Margarit Gjoka | Insitute of Matelials Science, NCSR "Demorktios" (original) (raw)

Papers by Margarit Gjoka

The ternary Pr2Er (Fe, Ti) 29 and SmNd2 (Fe, Ti) 29 intermetallic compounds were successfully syn... more The ternary Pr2Er (Fe, Ti) 29 and SmNd2 (Fe, Ti) 29 intermetallic compounds were successfully synthesised and crystallographically and magnetically characterised. The anisotropy constants, the anisotropy field and the easy magnetization directions were determined at 5 and 300 K.

An interstitial Pr3 (Fe, Ti) 29 hydride was synthesised by gas-phase hydrogenation on Pr3 (Fe, Ti... more An interstitial Pr3 (Fe, Ti) 29 hydride was synthesised by gas-phase hydrogenation on Pr3 (Fe, Ti) 29 powder using H2. The reaction kinetics between Pr3 (Fe, Ti) 29 and H2 gases was studied in a constant-volume reactor. The sample starts to rapidly absorb hydrogen, interstitially, at about 533K. Absorption passes through a maximum at about 598K (1.6 H/fu) and then interstitial hydrogen desorption takes place up to the temperature of 673K.

Abstract Cobalt carbide nanoparticles were processed using polyol reduction chemistry that offers... more Abstract Cobalt carbide nanoparticles were processed using polyol reduction chemistry that offers high product yields in a cost effective single-step process. Particles are shown to be acicular in morphology and typically assembled as clusters with room temperature coercivities greater than 3.4 kOe and maximum energy products greater than 20 kJ m− 3. Consisting of Co3C and Co2C phases, the ratio of phase volume, particle size and particle morphology all play important roles in determining permanent magnet properties.

Abstract We present a combined experimental and computational study of high temperature magnetic ... more Abstract We present a combined experimental and computational study of high temperature magnetic properties of Fe–Cr alloys with chromium content up to about 20 at.%. The magnetic cluster expansion method is applied to model the magnetic properties of random Fe–Cr alloys, and in particular the Curie transition temperature, as a function of alloy composition. We find that at low (3–6 at.%) Cr content the Curie temperature increases with the increase of Cr concentration.

Page 1. K. Mergia1, M. Gjoka1, D. Niarchos1, S. Messoloras1 and A.

Pr3 (Fe, Ti) 29 hydrocarbide has been synthesised by gas–solid reaction. The hydrocarbide shows a... more Pr3 (Fe, Ti) 29 hydrocarbide has been synthesised by gas–solid reaction. The hydrocarbide shows a lattice expansion of 5.1%. The Curie temperature, TC,(119° C for the parent alloy) was increased to 373° C. The room temperature saturation magnetisation, MS, of the hydrocarbide is 138.1 Am2kg− 1 and the average hyperfine field at room temperature is 25.1 T. The magnetic anisotropy of the hydrocarbide changes from an easy cone with an angle of 34°(parent alloy) to a narrower cone with an angle of 26°.

Synthesis of two novel series of intermetallic compounds Tb3 (Fe1− xCox) 27.4 V1. 6 (x= 0, 0.1, 0... more Synthesis of two novel series of intermetallic compounds Tb3 (Fe1− xCox) 27.4 V1. 6 (x= 0, 0.1, 0.2, 0.3, 0.4) and Dy3 (Fe1− xCox) 27.8 V1. 2 (x= 0, 0.1, 0.2, 0.3) with the monoclinic Nd3 (Fe, Ti) 29-type structure (3: 29) is presented. In the Dy series for x= 0.4 a disordered variant of the hexagonal Th2Ni17-type structure is formed. The cell parameters decrease and the Curie temperature increases with increasing of the Co content. In the case of the Tb3 (Fe1− xCox) 27.4 V1.

The R3 (Fe, V) 29 compounds, with R= Dy, Er, Y, and the Gd3 (Fe, TM) 29, with TM= Ti and V, after... more The R3 (Fe, V) 29 compounds, with R= Dy, Er, Y, and the Gd3 (Fe, TM) 29, with TM= Ti and V, after heat treatment between 1123 and 1233 K form disordered structures that belong in the CaCu5 type family. The compounds with R= Y or Dy and TM= V crystallize in a disorder CaCu5 structure type (space group (SG): P6/mmm with cell dimensions a= 4.8769 (1) Å, c= 4.1729 (3) Å and a= 4.8692 (2) Å, c= 4.1750 (3) Å, respectively), with main structural characteristic the substitutional disorder observed at the R crystallographic site.

Structural and magnetic properties of a novel series of intermetallic compounds, with nominal sto... more Structural and magnetic properties of a novel series of intermetallic compounds, with nominal stoichiometry Nd 3 (Fe 1−x Co x ) 27.7 Ti 1.3 (0<x≤0.4) are presented. The samples crystallise in the Nd 3 (Fe,Ti) 29 -type structure with monoclinic symmetry (space group A2/m). The unit cell volume is decreasing as the Co content increases; the cell parameters show anisotropic decrease with the Co content.

The magnetocrystalline anisotropy of the compounds with stoichiometry Y3Fe27. 5V1. 5 (Y (Fe, V) 9... more The magnetocrystalline anisotropy of the compounds with stoichiometry Y3Fe27. 5V1. 5 (Y (Fe, V) 9.66) and Y3Fe27. 5V1. 5Nx (Y (Fe, V) 9.66 Nx) with a CaCu5-type structure has been studied by magnetization measurements in the temperature range 5–300K, analyzed by the Sucksmith–Thompson method, and by torque measurements at room temperature on powder samples oriented in a rotating magnetic field.

