En este trabajo, presentamos medidas de magnetización dc, susceptibilidad ac e impedancia en cintas de la aleación amorfa Co80-xFexB10Si10 con x = 0, 6, 8 y 10 %.at. Esas medidas indican que a temperatura ambiente esas muestras tienen buen comportamiento magnético blando incluyendo el efecto de magneto-impedancia gigante. La parte real de la susceptibilidad ac, χ’ac, revela un campo de irreversibilidad, Hirr, el cual corresponde al campo de anisotropía transversal, Hk, donde la razón de la magneto-impedancia alcanza su valor máximo.In this paper we present dc magnetization, ac susceptibility and impedance measurements on amorphous alloy ribbons Co80-xFexB10Si10 with x = 0, 6, 8 and 10 at.%. They indicate that at room temperature these samples have good soft magnetic behavior including the giant magneto-impedance effect. The real part of the ac susceptibility χ’ac reveals an irreversibility field, Hirr, which corresponds to the transverse anisotropy field, Hk, at which the magneto-impedance ratio reaches its maximum value

Gomez Hermida, Monica

Rosales Rivera, Andres

Velasquez, Abilo A.

Spanish

In this paper we present dc magnetization, ac susceptibility and impedance measurements on amorphous alloy ribbons Co80-xFexB10Si10 with x = 0, 6, 8 and 10 at.%. They indicate that at room temperature these samples have good soft magnetic behavior including the giant magneto-impedance effect. The real part of the ac susceptibility χ’ac reveals an irreversibility field, Hirr, which corresponds to the transverse anisotropy field, Hk, at which the magneto-impedance ratio reaches its maximum value.En este trabajo, presentamos medidas de magnetización dc, susceptibilidad ac e impedancia en cintas de la aleación amorfa Co80-xFexB10Si10 con x = 0, 6, 8 y 10 %.at. Esas medidas indican que a temperatura ambiente esas muestras tienen buen comportamiento magnético blando incluyendo el efecto de magneto-impedancia gigante. La parte real de la susceptibilidad ac, χ’ac, revela un campo de irreversibilidad, Hirr, el cual corresponde al campo de anisotropía transversal, Hk, donde la razón de la magneto-impedancia alcanza su valor máximo.

