Peter Klein | University of Pavol Jozef Safarik, Faculty of Law, Slovakia (original) (raw)

Papers by Peter Klein

For the control and study of the post-implantation biomechanical processes of TiAl 6 V 4 implants... more For the control and study of the post-implantation biomechanical processes of TiAl 6 V 4 implants, the ability of wireless in vivo measurement of various parameters (i.e., temperature in this case) at the tissue–implant interface is required. Compared with other types of sensors, which consist of sensing and transmitting elements , nanocrystalline magnetic glass-coated microwires combine both of these features into unit. Thanks to a Pyrex coating, the microwires are biocompatible, and due to their size, they do not intervene into the surface structures of implants. The studied as-cast microwire has a low Curie temperature due to the high amount of molybdenum, and is not magnetically bistable at room temperature. In order to create its bistability at room temperature and enhance its temperature sensitivity in the range from 37 °C up to 42 °C, the microwire is specially annealed under axial stress above crystallization temperature. Extreme temperature sensitivity in the required temperature range is achieved using the superparamagnetism effect; moreover, due to this effect, the switching field increased in an almost linear way. The temperature dependence of the switching field is employed to sense the temperature in two TiAl 6 V 4 samples produced by additive manufacturing and representing implants with different types of fixations of the microwire onto the surface. Sensitivity up to 0.01 K is achieved.

The remagnetization process of most amorphous and nanocrystalline glass-coated microwires with po... more The remagnetization process of most amorphous and nanocrystalline glass-coated microwires with positive magnetostriction coefficient occurs through the single and large Barkhausen jump. This article encompasses a study on the magnetization process of thin Hitperm-type glass coated microwires. The complex stress distribution inside these microwires enables us to investigate the influence of; the measuring frequency, applied tensile stresses, as well as current annealing, and conventional annealing at wide range of temperatures. A systematic elucidations have been discussed in the framework of the microwire's geometries and the shape anisotropy that arises during its fabrication process, with the aim to provide an assessment of the criteria for selecting the necessary conditions to be designed in high-performance sensors.

We have studied the effect of stress induced anisotropy on domain wall dynamics in as-cast and an... more We have studied the effect of stress induced anisotropy on domain wall dynamics in as-cast and annealed nanocrystalline Hitperm-type microwires. Annealing without stress leads to stress relaxation of the strong stresses frozen-in post the production process. Stress annealing at 300 o C under 222.7 and 270.9 MPa, respectively, has triggered most complex domain wall dynamics.

We have studied Hitperm-type and Finemet-type glass-coated microwires with a nanocrystalline stru... more We have studied Hitperm-type and Finemet-type glass-coated microwires with a nanocrystalline structure. In Hitperm-type microwires where the nanocrystalline structure has been obtained directly after melt quenching using the Taylor-Ulitovsky fabrication technique, we observed rectangular hysteresis loops and studied the domain wall propagation. We measured and analyzed the switching field dependence on the frequency in as-prepared and annealed Hitperm-type microwires. A conventional annealing results in a drastic change of the frequency dependence of the switching field. This effect might be interpreted considering the stress relaxation process. We have also studied the correlation of magnetic properties, structure, and giant magnetoimpedance (GMI) effect in Finemet-type FeCuNbSiB microwires prepared by the Taylor-Ulitovsky technique. We observed that both GMI effect and magnetic softness of Finemet-type glass-coated microwires can be tailored by heat treatment, and after annealing a considerable magnetic softening of studied samples has been achieved. This magnetic softening correlates well with the devitrification of amorphous samples. Amorphous Fe-rich microwires exhibit a low GMI effect (GMI ratio below 1%). A considerable enhancement of the GMI effect (GMI ratio up to 100%) has been observed in heat-treated microwires developing a nanocrystalline structure.

