This paper investigates the performance of off-diagonal magnetoimpedance in Co-based amorphous 
wire subjected to dc bias fields: circular and orthogonal (with respect to the wire axis). Typically it is as-sumed that the wire impedance is insensitive to the orthogonal field so the wire element can be used to 
construct 3D sensors. Our results demonstrated the possibility of large impedance change due to this field, 
in the range of 10 mV/Oe. The dc current in a wire generating a circular field results in improved sensitivi-ty due to elimination of the domain structure and smoothing the effect of the anisotropy deviations.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3633

Kolesnikov, A.V.

Kostishyn, V.G.

Morchenko, A.T.

Panina, L.V.

Rudyonok, A.A.

Yudanov, N.A.

Electronic Sumy State University Institutional Repository

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ Vol. 6 No 3, 03046(4pp) (2014) Том 6 № 3, 03046(4cc) (2014)   The article was reported at the International Conference «The Advanced Technology, Equipment and Analytical Systems for Materials», Kursk, 13-14 May, 2014 2077-6772/2014/6(3)03046(4) 03046-1  2014 Sumy State University Effect of Bias Fields on off-Diagonal Magnetoimpedance (MI) Sensor Performance  N.A. Yudanov1, A.A. Rudyonok1, L.V. Panina1,2,*, A.V. Kolesnikov1, A.T. Morchenko1, V.G. Kostishyn1  1 National University of Science and Technology, MISIS, Moscow, Russia 2 Institute for Design problems in Microelectronics, RAS, Moscow, Russia  (Received 19 May 2014; revised manuscript received 03 July 2014; published online 15 July 2014)  This paper investigates the performance of off-diagonal magnetoimpedance in Co-based amorphous wire subjected to dc bias fields: circular and orthogonal (with respect to the wire axis). Typically it is as-sumed that the wire impedance is insensitive to the orthogonal field so the wire element can be used to construct 3D sensors. Our results demonstrated the possibility of large impedance change due to this field, in the range of 10 mV/Oe. The dc current in a wire generating a circular field results in improved sensitivi-ty due to elimination of the domain structure and smoothing the effect of the anisotropy deviations.  Keywords: Off-diagonal magnetoimpedance, Pulsed magnetoimpedance, Magnetoimpedance sensor,  Linear sensor, Amorphous magnetic wire, Bias field.    PACS numbers: 85.75.Ss, 87.85.fk                                                             * l.panina@plymouth.ac.uk 1. INTRODUCTION  The effect of off-diagonal impedance in magnetic conducting elements referred to as off-diagonal magne-toimpedance (MI) has attracted a considerable interest over the last decade due to its importance for micro-magnetic sensor development. AC current passing through a magnetic wire with a helical magnetisation generates a voltage not only across the wire but also in a coil mounted on it. The coil voltage is caused by cross magnetisation processes and is described by off-diagonal impedance [1-3]. A characteristic feature of this impedance is antisymmetric behaviour with re-spect to dc magnetisation which results in the possibil-ity to realise near linear dependence on an external magnetic field within a certain field interval around zero point. A linear output is a desirable sensor charac-teristic allowing the direction of the magnetic field to be determined. Because of this, the off-diagonal config-uration is preferable for sensor applications.  Practical off-diagonal impedance sensor design based on pulsed-current excitation was developed in a number of papers and successfully applied in commer-cial products as miniature magnetic compass [4-6]. Pulse excitation in MI sensors is typically realised with the help of CMOS inverter IC chip [7, 8] or a microcon-troller [9, 10]. In spite of its simple scheme, the pulse excitation is described by a large number of input pa-rameters: excitation current peak value, frequency of pulse repetitions, pulse width, pulse shape (rise and fall times), and all of them affect the sensor parame-ters. The investigation of the effect of all these factors would be difficult utilising the mentioned schemes. In the present paper, we used a functional generator to supply various ac excitations to the MI wire to investi-gate the effect of pulse shape and low frequency com-ponents on the off-diagonal voltage. The latter is of a particular importance to increase the output voltage since the existence of the domain structure may elimi-nate this voltage completely.  2. BASICS OF OFF-DIAGONAL SENSOR DESIGN  An ac current i passing through a magnetic wire (see Fig. 1a) generates a voltage Uw which may be very sensitive to the external magnetic field. This is known as a magnetoimpedance (MI) effect. If the wire has a helical magnetisation the voltage Uc is also generated in a coil mounted on it (Fig. 1b). The ratio Zc  Uc/i may be called off-diagonal impedance. In single-domain wires with the circumferential anisotropy Zc is anti-symmetrical with respect to axial magnetic field Hex having near-linear region around zero field point. This characteristic can be used in linear sensing. A practical design of such a sensor is given in [7-10] where the wire element is exited by a pulse current of C-MOS IC mul-tivibrator or a microcontroller.    