Wide-angle magnetoimpedance field sensor based on twocrossed amorphous ribbons
Victor M. De La Prida a,∗, Hector Garcıa-Miquel b, Galina V. Kurlyandskaya c
a Depto. Fısica, Universidad de Oviedo, Calvo Sotelo s/n, 33007 Oviedo, Asturias, Spainb Depto. Ing. Electronica, ETSIT, Universidad Politecnica de Valencia, Camino de Vera s/n, 46022 Valencia, Spain
c Depto. Electricidad y Electronica, Universidad del Pais Vasco UPV-EHU, Apdo. 644, 48080 Bilbao, Spain
Received 16 January 2007; received in revised form 20 August 2007; accepted 29 August 2007Available online 4 September 2007
bstract
Soft magnetic amorphous ribbons have been exhaustively studied in order to use them as magnetic field sensitive elements based on theagnetoimpedance effect, MI. In comparison with other materials they exhibit some disadvantages like double-peak response for small values of
he applied magnetic field due to the peculiarities of the surface anisotropy. In this work, magnetic properties, MI effect, and the angular dependencef the impedance on the applied magnetic field direction have been studied for CoFeMoSiB amorphous ribbon based sensitive elements in twoonfigurations. The first one is a classic MI prototype with one amorphous ribbon sensitive element installed on a printed circuit board. In theecond configuration two amorphous ribbons with the same size are placed in the board forming an angle of 15◦ between them. MI effect iseasured in a frequency range from 0.4 to 10 MHz for exciting current amplitudes ranging from 2 to 20 mA. For this prototype of sensor device
ormed by two crossed amorphous ribbons, it is possible to obtain single-peak MI response and independent on the orientation of the external field◦
utput signal in a wide range of the angles from 0 to 45 , in contrast with the double peak and angle dependent response obtained for single ribbon
ensitive element.2007 Elsevier B.V. All rights reserved.
Along last decades the magnetoimpedance effect, MI, haseen extensively studied as a basic phenomenon for a wide vari-ty of technological applications, and also as a powerful researchool for determining the magnetic properties of the materials1–4]. This basic phenomenon was first reported long time agon the 1930s [5], but without attracting so much noticeably forpplications. The re-discovering of MI effect has overcome hugefforts from then up to nowadays, in order to find the moreppropriated magnetic materials and treatments for using them
s sensitive elements in sensor devices with high MI responses6–8]. Descriptions of different MI-based field sensor proto-ypes are widely available in the literature together with their
∗ Corresponding author. Tel.: +34 985 10 2897; fax: +34 985 10 3324.E-mail address: [email protected] (V.M. De La Prida).
dvantages, disadvantages and comparative analysis of MI sen-ors with other types of magnetic detectors [3,8–11]. Althoughany attempts have been made in order to study the angular
ependence of the MI on the application of the external mag-etic field in different materials [9,12–15], at the same time,hese data are still non-systematic and they are mainly focused
ore on the material properties than on the design of a particularagnetic field sensor prototype [11].Nevertheless, a given MI sensor can operate in a different
anner depending on the specific solution that is required: Pirotat al. [12] have developed a theoretical model to explain MI foribbons or thin films with well defined uniaxial anisotropy foragnetic fields applied at arbitrary angles. Kurlyandskaya et al.
13] have studied the angular dependence and the way to con-
rol the hysteretic MI for magnetic fields applied non-parallelo the FeCoCrSiB ribbon. The experimental data in both above
entioned cases are related to amorphous ribbons with specificnduced transverse magnetic anisotropy, which is favourable for
Fig. 1. Photographs showing the schematic description of (a) MI prototype withone ribbon A: 1, Cu-leads for the exciting current; 2, Cu leads for the inducedvoltage collection; 3, Ag paint electrical contacts; (b) MI prototype with two-crossed ribbons A and B: 1, 2 and 3 are the same than above for each ribbon,respectively; 4, insulated part in centre to avoid an electrical contact betweenribbons; (c) equivalent circuit for two ribbons element: A and B ribbons are con-nected in parallel, U is total induced voltage, R1, I1 and R2, I2 are the resistanceand exciting current for A and B ribbons, accordingly. Angle between A ribbonaxis and external field is denominated α in case of single ribbon element and α*for two ribbons element.
