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Papers by I. Pasuk

New magnetic composite materials, ribbon samples, with nominal compositions FexCu1-x (x = 0.2; 0.... more New magnetic composite materials, ribbon samples, with nominal compositions FexCu1-x (x = 0.2; 0.5; 0.8) were obtained by the melt spinning technique. Various information was provided via X-ray diffraction, Mössbauer and magnetic measurements. The structural aspects: phase composition, size and texture effects, have been corroborated with magnetic properties. Finally, the possibility to choose the adequate composition and the suitable processing in order to obtain desired anisotropic magnetic materials were presented.

Epitaxy, 2018

In the context of miniaturization of devices, ferroelectric materials are used as multifunctional... more In the context of miniaturization of devices, ferroelectric materials are used as multifunctional materials for their well-known intrinsic properties, especially for the switching of polarization in an applied electric field. The high-quality epitaxial thin film structures are used for the possibility to study different effects as low dimensions, interface, strain and strain gradients on ferroelectric materials and other electric characteristics, also representing a possibility to obtain new phenomena and properties that can be used for development of new devices with different functionalities. This chapter is a summary of the ferroelectric and dielectric behaviour of epitaxial thin films of Pb(Zr,Ti)O 3 (PZT) and BaTiO 3 (BTO) obtained by pulsed laser deposition and the correlation with structural quality of the layers and with different electrostatic conditions induced either by electrodes or by the different interlayers. For this purpose in the first part, studies regarding the influence of the substrates and of different top electrodes are performed for Pb(Zr,Ti) O 3 (PZT) 52/48. In the second part, we focused on artificial multiferroic structures from alternating layers of PZT 20/80 or BaTiO 3 (BTO) as ferroelectric phase and CoFe 2 O 4 (CFO) as magnetic material. We found that interface configuration and strain engineering could control ferroelectric hysteresis, the capacitance or the leakage current magnitude.

Superconductor Science and Technology, 2021

Almost all proposed configurations and practical achievements based on superconductor/ferromagnet... more Almost all proposed configurations and practical achievements based on superconductor/ferromagnet (S/F) heterostrucutres focus on s-wave superconductors. However, several attempts targeted also high temperature superconductors, most of them using manganite ferromagnets LaXMnO3 (X: Ca or Sr) and Y1Ba2Cu3O7−x (YBCO). Here we propose a new ferromagnetic material that can be used with YBCO for the fabrication of S/F hybrid structures. We show that a ferromagnetic order can be induced in a thin layer (∼130 nm thickness) of CaRuO3 grown by pulsed laser deposition on epitaxial YBCO film. Detailed magnetic and structural investigations show that the observations of the weak ferromagnetism are consistent with the magnetic order induced by in-plane tensile strain of about 1.7% and the easy-magnetization axis forms an angle of ∼180º with the layer plane. The value of the Curie temperature T Curie estimated using the Curie–Weiss law was 340 K. An unusual temperature dependence of the magnetic moment around the superconducting transition was observed in both field-cooled and zero-field-cooled configurations which is attributed to the paramagnetic Meissner effect.

Scientific Reports, 2020

Bulk discs (20 mm diameter and 4.3 mm thickness) of MgB2 added with Ge2C6H10O7 were obtained by S... more Bulk discs (20 mm diameter and 4.3 mm thickness) of MgB2 added with Ge2C6H10O7 were obtained by Spark Plasma Sintering. Six samples with composition MgB2(Ge2C6H10O7)0.0014 and one undoped sample were fabricated under similar conditions and were magnetically characterized in order to determine the scattering of properties and reproducibility. The main source of the scattering of the properties is the decomposition of the additive due to elimination of the organic part in gas form, which occurs stepwise with intensive vacuum drops at around ~ 560 and ~ 740 °C. A third drop, which is sometimes not well resolved being part of the second peak at 740 °C, occurs at ~ 820 °C. The critical temperature at the midpoint of the transition, Tc, shows only a relatively small variation between 37.4 and 38 K, and the irreversibility field at a low temperature of 5 K takes values between 8 and 10 T. The pinning force and pinning force related parameters do not correlate with the carbon substituting f...

Journal of Materials Research and Technology, 2020

Please cite this article in press as: Batalu D, et al. Enhanced critical current density at high ... more Please cite this article in press as: Batalu D, et al. Enhanced critical current density at high magnetic fields in MgB 2 with Ga/In acetylacetonate processed by spark plasma sintering.