Fig. 1 – Methods of excitation and detection for MI sensing element. A high frequency current is provided to the MI ele-ment and the output voltage is measured across the wire (a) or from a coil mounted on it (b)  The off-diagonal MI can be also realised by eхciting the wire by ac axial magnetic field induced by the coil and measuring the voltage across the wire. However, the coil self-inductance may considerably limit the exci-tation current at high frequencies. Therefore, the excitation scheme of Fig. 1b is preferable.   3. EXPERIMENTAL  The sensor design based on multivibrator or micro-controller excitation is important for practical applica-tion. But the setup suggested in Fig. 2 allows detailed investigation of the influence of various excitation pa- N.A. YUDANOV, A.A. RUDYONOK, ET AL. J. NANO- ELECTRON. PHYS. 6, 03046 (2014)   03046-2 rameters on the sensor operation. The pulse generator may supply to the wire narrow current pulses of vari-ous shape and magnitude as well as a harmonic wave-form with various dc bias current. The wire with a coil is placed in a long solenoid which produces a magnetic field in the range of ± 60 Oe. As a result of cross mag-netization (off-diagonal MI), electromotive force is in-duced in the pickup coil wounded on the wire. The de-pendence Uc  Hex is captured by digital oscilloscope.     Fig. 2 – Experimental setup for off-diagonal MI    Fig. 3 – Schematics of non-diagonal MI sensor element con-sisting of Co-based amorphous wire on a polymer substrate and detection coil (40 mm diameter, 40 turns)   Fig. 4 – Pulsed excitation waveform applied to MI element. The peak of current in a wire is 5.77 mA  The sensor output was also investigated in orthogo-nal fields produced with a help of two Helmholtz coils.  An amorphous glass-coated wire of composition Co66.94Fe3.83Ni1.44B11.57Si14.59Mo1.69 was used as MI ele-ment. The metal core diameter was 16 m and the total diameter was 16.8 m. The wire of length was fixed on a plastic substrate. In the off-diagonal configuration, the high frequency excitation is applied across the MI ele-ment and the output signal is taken from the coil mount-ed on it. A detection coil was made of 40 m diameter copper wire and had 40 turns. The overall sensor dimen-sions are 3.2  1.8  0.5 mm. The sensing element is shown in Fig. 3. Two kinds of high frequency excitation waveforms produced by functional generator were supplied to the MI wire: pulsed and sinusoidal with a dc bias. The pulsed waveform is shown in Fig. 4. In this case, the rise / fall time is 20 ns which corresponds to a frequency of 50 MHz and the frequency of pulse repetitions is 8 MHz. The analysis of frequency response of the sensor re-viled that the LC-resonance of the sensor cell is around 8 MHz. The sinusoidal excitation with this frequency produced the largest output voltage as shown in Fig. 5. It is seen that there is another resonance mode with a frequency of 4 MHz.    Fig. 5 – Frequency characteristics of the sensor output at sinusoidal excitation with zero dc bias current and in the presence of axial field of 1.5 Oe  4. EXPERIMENTAL RESULTS AND  DISCUSSIONS  Typical output sensor characteristics as functions of external field are shown in Fig. 6 for different soldering methods. A pulsed excitation waveform shown in Fig. 4 was supplied to the MI wire. The soldering tempera-ture was 300 C and 100 C for samples 1 and 2, re-spectively, and conducting glue at room temperature was used for sample 3. It is seen that the soldering method does not change significantly the curves where the sensitivity is maximal.  0204060801001201400 0,5 1 1,5 2 2,5 3Field, OeOutput signal, mVsample1sample2sample3  Fig. 5 – Output characteristics of 3 MI wire samples with different soldering process. The soldering temperature was 300 C and 100 C for samples 1 and 2, respectively, and con-ducting glue at room temperature was used for sample 3 MI wire    1.8 mm 3.2mm  Substrate Detection coil Working area    Soldering area   U  t   20 ns 42.5 ns 42.5 ns 0.75V   20 ns  EFFECT OF BIAS ON OFF-DIAGONAL MAGNETOIMPEDANCE… J. NANO- ELECTRON. PHYS. 6, 03046 (2014)   03046-3 Therefore, the soldering process even at relatively high temperatures does not change substantially the magnetic structure. In fact, a moderate temperature may improve the MI sensitivity. This can be related with a relaxation of certain internal stresses. The sen-sitivity is in the range of 600-700 mV/Oe and the line-arity range is ± 0.3 Oe.     Fig. 7 – Effect of axial bias field on off-diagonal sensor re-sponse. DC current in a wire is: 1 – 0 mA, 2 – 1.59 mA,  3 – 3.17 mA, 4 – 4.76 mA  The range of linearity is rather small and if neces-sary the operational point could be moved by applying a dc axial bias using the same detection coil. The output signal for different axial bias is shown in Fig. 7. For a dc current of 4.76 mA creating a field of about 1.4 Oe in the direction opposite to the sensed field the linearity region is 0.6-1.3 Oe. It is also seen that the curves for different axial bias cannot be obtained by shifting along the field axis. This behaviour can be attributed to the existence of deviations of the easy anisotropy from the circular direction.  