V.M. De La Prida et al. / Sensors
btaining a high MI response, and particularly, high MI sensitiv-ty with respect to applied magnetic field in the low field interval1,9]. Yamaguchi et al. [14] have studied the dependence of totalmpedance as well as resistance and the reactance variations inhe external static field applied under different angles to the planef rectangular thin film sensitive element. Both, weak and strongngular dependencies are useful for sensor applications, but eachne can be used for designing different kind of magnetic sensors:on-oriented field sensors in the first and position/displacementensors in the second case.
The main purpose of the present work is to study the mag-etic properties, MI effect, and the angular dependence of thempedance on the direction of the applied magnetic field foroFeMoSiB amorphous ribbons with no transverse inducedagnetic anisotropy. Two configurations of the sensitive elementere designed and tested. The first one corresponds to a clas-
ic MI prototype with one amorphous ribbon sensitive elementnstalled in an imprinted circuit board. In the second configura-ion two amorphous ribbons were installed in the board with anngle of 15◦ to each other. In this sense, we would like to presentnd discuss the proofs of the correctness of this proposed novelI sensor device prototype.
. Experimental
The rapidly quenched Co67Fe4Mo1.5Si16.5B11 amorphousibbons, commercially labelled as Vitrovac® 6025, were sub-ected to relaxation heat treatment in vacuum furnace at40 ◦C for 1 h without stress, in order to reduce the frozen inesidual internal stresses and improving its soft magnetic prop-rties. Their amorphous state was checked before and afterhe treatment by X-ray diffraction in Cu K� radiation. Theaturation magnetostriction coefficient, λs, was measured bymall Angle Magnetization Rotation (SAMR) method show-
ng a value of about 3 × 10−7 [16]. The ribbon geometryf all samples for magnetic and magnetoimpedance measure-ents in all sensor prototype configurations were chosen to be
00 mm × 0.8 mm × 0.028 mm.The hysteresis loops of the ribbons were measured by induc-
ive method at a frequency of 46 Hz in the magnetic field createdy a pair of Helmholtz coils. External field was applied in planef the ribbons in all cases under consideration. The parallel direc-ion to the long side of the ribbon was called “ribbon axis” (seelso Fig. 1a). As it can be seen in Fig. 1a, the angle between the Aibbon axis and the direction of the external magnetic field wasenominated as α in the case of single ribbon prototype. Theysteresis loops of the ribbons were measured for the anglesof 0◦, 15◦, 45◦, 75◦, and 85◦. In the second configuration,
wo amorphous ribbons with the same size were symmetricallynstalled in the imprint circuit board forming an angle of β = 15◦etween them. In the case of two ribbons sensing prototypehown in Fig. 1b), the angle between the A ribbon axis and thepplied magnetic field was denominated α*, therefore forming
n angle of α* − 15◦ between B ribbon axis and the externalagnetic field. In the two ribbons prototype, the two ribbonsere electrically connected in parallel with Cu-leads. In order to
xclude any electrical contact in central part they were suitability
4 and A
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vba108 Oe (b), respectively. At the magnetic field value of 108 Oethe amorphous ribbons appear to be magnetically saturated, i.e.their effective magnetic permeability reach its minimum value.The decreasing in the induced voltage at all the frequencies range
98 V.M. De La Prida et al. / Sensors
eparated by a very thin insulating layer. The magnetic sen-itive element/elements were installed in the imprinted circuitoard using Ag conductive paint. The MI changes were definedhrough the voltage drop across the sample, both in increasing“up” branch) and decreasing (“down” branch) applied field athe constant amplitude of the driving current, following schemes depicted in Fig. 1c. The frequency range for MI measurementsas varied from 0.4 to 10 MHz. In this study a relatively low
ntensity of the driving current of Irms = 1.5 mA was selectedor each sensing element. It is also important to mention thator the ribbons of this kind of composition, rather weak depen-ence on the intensity of the exciting currents in the interval of.5–15 mA was previously reported [17]. The MI ratio can beefined as �Z/Z = 100 × [Z(H) − Z(H = 135 Oe)]/Z(H = 135 Oe)n case of MI measurements with respect to external mag-etic field and for frequency dependence of MI effect weave used the following ratio; �Z/Zmin = 100 × [Z(H = 0) − ZH = 108 Oe)]/Z(H = 108 Oe).
