Dimitris Niarchos

Dimitris Niarchos
National Center for Scientific Research Demokritos | ncsr · Institute of Nanoscience and Nanotechnology

Ph.D, ΜΒΑ

About

512
Publications
32,047
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7,937
Citations
Additional affiliations
February 1985 - September 2015
National Center for Scientific Research Demokritos
Position
  • Managing Director
February 1985 - December 2016
National Center for Scientific Research Demokritos
Position
  • Managing Director
September 1981 - August 1986
Illinois Institute of Technology
Position
  • Professor
Description
  • Teaching Ungraduate and Graduate course and performing research in materials science
Education
September 1973 - February 1980
September 1967 - February 1972

Publications

Publications (512)
Chapter
Magnetic materials have been widely used for non-volatile information storage due to their spontaneous magnetic polarization. Bits of binary information may be materialized by magnetizing elements of ferromagnetic materials toward opposing pre-defined directions. The past few years, the advent of spintronics has created advanced magnetic memory sch...
Preprint
Full-text available
MnBi has attracted large attention due to its potential for permanent magnetic applications. However, pure LTP MnBi decomposes easily and the magnetic properties are very sensitive to both microstructure and processing. In this work we extend a previous research on stability of modified MnBi alloys by small partial addition of Co and small substitu...
Article
A novel concept for a simple, cost effective, readily integrable with Si electronics and self-powered photodetector is presented. The device consists of a semitransparent Au film deposited on an n-type Si substrate with contacts on the Au layer. The operation of the device relies on the recently demonstrated “shadow effect.” The device is shown to...
Article
Full-text available
A series of (Nd1−xSmx)Fe11Ti alloys with the ThMn12 crystal structure have been fabricated and characterized in order to promote a strong uniaxial anisotropy in NdFe11Ti without the need of nitrogenation. The compounds show small changes in the lattice parameters and cell volume, as well as Curie temperature and spontaneous magnetization. The aniso...
Article
The influence of the magnetic field on the thermoelectric figure of merit in semiconducting materials is studied theoretically. One of the important issues is the urgency to distinguish the various conditions under which the magneto-thermoelectric effects can be observed. Isothermal effects take place when there is no temperature gradient in the di...
Article
This study reports the stabilization of the RFe12-type based compounds where part of R and Fe are substituted with Zr and Co and Si, respectively, in order to examine whether these rare-earth-lean materials are suitable for applications as permanent magnets. Structural and magnetic characterization of the family of alloys with the general formula N...
Article
Nd-xZrxFe10Si2 alloys have been prepared in the tetragonal ThMn12-type structure by arc-melting and melt spinning and then nitrogenated to improve their magnetic properties. For x = 0.4 and 0.6 the Curie temperature and magnetic anisotropy fields increases from 280 to 300 °C to about 390 °C and from 2.8 to 3 Tesla to 4.5–5 Tesla respectively. The s...
Article
Full-text available
Iron-rich compounds with the tetragonal ThMn12-type structure have the potential to meet current demands for rare-earth-lean permanent magnets with high energy density and operating temperatures of 150–200 °C. However, while it is normal for magnet technology to lag behind the development of underlying magnetic material, this gap has always been un...
Poster
Full-text available
Tetragonal L10 FeNi is a promising rare-earth-free permanent magnet material, but synthesizing bulk material with proper chemical ordering remains challenging. However, micromagnetic simulations reveal that a chemical ordering S > 0.65 is necessary to achieve an energy density product BHmax > 200 kJ/m³ for grains with a diameter of 50 nm. With incr...
Article
Full-text available
Structure and magnetic properties of Sm1-xZrxFe10Si2 (0.1 ≤ x ≤ 0.6) alloys have been characterized using X-ray diffraction, thermomagnetic analysis and Mössbauer spectroscopy. The formation of the tetragonal ThMn12 -type structure was been observed in all alloys, without further annealing. The Curie temperature decreases linearly with Zr substitut...
Article
Full-text available
In recent years, there is a great demand in materials suitable for permanent magnets which led to shortages in the supply of rare earth elements, a basic ingredient of high performance magnets. Research for rare earth free magnetic materials is considered as a viable alternative. Various Heusler alloys are investigated as possible candidates. Among...
Preprint
Thermoelectric materials may be used in devices as thermoelectric “air conditioner” in a smart house for improved energy efficiency. Energy harvesting uses ambient energy to generate electricity. It provides potentially low-cost, maintenance-free, long-life equipment by reducing the need for batteries or power chords. Energy harvesting (EH) is also...
Article
Permanent magnets have attracted research interest in the last decades as they are used in wide range of applications, in consumer electronics, motors, electric generators and nano-micro scale applications (MEMS, NEMS). Plastic bonded magnets - composites with permanent magnetic powder embedded in a polymer binder - are considered among the most in...