The sensor is sensitive to the field applied along the wire and the orthogonal field should not produce no-ticeable changes. This was investigated by considering the sensor output in orthogonal fields and the corre-sponding characteristics are shown in Fig. 8. It is seen that the sensitivity in the low field region indeed al-most does not change; however, a rather large change in the range of 10 mV/Oe is seen for larger axial fields when the main contribution to the voltage response is related with the change in ac permeability. The analy-sis of off-diagonal impedance for a single-domain wire shows that the effect of the radial field of the order of few Oe should be negligible since the demagnetising field is about 3 kOe. However, the orthogonal field has a circular component depending on the position on the wire. For ideal homogeneous helical magnetisation this component will not affect the averaged ac permeability. However, due to deviations of the anisotropy, this in-fluence may be noticeable. The normal field may also affect the circular domain coercivity since the existence of circular domain structure is probably related with the surface inhomogeneity and radial magnetisation. This behaviour requires additional investigation which is important for the development of 3D sensors with the use of orthogonal system of amorphous wires.  Orthogonal field, Oe01020304050607080901001100 1 2 3 4 5Axial field, OeOutput signal,  mV0,2 Oe0,4 Oe0,8 Oe1 Oe0 Oe  Fig. 8 – Sensor output as a function of axial field with orthogonal field as a parameter         0204060801001200 0,5 1 1,5 2 2,5 3 3,5 4Field, OeOutput signal, mV4 3 2 1  N.A. YUDANOV, A.A. RUDYONOK, ET AL. J. NANO- ELECTRON. PHYS. 6, 03046 (2014)   03046-4 Existence of a domain structure substantially dete-riorates the sensor performance. In the case of ideal circular anisotropy and bamboo domain structure the output signal would be zero. The pulsed current excita-tion containing low frequency components suppresses the circular domain structure. However, if the field generated by low frequency harmonics is too large, the sensor sensitivity will decrease due to increase of the magnetic hardness in circular direction. To investigate the conditions for optimal bias, a sinusoidal excitation with a dc bias was used. The frequency of excitation was 8 MHz. The sensor output in the presence of dc current flowing through the wire is shown in Fig. 9.    Fig. 9 – Sensor output at a sinusoidal excitation with a fre-quency of 8 MHz vs axial field in the presence of dc current: 1 – 0 mA, 2 – 2.31 mA, 3 – 7.7 mA, 4 – 9.24 mA, 5 – 13.09 mA    It is seen that the sensitivity and linearity region increase with increasing the dc current. However, for relatively large current of 10-15 mA the sensitivity in the low frequency region almost does not change, but at higher fields the sensitivity drops considerably. For the considered sensor configuration the optimal bias is around 2-3 mA. This current generates a circular mag-netic field about 0.4 Oe at the wire surface (considering that the wire radius is about 10 m). This field is larger than the typical value of circular coercivity so the do-main structure is eliminated. This field may also de-crease the effect of the anisotropy deviation from the circular direction which also results in the improved sensitivity.  5. CONCLUSIONS  The main aim of this work was to investigate the ef-fect of dc bias fields on the characteristics of off-diagonal magnetoimpedance sensor. It was revealed that the effect of the orthogonal field (with respect to axial field) may be quite strong which imposes some limitations on the use of magnetic wires for the con-struction of 3D sensors. The dc current in a wire gener-ating a circular field results in improved sensitivity due to elimination of the domain structure and smoothing the effect of the anisotropy deviations.   ACKNOWLEDGMENT  This work was financially supported by the Russian Foundation for Basic Research, grant № 13-08-01319. The authors would like to thank Dr. V. Larin from MFTI Ltd, Moldova, for donating the wire samples for this work.   REFERENCES  1. D.P. Makhnovskiy, L.V. Panina, D.J. Mapps, Phys. Rev. B 63, 144424 (2001). 2. S. Sandacci, D.P. Makhnovskiy, L.V. Panina, K. Mohri, Y. Honkura, IEEE T. Magn. 40, 3905 (2004). 3. M. Ipatov, V. Zhukova, J.M. Blanko, J. Gonzales, A. Zhukov, phys. status solidi a 205, 1779 (2008). 4. K. Mohri, Y. Honkura, Sensor Lett. 5, 267 (2007). 5. K. Mohri, Y. Honkura, L.V. Panina, T. Uchiyama,  J. Nanosci. Nanotechnol. 12, 7491 (2012). 6. T. Uchiyama, K. Mohri, Y. Honkura, L.V. Panina, IEEE T. Magn. 48, 3833 (2012). 7. T. Kanno, K. Mohri, T. Yagi, T. Uchiyama, L.P. Shen, IEEE T. Magn. 33 No 5, 3353 (1997). 8. T. Uchiyama, K. Mohri, S. Nakayama, IEEE T. Magn. 47, No 10, 3070 (2011).  9. B. Fisher, L.V. Panina, D.J. Mapps, N. Fry, IEEE T. Magn. 49, 89 (2013). 10. N.A. Yudanov, L.V. Panina, A.T. Morchenko, V.G. Kostishyn, P.A. Ryapolov, J. Nano- Electron. Phys. 5, No 4, 04004 (2013).  

