Recent Developments of Magnetoresistive Sensors for Industrial Applications

The research and development in the field of magnetoresistive sensors has played an important role in the last few decades. Here, the authors give an introduction to the fundamentals of the anisotropic magnetoresistive (AMR) and the giant magnetoresistive (GMR) effect as well as an overview of various types of sensors in industrial applications. In addition, the authors present their recent work in this field, ranging from sensor systems fabricated on traditional substrate materials like silicon (Si), over new fabrication techniques for magnetoresistive sensors on flexible substrates for special applications, e.g., a flexible write head for component integrated data storage, micro-stamping of sensors on arbitrary surfaces or three dimensional sensing under extreme conditions (restricted mounting space in motor air gap, high temperatures during geothermal drilling).DFG/CRC/653German Federal Ministry of Education and Researc

Material-inherent Data Storage Using Magnetic Magnesium-cobalt Alloys

Magnetic magnesium alloys have an inherent load-sensitive behavior. These alloys are manufactured by casting of magnesium alloyed with the ferromagnetic element cobalt. In this context, the magnetoelastic effect can be used in order to measure mechanical loads during the component's service by means of a harmonic analysis of eddy current signals. The utilization of magnetic magnesium as a load-sensitive material in order to measure mechanical loads in structural components has been demonstrated in previous works. Another application is the magnetic labeling of the alloy. In this context the magnetic remanence is a significant characteristic value. A data track can be written directly on the material's surface by means of an electromagnetic write head. The track may contain relevant component-specific information like serial numbers, manufacture date and expected lifetime. This information can be read out by means of a sensor utilizing the giant magnetoresistive (GMR) effect. The magnetic labeling in relation to the manufactured alloy and the cooling rate during the casting process is examined in this work. The magnetic labeling of three alloys based on magnesium, cobalt and zinc has been investigated; these are MgCo4 and MgCo4Zn2. The alloys’ mechanical as well as their magnetic properties are significantly influenced by these additional alloying elements. In order to investigate the alloys’ suitability for magnetic data storage the quality of the data tracks read out using a GMR sensor are compared depending on the alloy composition. The magnetic labeling is influenced by the microstructure regarding solidification and cooling rate. A conical casting geometry with different solidification rates in top and bottom sections was used for an examination of the relationship between the density of the magnetic phases and the quality of the magnetic labeling

Flexible Magnetic Reading/Writing System: Heat-assisted Magnetic Recording

Data storage is one of indispensable technical assets defined in a frame work of Industry 4.0. Among many data storage technologies, inherent magnetic data storage on surfaces of technical components is promising, especially when the components are employed in harsh environments. Comparing with other storage technologies like labels, RFID tags and engraving, the inherent magnetic storage is rewritable and resistant to weathering. High temperature and a high magnetic field, however, can degrade or even delete magnetically stored data. This limitation can be coped with using a medium with higher coercivity that can withstand external magnetic fields and high temperature. As a consequence of higher coercivity, a higher write field is required to magnetize the medium. A design of a flexible write head that is suitable for storage applications on surfaces of technical components, is restricted by head-medium interface criterions, and hence field strength generated from the write head cannot be arbitrary large. To solve this problem, a heat-assisted magnetic recording (HAMR) is proposed as a means to temporarily reduce coercivity of a medium during writing. A realization of a HAMR module and an experiment as well as its positive results are presented in this work

Flexible Magnetic Writing / Reading System: Polyimide Film as Flexible Substrate

In the frame work of Collaborative Research Center (CRC) 653, magnetic data storage on surfaces of components has been developed. The principle is based on magnetic data storage of hard disk drives. Rigid magnetic writing heads successfully developed so far still have limited capabilities; they cannot be adapted to rough or curved surfaces and cannot withstand high mechanical shock. To overcome such drawbacks, a new design of a writing head based on a flexible substrate is proposed. This publication focuses on an investigation of a material which serves as a required substrate for this application. Baseline examinations for asserting compatibility of the flexible substrate to production processes for microelectromechanical systems (MEMS) are presented. Successfully fabricated micro structures using simple fabrication techniques based on photolithography and thin film processes are demonstrated as well. Obtained results through this work indicate that the polyimide film, namely Kapton film, is suitable as the flexible substrate for the flexible magnetic writing / reading system

In vitro and in vivo accumulation of magnetic nanoporous silica nanoparticles on implant materials with different magnetic properties

Abstract Background In orthopedic surgery, implant-associated infections are still a major problem. For the improvement of the selective therapy in the infection area, magnetic nanoparticles as drug carriers are promising when used in combination with magnetizable implants and an externally applied magnetic field. These implants principally increase the strength of the magnetic field resulting in an enhanced accumulation of the drug loaded particles in the target area and therewith a reduction of the needed amount and the risk of undesirable side effects. In the present study magnetic nanoporous silica core–shell nanoparticles, modified with fluorophores (fluorescein isothiocyanate/FITC or rhodamine B isothiocyanate/RITC) and poly(ethylene glycol) (PEG), were used in combination with metallic plates of different magnetic properties and with a magnetic field. In vitro and in vivo experiments were performed to investigate particle accumulation and retention and their biocompatibility. Results Spherical magnetic silica core–shell nanoparticles with reproducible superparamagnetic behavior and high porosity were synthesized. Based on in vitro proliferation and viability tests the modification with organic fluorophores and PEG led to highly biocompatible fluorescent particles, and good dispersibility. In a circular tube system martensitic steel 1.4112 showed superior accumulation and retention of the magnetic particles in comparison to ferritic steel 1.4521 and a Ti90Al6V4 control. In vivo tests in a mouse model where the nanoparticles were injected subcutaneously showed the good biocompatibility of the magnetic silica nanoparticles and their accumulation on the surface of a metallic plate, which had been implanted before, and in the surrounding tissue. Conclusion With their superparamagnetic properties and their high porosity, multifunctional magnetic nanoporous silica nanoparticles are ideal candidates as drug carriers. In combination with their good biocompatibility in vitro, they have ideal properties for an implant directed magnetic drug targeting. Missing adverse clinical and histological effects proved the good biocompatibility in vivo. Accumulation and retention of the nanoparticles could be influenced by the magnetic properties of the implanted plates; a remanent martensitic steel plate significantly improved both values in vitro. Therefore, the use of magnetizable implant materials in combination with the magnetic nanoparticles has promising potential for the selective treatment of implant-associated infections