Mirosław Werwiński

Mirosław Werwiński
Institute of Molecular Physics, Polish Academy of Sciences

PhD

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68
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Publications

Publications (68)
Article
(Fe,Co)2B-based compounds with specific 5d substitutions are considered as promising materials for permanent magnets without rare-earth elements. We conducted a combined first-principles and experimental study focused on (Fe0.7Co0.3)2B alloys doped with W and Re. First, we used full-potential local-orbital scheme to systematically investigate (Fe,C...
Article
Ostwald ripening is a well‐known physicochemical phenomenon in which smaller particles, characterized by high surface energy, dissolve and feed the bigger ones that are thermodynamically more stable. The effect is commonly observed in solid and liquid solutions, as well as in systems consisting of supported metal clusters or liquid droplets. Here,...
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Due to its strong magnetocrystalline anisotropy, FePt L1$\mathrm{_0}$ phase is considered as a promising magnetic recording media material. Although the magnetic properties of this phase have already been analyzed many times using density functional theory (DFT), we decided to study it again, emphasizing on full potential methods, including spin-po...
Article
Due to its strong magnetocrystalline anisotropy, FePt L10 phase is considered as a promising magnetic recording media material. Although the magnetic properties of this phase have already been analyzed many times using density functional theory (DFT), we decided to study it again, emphasizing on full potential methods, including spin-polarized rela...
Article
Depending on their chemical composition, Yb compounds often exhibit different valence states. Here we investigate the valence state of YbFe4Al8 using X-ray photoelectron spectroscopy (XPS) and first-principles calculations. The XPS valence band of ybFe4Al8 consists of two contributions coming from divalent (Yb²⁺) and trivalent (Yb³⁺) configurations...
Article
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ThMn12-type ternary cerium alloys with tetragonal structure (Pearson symbol tI26, space group I4/mmm) are considered as promising materials for permanent magnets. In this work, compositions of CeFe11X (s.g. Pmmn, No. 59) and CeFe10X2 (s.g. P4/mmm, No. 123) with all 3d, 4d, and 5d transition metal substitutions are considered. Since many previous st...
Article
Previous studies have accurately determined the effect of transition metal point defects on the properties of bcc iron. The magnetic properties of transition metal monolayers on the iron surfaces have been studied equally intensively. In this work, we investigated the magnetic properties of the 3d, 4d, and 5d transition-metal (TM) atomic monolayers...
Article
The close-packed AB2 structures called Laves phases constitute the largest group of intermetallic compounds. In this paper we computationally investigated the pseudo-binary Laves phase system Y1−xGdx(Fe1−yCoy)2 spanning between the YFe2, YCo2, GdFe2, and GdCo2 vertices. While the vast majority of the Y1−xGdx(Fe1−yCoy)2 phase diagram is the ferrimag...
Preprint
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In this work, compositions of CeFe11X and CeFe10X2 with all 3d, 4d, and 5d transition metal substitutions are considered. Since many previous studies have focused on the CeFe11Ti compound, this particular case became the starting point of our considerations, and we gave it special attention. First, we determined the optimal symmetry of the simplest...
Preprint
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Previous studies have accurately determined the effect of transition metal point defects on the properties of bcc iron. The magnetic properties of transition metal monolayers on the iron surfaces have been studied equally intensively. In this work, we investigated the magnetic properties of the 3d, 4d, and 5d transition-metal (TM) atomic monolayers...
Preprint
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The close-packed AB$_2$ structures called Laves phases constitute the largest group of intermetallic compounds. In this paper we computationally investigated the pseudo-binary Laves phase system Y$_{1-x}$Gd$_x$(Fe$_{1-y}$Co$_y$)$_2$ spanning between the YFe$_2$, YCo$_2$, GdFe$_2$, and GdCo$_2$ vertices. While the vast majority of the Y$_{1-x}$Gd$_x...
Preprint
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Depending on their chemical composition, Yb compounds often exhibit different valence states. Here we investigate the valence state of YbFe$_4$Al$_8$ using X-ray photoelectron spectroscopy (XPS) and first-principles calculaions. The XPS valence band of YbFe$_4$Al$_8$ consists of two contributions coming from divalent (Yb$^{2+}$) and trivalent (Yb$^...
