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Superparamagnetic ferrite nanoparticles coated with a polymer layer are widely used for biomedical applications. The objective of this work is to design nanoparticles as a magnetic resonance imaging (MRI) temperature-sensitive contrast agent. Copper-zinc ferrite nanoparticles coated with a poly(ethylene glycol) (PEG) layer are synthesized using a one-step thermal decomposition method in a polymer matrix. The resulting nanoparticles are stable in water and biocompatible. Using Mössbauer spectroscopy and magnetometry, it was determined that the grown nanoparticles exhibit superparamagnetic properties. Embedding these particles into an agarose gel resulted in significant modification of water proton relaxation times

Purpose The purpose of this paper is to examine scaling algorithms in the description and modelling of power loss in soft magnetic composites (SMCs). Design/methodology/approach Three scaling algorithms are examined to determine the most appropriate description of power loss in magnetic composites. The scaling coefficients are estimated in such a way that all measurement data should be collapsed onto a single curve, given in the scaled coordinates. The coefficient estimation is based on a non-linear optimization using the generalized reduced gradient method. The obtained formulae are then used in the power loss modelling. Findings It is revealed that only two-component formulae are suitable for the scaling analysis of power loss because these allow obtaining of the collapse of measurement data. Research limitations/implications This study considers just one type of SMC (Somaloy 700). Further research will be devoted to the verification of the scaling approach to the power loss modelling for other types of magnetic composites. Practical implications The power loss is a basic property of soft magnetic materials, which determines their practical applications. The scaling approach to the power loss modelling gives quite simple models that require a reduced number of measurement data to estimate coefficients. Originality/value The scaling algorithms can be a useful tool in the analysis and designing of magnetic circuits made of SMCs.

Soft magnetic composite (SMC) materials made of iron powder are more frequently used in construction of electric actuators and motors because of their advantages with respect to Fe&ndash, Si electric steel sheets and because they have almost no powder loss. The study deals with measurements of temperature and torque of a low-power rotary switched reluctance actuator, with reference to a commercial actuator and a prototype actuator characterized by stator and rotor cores made of soft magnetic composite materials. Further power loss analysis was also conducted. To assess the actuators, magnetization characteristics and iron loss vs. magnetic flux density at a given frequency were measured according to IEC standards. Results show that the actuator made of soft magnetic composites exhibits higher efficiency and a lower temperature rise of stator and windings in comparison with the commercial actuator.

Applications of soft magnetic elements and permanent magnets increase due to broaden range of products with their usage. Nowadays magnetic elements are prepared mainly by casting, sintering or bonding technology. Presently research is focused on two ways: improvement of known magnetic materials and elaboration of new technology of fabrication magnetic elements. Development of new technologies enables obtaining magnetic elements with complicated geometry and can be made in a near net shape. These technologies that can be used are called additive manufacturing or 3D printing. 3D printing are divided in different methods. Article presents a review of different methods of 3D printing that are applied to manufacturing magnetic elements.

Switched reluctance drives are still under development, because of its advantages in comparison to other types of electric motors and drives. New magnetic materials cause development of electric machines. Soft magnetic materials such as soft magnetic composites, made mainly of iron powder, are more and more applied in new structures of electric machines. Thermal measurements of motors are final tests of a machine design and manufacturing. Temperature of parts of a motor, mainly winding limits the load of a motor. A low power switched reluctance motor with soft magnetic composite core was measured. It was loaded with constant power and was thermally tested. Winding and outer stator core temperature was measured. Reached temperatures of parts of the machine are about 60°C, which shows that this motor can work with higher loading, which is limited by a supply controller.

Author(s): Daobrowski, M; Cinal, M; Schmid, AK; Kirschner, J; Przybylski, M | Abstract: We present a joint experimental and theoretical study that demonstrates how to efficiently control a canted state of magnetization in Fe films grown on Ag(001) vicinal surface and precisely characterize it with the magneto-optical Kerr effect. It is shown that by employing different mechanisms to tune the magnetization tilting angle, any magnetization orientation within the plane perpendicular to the step edges can be achieved. In particular, increasing the Fe film thickness leads to continuous rotation of the magnetization easy axis toward the film surface and the sense of this rotation in uncovered films is opposite to that in films covered with Au. Another tuning mechanism is provided by oscillatory changes of the tilting angle at low temperatures due to formation of quantum well states in Fe films. The observed canting of magnetization is explained within a phenomenological model by an interplay of the shape anisotropy and two magnetocrystalline anisotropy terms, perpendicular and step-induced anisotropies, which results in an effective uniaxial magnetic anisotropy. The fitted thickness dependencies of the anisotropy constants accurately reproduce experimental variations of the tilting angle with both Fe and Au thicknesses as well as transient changes of the magnetization orientation in ultrathin Fe films upon submonolayer Au coverage, observed with spin-polarized low-energy electron microscopy.