Article
Full-text available
Appearance of a transverse component in dc electric field with respect to the applied current is investigated in periodic multilayer composite structures made of nanometer-to-micrometer scale alternating layers of two different homogeneous and isotropic conducting materials. Dependence of the transverse electric field on geometrical orientation of...
Article
In this work we investigate the potential of tetragonal L10 ordered FeNi as candidate phase for rare earth free permanent magnets taking into account anisotropy values from recently synthesized, partially ordered FeNi thin films. In particular, we estimate the maximum energy product (BH)max of L10-FeNi nanostructures using micromagnetic simulations...
Article
Full-text available
MnBi particles are obtained from bulk MnBi using mechanochemical processing. The structure and magnetic properties of the MnBi particles are investigated by means of X-ray diffraction analysis, scanning electron microscopy and magnetometry. Surfactant assisted high energy ball milling results to the samples’ degradation even after one hour of milli...
Article
Magnetic anisotropy phase-graded A1/L10-FePt films deposited on amorphous glass substrates were investigated combining ultra-high resolution electron microscopy and angular-dependent magnetic measurements. A highly textured (001) L10 FePt film was first deposited at a relative low temperature of 625 K using an MgO/Cr underlayer stack, hence a secon...
Article
Full-text available
Ultrathin FePt films (thickness between 1 nm and 5 nm) were studied for non‐volatile memories applications. The films were magnetron sputtered on monocrystalline MgO⟨001⟩ substrates at 500 °C. The films are polycrystalline, except the 1 nm thick film which is not continuous. It is shown that films with thickness higher than 2.7 nm have L10 structur...
Article
The uncertainty in rare-earth market resulted in worldwide efforts to develop rare-earth-lean/free permanent magnets. In this paper, we discuss about this problem and analyse how advances in computational and theoretical condensed matter physics could be essential in the development of a new generation of high-performance permanent magnets via high...
Poster
Full-text available
This poster was presented in ”XXXII Panhellenic Conference on Solid State Physics and Materials Science” which was held in Ioannina (18-21 September, 2016).
Poster
Full-text available
Nowadays, the field of magnetic applications is dominated by high performance permanent magnets containing rare-earth metals. However, the high cost along with limited supply of rare-earth elements resulted in search of potential substitutions. The intermetallic compound MnBi is a rare-earth-free permanent magnetic material and its low temperature...
Poster
Full-text available
This poster was presented in the 13th International Conference on N&N, in Thessaloniki - July 2016
Article
FePt-based exchange-coupled composites consisting of a magnetically hard L10-FePt phase exchange-coupled with a soft ferromagnetic material are promising candidates for future ultra-high density (>1 Tbit/in2) perpendicular magnetic recording media, also being of interest for other applications including spin torque oscillators and micro-electro-mec...
Article
Alloys of the ThMn12-type structure with the general formula Nd1−xZrxFe10Si2 (0.4 ≤ x ≤ 0.8) have been prepared by arc-melting the constituent elements. X-ray diffraction and Mössbauer spectroscopy measurements indicate the formation of the tetragonal ThMn12 -type structure with substitution of Nd with Zr, without further annealing. The lattice par...
Article
Full-text available
Hard-soft bilayers are analogous to prototype exchange-biased ferromagnetic–antiferromagnetic systems as the minor loop of the soft layer is biased by the hard, and furthermore they offer bias layer tunability. In sputtered CoPt/Co hard-soft bilayers, we demonstrate that the exchange bias field shows a linear dependence on the hard layer magnetizat...
Article
Analytical design of a periodic composite structure allowing re-direction (bending) of dc magnetic flux with respect to applied external field is presented using methods of transformation optics. The composite structure is made of micrometer scale alternating layers of two different homogeneous and magnetically isotropic materials. Dependence of th...
Article
Full-text available
The effect of arrays of nanometer scale pores on the magnetic properties of thin films has been analyzed. Particularly, we investigated the influence of the out-of-plane magnetization component created by the nanopores on the in-plane magnetic behavior of patterned hard/soft magnetic thin films in antidot morphology. Its influence on the coupling i...
Article
Full-text available
Multilayered thin films from various soft magnetic materials were successfully prepared by magnetron sputtering in Ar atmosphere. The magnetic properties and microstructure were investigated. It is found that the films show good soft magnetic properties: magnetic coercivity of 1-10Oe and saturation magnetization higher than 1T. The initial permeabi...
Article
In the framework of the ongoing research for novel rare earth free permanent magnet materials, the alloy Fe–Co–C has attracted interest from theorists, since carbon could induce a magneto-crystalline anisotropy. In this work structural and magnetic properties of strongly doped magnetron sputtered thin films were investigated. Au–Cu buffers on MgO (...