Preprint
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Oxides-on-metals are the well-known "inverse" catalysts. Fundamental knowledge on the structural transformations that occur in such systems under oxidizing and reducing conditions is crucial for maximizing their catalytic activity. Sintering of oxide species is one of the effects that may, on one hand, lead to catalyst deactivation, but on the othe...
Preprint
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(Fe,Co)$_2$B-based compounds with specified 5$d$ substitutions are considered as promising materials for permanent magnets without rare-earth elements. We conducted a combined first-principles and experimental study focused on (Fe$_{0.7}$Co$_{0.3}$)$_2$B alloys doped with W and Re. First, we used full-potential local-orbital scheme to systematicall...
Article
We present the results of our investigations of physical properties for the novel Ce1−xPrxCoGe3 system performed with a number of experimental methods: magnetic susceptibility, specific heat, electrical resistivity, magnetoresistance, and thermoelectric power. Moreover, the electronic structure was studied by means of photoelectron spectroscopy mea...
Preprint
We present the results of our studies of physical properties for the novel Ce$_{1-x}$Pr$_x$CoGe$_3$ system performed with a number of experimental methods: magnetic susceptibility, specific heat, electrical resistivity, magnetoresistance and thermoelectric power. All investigated materials of the Ce$_{1-x}$Pr$_x$CoGe$_3$ series crystallize in the t...
Article
We investigated experimentally and computationally the concentration dependence of the electronic specific heat coefficient γ in the Y(Fe1−xCox)2 pseudobinary Laves phase system. The experimentally observed maximum in γ(x) around the magnetic phase transition was interpreted within the local density approximation combined with the virtual crystal a...
Article
We present the results of our comprehensive structural investigation performed on single crystals of CePtIn4 grown from In flux in a platelet-like morphology. They were found to crystalize in an orthorhombic structure having space group Cmcm (no. 63) with the lattice parameters a = 4.52175 (15) Å, b = 16.7777 (5) Å, and c = 7.3903 (2) Å. The unit c...
Preprint
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We investigated experimentally and computationally the concentration dependence of electronic specific heat coefficient $\gamma$ in Y(Fe$_{1-x}$Co$_x$)$_2$ pseudobinary Laves phase system. The experimentally observed maximum in $\gamma$($x$) around the magnetic phase transition was interpreted within the local density approximation (LDA) combined w...
Article
A transformation between the magnetically ordered CeCoGe 3 and heavy fermion CeFeGe 3 is isostructural but not isoelectronic, therefore the characterization of the electronic structure of the CeCo 1−x Fe x Ge 3 series is of special importance. We report both the experimental investigation by the X-ray photoelectron spectroscopy (XPS) measurements a...
Article
The Fe5PB2 compound offers tunable magnetic properties via the possibility of various combinations of substitutions on the Fe and P sites. Here, we present a combined computational and experimental study of the magnetic properties of (Fe1−xCox)5PB2. Computationally, we are able to explore the full concentration range, while the real samples were on...
Article
In this paper the changes of magnetic properties with increasing disorder in the exchange-enhanced Pauli paramagnet YCo2 are discussed. The structural disorder is initially introduced by rapid quenching, while further changes on a micro- or nanoscale are caused by a high-pressure torsion (HPT). Values of the magnetic moment determined for the plast...
Article
In this work we investigate the effect of Gd and Co substitutions on the electrochemical and electronic properties of La1.5Mg0.5Ni7 alloy. Two series of La1.5−xGdxMg0.5Ni7 (x = 0.0, 0.25, 1.0) and La1.5Mg0.5Ni7−yCoy (y = 0.0, 0.5, 1.5) alloys are produced using mechanical alloying technique. The X-ray diffraction indicates multi-phase character of...
Preprint
Full-text available
The Fe$_5$PB$_2$ compound offers tunable magnetic properties via the possibility of various combinations of substitutions on the Fe and P-sites. Here, we present a combined computational and experimental study of the magnetic properties of (Fe$_{1-x}$Co$_{x}$)$_5$PB$_2$. The calculated magnetic moments, Curie temperatures, and magnetocrystalline an...