Magnetic composites are manufactured as magnetic powder bonded by dielectric material, which bond and insulate powder grains. Magnetic composites are applied in electric machines due to their favorable magnetic and mechanical properties as well as possibility of tailoring their physical properties. The paper is a review of soft and hard magnetic composites, their internal structure, properties, and advantages resulted from their application on magnetic circuits of electric motors.

In the paper, the Wind Driven Optimization WDO algorithm is applied to the optimal shape design of a class of switched reluctance motors. The goal of the optimization is to identify a class of geometries which maximize the torque and simultaneously minimize the iron losses of the motor. Because of the twofold design criterion, the multi-objective version of the wind driven algorithm M-WDO is used. Results are eventually compared with those obtained by means of a standard genetic algorithm GA.

We conducted a structural and magnetic analysis of ultrathin Fe films on Rh (001) surfaces by using low electron energy diffraction (LEED), magneto-optical Kerr effects (MOKE) and spin-polarized scanning tunneling microscopy (SP-STM). The films in the investigated thickness range up to 6 monolayers (ML) are pseudomorphic to the Rh (001) substrate. While Fe films thinner than 3 ML grow layer-by-layer at room temperature (RT), Fe films thicker than 4 ML form islands. 1 ML Fe films do not show any hysteresis loops even at low temperature. Polar hysteresis loops for the 2 ML and 3 ML thick films appear at low temperatures. When 1 ML thick Fe films were studied by Cr- and Fe-coated W tips, a (2×3) and stripe structures were observed, respectively. The structures originate from a complex magnetic structure of 1 ML Fe. Based on the SP-STM results we propose a spin configuration model of a 1 ML Fe film.

This article describes an experiment for investigation of the tensile strength of adhesives used in production of electric motors. The study was conducted for an application of adhesives in production of hybrid components composed from various materials. Composite elements were made from iron powder and Nd-Fe-B alloy powder. Hybrid elements may consist of layers of different physical properties. The test is also expected to answer the question whether the type of layers used can influence the bond strength. In addition, the article describes an attempt to compare tensile strengths of hybrid elements made in different techniques, such as one-step pressing and gluing of hybrid elements. The study confirms that the type of surfaces and adhesives influences the strength of the hybrid element.

The article presents the results of physical properties investigation of bonded permanent magnets — so-called dielectromagnets. These permanent magnets Nd-Fe-B were made by bonding a hard magnetic powder with a binding agent. For purposes of this research several hard magnetic powders were selected. Hard magnetic powders were obtained from melt-spun ribbon of Nd-Fe-B alloy. The physical properties of sintered magnets from groups such as: ferrite, Nd-Fe-B and Sm-Co were also measured.

The evolution of the domain structure with the thickness of bcc Fe films deposited on the Ag(116) vicinal surface is studied by spin-polarized low-energy electron microscopy. We show that a spin reorientation transition proceeds via two mechanisms: continuous rotation of magnetization within the vertical plane perpendicular to the steps and discontinuous reorientation of the in-plane component of magnetization, leading to splitting of the domains. In contrast to previously investigated systems with stripe domains, we reveal that in the case of a vicinal ferromagnetic surface, the domain width increases while changing the orientation of the magnetization from a canted out-of-plane state into an in-plane state. A theoretical model developed in this work successfully describes the domain structure behavior observed in our experiments and can be equally applied to other ferromagnetic films grown on vicinal surfaces.

article i nfo The local electronic structure of a submonolayer-thick corrugated Cu3N-Cu(110) network is investigated by low temperature scanning tunneling spectroscopy (LT-STS). The corrugation present in the Cu3N network plays a vital role by causing the surface electronic features to vary locally due to different N-Cu bonding. Our studies indicate a work function larger by 0.9 eV for Cu3N compared to bare Cu(110), suggesting the for- mation of a significant surface dipole. Theoretically predicted various N 2p, Cu 3d hybridized states have been shown and explicitly verified by a combination of constant height and constant current tunneling spectros- copy measurements, thereby providing information about the chemical composition of the N-Cu(110) network.