Article
Full-text available
A new material platform is presented to manipulate heat and charge transportation in steady-state conditions. More precisely, we investigate the conceptual realization of a concentric composite made of the same isotropic and homogeneous semiconductor material with layers of different porosity, and show the possibility of a simultaneous cloaking per...
Presentation
Full-text available
In this presentation the processing of MnBi ingots by the means of surfactant assisted ball milling was shown. The particles that were produced were characterised both structurally and magnetically.
Article
Full-text available
The present study is focused on our effort towards high performance permanent magnets with no rare earth elements. For this reason, high magnetization FeCo system is proposed as an alternative candidate. High magneto-crystalline anisotropy along with high magnetic moment is required for permanent magnets. According to theoretical calculations FeCo...
Article
Full-text available
MnBi has recently attracted large attention due to its potential for permanent magnetic applications. Although it does not present high saturation magnetization, it has large coercivity, above 1 T, which results in a theoretical BHmax value above 17 MGOe [1-2]. The MnBi single phase is difficult to prepare by using techniques as arc-melting, rapid...
Article
The magnetic properties of magnetron sputtered bilayers consisting of Fe45Co55 ultrathin layers on top of L10 FePt films epitaxially grown on MgO substrates are studied in view of their possible application as rare earth free permanent magnets. It is found that FePt layers induce a tetragonal distortion to the Fe-Co layers which leads to increased...
Article
The peculiarities of the Seebeck coefficient and power factor are studied in porous thermoelectric materials with spherical hollow pores of varying diameter from nanometer to micrometer length scales. The pores are assumed to be randomly dispersed throughout the matrix material. The influence of trap centers situated at pore interfaces on the power...
Article
Full-text available
The objective of the rare-earth free permanent magnets (REFREEPM) project is to develop a new generation of high-performance permanent magnets (PMs) without rare earths. Our approach is based on modeling using a combinatorial approach together with micromagnetic modeling and the realization of the modeled systems (I) by using a novel production of...
Article
Full-text available
A tetragonally distorted FeCo structure is obtained in Fe/Co multilayers epitaxially grown on Au 50Cu50 buffer using MgO single crystal substrates as a result of the lattice mismatch between the buffer and the FeCo ferromagnetic layer. The presence of large magnetic anisotropy energy (MAE) of the order of 1 MJ/m3 has been confirmed by ferromagnetic...
Article
L10 FePt thin films with an island-like morphology and magnetic perpendicular anisotropy were grown at low temperature (300 < Tdep < 375 °C) by magnetron sputtering on Hoya glass substrates using a 30-nm thick Cr (2 0 0) underlayer. An MgO buffer layer with a thickness of 2 nm was used to inhibit the diffusion from the Cr underlayer and promote the...
Article
The Nd-Fe-B magnets were prepared using conventional and microware sintering processes. A finely tuned microwave cavity operating in the 2.45 GHz, which works in single mode of electric field (e-field), was used to investigate the microwave sintering of Nd-Fe-B powders. The highest sintering temperature used was 1173 K, and the sintering lasted up...
Article
Full-text available
In this paper, we study the effect of B introduction in various Heusler alloys on their structural and magnetic properties. Samples with nominal stoichiometry Fe50+xCu25-xGa25, Fe50+xCu25-xAl25, and Fe50+xCo25-xGa25(x= 0-10) with the addition of excess B up to 12 at% were prepared with Ar arc-melting as base materials. The starting materials were s...
Article
Full-text available
Rare earth free alloys are in focus of permanent magnet research since the accessibility of the elements needed for nowadays conventional magnets is limited. Tetragonally strained iron-cobalt (Fe-Co) has attracted large interest as promising candidate due to theoretical calculations. In experiments, however, the applied strain quickly relaxes with...
Article
Full-text available
A highly sensitive open sample measurement system for soft magnetic strips, ribbons and films is described. It is a system built on a PXI platform combining PXI modules for control signal generation and data acquisition. The physical signals are digitized and the respective data streams are processed, presented and recorded in LabVIEW 7.0.
Article
Full-text available
The reduction in lattice thermal conductivity (LTC) of porous materials is investigated in "gray medium" approximation. Four different models of thermoelectric materials are examined including model with randomly distributed hollow pores of varying diameter from nano-to micro-scale sizes. In all cases we have suggested simple and general relations...
Article
Full-text available
In the present work we study the effect on structural and magnetic properties due to the introduction of Fe in Mn2Ga system. Mn0.7-xFexGa0.3 (x = 0.1 to 0.3) alloys were prepared with Ar arc-melting as base materials which were subsequently converted to ribbons using melt-spinning technique with velocity ranged from 20 to 35 m/s. Some of the materi...
Article
Full-text available
Achieving magnetic recording densities in excess of 1Tbit/in(2) requires not only perpendicular media with anisotropies larger than 7 MJ/m(3), making FePt alloys an ideal choice, but also a narrow distribution below 10 nm for a reduced S/N ratio. Such grain size reduction and shape control are crucial parameters for high density magnetic recording,...