Article
La-Mg-Ni-based alloys are promising negative electrode materials for 3rd generation of Ni-MHx batteries. In this work we investigate the effect of Mg substitution on the electrochemical and electronic properties of La2-x MgxNi7 materials. The mechanical alloying technique is used to produce a series of La2-xMg xNi7 alloys (x = 0.00, 0.25, 0.50 and...
Article
Cubic Laves phases including YFe2, YCo2, ZrFe2, and ZrCo2 are considered as promising candidates for application in hydrogen storage and magnetic refrigeration. While YFe2 and ZrFe2 are ferromagnets, alloying with Co decreases magnetic moments and Curie temperatures (TC) of pseudobinary Y(Fe1-xCox )2 and Zr(Fe1-xCox )2 systems, leading to the param...
Article
The substitutional effects of cobalt in (Fe1-xCox)5PB2 have been studied with respect to crystalline structure and chemical order with X-ray diffraction and Mössbauer spectroscopy. The magnetic properties have been determined from magnetic measurements, and density functional theory calculations have been performed for the magnetic properties of bo...
Article
We present results of ab initio calculations of several L10 FeNi characteristics, such as the summary of the magnetocrystalline anisotropy energies (MAEs), the full potential calculations of the anisotropy constant K3, and the combined analysis of the Fermi surface and 3D k-resolved MAE. Other calculated parameters are the spin and orbital magnetic...
Article
The magnetic properties of the compound Fe5Si1−xPxB2 have been studied, with a focus on the Curie temperature TC, saturation magnetization MS, and magnetocrystalline anisotropy. Field and temperature dependent magnetization measurements were used to determine TCx and MSx. The saturation magnetization at 10 K (300 K) is found to monotonically decrea...
Article
The five crystal structures of selected UNixSb2 compositions are investigated by density functional theory supercell calculations. The considered phases are USb2, UNi0.33Sb2, UNi0.5Sb2, UNi0.66Sb2, and UNiSb2 (x = 0, 1/3, 1/2, 2/3, 1). The occupation deficiency of Ni is modeled by removing the Ni layers from constructed supercells followed by relax...
Article
The L1$_0$ FeNi phase is studied from first principles as a promising candidate for the rare-earth free permanent magnets applications. The geometry optimization leads to a tetragonal structure with lattice parameters 3.56 \AA{} and 3.58 \AA{}, $c$/$a$ ratio 1.0036, and bulk modulus B$_0$ 194 GPa. The magnetocrystalline anisotropy energies (MAE) ca...
Article
Full-text available
While the performance of magnetic tunnel junctions based on metal/oxide interfaces is determined by hybridization, charge transfer, and magnetic properties at the interface, there are currently only limited experimental techniques with sufficient spatial resolution to directly observe these effects simultaneously in real-space. In this letter, we d...
Article
Magnetic and magnetocaloric properties of Y1-xGdxCo2 compounds, where x = 0.2, 0.4, 0.6, 0.8 and 1.0, were investigated experimentally and theoretically. Crystal structures were characterized by X-ray diffraction (Rietveld analysis) and investigated samples possess the MgCu2-type single phase with Fd-3m space group. Melt-spinning process introduced...
Article
High-pressure induced structural transition from zircon-type phase into scheelite-type phase in YVO4 is studied using ab initio calculations. Several structures with compressed volumes are evaluated, where for every considered volume the c/a ratio and atomic positions are optimised. The transition pressure and transition volume change are calculate...
Article
The PdZr alloy thin films were prepared onto oxidised Si(100) substrates in the temperature range of 295 K up to 700 K using computer-controlled UHV magnetron co-sputtering. The chemical composition and the cleanness of all layers were checked in-situ, immediately after deposition, transferring the samples to an UHV (4 × 10− 11 mbar) analysis chamb...
Article
Fe$_5$SiB$_2$ has been synthesized and magnetic measurements have been carried out, revealing that M$_{\text{sat}}$ = 0.92 MA/m at T = 300 K. The M vs T curve shows a broad peak around T = 160 K. The anisotropy constant, K$_1$, estimated at T = 300 K, is 0.25 MJ/m$^3$. Theoretical analysis of Fe$_5$SiB$_2$ system has been carried out and extended t...