The dominating trend in the reduction of dimensions, power consumption and cost of sensors in con... more The dominating trend in the reduction of dimensions, power consumption and cost of sensors in conjunction with the requirement of their precision and dynamics improvement and also in the range of the measured fields leads in the area of the fluxga te magnetometers to the replacement of the conventional sensors by their microwire substitutions. The article summarizes results of the transfer characteristics measurements of the developed microwire fluxgate sensors. These sensors are designed for the vec tor measurements of the low frequency weak magnetic fields. The basis for a determination of the sensors' characteristics lies in the repeated measurements during the one second time intervals in the defined operating points and also in the measurement of the differentials of the time intervals obtained during the alternating magnetizations in the defined magnetic field. Based on the measured static and dynamic transfer characteristics microwire fluxgate sensors with a different chemical composition and core geometr y from various manufacturers are compared. The results of the experiments creates the basis for a consideration of the possibility to replace currently used amorphous ribbon core sensors in the VEMA series magnetometers with the fluxgate sensors based on magnetic microwires.

In the presented short communication the authors refer on the first testing of microwires for mon... more In the presented short communication the authors refer on the first testing of microwires for monitoring the position of rats. Single piece of microwires was implanted in general inhalatory anaesthesia (by 1.5% Isoflurane with oxygen) via two small surgical i nci-sions into subcutaneous tissue at the back of the rat. By help of the simple cont actless coil, produced on the plastic tube, it was possible to assess the position of the rat inside the tube and monitor eventual movements of the animal.

Complex magnetoimpedance study is an alternating current technique that can be used to probe some... more Complex magnetoimpedance study is an alternating current technique that can be used to probe some properties of magnetic materials. We report on complex impedance measurements in low-negative magnetostrictive ferromagnetic CoFeSiB microwire. In these wires, the domain structure consists of two parts: an inner core, with domains oriented to the longitudinal direction of the wire, and an outer shell with circumferentially oriented domains. This magnetic structure is modified by AC current flowing through the microwire which produces an additional circumferential magnetic field HΦand significantly affects magnetic structure inside the wires. The additional circular magnetization process in wires was studied by impedance measurements as a function of the amplitude and the frequency of the AC current after gradual Joule heating. Changes in the magnetization processes are reflected in the real permeability values and loss factor values.

Few examples of technical and biomedical applications of bistable magnetic microwires are shown. ... more Few examples of technical and biomedical applications of bistable magnetic microwires are shown. Particularly, application of microwires in civil engineering are shown for sensing the mechanical stress in concrete, steel structure or steel cable by simple gluing it on the surface of studied structure. On the other hand, biomedical applications for sensing the stress, temperature, and position inside the human or animal body are shown. Experiments with pig intestine cells points to the biocompatibility of glass coated microwires.

The influence of current annealing on the complex domain structure in amorphous and nanocrystalli... more The influence of current annealing on the complex domain structure in amorphous and nanocrystalline FeCo-MoB microwire has been studied. The thickness of radial domain structure together with the switching field of single domain wall change as a consequence of variation of complex internal stress distribution inside metallic core. Firstly, radial domain structure thickness monotonously increases with increasing annealing DC current density for amorphous state. Switching field exhibits local minimum in nanocrystalline sample annealed at 500 MA/m 2 for 10 min when the lowest thickness of outer shell (182 nm) was observed. Such annealed sample (which magnetic properties exhibit excellent temperature stability) is suitable candidate for miniaturized sensor construction for sensing the magnetic field or mechanical stress.

Amorphous glass-coated microwires are ideal material for miniaturized applications for sensing th... more Amorphous glass-coated microwires are ideal material for miniaturized applications for sensing the temperature, stress and magnetic eld. One of the key parameters for future applications is their time and thermal stability. It has been shown that stability can be improved by using nanocrystalline materials that combine good soft magnetic properties of amorphous matrix with high structural stability of crystalline grains. Such nanocrystalline materials are usually obtained by annealing of amorphous precursor. In the given contribution, the inuence of dc current annealing on the domain structure and GMI eect in amorphous and nanocrystalline Fe40Ni38Mo4B18 magnetic microwire has been studied. The annealing induces additional circular magnetic anisotropy, stress relief and structure homogenization. However, the increase of magnetostriction results in the decrease of GMI. Annealing at optimum crystallisation temperature results in an increase of the relative permeability due to the formation of the nanosized grains. Consequently, GMI amplitude is comparable to that of as-cast state.