So-called split hysteresis loops have been measured for ultrathin ferromagnetic films grown on stepped surfaces. Since the shape of the loops is sensitive to the direction in which the magnetic field is applied with respect to the steps, the sample orientation against the field is particularly important. We performed systematic magneto-optical Kerr effect studies for 15 and 58 ML of Fe grown on Au(1,1,13). In view of the complex magnetic anisotropy of such systems we discuss representative hysteresis loops taken at sample orientations misaligned from the field (and laser beam) direction. In particular, the presence of a so-called low field component to the hysteresis loops is discussed and its reversed polarity is explained.

The magnetic anisotropy of Fe film grown on vicinal Ag(1,1,10) surfaces studied with the in situ magneto-optic Kerr effect shows oscillatory behavior. We found that both the in-plane step-induced uniaxial anisotropy and the perpendicular anisotropy measured at low temperature show strong oscillations as a function of Fe thickness with a period of ~ 5.7 monolayers. Such novel oscillation of the anisotropy is attributed to the quantum well states (QWS) of d-band electrons at the Fermi level in the Fe film. These QWS have been observed by angle-resolved photoemission spectroscopy from a Fe wedge films grown on Ag(001) surface.

The detection of volatile organic compounds (VOCs) from exhaled breath has been recognized as a new frontier non-invasive medical diagnosis method especially in medical treatment, which requires frequent monitoring of the patients’ health status. Recently, numerous studies are related to acetone detection in the exhaled human breath, due to the fact that acetone, together with isoprene and methyl nitrate are considered as the most important candidates for biomarkers of diabetes mellitus [1]. Those type of medical applications require the high sensor sensitivity and the low detection limit of a given biomarker (usually below 1 ppm). This issue is difficult for p-types of materials like CuO, which have a low detection limit, but in general lower response than n-type material. Modifying sensor material by doping, nanostructurizing, mixing two types of metal oxides or combining with graphene, graphene oxides or carbon nanotubes can significantly improve sensitivity and the detection limit. This work is focused on fabrication of hetero-junction, which has two components: p-type CuO and n-type Fe2O3, deposited by magnetron sputtering. The Fe2O3/CuO bilayered system exhibit very good performance towards recognition of acetone and allow for detection of low gas concentrations. The deposited thin films have been broadly characterized. The phase composition, obtained by XRD analysis showed that both films CuO and Fe2O3 are polycrystalline composed of small nanograins 2O3 layer (Fig. 1b) as well as an optimal operating temperature, which is around 375°C. Moreover, it appears that acetone concentration as low as 0.8 ppm can still be detected using Fe2O3/CuO (tdepFe2O3=10 min) sensor operating at 430oC (Fig. 1c). Comparing to the acetone detection limits reported in the available literature, the CuO–Fe2O3 system studied within this work is especially interesting concentrations of acetone close to 1 ppm. Fig. 1 a) Resistance vs. operating time of Fe2O3/CuO (tdepFe2O3=12 min) sensor upon exposure to various concentration of acetone, the inset shows TEM cross-section image with EDX analysis b) sensor response upon interaction with acetone at various temperatures of Fe2O3/CuO heterostructures with different thickness of Fe2O3 layer c) sensor response of Fe2O3/CuO (tdepFe2O3=10 min) hetero-junction to various concentration of acetone. The work was financial supported by the National Centre for Research and Development under LIDER/252/L-6/NCBR/2015. [1] M. Ye, P.-J. Chien, K. Toma, T. Arakawa, K. Mitshubayashi, Biosens. Bioelectron., 73 (2015) 208. Figure 1

Operating parameters of electric machines depend, among other things, on the parameters of magnetic circuit used in the machine…

For Co films on Pd(1 1 0) covered with Au, the polar hystersis loops measured at 120 K are reversed below 2.7 ML with respect to those of thicker Co films, which is due to the negative contribution to polar Kerr rotation from the Co/Pd interface dominating in this thickness range over the positive polar Kerr rotation from the non-interface part of the Co film. Near the film thickness where the Kerr rotation changes sign a remarkable combination of two loops (normal and reversed) of two slightly different coercivities is observed regarded as a superposition of two different magneto-optical contributions corresponding to thinner and thicker parts of the Co film. The thin and thick film areas could have different temperature dependence of magnetization (the negative contribution could depend stronger on temperature since it is related to the thinner part of the film), leading to the increasing total polar Kerr rotation with increasing temperature.