Universidad Nacional de Colombia

COMPORTAMIENTO MAGNÉTICO Y EFECTO DE MAGNETO-IMPEDANCIA EN CINTAS DE CoFeBSi

Universidad Nacional De Colombia - Repositorio Institucional UN

momento Revista de F́ısica, No 45, Diciembre 2012 21MAGNETIC BEHAVIOR ANDMAGNETO-IMPEDANCE EFFECT IN CoFeBSiRIBBONSCOMPORTAMIENTO MAGNÉTICO Y EFECTO DEMAGNETO-IMPEDANCIA EN CINTAS DE CoFeBSiAbilo A. Velásquez†‡*, Mónica Gómez-Hermida§, AndrésRosales-Rivera†x† Laboratorio de Magnetismo y Materiales Avanzados, Facultad de Ciencias Exactas yNaturales, Universidad Nacional de Colombia, Sede Manizales, Manizales, Colombia‡ Departamento de Ingenieŕıa Eléctrica, Electrónica y Computación, Facultad de Ingenieŕıay Arquitectura, Universidad Nacional de Colombia, Sede Manizales, Manizales, Colombia.§ Departamento de Ciencias Básicas, Universidad Católica de Pereira, Pereira, Colombia yFacultad de Minas, Universidad Nacional de Colombia, Sede Medelĺın, Medelĺın, Colombia.(Recibido: 09/2012. Aceptado: 12/2012)AbstractIn this paper we present dc magnetization, ac susceptibilityand impedance measurements on amorphous alloy ribbonsCo80−xFexB10Si10 with x = 0, 6, 8 and 10 at.%.They indicate that at room temperature these sampleshave good soft magnetic behavior including the giantmagneto-impedance effect. The real part of the acsusceptibility χ′ac reveals an irreversibility field, Hirr, whichcorresponds to the transverse anisotropy field, Hk, at whichthe magneto-impedance ratio reaches its maximum value.PACS: 75; 75.50.-y; 75.50.BbKeywords: Soft ferromagnetic alloys, magnetic behavior, giantmagneto-impedance effect.ResumenEn este trabajo, presentamos medidas de magnetización dc,susceptibilidad ac e impedancia en cintas de la aleación* aavelasquezs@unal.edu.cox arosalesr@unal.edu.co22 Abilo A. Velásquez et. alamorfa Co80−xFexB10Si10 con x = 0, 6, 8 y 10 %.at.Esas medidas indican que a temperatura ambiente esasmuestras tienen buen comportamiento magnético blandoincluyendo el efecto de magneto-impedancia gigante. Laparte real de la susceptibilidad ac, χ′ac, revela un campode irreversibilidad, Hirr, el cual corresponde al campode anisotroṕıa transversal, Hk, donde la razón de lamagneto-impedancia alcanza su valor máximo.Palabras clave: Aleaciones magnéticas blandas, comportamientomagnético, efecto de magneto-impedancia gigante.IntroductionCobalt-based amorphous magnetic alloy ribbons have beenintegrated in high-frequency transformer and magnetic recordingheads since 1980 [1] due to their interesting physical properties suchas high magnetic permeability and low magnetostriction. Interestin this alloy system is also associated with the presence of giantmagneto-impedance (GMI) effect in soft magnetic materials, asdetected at the beginning of the 1990s [2–5]. The GMI effectconsists of large variations in impedance of a soft ferromagneticconductor upon the application of a small dc magnetic field whenan ac current flows through it. The GMI ratio with H isdefined as ∆Z/Z (%) = 100[Z(H)-Z (Hmax)]/Z(Hmax), where Z(H)and Z(Hmax) are the impedance measured at any and maximumapplied magnetic field Hmax (Hmax ≈ 80 Oe in our case) atwhich the soft magnets are practically saturated. In general,the GMI effect depends on the dc applied magnetic field, theworking frequency of the ac current, the domain structure of thematerial, and the magnetic anisotropies that are present in thematerial. The magnetic penetration depth, δ = c(4π2fσµ)−1/2,where f denotes the frequency of the current along the sample,σ the electrical conductivity, and µ the magnetic permeability(transversal, in case of the ribbons), is also relevant to determine themagneto-impedance (MI) response [5]. Depending on the frequencyof the ac current, the experimentally observed GMI curves usuallyexhibit two types of behaviors, specifically single-peak (SP),Magnetic Behavior and Magneto-Impedance Effect in CoFeBSi Ribbons 23and two-peaks (TP). These behaviors depend upon the relativecontributions of domain-wall motion and magnetization rotationprocesses to the magnetic permeability, µ = µwall + µrot [5–9]. Atlow frequencies (on the order of f ≤ 2 MHz), the main event isthe SP behavior and the magnetoimpedance is due to domain-wallmotion [5]. At higher frequencies (in the range 2 ≤ f ≤ 20MHz), the important event is the TP behavior and in this case themagnetization rotation process is dominant [10] since domain-wallmotion is absent by the eddy currents damping. The damping of thedomain wall has been confirmed by Kerr effect domain inspection[11].The ac magnetic susceptibility, on the other hand, in which asmall ac magnetic field is applied to a sample and the resultingac moment is measured, is a basic tool for characterizing manymaterials. Due to that the induced moment in the sample dependsupon the time, ac magnetic susceptibility measurements provideinformation on magnetization dynamics which plays an importantrole in the interpretation of GMI effect. Gonçalves et. al. [12]claim from ac susceptibility studies, that small samples of softferromagnetic materials become magnetically harder because themagnetic domain configurations are strongly influenced by thedemagnetizing field.In this paper a systematic study of the dc magnetization, acsusceptibility and magneto-impedance effect, in amorphous alloyribbons Co80−xFexB10Si10 with x = 0, 6, 8 and 10 (here x is referredto Fe concentration in atomic percentage, at.