Journal of Thermal Analysis and Calorimetry, 2019

Fe–14Cr–3 W–0.4Ti–0.25Y2O3 ferritic steels were produced by ball milling of initial mixture of el... more Fe–14Cr–3 W–0.4Ti–0.25Y2O3 ferritic steels were produced by ball milling of initial mixture of elemental powders with various amounts of process control agent (PCA), ethanol (0.25 mass%, 2.5 mass%, 4 mass% and 20 mass%) under an Ar atmosphere and spark plasma sintering (SPS) consolidation at 1070 °C. The influence of the quantity of PCA on the properties (microstructure, density and Vickers hardness) of the as-milled powders and of the consolidated steels was investigated. X-ray diffraction shows a bcc–α-phase with fine crystallite size, 6.7–11 nm, for all powders. The particle size and the lattice constant of α-ferrite of the as-milled powders decrease as the amount of PCA increases. The powder milled with the highest amount of PCA, 20 mass%, contains carbides (M3C) and oxides ((Fe,Cr)2O3). The thermal analysis shows that as the amount of PCA increases, (1) the Curie temperature, Tc, increases, (2) the temperature of α → γ transition, Tα→γ, decreases, (3) the mass loss with CO/CO2 degassing increases, and (4) the milling with PCA hinders the nitrogen incorporation from milling media and air. The density and Vickers hardness of the SPS-consolidated and post-SPS annealed steels show an increasing trend with the increase in the amount of PCA. Carbides and oxides were detected in the post-SPS annealed steels derived from the powders milled with 2.5 mass% PCA and 4 mass% PCA (M23C6 and (Fe,Cr)2O3), and 20 mass% PCA (M3C and (Fe,Cr)2O3). The obtained results were discussed in terms of: (1) dissolution into the alloy matrix of carbon and oxygen released after the disintegration of PCA, (2) carbides and oxides precipitation during milling and/or upon heating and (3) promotion of thermally activated processes (such as carbothermal reaction) upon heating which can develop as well at the contact points/particle surfaces during SPS consolidation and can influence the process of densification.

Materials Chemistry and Physics, 2016

Abstract High density (above 92%) superconducting bulks of MgB 2 co-added with cubic BN (c-BN) an... more Abstract High density (above 92%) superconducting bulks of MgB 2 co-added with cubic BN (c-BN) and fullerenes (C 60 ) were obtained by the ex-situ spark plasma sintering (SPS). Compositions were (MgB 2 ) (1−x) (C) x (c-BN) 0.01 , x = 0.0125, 0.025, 0.05, 0.075. The co-added sample (MgB 2 ) 0.975 (C) 0.025 (c-BN) 0.01 shows a marginally higher critical current density J c at intermediate magnetic fields and below 15 K than for optimum samples added with c-BN or C 60 . For this sample, pinning is in the point pinning limit and the δ T c mechanism is dominant. At high magnetic fields co-added samples are inferior to samples added with one additive, but are superior to pristine sample. Co-addition of c-BN and C 60 is not effective for vortex pinning when compared with individual addition. The result is discussed based on phase formation aspects, microstructural details and residual strain. It was found that in the presence of C 60 , c-BN consumption with formation of MgNB 9 is intensified with implications on different elements that influence pinning.

Current Applied Physics, 2015

Superconductivity, 2019

Dense samples with starting composition (MgB2)0.99(Tex(HoO1.5)y)0.01, x/y = 0/0, 0.73/027, 0.57/0... more Dense samples with starting composition (MgB2)0.99(Tex(HoO1.5)y)0.01, x/y = 0/0, 0.73/027, 0.57/043, 0.4/0.6, 0.31/0.69, and 0.25/0.75 were processed by spark plasma sintering. Material is a bi-composite with a systematic microstructural change between “clean” and “dirty” MgB2 regions. The maximum self-field critical current density Jc0 and volume pinning force Fp, max are obtained for x/y = 0.4/0.66 = 0.67 where “clean” regions separate as isolated islands in a “dirty” matrix. The maximum value of Fp, max is high (9.2 GN/m3 at 5 K and 4.4 GN/m3 at 20 K). In the samples with x/y > 0.67 variation of the pinning-force-related parameters is small, while a decreasing x/y < 0.67 promotes a strong variation towards grain boundary pinning. In the curves of the pinning force vs. magnetic field, a shoulder occurs for a decreasing x/y (x/y < 0.67). Two pinning-behavior regimes can be defined, namely, below and above ∼25 K. When x/y decreases, variation of the midpoint critical temper...