We report on the growth of thin Co films on Pd(1 1 1) at three different temperatures 180 K, 300 K, and 550 K. The structure and morphology was determined by scanning tunneling microscopy and low energy electron diffraction. The growth mode was found to vary with temperature. For 180 K and 300 K, we observed a tendency to double layer growth for the initial layers while at elevated temperatures, the initial film grows in single layer. For most conditions, non-ideal three-dimensional growth was observed. Two-dimensional growth was only found for growth temperature of 550 K and coverages above 5 ML. Depending on temperature, the Co islands at low coverages exhibit three principally different shapes: dendritic at 180 K, hexagonal at 300 K and triangular at 550 K. For growth at 550 K and coverages above 5 ML, the islands changed to an irregular shape. This transition is most likely responsible for the transition to 2D growth. Further, the large strain is relaxed by the creation of a dislocation network with mixed fcc and hcp stacking. Depending on the temperature and coverage, a hexagonal or a triangular network was observed. Finally, we have investigated the effect of annealing Co films prepared at 180 K and 300 K. Heating to 490 K leads to coarsening and intermixing.

The paper deals with numerical analyses of a radial flux motor with double-sided rotor. The motor was designed with Nd-Fe-B sintered magnets and soft magnetic stator made of iron powder. The motor was designed for assessment of possibility of construction high torque motors with the powder stator for e.g. electric vehicles or washing machines. The motor is assumed to have stator composed from segmented parts made of iron powder. Those parts are assumed to be made by pressing the powder in a die or cut from larger parts by electric discharge machining. The motor stator was designed with uses of special construction powder components and is subjected of a Polish patent application. Designed stator should have better mechanical performance than stator made of electrical steel.

We have grown ultra-thin epitaxial Co films on (0 0 1) and (1 1 1) surfaces of Pd. Their magnetic properties are studied by magneto-optical Kerr effect (MOKE). They are correlated with surface morphology analyzed by scanning tunneling microscopy (STM). In agreement with theoretical predictions, reversed polar Kerr rotation loops with respect to those of thicker Co films were observed below the thickness of 2.5 monolayers. This is interpreted as being due to a dominating negative contribution of Co/Pd interface with respect to the positive contribution from the non-interface part of the Co film. There is no change of sign of the polar Kerr rotation at low Co coverage on Pd(1 1 1) due to the growth which starts by formation of double-layer patches in this case.

Single-crystalline Fe/MgO/Fe magneto-tunnel junctions were grown epitaxially on GaAs(0 0 1). Independent magnetization switching was achieved by pinning the magnetization of one of the Fe electrodes by antiferromagnetic coupling via Cr to another Fe layer (GaAs/Fe/Cr/Fe/MgO/Fe). For the antiparallel magnetization orientation in the Fe/Cr/Fe trilayer, “reversed” minor hysteresis loops are measured with longitudinal MOKE. The shape of the loop corresponding to the top “free-Fe” electrode is determined by four-fold magnetic anisotropy with the easy-axis along [1 0 0], superimposed by a weak uniaxial anisotropy with [0 1 0] easy-axis. The loops are asymmetric due to a delicate balance between the uniaxial anisotropy and magnetic interlayer coupling between the Fe electrodes separated with a thin MgO spacer.

We report on the out-of-plane magnetization in Fe/Ni and Fe/Au bilayers grown on GaAs(0 0 1). For Ni thicknesses of several monolayers, the magnetization of the Fe/Ni bilayer increases linearly with the Fe film thickness, which is typically observed when Fe grows in the BCC-structure. For thicknesses up to 8 ML, Ni is nonmagnetic such as in the Fe/Ni/GaAs(0 0 1) structure. This could be due diffusion of Ga. Up to thickness of 2 ML the Fe overlayer is magnetized out-of-plane, however at low temperatures only. The nature of the out-of-plane spin orientation is discussed, also in view of the crystallographic structure of the Fe/Ni bilayer and by comparison with the Fe/Au bilayer grown on GaAs(0 0 1).