Effect of Bias Fields on off-Diagonal Magnetoimpedance (MI) Sensor Performance

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 6 No 3, 03046(4pp) (2014) Том 6 № 3, 03046(4cc) (2014) 
 
 
The article was reported at the International Conference «The Advanced Technology, Equipment and Analytical Systems for Materials», Kursk, 13-14 May, 2014 
2077-6772/2014/6(3)03046(4) 03046-1  2014 Sumy State University 
Effect of Bias Fields on off-Diagonal Magnetoimpedance (MI) Sensor Performance 
 
N.A. Yudanov1, A.A. Rudyonok1, L.V. Panina1,2,*, A.V. Kolesnikov1, A.T. Morchenko1, V.G. Kostishyn1 
 
1 National University of Science and Technology, MISIS, Moscow, Russia 
2 Institute for Design problems in Microelectronics, RAS, Moscow, Russia 
 
(Received 19 May 2014; revised manuscript received 03 July 2014; published online 15 July 2014) 
 
This paper investigates the performance of off-diagonal magnetoimpedance in Co-based amorphous 
wire subjected to dc bias fields: circular and orthogonal (with respect to the wire axis). Typically it is as-
sumed that the wire impedance is insensitive to the orthogonal field so the wire element can be used to 
construct 3D sensors. Our results demonstrated the possibility of large impedance change due to this field, 
in the range of 10 mV/Oe. The dc current in a wire generating a circular field results in improved sensitivi-
ty due to elimination of the domain structure and smoothing the effect of the anisotropy deviations. 
 
Keywords: Off-diagonal magnetoimpedance, Pulsed magnetoimpedance, Magnetoimpedance sensor,  
Linear sensor, Amorphous magnetic wire, Bias field.  
 