Some of the frequent reasons of titanium implant failures in human body are incorrect biomechanic... more Some of the frequent reasons of titanium implant failures in human body are incorrect biomechanical interactions within the tissue-implant interface and inammatory processes arising around the implant's application area. For both processes, it is crucial to locate them and intervene in time. One of the monitoring possibilities of the mentioned processes is the application of amorphous glass-coated sensoric microwires (AGCSM). Magnetic characteristics of these microwires are inuenced by both mechanical tension (magnetoelastic interaction of the magnetic moment with mechanical stress) and by temperature (dierent coecient of thermal expansion of the metal core and glass coating). The key task, in order to change the magnetic characteristics of AGCSM from both clinical and scanning point of view, appears to be the xation pattern of AGCSM in the implant's body. The presented study shows the impact of four types of AGCSM xation patterns (at one ending, at both endings, in the middle and along the entire length) on the thermal response process tested in laboratory conditions. The obtained results will enable to establish the AGCSM xation methodology in the implant's body in order to achieve optimal output temperature parameters form the implant and the tissue-implant interface by magnetic contactless measurements.

We have studied temperature dependencies of the switching eld in as-cast and nanocrystalline glas... more We have studied temperature dependencies of the switching eld in as-cast and nanocrystalline glass-coated Fe40Ni38Mo4B18 microwires. The switching eld shows complex temperature dependence in the as-cast state reecting the complex stress distribution induced during annealing. The temperature dependence of the switching eld depends strongly on the stage of nanocrystallization being negative for low temperatures of annealing and positive for annealing at 700 K.

We have studied magnetization process in amorphous bistable Fe80W3B17 microwires with reduced Cur... more We have studied magnetization process in amorphous bistable Fe80W3B17 microwires with reduced Curie temperature. High mechanical stresses from glass-coating, induced during production process, result in high switching eld. Reducing the length of microwire, the switching eld decreases as a result of reduction of magnetoelastic anisotropy. Moreover, the decrease of magnetoelastic anisotropy results in a complex temperature dependence of the switching eld. On the other hand, strong variations of the switching eld with temperature can be employed in miniaturised temperature sensor.

We are dealing with the fast domain wall dynamics in glass-coated microwires. Three main paramete... more We are dealing with the fast domain wall dynamics in glass-coated microwires. Three main parameters are recognized that results in a very high domain wall velocity that can reach more than 10 km/s. Firstly, it is a low Gilbert damping that decreases the domain wall damping. Secondly, it is the presence of two perpendicular anisotropies (that can be modified by proper thermal treatment). Finally, the radial domain structure shields the domain wall from the pinning at the surface.

We present a new-Fe 38.5 Co 38.5 B 18 Mo 4 Cu 1 Hitperm glass-coated microwires obtained by Taylo... more We present a new-Fe 38.5 Co 38.5 B 18 Mo 4 Cu 1 Hitperm glass-coated microwires obtained by Taylor-Ulitovsky technique with nanocrystalline structure consisting of about 23 nm of BCC α-FeCo and an amorphous precursors in as-prepared samples. Annealing resulted in a considerable decrease of such nano-grains down to (11 nm). Obtained results are discussed in terms of the stress diffusion of limited crystalline growth and the chemical composition. Rectangular hysteresis loops have been observed on all annealed samples that are necessary conditions to obtain fast domain wall propagation. An enhancement of the domain wall velocity as well as mobility after annealing has been obtained due to the structural relaxation of such grains with positive magnetostriction. These structure benefits found in the nanocrystalline Hitperm glass-coated microwires are promising for developing optimal magnetic properties.

We have studied the effect of thermal treatment on the magnetic domain structure and magnetic rev... more We have studied the effect of thermal treatment on the magnetic domain structure and magnetic reversal process of amorphous and nanocrystalline Fe 40 Co 38 Mo 4 B 18 microwires. The domain structure and the magnetization reversal of amorphous FeCoMoB microwires reflect the complex stress distribution introduced by the glass coating. Hence, the thickness of radial domain structure decreases with temperature and the temperature dependence of the switching field presents a discontinuous behavior. After nanocrystallization, the domain structure of FeCoMoB microwire is almost constant within the temperature range 10-400 K and the switching field decreases almost linearly with temperature mostly because of the decrease of saturation magnetization.