Physical Review Materials

We explore the cross coupling between the ferroelectric and ferromagnetic phases in Ni/BaTiO 3 (0... more We explore the cross coupling between the ferroelectric and ferromagnetic phases in Ni/BaTiO 3 (001) heterostructures and demonstrate the modulation of the magnetism and incidence of exchange bias in the ultrathin metallic Ni overlayer, depending on the ferroelectric state of the bottom layer. We establish that 5-nm-thick monocrystalline Ni film deposited on BaTiO 3 with ferroelectric polarization pointing towards the surface (P+) favors the organization of Ni into uniform ferromagnetic domains. Ni grown on BaTiO 3 with opposite ferroelectric polarization is featured by emerging exchange-bias coupling between the ferromagnetic Ni top layers and the antiferromagnetic reacted interface, as theoretically explained by first-principles calculations. We explicitly obtain the morphology of the magnetic domains of the crystalline Ni layer in atomic and magnetic force microscopy measurements (AFM/MFM). The resemblance of AFM and MFM images indicate that, although with radically different morphologies, in both cases all spins orient in the Ni plane. Consequently, the distinct signature of the ferroelectric-ferromagnetic coupling extracted from the magneto-optical Kerr effect measurements encodes all the information of sample magnetism. The peculiar magnetic coupling depending on the ferroelectric state indicates new ways of engineering the functionality of metal/ferroelectric interfaces.

Scientific Reports

Mixtures of B4C, α-AlB12 and B powders were reactively spark plasma sintered at 1800 °C. Crystall... more Mixtures of B4C, α-AlB12 and B powders were reactively spark plasma sintered at 1800 °C. Crystalline and amorphous boron powders were used. Samples were tested for their impact behavior by the Split Hopkinson Pressure Bar method. When the ratio R = B4C/α-AlB12 ≥ 1.3 for a constant B-amount, the major phase in the samples was the orthorhombic AlB24C4, and when R

Journal of Superconductivity and Novel Magnetism

Short powder-in-tube tapes of MgB2 in the Fe sheath were fabricated by ex situ route from a comme... more Short powder-in-tube tapes of MgB2 in the Fe sheath were fabricated by ex situ route from a commercial powder containing some free Mg and MgO impurity phases. The final heat treatment was performed by spark plasma sintering (SPS). Tapes were with open (OT) or closed (CT) endings. Closed endings were made by folding and pressing. The MgB2 core of the OT sample has shown a higher low-field critical current density, a higher maximum pinning force, a slightly higher disorder, smaller average MgB2 crystallite size, a weak contact between Fe and MgB2 core, and more macro-flux jumps. The upper and irreversibility fields were similar for OT and CT samples. In the center of the MgB2 cores, the detected impurity phase is MgO, while at the interface with Fe, MgB4 also occurs. Impurity phases found at interface, MgO and MgB4, are present in the center of the bulk SPSed samples. Reactions and pinning-force-related parameters are discussed with respect to Mg behavior influenced by condition of endings. It is inferred that the presence of free Mg in the raw MgB2 powder has an important contribution to observed differences, and its removal or control is recommended.

Journal of Alloys and Compounds

Abstract Temperature dependent interfacial coupling mechanisms in SRO/BFO/Fe layered structures w... more Abstract Temperature dependent interfacial coupling mechanisms in SRO/BFO/Fe layered structures were investigated. The BFO/Fe heterostructures were prepared by PLD and sputtering, respectively, on the STO(0 0 1) substrate with a 20 nm SRO buffer layer. An annealing treatment in external magnetic field was further applied. Complex characterizations with X-ray diffraction, atomic force microscopy, Transmission Electron Microscopy, Mossbauer spectroscopy, magneto-optic Kerr effect and SQUID magnetometry were performed. Before annealing, the films show good crystallization and epitaxy of the SRO and BFO layers with smooth interfaces. Two coupling mechanisms of the ferromagnetic layers (top Fe and bottom SRO, respectively) to the epitaxial BFO film with mainly antiferromagnetic structure were evidenced in the as deposited samples at low temperatures. Negative exchange bias fields of up to 67(10) Oe and 37(5) Oe at low temperatures were observed for the two ferromagnetic components, respectively, depending on the thickness of the Fe layer. The field annealing treatments induce a specific morphology and magnetic spin structure at both interfaces of the BFO spacer layer, giving rise to a long range magnetostatic coupling between the two ferromagnetic films, in addition to the interfacial couplings. Moreover, the experimentally evidenced Fe clusters penetrating the BFO/Fe interface toward the BFO layer give support for this interaction. As an additional consequence, a considerable enhancement of both uniaxial and unidirectional anisotropies as well as an increased blocking temperature of exchange bias were obtained. The involved exchange coupling mechanisms were discussed in detail.

