Abstract
Micromagnetic sensors, viz., Hall elements, fluxgate, magnetoresistance and magnetoimpedance sensors, play a major role towards the miniaturization in the industrial society.
Original language | English |
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Title of host publication | 2017 IEEE International Magnetics Conference, INTERMAG 2017 |
Publisher | IEEE |
ISBN (Electronic) | 9781538610862 |
ISBN (Print) | 978-1-5386-1087-9 |
DOIs | |
Publication status | Published - 10 Aug 2017 |
Externally published | Yes |
Event | 2017 IEEE International Magnetics Conference, INTERMAG 2017 - Dublin, Ireland Duration: 24 Apr 2017 → 28 Apr 2017 |
Publication series
Series | INTERMAG |
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ISSN | 2150-4598 |
Conference
Conference | 2017 IEEE International Magnetics Conference, INTERMAG 2017 |
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Country/Territory | Ireland |
City | Dublin |
Period | 24/04/17 → 28/04/17 |
Austrian Fields of Science 2012
- 103017 Magnetism
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2017 IEEE International Magnetics Conference, INTERMAG 2017. IEEE, 2017. 8007557 (INTERMAG).
Publications: Contribution to book › Contribution to proceedings › Peer Reviewed
TY - GEN
T1 - Vortex magnetization state in a GMR spin-valve type field sensor
AU - Brueckl, H.
AU - Satz, A.
AU - Pruegl, K.
AU - Wurft, T.
AU - Luber, S.
AU - Raberg, W.
AU - Zimmer, J.
AU - Suess, D.
N1 - Funding Information: Micromagnetic sensors, viz., Hall elements, fluxgate, magnetoresistance and magnetoimpedance sensors, play a major role towards the miniaturization in the industrial society. Among them, magnetoresistive spin-valves have been extensively investigated and applied in a variety of device applications. These include, for example, magnetic read heads, magnetic field sensors and giant magnetoresistance (GMR) isolators. On-going technical developments concentrate on sensor parameters like sensitivity, size, full range, linearity, bandwidth, power consumption and resolution. Typically, spin-valve-type magnetoresistive sensors are embedded in a Wheatstone bridge configuration with rectangular, meander-like or elliptically shaped thin film elements. Such elements usually switch via multi-domain, Cor S-shaped magnetization states and, therefore, often exhibit an open non-linear hysteresis curve. Linearity and hysteretic effects are key features in the improvement of such sensors. In this paper, we present a different approach by using circularly shaped elements exhibiting a different magnetization state. The magnetic vortex is one of the fundamental magnetization ground states occurring in disk-shaped thin film elements and is characterized by minimization of the demagnetizing energy at the expense of exchange energy. The state is described as free of hysteresis and planar stray-fields, and discussed as potential oscillator in spin-torque systems, memory bits and magnetic field sensors. In order to compare important parameters like resistance, magnetoresistance amplitude, sensitivity, hysteresis, critical fields like nucleation and annihilation fields in dependence on the free layer thickness and disk radius, single and arrays (10 and 1750 in number) of GMR disks have been fabricated by optical lithography and contacted. A sputter-deposited layer stack, consisting of a PtMn-pinned synthetic antiferromagnet CoFe/Ru/CoFe as reference magnetization, a Cu spacer layer in the second antiferromagnetic coupling maximum and a CoFeB free layer with thicknesses varying between 30 and 80 nm have been processed to disks of varying diameters between 1 and 2 microns. Contacts overlapping the disk area by ~30% have been realized such that the current flow between opposite contacts is along the magnetization of the reference layer which has been configured by an annealing step. An external field parallel to this same direction causes an orthogonal vortex core shift either left or right from the current flow depending on the vortex rotation sense, giving rise to a change in the magnetoresistive signal. A clear vortex signature is found in major loop hysteresis with nucleation / annihilation fields of 20 / 30 mT up to 80 / 100 mT depending on the free layer thickness and disk diameter (Fig. 1). The following advantages will be discussed and compared to typical hysteresis curves of standard elliptical or rectangular sensor elements. (a) The vortex state shows essentially no hysteresis in the minor loop. (b) Since the vortex nucleation happens prior to the zero field, the M(H=0)=0 crossing is independent of history. (c) The critical fields can be easily determined by the element geometry. Some disadvantages have also been identified and quantified: (a) the magnetoresistive amplitude is lower due to the increased free layer thickness. (b) A lower sensitivity is seen due to lower magnetoresistive amplitudes and larger critical fields. (c) And, a non-linear hysteresis curve leads to non-linear magnetoresistive response curve. All characteristic experimental values have been determined in dependence of free layer thickness tFL and disk diameter D. An example is given in Fig. 2 which shows the linear dependence of the annihilation field Han on the ratio tFL/D. These findings are discussed in the frame of the semi-analytical rigid-vortex-model [1] and micromagnetic simulations with OOMMF (NIST). The financial support by the Austrian Federal Ministry of Science, Research and Economy and the Christian Doppler Research Association in Austria in the frame of the ‘Christian Doppler Laboratory for future magnetic sensors and materials’ is gratefully acknowledged. Publisher Copyright: © 2017 IEEE. Copyright: Copyright 2017 Elsevier B.V., All rights reserved.
PY - 2017/8/10
Y1 - 2017/8/10
N2 - Micromagnetic sensors, viz., Hall elements, fluxgate, magnetoresistance and magnetoimpedance sensors, play a major role towards the miniaturization in the industrial society.
AB - Micromagnetic sensors, viz., Hall elements, fluxgate, magnetoresistance and magnetoimpedance sensors, play a major role towards the miniaturization in the industrial society.
UR - http://www.scopus.com/inward/record.url?scp=85034646148&partnerID=8YFLogxK
U2 - 10.1109/INTMAG.2017.8007557
DO - 10.1109/INTMAG.2017.8007557
M3 - Contribution to proceedings
AN - SCOPUS:85034646148
SN - 978-1-5386-1087-9
T3 - INTERMAG
BT - 2017 IEEE International Magnetics Conference, INTERMAG 2017
PB - IEEE
T2 - 2017 IEEE International Magnetics Conference, INTERMAG 2017
Y2 - 24 April 2017 through 28 April 2017
ER -