We studied the magnetic properties of two different kinds of Fe-rich glasscoated microwires with ... more We studied the magnetic properties of two different kinds of Fe-rich glasscoated microwires with nanocrystalline structure: Finemet-type and Hitpermtype microwires. We have determined that the nanostructure obtained after appropriate annealing conditions of as-prepared samples results in a better magnetic softness. Accordingly, two different nanostructures of either a-FeSi in the case of Finemet, or a-FeCo in the case of Hitperm, with zero and positive magnetostriction sign, respectively, have been observed. As a consequence, we have implemented these findings in order to investigate the giant magnetoimpedance (GMI) effect and domain wall dynamics of glass-coated microwires. In the case of Finemet-type microwires, we observed a considerable improvement of both the poor GMI effect and magnetic softness observed in as-prepared microwires after an appropriate annealing at temperature, T ann ‡ 550°C when FeCuNbSiB microwires exhibited nanocrystalline structure. In the case of Hitperm-type microwires, we observed an enhancement of the domain wall velocity as well as of domain wall mobility, owing to the nanocrystallization and structural relaxation processes obtained after a suitable current annealing.

In situ multifrequency ferromagnetic resonance and x-ray magnetic circular dichroism investigatio... more In situ multifrequency ferromagnetic resonance and x-ray magnetic circular dichroism investigations on Fe/GaAs(110): Enhanced g-factor Appl. Phys. Lett. 100, 092402 Electrical determination of spin mixing conductance at metal/insulator interface using inverse spin Hall effect J. Appl. Phys. 111, 07C307 Magnetic properties of ultrathin single crystal Fe3O4 film on InAs(100) by ferromagnetic resonance J. Appl. Phys. 111, 07C108 Ferromagnetic resonance of micro-and nano-sized hexagonal ferrite powders at millimeter waves Magnetic properties of FeCoMoB glass-coated microwires with high positive magnetostriction have been investigated during the process of devitrification in the temperature range: 0-600 C by ferromagnetic resonance (FMR) studies. The FeCoMoB microwire shows natural ferromagnetic resonance that reflects a complex anisotropy distribution. FMR spectrum for as cast sample shows up to four resonance maxima when ranging frequency from 10 MHz up to 11.3 GHz. After annealing, the anisotropy distribution becomes more regular and the number of FMR peaks decreases. The anisotropy and stress amplitude has been estimated from the FMR spectra, showing a strong decrease with annealing temperature and being low and constant for the nanocrystalline state. In addition, Gilbert damping decreases with annealing temperature, too. The low Gilbert damping ($0.01) for the nanocrystalline state makes the nanocrystalline FeCoMoB microwire an ideal material for applications in which fast magnetization processes are required. V C 2012 American Institute of Physics. [http://dx.

We studied magnetic properties of Fe 38.5 Co 38.5 B 18 Mo 4 Cu 1 Hitperm-like glass-coated microw... more We studied magnetic properties of Fe 38.5 Co 38.5 B 18 Mo 4 Cu 1 Hitperm-like glass-coated microwires obtained by Taylor-Ulitovsky technique with nanocrystalline structure consisting of about 20e30 nm BCC a-FeCo and an amorphous precursor in as-prepared samples. We observed a considerable decrease of the average grain size (from about 23 to 11 nm) after annealing. As-prepared and annealed Fe 38.5 Co 38.5 B 18-Mo 4 Cu 1 Hitperm-like glass-coated microwires present rectangular hysteresis loops and fast domain wall propagation. We measured and analyzed the frequency dependence of the switching field dependence and domain wall dynamics in as-prepared and annealed Hitperm-type microwires. Obtained results are discussed in terms of the microstructural relaxation, grains refinement and internal stresses relaxation. An enhancement of the domain wall velocity as well as mobility after annealing has been attributed to the structural relaxation of such grains with positive magnetostriction.