraction pattern of the Tb_7Fe_73Ga_20 shows the presence of two different phases related to binary Tb -Fe and Fe-Ga alloys. This microstructure evolves as the Tb content is increased, and for a Tb of 11 at.% X-ray diffractometry only evidences the presence of a phase close to the TbFe_2. Although none of the studied samples show perpendicular magnetic anisotropy, there is a significant component of the magnetization perpendicular to the sample plane. The increase of the Tb content on the compounds from 7 at.% to 11 at.% enhances this component most probably due to the shift of the microstructure towards one similar to the TbFe_2.Progetti di Rilevante Interesse Nazionale (PRIN), ItaliaMinistero dell’Istruzione, dell’Università e della Ricerca (MIUR), ItaliaUniversidad Complutense de MadridDepto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu
Samuele R. Bacchiocchi and Family
No full textSeventh-day Adventist author and theologian, Samuele R. Bacchiocchi and his wife and their children at a graduation ceremony at Pontifical University
TAILORING THE MAGNETIC DOMAIN PATTERNS AND MAGNETIC ANISOTROPY OF SPUTTERED TbFeGa ALLOYS
No full textThe control of the domain patterns in systems with perpendicular magnetic anisotropy (PMA) is of great interest because of their applications on magnetic storage or spintronic devices.
Amorphous Tb-Fe alloys exhibit a pretty large PMA constant that reachs 106 J/m3. Recently, it has been reported a constant of at least 1×105 J/m3 in TbFeGa alloys [1]. We have deposited TbFeGa films by cosputtering using two targets with a composition of TbFe2 and Fe3Ga. Two series of samples were obtained by applying a different type of power source (DC or pulsed) in each target. The evaporation of TbFe2 by means of the DC source enhances the out of plane component of the magnetization. The results indicate that this can be due to the Tb enrichment of the TbFe2-based phases present in the alloys.
Magnetic force microscopy (MFM), which shows the presence of stripe domains, has been used to investigate the rotatable anisotropy of these films. A magnetic field of variable intensity placed at 90 degrees with respect to the stripes direction has been applied, while in-field MFM images were recorded. The results clearly show the correlation between OOP and rotatable anisotropies, which allows to tailor the magnetic domain patterns by changing the films preparation conditions
Tuning the magnetic domain patterns of sputtered TbFeGa alloys
No full textThe control of the magnetic domain patterns together with their time and temperature stability are key issues for the development of new devices. Materials systems with perpendicular magnetic anisotropy (PMA) are of great interest because of their applications on patterned media for magnetic storage or in spintronic devices. Nowadays, different approaches are analyzed to reach this high magnetic anisotropy, leading to various structures such as FePt and CoPt layers, multilayers comprising magnetic transition metals (Co, Fe, CoFe) and noble metals (Pt, Pd, Au) or FeCoB layers with PMA.
Some years ago, Tb-Fe alloys were greatly investigated because of their large out-of-plane anisotropy constant. In spite of this high PMA, for industrial applications it is desirable to have materials with a reduced heavy rare earth content. Some works on bulk TbFeGa alloys have focused on their magnetostrictive properties but the magnetic anisotropy of TbFeGa thin films has just started to be studied.
In this work, we present our investigations on the magnetic properties of TbFeGa thin films. The alloys were obtained by the cosputtering technique using two targets with a composition of TbFe2 and Fe3Ga. Different compositions can be achieved by modifying the power in each sputtering target. Moreover, we have also observed that the magnetic anisotropy and domain patterns also depends on the type of power source used (DC or pulsed). In particular, the evaporation of TbFe2 by means of the DC source enhances the out of plane component of the magnetization being obtained an anisotropy constant of at least 1×10^6 erg/cm3 . The results indicate that this is due to the Tb enrichment of the TbFe2-based phases present in the alloys. Therefore, the magnetic domain pattern can be tailored by means of the composition and the type of power source used in each sputtering target
STRIPES ROTATION AND MAGNETIC ANISOTROPY OF TbFeGa ALLOYS
No full textMagnetic films with perpendicular magnetic anisotropy (PMA) are attractive materials for applications in the fields of high density magnetic recording and spintronics. The magnetic domains orientation is known to affect the signal propagation through these materials when used in spintronic devices.
Recently, the PMA of TbFeGa alloys has been demonstrated [1]. In this work TbFeGa films were deposited by cosputtering, using two targets of TbFe2 and Fe3Ga. The effect of the type of power source (DC or pulsed) used in each target on the magnetic domain configuration has been investigated. It was found that the evaporation conditions strongly influence the out of plane (OOP) anisotropy of the films. Magnetic force microscopy (MFM), which shows the presence of stripe domains (fig. 1), has been used to investigate the rotatable anisotropy of these alloys. A magnetic field of variable intensity placed at 90 degrees with respect to the stripes direction has been applied, while in-field MFM images were recorded. The results clearly show the correlation between OOP and rotatable anisotropies, which allows to control the stripe domains rotation process and therefore the stripes orientation, by changing the films preparation conditions
TAILORING THE MAGNETIC DOMAIN PATTERNS OF SPUTTERED TbFeGa ALLOYS
No full textThe control of the domain patterns in systems with perpendicular magnetic anisotropy (PMA) is of great interest because of their applications on magnetic storage or spintronic devices. Different approaches are investigated to achieve a high magnetic stability. In systems comprised of noble metals such as Pt or Pd, the principal drawback is the high spin orbit interaction that increases the magnetic damping constant.
Amorphous Tb-Fe alloys exhibit a pretty large PMA constant that reaches 106 J/m3. Recently, it has been reported a constant of at least 1×105 J/m3 in TbFeGa alloys [1]. We have deposited TbFeGa films by cosputtering using two targets with a composition of TbFe2 and Fe3Ga. Two series of samples were obtained by applying a different type of power source (DC or pulsed) in each target. In particular, the evaporation of TbFe2 by means of the DC source enhances the out of plane component of the magnetization (Fig. 1). The results indicate that this can be due to the Tb enrichment of the TbFe2-based phases present in the alloys. Therefore, the magnetic domain pattern can be tailored by means of the composition and the type of power source used in each sputtering target
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