%), is presented.CoFe-based amorphous magnetic alloy ribbons have interestingphysical properties [13, 14], such as low magnetostriction,which make them promissory materials in order to obtain highmagneto-impedance response. Although there are several reports[5] of their good soft magnetic properties, the relation betweenac susceptibility and magneto-impedance effect in these alloyshas been scarcely studied. The main purpose of this paper isto gain an understanding on the ac magnetic susceptibility andmagneto-impedance of alloy system Co80−xFexB10Si10 where Co wasgradually replaced by Fe.24 Abilo A. Velásquez et. alExperimental DetailsThe experiments were performed on samples of as-cast ribbonsCo80−xFexB10Si10 with x = 0, 6, 8 and 10, prepared by the meltspinning technique. The amorphous state of each of the sampleswas verified by X-ray diffraction (XRD) using a Rigaku Miniflex IIdiffractometer with CuKα radiation (λ = 1.5405 Å) in the 20o ≤2θ ≤ 100o range at steps of 0.02 s−1. The dc magnetic field (H)dependence of the magnetization, M(H), of the samples understudy was measured, from -1 to 1 KOe at room temperature, witha home-made Foner-type vibrating sample magnetometer. H wasapplied parallel to the longitudinal direction of the samples. Datawere obtained for consecutive H-steps, stabilizing H before eachreading with a precision of ±20 Oe. The ac susceptibility of thesamples was measured for dc magnetic field (H) applied in therange -80 to 80 Oe at room temperature, using the standard acinductance method. The frequency of the ac modulating fieldwas applied in the range 10 to 104 Hz, while its amplitude wasmaintained at Hac ∼ 1 Oe. Both H and Hac were applied alongthe longitudinal direction of the samples. The impedance inthe samples was measured for dc magnetic field (H) applied inthe range -80 to 80 Oe at room temperature, via the so-calledfour-probe technique. H was applied parallel to the ac drivingcurrent along the longitudinal direction of the samples and wasswept at a step of approximately 1 Oe. The frequency of the acdriving current was applied in the range 0.5 to 10 MHz, while itsamplitude was kept at 1 mA (rms value).Results and DiscussionThe M(H)-cycle at room temperature for samples x = 6, 8 and10 is presented in Fig.1. The curves in Fig. 1 are typicalof a soft magnetic material, i,e. the hysteresis loop is closedand narrow. Furthermore, these loops have low coercivity andthe inclination of the initial magnetization curve (called initialdc susceptibility, χi) is very high. Note that χi increases withincreasing x concentration. It is known [15] that for soft magneticMagnetic Behavior and Magneto-Impedance Effect in CoFeBSi Ribbons 25Figure 1. M vs. H measured on Co80−xFexB10Si10 with x = 6, 8 and 10 atroom temperature.materials with high permeability, the initial magnetic permeabilityis roughly equal to the initial dc susceptibility (µi ≈ χi) which isgiven byχi = (∂M/∂H)|H→0 = (µoM2s /cEA) (1)where EA represents several types of anisotropy energy includingthe magnetoelastic energy. It can be noted by inspection of datain Fig. 1 that the initial magnetic permeability increases withincreasing x values. This behavior is compatible with the equation(1) and supported by the Fig. 2, where is plotted the χi vs H curvefor samples x = 6, 8 and 10. The χi vs. H curve (not shown here)for the sample x = 0 lies below those ones corresponding to thesamples x = 6, 8 and 10. This permeability behavior indicates thatthe anisotropy energy decreases with increasing x concentration.It has been proposed [13] that for amorphous and nanocrystallinealloys, the permeability will have the dependence on the grain size Das µ 1/D6. This relation has been confirmed by some permeabilityexperiments [16] for grains smaller than 40nm. However, adetailed and quantitative study on the grain size dependence ofthe permeability is beyond the scope of this work. In addition,the χi vs. H curve quickly decreases with increasing H, whichreflects magnetization processes ascribed to domain wall motion26 Abilo A. Velásquez et. alFigure 2. Field dependence of χi = dM/dH for Co70Fe10B10Si10 at roomtemperature.