. Results and discussion
Inductive hysteresis loops of single ribbon measured withoutlectrical contacts for different angles are shown in Fig. 2. Theysteresis loop at 85◦ was used for the comparative analysisogether with 90◦ MI response. It can be seen that ribbons are
agnetically soft with coercive field less than 0.75 Oe for allases under consideration. The hysteresis loops for angles of–15◦ are very similar and an effective anisotropy is close toongitudinal one. Although, taking into account the shape of theysteresis loop (non-zero remanence and coercivity), one canxpect very small contribution from the surface anisotropy. Ast can also be seen in Fig. 2, an increase of the angle α leads ton enhancement in the coercivity and consequently, to rise thepplied magnetic field value necessary for reaching the magneticaturation, and therefore to a decay in the magnetic permeability.
For a magnetic material having a longitudinal effectiveagnetic anisotropy, the coercivity is the most appropriated
arameter for the characterization of its magnetic state. Verymall contribution of the surface anisotropy results in the split of
ig. 2. Hysteresis loops of Co67Fe4Mo1.5Si16.5B11 amorphous ribbons afterelaxation heat treatment in vacuum at 340 ◦C for 1 h, measured for different α
ngles between the applied external magnetic field and the ribbon axis.
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single peak GMI in two peaks for very low applied magneticelds. One can associate the anisotropy field as the appropri-ted parameter for characterization of the magnetic state of theibbon surface, which gives small contribution to the effectivenisotropy. As a consequence of the increase in the coercivitynd the anisotropy field, the value of the applied magnetic fieldo reach the magnetic saturation increases.
Fig. 3a and b shows the frequency dependence of the totaloltage U for a single ribbon element (at different angles α
etween the applied magnetic field and the ribbon axis) for zeropplied field (a) and the maximum applied magnetic field of
ig. 3. (a) and (b) Frequency dependence of voltage U, for single ribbon pro-otype at different α angles for Irms = 1.5 mA and for the applied field values of
and 108 Oe, respectively; (c) frequency dependence of the MI responses foringle ribbon element prototype at the same selected α angles.
and A
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V.M. De La Prida et al. / Sensors
nd in the case of the maximum applied magnetic field, is con-ected with a decrease of the magnetic permeability of the softagnetic sample.Fig. 3c shows the �Z/Zmin frequency dependences at selected
ngles α for one ribbon sensor prototype. The responses for= 0◦ and 15◦ are very close to each other for all frequenciesnder consideration. The further increase of the angle results inI ratio decrease down to the value of about 60% for α = 90◦.ne could expect this behaviour for both very small and high
ngles taking into account the magnetization curves. Relativelyigh value of the MI response even for perpendicular orientation
nd very low frequency dependence of MI ratio in the intervalf 2–10 MHz makes possible a detection of arbitrary orientedeld by using such a sensitive element.
ig. 4. (a) and (b) Frequency dependence of total voltage U for double ribbonrototype at different α* angles and for the applied field values of 0 and 108 Oe,espectively; (c) frequency dependence of the MI responses for double ribbonlement prototype at the same selected α* angles.