 PACS numbers: 85.75.Ss, 87.85.fk 
 
 
                                                          
*
 l.panina@plymouth.ac.uk 
1. INTRODUCTION 
 
The effect of off-diagonal impedance in magnetic 
conducting elements referred to as off-diagonal magne-
toimpedance (MI) has attracted a considerable interest 
over the last decade due to its importance for micro-
magnetic sensor development. AC current passing 
through a magnetic wire with a helical magnetisation 
generates a voltage not only across the wire but also in 
a coil mounted on it. The coil voltage is caused by cross 
magnetisation processes and is described by off-
diagonal impedance [1-3]. A characteristic feature of 
this impedance is antisymmetric behaviour with re-
spect to dc magnetisation which results in the possibil-
ity to realise near linear dependence on an external 
magnetic field within a certain field interval around 
zero point. A linear output is a desirable sensor charac-
teristic allowing the direction of the magnetic field to 
be determined. Because of this, the off-diagonal config-
uration is preferable for sensor applications.  
Practical off-diagonal impedance sensor design 
based on pulsed-current excitation was developed in a 
number of papers and successfully applied in commer-
cial products as miniature magnetic compass [4-6]. 
Pulse excitation in MI sensors is typically realised with 
the help of CMOS inverter IC chip [7, 8] or a microcon-
troller [9, 10]. In spite of its simple scheme, the pulse 
excitation is described by a large number of input pa-
rameters: excitation current peak value, frequency of 
pulse repetitions, pulse width, pulse shape (rise and 
fall times), and all of them affect the sensor parame-
ters. The investigation of the effect of all these factors 
would be difficult utilising the mentioned schemes. In 
the present paper, we used a functional generator to 
supply various ac excitations to the MI wire to investi-
gate the effect of pulse shape and low frequency com-
ponents on the off-diagonal voltage. The latter is of a 
particular importance to increase the output voltage 
since the existence of the domain structure may elimi-
nate this voltage completely. 
 
2. BASICS OF OFF-DIAGONAL SENSOR DESIGN 
 
An ac current i passing through a magnetic wire 
(see Fig. 1a) generates a voltage Uw which may be very 
sensitive to the external magnetic field. This is known 
as a magnetoimpedance (MI) effect. If the wire has a 
helical magnetisation the voltage Uc is also generated 
in a coil mounted on it (Fig. 1b). The ratio Zc  Uc/i may 
be called off-diagonal impedance. In single-domain 
wires with the circumferential anisotropy Zc is anti-
symmetrical with respect to axial magnetic field Hex 
having near-linear region around zero field point. This 
characteristic can be used in linear sensing. A practical 
design of such a sensor is given in [7-10] where the wire 
element is exited by a pulse current of C-MOS IC mul-
tivibrator or a microcontroller. 
 
 
 
Fig. 1 – Methods of excitation and detection for MI sensing 
element. A high frequency current is provided to the MI ele-
ment and the output voltage is measured across the wire (a) or 
from a coil mounted on it (b) 
 
The off-diagonal MI can be also realised by eхciting 
the wire by ac axial magnetic field induced by the coil 
and measuring the voltage across the wire. However, 
the coil self-inductance may considerably limit the exci-
tation current at high frequencies. Therefore, the 
excitation scheme of Fig. 1b is preferable.  
 
3. EXPERIMENTAL 
 
The sensor design based on multivibrator or micro-
controller excitation is important for practical applica-
tion. But the setup suggested in Fig. 2 allows detailed 
investigation of the influence of various excitation pa-
 N.A. YUDANOV, A.A. RUDYONOK, ET AL. J. NANO- ELECTRON. PHYS. 6, 03046 (2014) 
 
 
03046-2 
rameters on the sensor operation. The pulse generator 
may supply to the wire narrow current pulses of vari-
ous shape and magnitude as well as a harmonic wave-
form with various dc bias current. The wire with a coil 
is placed in a long solenoid which produces a magnetic 
field in the range of ± 60 Oe. As a result of cross mag-
netization (off-diagonal MI), electromotive force is in-
duced in the pickup coil wounded on the wire. The de-
pendence Uc  Hex is captured by digital oscilloscope.  
 