Article
We have explored, computationally and experimentally, the magnetic properties of (Fe1-xCox)2B alloys. Calculations provide a good agreement with experiment in terms of the saturation magnetization and the magnetocrystalline anisotropy energy with some difficulty in describing Co2B, for which it is found that both full potential effects and electron...
Article
In order to convert the well-known Fe-Co-B alloy from a soft to a hard magnet, we propose tetragonal strain by interstitial boron. Density functional theory reveals that when B atoms occupy octahedral interstitial sites, the bcc Fe-Co lattice is strained spontaneously. Such highly distorted Fe-Co is predicted to reach a strong magnetocrystalline an...
Article
Full-text available
In order to convert the well-known Fe-Co-B alloy from a soft to a hard magnet, we propose tetragonal strain by interstitial boron. Density functional theory reveals that when B atoms occupy octahedral interstitial sites, the bcc Fe-Co lattice is strained spontaneously. Such highly distorted Fe-Co is predicted to reach a strong magnetocrystalline an...
Article
A magnetization study of a La2Co7 single crystal has obtained the following anisotropy constants: K 1 = 1.4 MJ/m3 and K 2 = 0.02 MJ/m3 (at room temperature). The corresponding anisotropy field is 6.7 T; an earlier report of a much higher value (17 T) has not been confirmed. A significant (10%) magnetization anisotropy has been observed. Density-fun...
Article
The electronic structure of a heavy-fermion superconductor Ce2PdIn8 was investigated by means of X-ray photoelectron spectroscopy (XPS) and ab initio density functional band structure calculations. The Ce 3d core-level XPS spectra point to stable trivalent configuration of Ce atoms that is also reproduced in the band structure calculations within t...
Article
Full-text available
We have explored computationally and experimentally the magnetic properties of (Fe$_{1-x}$Co$_x$)$_2$B alloys. Calculations provide a good agreement with experiment in terms of the saturation magnetization and the magnetocrystalline anisotropy energy. The material exhibits an uniaxial magnetic anisotropy for a range of cobalt concentrations between...
Article
Full-text available
We show on the basis of electronic structure calculations that the uranium 5$f$ magnetic moment in URu$_2$Si$_2$ exhibits a unique Ising behavior, which surprisingly, arises from itinerant electronic states. The origin of the unusual Ising behavior is analyzed as due to the peculiar near-Fermi edge nested electronic structure of URu$_2$Si$_2$ invol...
Article
Intermetallic YCo2 compound is a Pauli exchange-enhanced paramagnet. Structural and magnetic properties melt-spun YCo2 pure and alloyed with Nb or Ti are presented. The samples crystallize in MgCu2-type phase with lattice constant a changing from 7.223 Å for YCo2, through 7.213 Å for Y0.9Nb0.1Co2 to 7.192 Å for Y0.9Ti0.1Co2, where Y atoms are repla...
Article
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We have analyzed by density functional theory calculations the structural and magnetic properties of Fe-Co alloys doped by carbon. In analogy with the formation of martensite in steels we predict that such a structure also forms for Fe-Co alloys in a wide range of concentrations. These alloys are predicted to have a stable tetragonal distortion, wh...
Article
The electronic structure of the ferromagnetic compound UCuSb2 calculated by ab initio procedures is presented in details. Several computational codes were used, based on the generalized gradient approximation (GGA) and also GGA+U approaches. Special attention is paid to calculations of the magnetic moment, motivated by reported in the literature la...
Article
We report the basic physical properties of monoclinic YCo determined by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. The crystal structure of YCo is monoclinic (P2/c) with lattice parameters a = 7.0582(6) Å, b = 7.2894(6) Å, c = 24.2234(19) Å, and β = 102.112(6)° as refined by using synchrotron powder x-...
Article
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The electronic band structure of UPdAs2 is calculated using full potential linearized augmented plane wave implemented in the WIEN2k code. Calculations were started with the exchange-correlation potential in the form proposed by Perdew, Burke and Ernzerhof (PBE). We additionally studied PBE+U approach with the Coulomb repulsion energies U applied t...