Journal of Alloys and Compounds

Abstract The effect of 1 and 2 mol % V addition on sintering conditions, structural and functiona... more Abstract The effect of 1 and 2 mol % V addition on sintering conditions, structural and functional properties of Nb Li co-doped PZT ceramics, prepared by conventional ceramic method, was systematically studied, by different experimental techniques. The reported results show that the increasing amount of vanadium, as a substitute for niobium, decreases the optimal sintering temperature with 100–150 °C, but slightly reduces the piezoelectric, ferroelectric, and electromechanical properties of these ceramics. In addition, the presence of vanadium increases the lattice tetragonality and grain size, promoting a harder piezoelectric behaviour, mostly in the absence of niobium. EPR spectra exhibit well-defined hyperfine splitting characteristics for V4+ state, dispersed in the lattice as VO2+ ion. Additionally, complex paramagnetic defects (charged oxygen vacancies and associated defects) are evidenced for 2 mol % vanadium addition. The results were explained by assuming that vanadium promotes the B-site Li substitution, compensated by oxygen vacancies, while niobium facilitates the A-site Li substitution with lead vacancies formation and partial reduction of V5+ to V4+. Thus, indirect information about lithium location is provided.

Materials Research Bulletin

Abstract Epitaxial Pb(Zr 0.2 Ti 0.8 )O 3 (PZT) thin films were grown by pulsed laser deposition o... more Abstract Epitaxial Pb(Zr 0.2 Ti 0.8 )O 3 (PZT) thin films were grown by pulsed laser deposition on two slightly different types of single crystal substrates, namely SrTiO 3 (STO) buffered with a thin layer of conductive SrRuO 3 (SRO) , and SrTiO 3 doped with 0.5% Nb (STON). Although self-poling effect was expected in both cases, due to the compressive strain imposed by the substrate, it was found that the pyroelectric response of as-grown samples is with about two orders of magnitude larger for the PZT film deposited on SRO/STO compared to the one deposited on STON substrate. In order to explain the finding, the electrical properties were investigated and it was found that the quantities involved in the equation giving the magnitude of the pyroelectric signal, namely dielectric constant and electrical resistivity, have about the same values Therefore, the different pyroelectric response in the as-grown samples was explained by different structure of ferroelectric domains induced by the different carrier concentration in the two substrates: 90° domains for PZT on SRO/STO and 180° domains for PZT on STON. It appears that the resistivity of the substrate and its ability to compensate the depolarization field affect the domain structure, with impact on the pyroelectric response, although the strain conditions are similar in both cases. The trying to increase the pyroelectric response for the PZT film deposited on STON substrate by applying a poling process was not successful, as the 180° domain structure restores shortly after removing the poling field.

CAS 2013 (International Semiconductor Conference), 2013

ABSTRACT This paper reports on the experimental realization and characterization of a wireless se... more ABSTRACT This paper reports on the experimental realization and characterization of a wireless sensing system for machine-tool condition based monitoring. The system comprises a vibration sensor, an ARDUINO Leonardo development board and an RM 42 Blue tooth module. The sensing principle is based on a vibration sensor which includes a piezoelectric AlN layer deposited by sputtering on a flexible stainless steel foil. The functional testing of the sensor using a test stand for asynchronous engines equipped with frequency convertors is demonstrated.

Journal of the European Ceramic Society, 2014

Cotton/polyester woven fabrics were functionalized with ZnO thin films or nanoparticles by pulsed... more Cotton/polyester woven fabrics were functionalized with ZnO thin films or nanoparticles by pulsed laser deposition, using a KrF* excimer laser source. Depending on the number of applied laser pulses, well-separated nanoparticles (for 10 pulses) or compact thin films (for 100 pulses) were deposited. The synthesized nanostructures were evaluated morphologically by scanning electron microscopy and atomic force microscopy, physico-chemically by x-ray

Superconductor Science and Technology

High density bulks (97%–99%) of MgB2 were prepared by spark plasma sintering (SPS) in nitrogen (N... more High density bulks (97%–99%) of MgB2 were prepared by spark plasma sintering (SPS) in nitrogen (N2) atmosphere for different heating rates (10, 20 and 100 °C min−1) and compared with reference samples processed in vacuum and Ar. N2 reacts with MgB2 and forms MgB9N along the MgB2 grain boundaries. The high-field critical current density is enhanced for the sample processed in N2 with a heating rate of 100 °C min−1. At 2–35 K, this sample shows the strongest contribution of the grain boundary pinning (GBP). All samples are in the point pinning (PP) limit and by increasing temperature the GBP contribution decreases.