 
 
Fig. 2 – Experimental setup for off-diagonal MI 
 
  
Fig. 3 – Schematics of non-diagonal MI sensor element con-
sisting of Co-based amorphous wire on a polymer substrate 
and detection coil (40 mm diameter, 40 turns) 
 
 
Fig. 4 – Pulsed excitation waveform applied to MI element. 
The peak of current in a wire is 5.77 mA 
 
The sensor output was also investigated in orthogo-
nal fields produced with a help of two Helmholtz coils.  
An amorphous glass-coated wire of composition 
Co66.94Fe3.83Ni1.44B11.57Si14.59Mo1.69 was used as MI ele-
ment. The metal core diameter was 16 m and the total 
diameter was 16.8 m. The wire of length was fixed on a 
plastic substrate. In the off-diagonal configuration, the 
high frequency excitation is applied across the MI ele-
ment and the output signal is taken from the coil mount-
ed on it. A detection coil was made of 40 m diameter 
copper wire and had 40 turns. The overall sensor dimen-
sions are 3.2  1.8  0.5 mm. The sensing element is 
shown in Fig. 3. 
Two kinds of high frequency excitation waveforms 
produced by functional generator were supplied to the MI 
wire: pulsed and sinusoidal with a dc bias. The pulsed 
waveform is shown in Fig. 4. In this case, the rise / fall 
time is 20 ns which corresponds to a frequency of 50 MHz 
and the frequency of pulse repetitions is 8 MHz. 
The analysis of frequency response of the sensor re-
viled that the LC-resonance of the sensor cell is around 
8 MHz. The sinusoidal excitation with this frequency 
produced the largest output voltage as shown in Fig. 5. 
It is seen that there is another resonance mode with a 
frequency of 4 MHz. 
 
 
 
Fig. 5 – Frequency characteristics of the sensor output at 
sinusoidal excitation with zero dc bias current and in the 
presence of axial field of 1.5 Oe 
 
4. EXPERIMENTAL RESULTS AND  
DISCUSSIONS 
 
Typical output sensor characteristics as functions of 
external field are shown in Fig. 6 for different soldering 
methods. A pulsed excitation waveform shown in Fig. 4 
was supplied to the MI wire. The soldering tempera-
ture was 300 C and 100 C for samples 1 and 2, re-
spectively, and conducting glue at room temperature 
was used for sample 3. It is seen that the soldering 
method does not change significantly the curves where 
the sensitivity is maximal. 
 
0
20
40
60
80
100
120
140
0 0,5 1 1,5 2 2,5 3
Field, Oe
O
u
tp
u
t 
s
ig
n
a
l,
 m
V
sample1
sample2
sample3
 
 
Fig. 5 – Output characteristics of 3 MI wire samples with 
different soldering process. The soldering temperature was 
300 C and 100 C for samples 1 and 2, respectively, and con-
ducting glue at room temperature was used for sample 3 
MI wire 
   
1.8 mm 
3.2mm  
Substrate Detection coil 
Working area 
 
 
 
Soldering area 
 
 
U  
t   
20 ns 
42.5 ns 
42.5 ns 
0.75V   
20 ns 
 EFFECT OF BIAS ON OFF-DIAGONAL MAGNETOIMPEDANCE… J. NANO- ELECTRON. PHYS. 6, 03046 (2014) 
 
 
03046-3 
Therefore, the soldering process even at relatively 
high temperatures does not change substantially the 
magnetic structure. In fact, a moderate temperature 
may improve the MI sensitivity. This can be related 
with a relaxation of certain internal stresses. The sen-
sitivity is in the range of 600-700 mV/Oe and the line-
arity range is ± 0.3 Oe.  
 
 
 
Fig. 7 – Effect of axial bias field on off-diagonal sensor re-
sponse. DC current in a wire is: 1 – 0 mA, 2 – 1.59 mA,  
3 – 3.17 mA, 4 – 4.76 mA 
 
The range of linearity is rather small and if neces-
sary the operational point could be moved by applying a 
dc axial bias using the same detection coil. The output 
signal for different axial bias is shown in Fig. 7. For a 
dc current of 4.76 mA creating a field of about 1.4 Oe in 
the direction opposite to the sensed field the linearity 
region is 0.6-1.3 Oe. It is also seen that the curves for 
different axial bias cannot be obtained by shifting along 
the field axis. This behaviour can be attributed to the 
existence of deviations of the easy anisotropy from the 
circular direction.  
The sensor is sensitive to the field applied along the 
wire and the orthogonal field should not produce no-
ticeable changes. This was investigated by considering 
the sensor output in orthogonal fields and the corre-
sponding characteristics are shown in Fig. 8. It is seen 
that the sensitivity in the low field region indeed al-
most does not change; however, a rather large change 
in the range of 10 mV/Oe is seen for larger axial fields 
when the main contribution to the voltage response is 
related with the change in ac permeability. The analy-
sis of off-diagonal impedance for a single-domain wire 
shows that the effect of the radial field of the order of 
few Oe should be negligible since the demagnetising 
field is about 3 kOe. However, the orthogonal field has 
a circular component depending on the position on the 
wire. For ideal homogeneous helical magnetisation this 
component will not affect the averaged ac permeability. 
However, due to deviations of the anisotropy, this in-
fluence may be noticeable. The normal field may also 
affect the circular domain coercivity since the existence 
of circular domain structure is probably related with 
the surface inhomogeneity and radial magnetisation. 
This behaviour requires additional investigation which 
is important for the development of 3D sensors with the 
use of orthogonal system of amorphous wires. 
 