[5, 17]. Another feature evidenced in Fig. 1 is that the saturationmagnetization Ms increases from 80 to 137 emu/g with increasingx values. This result may be due to the fact that Fe-basedintermetallic alloys do not have their 3d shells fully filled. Themoment associated to the atoms of Fe can be increased in agreementwith Slater-Pauling curve by increasing the number of electrons inthe 3d shell. This can be achieved in samples of CoFe-based alloyssince these alloys can host one electron additional in the 3d shellas compared with the Fe-based alloys.The dc magnetic field dependence of the dc susceptibility, χdc (H)= M/H, at room temperature, for samples x = 6, 8 and 10, ispresented in Fig. 3. Note that χdc(H) shows a peak around H = 0,whose amplitude increases with increasing x values. Furthermore,the χdc(H)-curve for the sample with x = 10 decreases more rapidlywith increasing field than that one for the samples with x = 6 and8. These features indicate that the sample with x = 10 is the softestmagnetically.The dc magnetic field dependence of the real part of the acsusceptibility, χ′ac, at room temperature, for sample x = 0 forfrequencies in the range 40 ≤ f ≤ 9000 Hz, is illustrated in Figs. 4,5 and 6.Magnetic Behavior and Magneto-Impedance Effect in CoFeBSi Ribbons 27Figure 3. Field dependence of the dc susceptibility, χdc = M/H forCo80−xFexB10Si10 with x = 6, 8 and 10 at room temperature.Figure 4. χ′ac vs. H measured on Co80B10Si10 at room temperature using f= 40 and 90 Hz. Filled symbols are field increasing data and open symbols arefield decreasing data.As shown in Fig. 5 for f = 400 and 700 Hz, the initial χ′ac curveshows a monotonous decrease from H = 0. A very similar decreasewas also observed for the frequencies f = 0.04, 0.09, 4, and 6KHz (not shown here). This behavior is a result of magnetizationprocesses attributed to domain wall motion [5, 17] and is consistent28 Abilo A. Velásquez et. alFigure 5. χ′ac vs.H measured on Co80B10Si10 at room temperature using f= 400 and 700 Hz. Filled symbols are field increasing data and open symbolsare field decreasing data. The red symbol corresponds to the initial χ′ac curve.Figure 6. χ′ac vs. H measured on Co80B10Si10 at room temperature using f= 4, 6 and 9 KHz. Filled symbols are field increasing data and open symbolsare field decreasing data.with the field dependence of the initial dc susceptibility χi discussedabove (see Fig. 2). Another interesting feature illustrated in theFigs. 4, 5, and 6 is the appearance both of a hysteretic peak atMagnetic Behavior and Magneto-Impedance Effect in CoFeBSi Ribbons 29H = ±Ho 6= 0 and an ac susceptibility irreversible behavior. Theac susceptibility irreversible behavior is limited to the vicinity ofHo and it is possible to define an irreversibility field Hirr as thatone above which irreversible behavior of ac susceptibility hysteresisloops disappears. The irreversibility field, Hirr, is correlated withthe field at which appears the GMI effect’s TP behavior as will beanalyzed in more detail later on.A slightly different behavior is observed at sample x = 10. In thiscase, χ′ac-curve exhibits very small hysteresis and the peak at closevicinity of H = 0 becomes excessively broad, as shown in Fig. 7,where is plotted χ′ac(H) for the sample with x = 10 at frequenciesf = 40 and 90 Hz. On the other hand, at low-frequency region anac measurement is very similar to a dc measurement [15]. In ourcase, this is easily seen by comparing the Figs. 2 and 7.The dc magnetic field dependence of the GMI ratio for samples x =0, 6, and 10 at room temperature, for 0.5 ≤ f < 10 MHz is shown inFigs. 7, 8 and 9, respectively. All samples exhibit GMI effect as itis expected to occur in materials with very soft magnetic propertiesand low magnetostriction [18]. In the frequency range used in ourexperiments (0.5 ≤ f < 10 MHz), the skin effect is very strongbecause both, domain wall motion and magnetization rotationcontribute to the effective transversal permeability. Consequently,it is expected to observe the SP and TP behaviors. In fact,these behaviors were observed in the samples here studied but theyoccur in different frequency regions that depend upon the sampleunder study. In this respect the following comments should beunderlined: (1) it is observed a relatively large (on the order of 20%)magneto-impedance in the three samples, (2) in the sample with x= 0 (Fig. 8) the SP behavior is not observed, and (3) in contrast tothe symmetric TP behavior observed in the samples with x = 6 and10, the GMI curve in the sample with x = 0 exhibits an asymmetricTP behavior characterized by an increase of one of the peaks whilethe other one is reduced. Looking at the magneto-impedance effectin detail for the sample with x = 0 we can observe that the TPbehavior that occurs at H = ±Hk 6= 0 coincides quite well withthe dc irreversibility field, ±Hirr, of the χ′ac curve, as evidencedby Figs. 4, 5, 6, and 8. This concordance clearly supports the30 Abilo A. Velásquez et. alFigure 7. χ′ac vs.H measured on Co70Fe10B10Si10 at room temperature usingf = 40 and 90 Hz. Filled symbols are field increasing data and open symbolsare field decreasing data.Figure 8. GMI ratio vs. H measured on Co80B10Si10 at room temperaturefor different frequencies f = 0.5, 2, 4 and 5 MHz.identification of the field at which the magneto-impedance ratioreaches its maximum value as the field at which the irreversiblemagnetization process is completed. In this context, Hk is thetransverse magnetic anisotropy field. This transversal anisotropy isMagnetic Behavior and Magneto-Impedance Effect in CoFeBSi Ribbons 31Figure 9. GMI ratio vs. H measured on Co74Fe6B10Si10 at room temperaturefor different frequencies f = 0.5, 1, 4 and 8 MHz.Figure 10. GMI ratio vs. H measured on Co70Fe10B10Si10 at roomtemperature for different frequencies f = 0.5, 0.75, 1 and 2 MHz.due to the combined effect of the negative magnetostriction and theinternal stress frozen during the fabrication process of the material[5, 18]. In the case of the sample with x = 10, Hirr is slightlyhigher than Hk, as evidenced by Figs. 7 and 10, and Hk shifts32 Abilo A. Velásquez et. alto higher fields, with increasing f . This shifting is attributed tothe increasing average magnetoelastic anisotropy involved in theskin-effect penetration depth [5].ConclusionWe have made a study of the dc magnetization, ac susceptibilityand magneto-impedance in the alloy system Co80−xFexB10Si10 withx = 0, 6, 8 and 10. All samples exhibit soft magnetic behaviorincluding the giant magneto-impedance effect. This behavior isconsistent with the field dependences of the dc magnetization andac susceptibility. The real part of the ac susceptibility, χ′ac, revealsan irreversibility field, Hirr, which corresponds to the transverseanisotropy field, Hk, at which the magneto-impedance ratio reachesits maximum value.AcknowledgmentsThe authors acknowledge Professor D. Muraca for fruitfuldiscussions and collaborations. The authors, A.A. Velásquez andM. Gómez, also acknowledge the support of Colciencias (Colombianagency). Work at the Universidad Nacional de Colombia, Branchof Manizales, is supported by the Research Office (DIMA). Thesamples were prepared at Laboratorio de Sólidos Amorfos, Facultadde Ingenieŕıa, Universidad de Buenos Aires, Argentina.References[1] Y. Makino, in Physics and Engineering Applications ofMagnetism, Springer Series in Solid-State Sciences, Vol. 92,edited by Y. Ishikawa and N. Miura (Springer BerlinHeidelberg, 1991) pp. 195–210.[2] V. Makhotkin, B. Shurukhin, V. Lopatin, P. Marchukov, andY. Levin, Sens. Actuators, A 27, 759 (1991).[3] F. L. A. Machado, B. L. da Silva, and E. Montarroyos, J.Appl. Phys. 73, 6387 (1993).[4] K. Mandal and S. K. Ghatak, Phys. Rev. B 47, 14233 (1993).Magnetic Behavior and Magneto-Impedance Effect in CoFeBSi Ribbons 33[5] K. Buschow, Handbook of Magnetic Materials , Handbook ofMagnetic Materials No. v. 15 (Elsevier Science, 2003) pp.497–563.[6] D. Atkinson and P. T. Squire, J. Appl. Phys. 83, 6569 (1998).[7] K. R. Pirota, L. Kraus, M. Knobel, P. G. Pagliuso, andC. Rettori, Phys. Rev. B 60, 6685 (1999).[8] L. Panina, K. Mohri, T. Uchiyama, M. Noda, and K. Bushida,IEEE Trans. Magn. 31, 1249 (1995).[9] M. Tejedor, B. Hernando, M. Sánchez, M. Vázquez, andM. Knobel, J. Magn. Magn. Mater. 152, 191 (1996).[10] K. Byon, S. Yu, J. Kim, and C. Kim, IEEE Trans. Magn. 37,3086 (2001).[11] L. Melo and A. Santos, in Magnetism, Magnetic Materialsand Their Applications, Materials Science Forum, Vol. 302-3,edited by Missell, FP (1999) pp. 219–223.[12] L. Gonçalves, J. Soares, F. Machado, and W. de Azevedo,Physica B: Condensed Matter 384, 152 (2006).[13] G. Herzer, Acta Materialia 61, 718 (2013).[14] M. Coisson, P. Tiberto, F. Vinai, P. Tyagi, S. Modak, andS. Kane, J. Magn. Magn. Mater. 320, 510 (2008).[15] R. Grossinger, H. Sassik, D. Holzer, and N. Pillmayr, Magneticcharacterization of soft magnetic materials: experiments andanalysis , Vol. 254-255 (2003) pp. 7 – 13.[16] G. Herzer, J. Magn. Magn. Mater. 157-158, 133 (1996).[17] L. Panina and K. Mohri, Magneto-impedance in multilayerfilms , Vol. 81 (2000) pp. 71 – 77.[18] M. Vazquez, J. Sinnecker, and G. Kurlyandskaya, inMagnetism, Magnetic Materials and their Applications,Materials Science Forum, Vol. 302-3, edited by Missell, FP(1999) pp. 209–218.

Comportamiento magnético y efecto de magneto-impedancia en cintas de cofebsi

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Comportamiento magnético y efecto de magneto-impedancia en cintas de cofebsi

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