New magnetic composite materials, ribbon samples, with nominal compositions FexCu1-x (x = 0.2; 0.... more New magnetic composite materials, ribbon samples, with nominal compositions FexCu1-x (x = 0.2; 0.5; 0.8) were obtained by the melt spinning technique. Various information was provided via X-ray diffraction, Mössbauer and magnetic measurements. The structural aspects: phase composition, size and texture effects, have been corroborated with magnetic properties. Finally, the possibility to choose the adequate composition and the suitable processing in order to obtain desired anisotropic magnetic materials were presented.

Epitaxy, 2018

In the context of miniaturization of devices, ferroelectric materials are used as multifunctional... more In the context of miniaturization of devices, ferroelectric materials are used as multifunctional materials for their well-known intrinsic properties, especially for the switching of polarization in an applied electric field. The high-quality epitaxial thin film structures are used for the possibility to study different effects as low dimensions, interface, strain and strain gradients on ferroelectric materials and other electric characteristics, also representing a possibility to obtain new phenomena and properties that can be used for development of new devices with different functionalities. This chapter is a summary of the ferroelectric and dielectric behaviour of epitaxial thin films of Pb(Zr,Ti)O 3 (PZT) and BaTiO 3 (BTO) obtained by pulsed laser deposition and the correlation with structural quality of the layers and with different electrostatic conditions induced either by electrodes or by the different interlayers. For this purpose in the first part, studies regarding the influence of the substrates and of different top electrodes are performed for Pb(Zr,Ti) O 3 (PZT) 52/48. In the second part, we focused on artificial multiferroic structures from alternating layers of PZT 20/80 or BaTiO 3 (BTO) as ferroelectric phase and CoFe 2 O 4 (CFO) as magnetic material. We found that interface configuration and strain engineering could control ferroelectric hysteresis, the capacitance or the leakage current magnitude.

Superconductor Science and Technology, 2021

Almost all proposed configurations and practical achievements based on superconductor/ferromagnet... more Almost all proposed configurations and practical achievements based on superconductor/ferromagnet (S/F) heterostrucutres focus on s-wave superconductors. However, several attempts targeted also high temperature superconductors, most of them using manganite ferromagnets LaXMnO3 (X: Ca or Sr) and Y1Ba2Cu3O7−x (YBCO). Here we propose a new ferromagnetic material that can be used with YBCO for the fabrication of S/F hybrid structures. We show that a ferromagnetic order can be induced in a thin layer (∼130 nm thickness) of CaRuO3 grown by pulsed laser deposition on epitaxial YBCO film. Detailed magnetic and structural investigations show that the observations of the weak ferromagnetism are consistent with the magnetic order induced by in-plane tensile strain of about 1.7% and the easy-magnetization axis forms an angle of ∼180º with the layer plane. The value of the Curie temperature T Curie estimated using the Curie–Weiss law was 340 K. An unusual temperature dependence of the magnetic moment around the superconducting transition was observed in both field-cooled and zero-field-cooled configurations which is attributed to the paramagnetic Meissner effect.

Scientific Reports, 2020

Bulk discs (20 mm diameter and 4.3 mm thickness) of MgB2 added with Ge2C6H10O7 were obtained by S... more Bulk discs (20 mm diameter and 4.3 mm thickness) of MgB2 added with Ge2C6H10O7 were obtained by Spark Plasma Sintering. Six samples with composition MgB2(Ge2C6H10O7)0.0014 and one undoped sample were fabricated under similar conditions and were magnetically characterized in order to determine the scattering of properties and reproducibility. The main source of the scattering of the properties is the decomposition of the additive due to elimination of the organic part in gas form, which occurs stepwise with intensive vacuum drops at around ~ 560 and ~ 740 °C. A third drop, which is sometimes not well resolved being part of the second peak at 740 °C, occurs at ~ 820 °C. The critical temperature at the midpoint of the transition, Tc, shows only a relatively small variation between 37.4 and 38 K, and the irreversibility field at a low temperature of 5 K takes values between 8 and 10 T. The pinning force and pinning force related parameters do not correlate with the carbon substituting f...

Journal of Materials Research and Technology, 2020

Please cite this article in press as: Batalu D, et al. Enhanced critical current density at high ... more Please cite this article in press as: Batalu D, et al. Enhanced critical current density at high magnetic fields in MgB 2 with Ga/In acetylacetonate processed by spark plasma sintering.