Orthogonal field, Oe
0
10
20
30
40
50
60
70
80
90
100
110
0 1 2 3 4 5
Axial field, Oe
O
u
tp
u
t 
s
ig
n
a
l, 
 m
V
0,2 Oe
0,4 Oe
0,8 Oe
1 Oe
0 Oe
 
 
Fig. 8 – Sensor output as a function of axial field with orthogonal field as a parameter 
 
 
 
 
 
 
 
 
0
20
40
60
80
100
120
0 0,5 1 1,5 2 2,5 3 3,5 4
Field, Oe
O
u
tp
u
t 
s
ig
n
a
l,
 m
V
4 
3 
2 
1 
 N.A. YUDANOV, A.A. RUDYONOK, ET AL. J. NANO- ELECTRON. PHYS. 6, 03046 (2014) 
 
 
03046-4 
Existence of a domain structure substantially dete-
riorates the sensor performance. In the case of ideal 
circular anisotropy and bamboo domain structure the 
output signal would be zero. The pulsed current excita-
tion containing low frequency components suppresses 
the circular domain structure. However, if the field 
generated by low frequency harmonics is too large, the 
sensor sensitivity will decrease due to increase of the 
magnetic hardness in circular direction. To investigate 
the conditions for optimal bias, a sinusoidal excitation 
with a dc bias was used. The frequency of excitation 
was 8 MHz. The sensor output in the presence of dc 
current flowing through the wire is shown in Fig. 9. 
 
 
 
Fig. 9 – Sensor output at a sinusoidal excitation with a fre-
quency of 8 MHz vs axial field in the presence of dc current: 
1 – 0 mA, 2 – 2.31 mA, 3 – 7.7 mA, 4 – 9.24 mA, 5 – 13.09 mA 
 
 
 
It is seen that the sensitivity and linearity region 
increase with increasing the dc current. However, for 
relatively large current of 10-15 mA the sensitivity in 
the low frequency region almost does not change, but at 
higher fields the sensitivity drops considerably. For the 
considered sensor configuration the optimal bias is 
around 2-3 mA. This current generates a circular mag-
netic field about 0.4 Oe at the wire surface (considering 
that the wire radius is about 10 m). This field is larger 
than the typical value of circular coercivity so the do-
main structure is eliminated. This field may also de-
crease the effect of the anisotropy deviation from the 
circular direction which also results in the improved 
sensitivity. 
 
5. CONCLUSIONS 
 
The main aim of this work was to investigate the ef-
fect of dc bias fields on the characteristics of off-
diagonal magnetoimpedance sensor. It was revealed 
that the effect of the orthogonal field (with respect to 
axial field) may be quite strong which imposes some 
limitations on the use of magnetic wires for the con-
struction of 3D sensors. The dc current in a wire gener-
ating a circular field results in improved sensitivity due 
to elimination of the domain structure and smoothing 
the effect of the anisotropy deviations.  
 
ACKNOWLEDGMENT 
 
This work was financially supported by the Russian 
Foundation for Basic Research, grant № 13-08-01319. 
The authors would like to thank Dr. V. Larin from 
MFTI Ltd, Moldova, for donating the wire samples for 
this work. 
 
 
REFERENCES 
 
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https://essuir.sumdu.edu.ua/bitstream/123456789/36339/1/Effect%20of%20Bias%20Fields%20on%20off-Diagonal%20Magnetoimpedance.pdf

Effect of Bias Fields on off-Diagonal Magnetoimpedance (MI) Sensor Performance

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