Article
Full-text available
The Exchange Bias (EB) effect is observed at the interface of Antiferromagnet/Ferromagnet (AF/FM) structures and depends on the interface roughness (IR). Until today, only low IR values, usually below 10 nm, have been investigated. Here we investigate an extended range of IR through controlling the surface roughness (SR) of the employed substrates....
Article
Full-text available
A computerized J-H loop tracer for soft magnetic thick films in the audio frequency range is described. It is a system built on a PXI platform combining PXI modules for control signal generation and data acquisition. The physiscal signals are digitized and the respective data strems are processed, presented and recorded in LabVIEW 7.0.
Article
A series of ordered mesoporous single phase Cu1-xZnxFe2O4 spinel ferrites, with x ranging from 0.00 to 0.75 with a step increment of 0.25, are prepared by a novel nanocasting route with the aid of vinyl-functionalized mesoporous silica as a hard template. All samples display a relatively high surface area and narrow pore size distribution from nitr...
Article
Full-text available
We study the effect of thermal phonon scattering on the reduction of lattice thermal conductivity (LTC) in porous materials with spherical pores and inclusions of varying diameters from nano-to microscale sizes. Using a model based on the Gamma distribution of the pore sizes, we calculate effective phonon mean free paths at scattering on randomly d...
Article
Full-text available
The use of microwave energy for materials processing has a major potential and real advantages over conventional heating such as (1) time and energy savings, (2) rapid heating rates (volumetric heating vs. conduction), (3) considerably reduced processing time and temperature, (4) fine microstructures and hence improved mechanical properties and bet...
Article
The hydrogen sorption performance of V55Ti21Cr17Fe7 and V55Ti21Mn17Fe7 alloys and their ribbons were evaluated by pressure composition temperature tests. Their hydrogen absorption kinetic properties were studied through hydrogen absorption curves. The crystallographic structures and microstructure of these alloys and ribbons before hydrogen absorpt...
Article
Full-text available
In this paper, we study the effect of B introduction in various Heusler alloys on their structural and magnetic properties. Samples with nominal stoichiometry Fe50+xCu25−xGa25, Fe50+xCu25−xAl25, and Fe50+xCo25−xGa25(x = 0–10) with the addition of excess B up to 12 at% were prepared with Ar arc-melting as base materials. The starting materials were...
Article
Full-text available
A physical model is developed for the enhancement of the Seebeck coefficient (S) in a porous thermoelectric material with inhomogeneous porosity. The pores are assumed to be hole and of spherical shape. We take into account the presence of trap centers situated at pore/medium interfaces and neglect changes in the carrier effective mass due to the b...
Article
We have prepared FePt L1 0 /A1 exchange spring graded media by controlling deposition temperature. The performance of the media was determined by the deposition conditions, partic-ularly the cooling rate. By varying the deposition conditions a coercivity of 4.0 kOe was achieved without loss in remanent magnetization, the value corresponds to 88% re...
Article
Full-text available
The superconducting magnetoresistance effect (SMRE) observed in trilayers (TLs) consisting of a superconducting (SC) Nb interlayer and two outer ferromagnetic (FM) Ni80Fe20 and Co layers is studied. We observed that the SMRE exhibits a pronounced magnitude (R max−R min)/R nor of order 45 % and 86 % for the NiFe-based and Co-based TLs, respectively....
Article
A physical model for the reduction in lattice thermal conductivity KL based on the diffuse scattering of phonons at the pore–medium interfaces is developed in case of inhomogeneous porosity. In “gray-medium” approximation, a theoretically sound expression is derived for the KL and the variation of that as a function of porosity, pore sizes and the...
Conference Paper
In this work we report on opportunities for a colossal reduction in lattice thermal conductivity (LTC) of graded micro-nanoporous structures with inhomogeneous porosity which leads to the considerable improvement in thermoelectric figure of merit ZT. We employ the effective medium theory to calculate the LTC of a porous media with hole pores of var...
Article
The bottom-up fabrication of anisotropic exchange-coupled nanocomposites brings out the necessity of fabrication of magnetically hard nanoparticles with high coercivity. In this study, we have fabricated Nd2Fe14B nanoparticles from die-upset Nd-Fe-B (MQ3) precursor materials using planetary milling. The MQ3 alloy consists of platelets which are app...
Article
In this work structural and magnetic properties of (L10-FePt/A1-FePt) exchange coupled nanocomposites are presented. Semi spherical “dome-like” nanocomposites with L10 FePt isolated nanoparticles and A1 FePt (fcc) cap layers were obtained by depositing A1-FePt on type L10 FePt nanoparticles in order to understand the influence of the soft magnetic...