Journal of Thermal Analysis and Calorimetry, 2019

Fe–14Cr–3 W–0.4Ti–0.25Y2O3 ferritic steels were produced by ball milling of initial mixture of el... more Fe–14Cr–3 W–0.4Ti–0.25Y2O3 ferritic steels were produced by ball milling of initial mixture of elemental powders with various amounts of process control agent (PCA), ethanol (0.25 mass%, 2.5 mass%, 4 mass% and 20 mass%) under an Ar atmosphere and spark plasma sintering (SPS) consolidation at 1070 °C. The influence of the quantity of PCA on the properties (microstructure, density and Vickers hardness) of the as-milled powders and of the consolidated steels was investigated. X-ray diffraction shows a bcc–α-phase with fine crystallite size, 6.7–11 nm, for all powders. The particle size and the lattice constant of α-ferrite of the as-milled powders decrease as the amount of PCA increases. The powder milled with the highest amount of PCA, 20 mass%, contains carbides (M3C) and oxides ((Fe,Cr)2O3). The thermal analysis shows that as the amount of PCA increases, (1) the Curie temperature, Tc, increases, (2) the temperature of α → γ transition, Tα→γ, decreases, (3) the mass loss with CO/CO2 degassing increases, and (4) the milling with PCA hinders the nitrogen incorporation from milling media and air. The density and Vickers hardness of the SPS-consolidated and post-SPS annealed steels show an increasing trend with the increase in the amount of PCA. Carbides and oxides were detected in the post-SPS annealed steels derived from the powders milled with 2.5 mass% PCA and 4 mass% PCA (M23C6 and (Fe,Cr)2O3), and 20 mass% PCA (M3C and (Fe,Cr)2O3). The obtained results were discussed in terms of: (1) dissolution into the alloy matrix of carbon and oxygen released after the disintegration of PCA, (2) carbides and oxides precipitation during milling and/or upon heating and (3) promotion of thermally activated processes (such as carbothermal reaction) upon heating which can develop as well at the contact points/particle surfaces during SPS consolidation and can influence the process of densification.

Materials Chemistry and Physics, 2016

Abstract High density (above 92%) superconducting bulks of MgB 2 co-added with cubic BN (c-BN) an... more Abstract High density (above 92%) superconducting bulks of MgB 2 co-added with cubic BN (c-BN) and fullerenes (C 60 ) were obtained by the ex-situ spark plasma sintering (SPS). Compositions were (MgB 2 ) (1−x) (C) x (c-BN) 0.01 , x = 0.0125, 0.025, 0.05, 0.075. The co-added sample (MgB 2 ) 0.975 (C) 0.025 (c-BN) 0.01 shows a marginally higher critical current density J c at intermediate magnetic fields and below 15 K than for optimum samples added with c-BN or C 60 . For this sample, pinning is in the point pinning limit and the δ T c mechanism is dominant. At high magnetic fields co-added samples are inferior to samples added with one additive, but are superior to pristine sample. Co-addition of c-BN and C 60 is not effective for vortex pinning when compared with individual addition. The result is discussed based on phase formation aspects, microstructural details and residual strain. It was found that in the presence of C 60 , c-BN consumption with formation of MgNB 9 is intensified with implications on different elements that influence pinning.

Current Applied Physics, 2015

Superconductivity, 2019

Dense samples with starting composition (MgB2)0.99(Tex(HoO1.5)y)0.01, x/y = 0/0, 0.73/027, 0.57/0... more Dense samples with starting composition (MgB2)0.99(Tex(HoO1.5)y)0.01, x/y = 0/0, 0.73/027, 0.57/043, 0.4/0.6, 0.31/0.69, and 0.25/0.75 were processed by spark plasma sintering. Material is a bi-composite with a systematic microstructural change between “clean” and “dirty” MgB2 regions. The maximum self-field critical current density Jc0 and volume pinning force Fp, max are obtained for x/y = 0.4/0.66 = 0.67 where “clean” regions separate as isolated islands in a “dirty” matrix. The maximum value of Fp, max is high (9.2 GN/m3 at 5 K and 4.4 GN/m3 at 20 K). In the samples with x/y > 0.67 variation of the pinning-force-related parameters is small, while a decreasing x/y < 0.67 promotes a strong variation towards grain boundary pinning. In the curves of the pinning force vs. magnetic field, a shoulder occurs for a decreasing x/y (x/y < 0.67). Two pinning-behavior regimes can be defined, namely, below and above ∼25 K. When x/y decreases, variation of the midpoint critical temper...