Single-crystalline (Fe/Cr/Fe) AFM /Cr/Fe structures were epitaxially grown on atomically flat GaAs(0 0 1). Choosing the same thickness of the antiferromagnetically (AFM) coupled Fe layers in the bottom (Fe/Cr/Fe) AFM structure, their net magnetization is balanced to zero, in particular up to a spin–flop transition when the field is applied along the [1 1 0] direction. For the Cr thicknesses at which the top Fe layer is weakly magnetically coupled to the bottom (Fe/Cr/Fe) AFM structure, at low fields, the magneto-optical Kerr effect and/or SQUID signal from the sample corresponds to the top Fe layer only. An influence of the Cr spin structure on the magnetization reversal in the Fe layer is reported. In particular, a strong increase of coercivity (by a factor of 12) is found at low temperatures. A 90° coupling is detected which affects the minor loops measured along the [−1 1 0] and [1 0 0] directions.

Fe/Cr/Fe trilayers were epitaxially grown on atomically flat GaAs(001). For the thickness of Cr spacer layer corresponding to antiferromagnetic coupling, “reversed” minor hysteresis loops were measured with longitudinal magneto-optical Kerr effect(MOKE), i.e., a negative “magnetization” signal was detected when the thicker bottom Fe layer was saturated along the applied field. This behavior is interpreted by depth variations of the MOKE sensitivity. Magnetization reversal shows that both antiferromagnetic switching and spin–flop transition fields depend on the ratio of both Fe film thicknesses. The shape of the MOKE loops becomes more complex with further deposition of MgO and Fe layers on the top of the Fe/Cr/F/GaAs(001) stack. Superconducting quantum interference device measurements confirm the interpretation of the MOKE loops and demonstrate homogeneity and sharpness of the interfaces in the structures.

The influence of a gate voltage on magnetic anisotropy is investigated in a thin Fe film epitaxially grown on a Ag(1,1,10) substrate and covered by MgO. Oscillations in step-induced magnetic anisotropy due to quantum well states (QWS) confined in the Fe film are observed and shown to persist up to room temperature at low Fe thicknesses. By systematically examining the voltage and thickness dependence of the magnetic hysteresis loop characteristics, we identify two distinct effects by which an applied voltage modifies the magnetic anisotropy. The first effect is due to voltage-induced changes to interfacial perpendicular magnetic anisotropy which, due to the vicinal geometry, leads to changes in the effective in-plane uniaxial magnetic anisotropy. A second effect is observed at lower film thicknesses and shows nonmonotonic voltage-induced effects on magnetic anisotropy. This nonmonotonic behavior coincides with the onset of significant QWS-induced effects on magnetic anisotropy and suggests a link between QWS- and voltage-induced anisotropy changes.

The effect of electron confinement on the magnetocrystalline anisotropy of ultrathin bcc Fe films is explored by combining photoemission spectroscopy, x-ray magnetic circular dichroism, and magneto-optical Kerr effect measurements. Pronounced thickness-dependent variations in the magnetocrystalline anisotropy are ascribed to periodic changes in the density of states at the Fermi level, induced by quantization of ${d}_{xz}$, ${d}_{yz}$ out-of-plane orbitals. Our results reveal a direct correlation between quantum well states, the orbital magnetic moment, and the magnetocrystalline anisotropy.

Following the concept of spin-injection into a semiconductor-based device, a ferromagnetic element (like a GMR multilayer structure) can be used as a spin filter. A high spin-polarization of the electrons can be realized by the preparation of a monocrystalline multilayer structure consisting of ultrathin films of a high magnetic polarization. In the case of ultrathin films, the manipulation of the easy-axis of magnetization is possible, by changing the anisotropy terms contributing to the effective anisotropy of the structure. We report on the structural and magnetic properties of Ni/Fe and Fe/Ni bilayers epitaxially grown on GaAs(0 0 1). By a proper choice of Fe and Ni sequences (Fe/Ni/GaAs) and their thickness (up to 3 ML of Fe on the top of Ni), the rotation of magnetization from the in-plane to the out-of-plane direction was achieved.