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ctuators A 142 (2008) 496–502 499
Fig. 4a and b shows the spectra of the total voltage U depen-ence on the frequency for the double ribbon sensor element, atifferent α* angles between the applied magnetic field and rib-on A axis in zero field (a) and in the maximum applied magneticeld of 108 Oe (b). First of all as in case of single ribbon element,
he decrease in the induced voltage for all frequencies underonsideration in the case of maximum applied field, compar-ng with the induced voltage for each one of the correspondingrequencies in zero field, can be explained by a decrease of theagnetic permeability of the ribbons. This behaviour is obtained
s a consequence of the MI sensor prototype design (see Fig. 1c)nd a weak angular dependence of the total impedance Z. Fig. 4chows the frequency dependence of �Z/Zmin for the double rib-on prototype at selected angles α*. The responses for the anglesf 0◦ and 45◦ are significantly modified comparing with the cor-esponding responses for single ribbon element. The responsest the frequencies below 1 MHz are higher for two ribbons ele-ent. In general, the angular dependence of the MI responses
s weaker for two ribbons element for all orientations in therequency range under consideration. In the frequency range ofbout 2–6 MHz, the MI responses for the two ribbons prototypeo not depend on the frequency and the orientation of the fieldor the angles of 0◦ and 45◦. The further increase of the angleesults in a MI ratio decrease down to the value of about 80% athe frequency of 1.5 MHz. This response shows weak frequencyependence up to the frequency of 6 MHz followed by a lin-ar decrease down to the value of about 50% at the frequencyf 10 MHz. This means that two ribbons element shows evenigher value of the MI response for perpendicular orientationnd very low frequency dependence of MI ratio in the intervalf 2–6 MHz.
Fig. 5a shows complete MI responses for α equal to 0◦ and5◦ corresponding to the one ribbon sensor prototype. They areery close to each other in all field intervals. Such behaviourakes impossible the construction of low angle rotation or
isplacement detector based on Co67Fe4Mo1.5Si16.5B11 amor-hous ribbons. On the other hand, it can be considered as andvantage for the development of MI based magnetic field sen-ors for the detection of the field parallel to the axis of theibbon. In this configuration, the calibration of the zero posi-ion/procedure for the exactly parallel installation of the sensitivelement with respect to zero magnetic field cannot be strictlyequired due to the weak dependence of the response on thexternal field orientation.
Fig. 5b shows complete MI responses of the two ribbonsrototype for α* equals to 0◦ and 15◦. They are close to eachther, but in all field intervals, the �Z/Z values correspondingo one ribbon prototype are higher than �Z/Z response of twoibbons prototype. At the same time, one can notice that the MIesponse for the double ribbon prototype shows more reducedalue of signal/noise ratio (inset of Fig. 5b) and very close tone peak shape of the MI curve. The absence of the pronouncedalley at zero field can be an useful feature to perform a less
omplicated design of the detector: in case of fatal functionalityrror of the system, when it riches the zero field value, the sen-or would not be affected by strong jump due to the inductionurrents. Dashed vertical lines show possible working interval
500 V.M. De La Prida et al. / Sensors and A
Fig. 5. (a) Field dependence of MI responses for single ribbon prototype atdifferent selected α angles and for Irms = 1.5 mA; (b) comparison of field depen-drr
ootw
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ence of the MI responses of one ribbon and two ribbons prototype (inset: highesolution of low field behaviour); (c) simulation of MI response for singleibbon element at the frequency value of 4 MHz and for α = 0.
f the prototypes, where the MI responses are close to linear: thene ribbon prototype shows sensitivity of about 28%/Oe and thewo ribbons prototype shows sensitivity of about 33%/Oe at theorking point of 1.8 Oe (in the working interval of 1.8 ± 1.3 Oe).One can see that the value of the MI response and the
hape of the MI responses are very close to one-peak responseheoretically modelled by Chen et al. [18] for the materials
ith very small intrinsic or induced anisotropy. Only preciseeasurements in very small external field oriented along the
ibbon axis shows the presence of very weak double peaktructure, most probably due to the existence of the local
tWt
ctuators A 142 (2008) 496–502
eviations of the local easy magnetization axes on the ribbonurface.