Physical Review Materials

We explore the cross coupling between the ferroelectric and ferromagnetic phases in Ni/BaTiO 3 (0... more We explore the cross coupling between the ferroelectric and ferromagnetic phases in Ni/BaTiO 3 (001) heterostructures and demonstrate the modulation of the magnetism and incidence of exchange bias in the ultrathin metallic Ni overlayer, depending on the ferroelectric state of the bottom layer. We establish that 5-nm-thick monocrystalline Ni film deposited on BaTiO 3 with ferroelectric polarization pointing towards the surface (P+) favors the organization of Ni into uniform ferromagnetic domains. Ni grown on BaTiO 3 with opposite ferroelectric polarization is featured by emerging exchange-bias coupling between the ferromagnetic Ni top layers and the antiferromagnetic reacted interface, as theoretically explained by first-principles calculations. We explicitly obtain the morphology of the magnetic domains of the crystalline Ni layer in atomic and magnetic force microscopy measurements (AFM/MFM). The resemblance of AFM and MFM images indicate that, although with radically different morphologies, in both cases all spins orient in the Ni plane. Consequently, the distinct signature of the ferroelectric-ferromagnetic coupling extracted from the magneto-optical Kerr effect measurements encodes all the information of sample magnetism. The peculiar magnetic coupling depending on the ferroelectric state indicates new ways of engineering the functionality of metal/ferroelectric interfaces.

Scientific Reports

Mixtures of B4C, α-AlB12 and B powders were reactively spark plasma sintered at 1800 °C. Crystall... more Mixtures of B4C, α-AlB12 and B powders were reactively spark plasma sintered at 1800 °C. Crystalline and amorphous boron powders were used. Samples were tested for their impact behavior by the Split Hopkinson Pressure Bar method. When the ratio R = B4C/α-AlB12 ≥ 1.3 for a constant B-amount, the major phase in the samples was the orthorhombic AlB24C4, and when R

Journal of Superconductivity and Novel Magnetism

Short powder-in-tube tapes of MgB2 in the Fe sheath were fabricated by ex situ route from a comme... more Short powder-in-tube tapes of MgB2 in the Fe sheath were fabricated by ex situ route from a commercial powder containing some free Mg and MgO impurity phases. The final heat treatment was performed by spark plasma sintering (SPS). Tapes were with open (OT) or closed (CT) endings. Closed endings were made by folding and pressing. The MgB2 core of the OT sample has shown a higher low-field critical current density, a higher maximum pinning force, a slightly higher disorder, smaller average MgB2 crystallite size, a weak contact between Fe and MgB2 core, and more macro-flux jumps. The upper and irreversibility fields were similar for OT and CT samples. In the center of the MgB2 cores, the detected impurity phase is MgO, while at the interface with Fe, MgB4 also occurs. Impurity phases found at interface, MgO and MgB4, are present in the center of the bulk SPSed samples. Reactions and pinning-force-related parameters are discussed with respect to Mg behavior influenced by condition of endings. It is inferred that the presence of free Mg in the raw MgB2 powder has an important contribution to observed differences, and its removal or control is recommended.

Journal of Alloys and Compounds

Abstract Temperature dependent interfacial coupling mechanisms in SRO/BFO/Fe layered structures w... more Abstract Temperature dependent interfacial coupling mechanisms in SRO/BFO/Fe layered structures were investigated. The BFO/Fe heterostructures were prepared by PLD and sputtering, respectively, on the STO(0 0 1) substrate with a 20 nm SRO buffer layer. An annealing treatment in external magnetic field was further applied. Complex characterizations with X-ray diffraction, atomic force microscopy, Transmission Electron Microscopy, Mossbauer spectroscopy, magneto-optic Kerr effect and SQUID magnetometry were performed. Before annealing, the films show good crystallization and epitaxy of the SRO and BFO layers with smooth interfaces. Two coupling mechanisms of the ferromagnetic layers (top Fe and bottom SRO, respectively) to the epitaxial BFO film with mainly antiferromagnetic structure were evidenced in the as deposited samples at low temperatures. Negative exchange bias fields of up to 67(10) Oe and 37(5) Oe at low temperatures were observed for the two ferromagnetic components, respectively, depending on the thickness of the Fe layer. The field annealing treatments induce a specific morphology and magnetic spin structure at both interfaces of the BFO spacer layer, giving rise to a long range magnetostatic coupling between the two ferromagnetic films, in addition to the interfacial couplings. Moreover, the experimentally evidenced Fe clusters penetrating the BFO/Fe interface toward the BFO layer give support for this interaction. As an additional consequence, a considerable enhancement of both uniaxial and unidirectional anisotropies as well as an increased blocking temperature of exchange bias were obtained. The involved exchange coupling mechanisms were discussed in detail.