Article
Based on experimental crystallographic data, electronic structure of UGe2 have been calculated and compared with our results of X-ray photoelectron spectroscopy (XPS) measurements. We employed two different advanced full potential (FP) methods: FP-local-orbital (FPLO) and FP-linear augmented plane waves (Wien2k) codes for non-magnetic and ferromagn...
Article
The room temperature X-ray photoemission spectrum of the ferromagnetic compound UCu2Si2 (TC = 100 K) was measured using an Al Kα source. Related theoretical spectra were computed from densities of electronic states obtained in the local density approximation (LDA), the generalized gradient approximation (GGA), and using the GGA + U method. The calc...
Article
The intermetallic compounds YbxGd1-xNi5 crystallize in the hexagonal CaCu5-type structure. Based on wide ranging SQUID-type magnetometer, it was shown that the saturation magnetization decreases with growing concentration of ytterbium. The opposite tendency was observed for the Sommerfeld coefficient obtained in the heat capacity measurements. Thes...
Article
Full-text available
The intermetallic compounds Yb x Gd 1−x Ni 5 crystallize in the hexagonal CaCu 5-type structure. Based on wide ranging SQUID-type magnetometer, it was shown that the saturation magnetization decreases with growing concentration of ytterbium. The opposite tendency was observed for the Sommerfeld coefficient obtained in the heat capacity measurements...
Article
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UNiAs 2 band structure has been calculated based on two full-potential methods: full potential linearized augmented plane wave implemented in WIEN2k code and full-potential local-orbital minimum-basis in FPLO code. Starting from the local (spin) density approximation (L(S)DA) we verified either the orbital polarization correction or the LSDA+U appr...
Article
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The crystal structures and the physical (magnetic, electrical transport and thermodynamic) properties of the ternary compounds CeRhSi2 and Ce2Rh3Si5 (orthorhombic CeNiSi2-?and U2Co3Si5-type structures, respectively) were studied over wide ranges of temperature and magnetic field strength. The results revealed that both materials are valence fluctua...
Article
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Single-crystalline CeRh3Si2 was investigated by means of x-ray diffraction, magnetic susceptibility, magnetization, electrical resistivity, and specific-heat measurements carried out in wide temperature and magnetic field ranges. Moreover, the electronic structure of the compound was studied at room temperature by cerium core-level x-ray photoemiss...
Article
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U5Ge4 crystallizes in a hexagonal Ti 5Ga4 type structure with two inequivalent crystallographic sites occupied by uranium atoms. The band structure calculations were performed by the full-potential local-orbital minimum basis band structure code. The calculations showed that on both types of uranium atoms small magnetic moments are formed and their...
Article
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Electronic structures of some ternary uranium compounds (U 2 Ru 2 Sn and UCu 5 M, M = Al, In, Sn) have been studied by theoretical (ab-initio calculations) and experimental (X-ray photoemission) me-thods. The band structure calculations have been performed based on the full potential local orbital me-thod. The calculated densities of electronic sta...
Article
ThCu5In and ThCu5Sn alloys crystallize in an orthorhombic CeCu5Au-type structure with the Pnma space group. Ab-initio band structure calculations have been performed based on the full-potential local-orbital (FPLO) method. The calculated densities of electronic states are used to obtain photoemission spectra. The spectra of valence bands are predom...
Article
UCo4B compound crystallizes in the hexagonal CeCo4B type structure. The electronic structure is calculated based on full-potential local-orbital full-relativistic method (FPLO). The calculated data show itinerant character of 5f electrons and reveal a dominant U(5f) and Co(3d) electron character for the states near the Fermi level.

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Project
The aim of the PRELUDIUM BIS 1 project is to develop a new generation of magnetic alloys for application as permanent magnets and study of influence of chemical composition on their magnetic and electronic properties. The motivation to undertake the above research is the search for new hard magnetic materials containing no rare-earth metals as the replacements for commonly used neodymium magnets. These searches are motivated by the volatile prices of rare earth metals and the risk of their resources being exhausted in the long run. The first-principles calculation results obtained in the project will become a signpost in the development of a new generation of permanent magnets. The project members closely collaborate with partners from the Department of Physics and Astronomy of Uppsala University in Sweden. The computational grant at Poznań Supercomputing and Networking Center (PSNC) ensures an effective implementation of the computational tasks.