Fig. 5c shows the simulation of the MI response for singleibbon element at the frequency value of 4 MHz corresponding tohe maximum of the impedance variation at α = 0. The variationf the MI at H = 0 as a function of the angle α can be approachedy a linear fit. As shown in Fig. 5c, from the linear fit at 4 MHzxhibited in the inset, we have gotten:
�Z
Z(%)
∣∣∣∣H=0
= 79.42 + 244.31 × cos(α) (1)
Therefore, we can make an approximated simulation of theI response with the following equation, according to the pro-
osed model of Machado et al. for the MI effect in ferromagneticonductors with ribbon shape geometry [19]:
�Z
Z(%) = [79.42 + 244.31 × cos(α)] e−K|H | (2)
And for the particular case of α = 0, and at the frequency valuef 4 MHz, we have gotten the equation for the simulation, shownn Fig. 5c:
�Z
Z(%) = 323.7 e−0.0544|H | (3)
It remains clear that the simulated values obtained for the MIesponse in the case of the single ribbon element are near to thexperimentally measured, as can be compared between the twoI curves 5a and c, respectively.The angular dependences of the total voltage U and MI
esponses for single ribbon element and double ribbon elementensor prototypes are comparatively analysed at four selectedrequencies of the driven current in Fig. 6a–f, respectively.here are two different contributions which can be considereds responsible for weaker angular dependence of the impedanceariation for the two ribbons element. The first one is the dipolarnteraction between the ribbons in the two ribbons circuit which
ay play an important role [20]. The second one is related tohe electric behaviour of the components of the circuit (Figs. 1cnd 5a). Here, only some examples supporting this point of viewill be given for the explanation of these experimental results,ut more detailed models are supposed to be developed in theext future.
Magnetic field features oriented along the longitudinal direc-ion of a plate shape sensor element was first analysed byamaguchi et al. [14]. These authors also made a calculation of
he effective field intensity for a rectangular magnetic body bynite elements method founding that the effective field inten-ity is not always equal to H cos(α) due to the demagnetizingelds at the body edges. It was found that the direction of theagnetization in the plate center remains almost parallel to the
late axis for all directions except α = 90◦, which means thathe direction of the effective field along the plate direction is aeasonable approximation.
Let us first to analyse very roughly the magnetization dis-ribution near the edges for the two ribbons element (Fig. 6g).
ithout the presence of the ribbon B the magnetization distribu-ion near the edges of the ribbon A would be such as shown by
V.M. De La Prida et al. / Sensors and Actuators A 142 (2008) 496–502 501
Fig. 6. Angular dependences of the total voltage U and MI responses for single ribbon element (a–c) and double ribbon element (d–f) sensor prototypes analyseda epreser gnetici red to
sbirietpti
ar
taA
t four selected frequencies of the driven current, respectively. (g) Schematic ribbon prototype. Dashed red arrows indicate possible change of the local manterpretation of the references to colour in this figure legend, the reader is refer
olid black and red arrows. The dipolar interaction establishedetween the two crossed ribbons, A and B, very probably resultsn the magnetization rotation from near the corner close to theibbon B, towards the external field direction (red dashed arrow),.e. for small fields the presence of the second ribbon is somehowquivalent to the increase of the effective field. Due to the elec-
rical contact connected in parallel, the exciting current passesreferably through the ribbon which has smallest impedance,herefore ribbon A biased by ribbon B will play a principal rolen the formation of the MI response which, at small angles will
datt
ntation of the magnetic structure near the edges of the ribbons for the doublemoments orientation due to dipolar-biased interaction between ribbons. (Forthe web version of the article.)
ppear to be the same or even higher than the one for singleibbon element [20].
Starting from the angle α* of 45◦, at the angle β between thewo ribbons, the magnetization component of the ribbon B willct on the magnetization of the closure domains near the ribbonedge corners, inducing them to rotate towards the external field
irection. The magnetization in the central part near the edge willlso begin to rotate towards the external field direction. It seemshat the biased fields near the edges, caused by the presence ofhe ribbon B, increase with the increase of the angle α*. At the
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ame time, the �Z/Z single ribbon element response decreasesith the angle increasing and therefore the dipolar interaction
ould not compensate it for relatively high angles above 45◦.Another possible reason of the �Z/Z ratio decay would have
ts origin in the parallel connection for the two ribbons. Whenhe values of their impedance are equal, the intensities of theowing currents I1 ≈ I2 ≈ 0.75 mA could be not enough in order
o reach the same value of �Z/Z ratio due to current intensityependence of the MI for a single ribbon. It might be not a case ofo67Fe4Mo1.5Si16.5B11 amorphous ribbons which shows rathereak dependence of MI ratio on the current intensity [14,17],ut this question requires a further additional study.