Journal of Alloys and Compounds

Abstract The effect of 1 and 2 mol % V addition on sintering conditions, structural and functiona... more Abstract The effect of 1 and 2 mol % V addition on sintering conditions, structural and functional properties of Nb Li co-doped PZT ceramics, prepared by conventional ceramic method, was systematically studied, by different experimental techniques. The reported results show that the increasing amount of vanadium, as a substitute for niobium, decreases the optimal sintering temperature with 100–150 °C, but slightly reduces the piezoelectric, ferroelectric, and electromechanical properties of these ceramics. In addition, the presence of vanadium increases the lattice tetragonality and grain size, promoting a harder piezoelectric behaviour, mostly in the absence of niobium. EPR spectra exhibit well-defined hyperfine splitting characteristics for V4+ state, dispersed in the lattice as VO2+ ion. Additionally, complex paramagnetic defects (charged oxygen vacancies and associated defects) are evidenced for 2 mol % vanadium addition. The results were explained by assuming that vanadium promotes the B-site Li substitution, compensated by oxygen vacancies, while niobium facilitates the A-site Li substitution with lead vacancies formation and partial reduction of V5+ to V4+. Thus, indirect information about lithium location is provided.

Materials Research Bulletin

Abstract Epitaxial Pb(Zr 0.2 Ti 0.8 )O 3 (PZT) thin films were grown by pulsed laser deposition o... more Abstract Epitaxial Pb(Zr 0.2 Ti 0.8 )O 3 (PZT) thin films were grown by pulsed laser deposition on two slightly different types of single crystal substrates, namely SrTiO 3 (STO) buffered with a thin layer of conductive SrRuO 3 (SRO) , and SrTiO 3 doped with 0.5% Nb (STON). Although self-poling effect was expected in both cases, due to the compressive strain imposed by the substrate, it was found that the pyroelectric response of as-grown samples is with about two orders of magnitude larger for the PZT film deposited on SRO/STO compared to the one deposited on STON substrate. In order to explain the finding, the electrical properties were investigated and it was found that the quantities involved in the equation giving the magnitude of the pyroelectric signal, namely dielectric constant and electrical resistivity, have about the same values Therefore, the different pyroelectric response in the as-grown samples was explained by different structure of ferroelectric domains induced by the different carrier concentration in the two substrates: 90° domains for PZT on SRO/STO and 180° domains for PZT on STON. It appears that the resistivity of the substrate and its ability to compensate the depolarization field affect the domain structure, with impact on the pyroelectric response, although the strain conditions are similar in both cases. The trying to increase the pyroelectric response for the PZT film deposited on STON substrate by applying a poling process was not successful, as the 180° domain structure restores shortly after removing the poling field.

CAS 2013 (International Semiconductor Conference), 2013

ABSTRACT This paper reports on the experimental realization and characterization of a wireless se... more ABSTRACT This paper reports on the experimental realization and characterization of a wireless sensing system for machine-tool condition based monitoring. The system comprises a vibration sensor, an ARDUINO Leonardo development board and an RM 42 Blue tooth module. The sensing principle is based on a vibration sensor which includes a piezoelectric AlN layer deposited by sputtering on a flexible stainless steel foil. The functional testing of the sensor using a test stand for asynchronous engines equipped with frequency convertors is demonstrated.

Journal of the European Ceramic Society, 2014

Cotton/polyester woven fabrics were functionalized with ZnO thin films or nanoparticles by pulsed... more Cotton/polyester woven fabrics were functionalized with ZnO thin films or nanoparticles by pulsed laser deposition, using a KrF* excimer laser source. Depending on the number of applied laser pulses, well-separated nanoparticles (for 10 pulses) or compact thin films (for 100 pulses) were deposited. The synthesized nanostructures were evaluated morphologically by scanning electron microscopy and atomic force microscopy, physico-chemically by x-ray

Superconductor Science and Technology

High density bulks (97%–99%) of MgB2 were prepared by spark plasma sintering (SPS) in nitrogen (N... more High density bulks (97%–99%) of MgB2 were prepared by spark plasma sintering (SPS) in nitrogen (N2) atmosphere for different heating rates (10, 20 and 100 °C min−1) and compared with reference samples processed in vacuum and Ar. N2 reacts with MgB2 and forms MgB9N along the MgB2 grain boundaries. The high-field critical current density is enhanced for the sample processed in N2 with a heating rate of 100 °C min−1. At 2–35 K, this sample shows the strongest contribution of the grain boundary pinning (GBP). All samples are in the point pinning (PP) limit and by increasing temperature the GBP contribution decreases.