. Conclusions
Magnetic properties, MI effect, and the angular dependencef the impedance on the applied magnetic field direction weretudied for CoFeMoSiB amorphous ribbon based prototypes inwo configurations: one amorphous ribbon based and two amor-hous ribbons based prototype, with the ribbons of same sizeymmetrically installed in the board and forming the angle of5◦ to each other.
MI effect was measured in the frequency range of.4–10 MHz for exciting current amplitudes ranging from 2 to0 mA. The equivalent circuit and dipolar interaction modelsere used in order to explain the MI behaviour.In two ribbons prototype it was possible to obtain one-peak
I response and independent on the orientation of the externaleld output signal in a wide range of the angles from 0 to 45◦ forrequencies of 2–6 MHz, in contrast with the double peak andngle dependent MI response obtained for one ribbon sensitivelement.
cknowledgements
This work has been supported by “Ramon y Cajal” Fel-owship of Spanish MEC and Basque Country UniversityPV-EHU. Dr. G.V. Kurlyandskaya wants to acknowledge Prof.lanca Hernando for thorough support during her stay at theniversity of Oviedo.Spanish FICyT research project no. PCTI06-041 is also
cknowledged.
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iographies
ictor M. De La Prida has got his PhD in physics at the Universidad de OviedoSpain) in 2000. He is currently working as associate professor at the Physicsepartment of Universidad de Oviedo. His main scientific activity is focused on
he study of magnetic properties of amorphous and nanocrystalline soft magneticaterials in ribbons, wires and microwires shape geometry; magnetoimpedance
nd magnetotransport effects; synthesis of metallic nanowires in nanoporouslumina and titania templates, their magnetic characterization and applicationsn sensing devices.
ector Garcıa-Miquel received his master degree in telecommunication engi-eering in 1992 at Polytechnic University of Catalonia (Spain), his PhD inelecommunication engineering in 1999 at Polytechnic University of Valen-ia (Spain) by his studies on Ferromagnetic Resonance in magnetic materials,nd his master degree in economics in 2001 at National University of Distanceducation (Spain). Since 1992, he is working in the Department of Electronicngineering at the Polytechnic University of Valencia (Spain), since 2002 asssociate professor. His research interest is in the area of the magnetic proper-ies, ferromagnetic resonance and magnetoimpedance effect in metallic glasses,morphous microwires and ultra-thin films, and their applications in magneticensor devices. He enjoyed research stays working in magnetic materials at Insti-ute of Applied Magnetism, Spain, in 1997–1998, at University of Maryland,SA, in 2000, at the Cavendish Laboratory, University of Cambridge, Unitedingdon, in 2003, and at The Racah Institute of Physics, The Hebrew Universityf Jerusalem, Israel, in 2005.
alina V. Kurlyandskaya was graduated from Ural State University, Ekater-nburg, Russia. She started her research work in 1983 at the Institute of Metalhysics UD RAS. She received her PhD in physics of magnetic phenomena
n 1990 followed by advanced training in the Institute of Applied Magnetism,niversity of Oviedo, University of the Basque Country (Spain), Universityf Dusseldorf named under Heinrich Heine (Germany), ENS-Cashan (France),niversity of Maryland (USA), Ural State University named under Gorky (Rus-
ia). Her main research areas are fabrication, magnetic and transport propertiesf amorphous and nanostructured materials, magnetic domains, resonant andon-resonant magnetoabsorption, magnetic sensors and biosensors. She is cur-ently developing her “Ramon y Cajal” project on biological applications ofagnetoimpedance biosensors.