Alloys with starting stoichiometry RCo7− xMnx (R= Sm, Gd; x= 0.1–1.4) were prepared by arc meltin... more Alloys with starting stoichiometry RCo7− xMnx (R= Sm, Gd; x= 0.1–1.4) were prepared by arc melting. The effect of Mn doping on the formation of the TbCu7-type structure and magnetic properties are studied. The SmCo7− xMnx as cast alloys with x< 0.4 present uniaxial anisotropy along the c-axis as determined by X-ray diffraction on magnetically oriented samples.

The structural and magnetic characteristics of Nd 3−x Dy x (Fe,Ti) 29 (0.1<x<3) based ternary all... more The structural and magnetic characteristics of Nd 3−x Dy x (Fe,Ti) 29 (0.1<x<3) based ternary alloys have been investigated. For each value of x, the optimum annealing temperatures were found in relation to the highest 3:29 phase content. Despite an extensive search concerning the annealing temperatures and the Dy content, no new phase was precipitated. The room temperature anisotropy field increases from 3.7 T for x=0 to 6.7 T for x=2.5.

The ternary Pr2Er (Fe, Ti) 29 and SmNd2 (Fe, Ti) 29 intermetallic compounds were successfully syn... more The ternary Pr2Er (Fe, Ti) 29 and SmNd2 (Fe, Ti) 29 intermetallic compounds were successfully synthesised and crystallographically and magnetically characterised. The anisotropy constants, the anisotropy field and the easy magnetization directions were determined at 5 and 300 K.

An interstitial Pr3 (Fe, Ti) 29 hydride was synthesised by gas-phase hydrogenation on Pr3 (Fe, Ti... more An interstitial Pr3 (Fe, Ti) 29 hydride was synthesised by gas-phase hydrogenation on Pr3 (Fe, Ti) 29 powder using H2. The reaction kinetics between Pr3 (Fe, Ti) 29 and H2 gases was studied in a constant-volume reactor. The sample starts to rapidly absorb hydrogen, interstitially, at about 533K. Absorption passes through a maximum at about 598K (1.6 H/fu) and then interstitial hydrogen desorption takes place up to the temperature of 673K.

Abstract Cobalt carbide nanoparticles were processed using polyol reduction chemistry that offers... more Abstract Cobalt carbide nanoparticles were processed using polyol reduction chemistry that offers high product yields in a cost effective single-step process. Particles are shown to be acicular in morphology and typically assembled as clusters with room temperature coercivities greater than 3.4 kOe and maximum energy products greater than 20 kJ m− 3. Consisting of Co3C and Co2C phases, the ratio of phase volume, particle size and particle morphology all play important roles in determining permanent magnet properties.

Abstract We present a combined experimental and computational study of high temperature magnetic ... more Abstract We present a combined experimental and computational study of high temperature magnetic properties of Fe–Cr alloys with chromium content up to about 20 at.%. The magnetic cluster expansion method is applied to model the magnetic properties of random Fe–Cr alloys, and in particular the Curie transition temperature, as a function of alloy composition. We find that at low (3–6 at.%) Cr content the Curie temperature increases with the increase of Cr concentration.

Page 1. K. Mergia1, M. Gjoka1, D. Niarchos1, S. Messoloras1 and A.

Pr3 (Fe, Ti) 29 hydrocarbide has been synthesised by gas–solid reaction. The hydrocarbide shows a... more Pr3 (Fe, Ti) 29 hydrocarbide has been synthesised by gas–solid reaction. The hydrocarbide shows a lattice expansion of 5.1%. The Curie temperature, TC,(119° C for the parent alloy) was increased to 373° C. The room temperature saturation magnetisation, MS, of the hydrocarbide is 138.1 Am2kg− 1 and the average hyperfine field at room temperature is 25.1 T. The magnetic anisotropy of the hydrocarbide changes from an easy cone with an angle of 34°(parent alloy) to a narrower cone with an angle of 26°.

Synthesis of two novel series of intermetallic compounds Tb3 (Fe1− xCox) 27.4 V1. 6 (x= 0, 0.1, 0... more Synthesis of two novel series of intermetallic compounds Tb3 (Fe1− xCox) 27.4 V1. 6 (x= 0, 0.1, 0.2, 0.3, 0.4) and Dy3 (Fe1− xCox) 27.8 V1. 2 (x= 0, 0.1, 0.2, 0.3) with the monoclinic Nd3 (Fe, Ti) 29-type structure (3: 29) is presented. In the Dy series for x= 0.4 a disordered variant of the hexagonal Th2Ni17-type structure is formed. The cell parameters decrease and the Curie temperature increases with increasing of the Co content. In the case of the Tb3 (Fe1− xCox) 27.4 V1.

The R3 (Fe, V) 29 compounds, with R= Dy, Er, Y, and the Gd3 (Fe, TM) 29, with TM= Ti and V, after... more The R3 (Fe, V) 29 compounds, with R= Dy, Er, Y, and the Gd3 (Fe, TM) 29, with TM= Ti and V, after heat treatment between 1123 and 1233 K form disordered structures that belong in the CaCu5 type family. The compounds with R= Y or Dy and TM= V crystallize in a disorder CaCu5 structure type (space group (SG): P6/mmm with cell dimensions a= 4.8769 (1) Å, c= 4.1729 (3) Å and a= 4.8692 (2) Å, c= 4.1750 (3) Å, respectively), with main structural characteristic the substitutional disorder observed at the R crystallographic site.

Structural and magnetic properties of a novel series of intermetallic compounds, with nominal sto... more Structural and magnetic properties of a novel series of intermetallic compounds, with nominal stoichiometry Nd 3 (Fe 1−x Co x ) 27.7 Ti 1.3 (0<x≤0.4) are presented. The samples crystallise in the Nd 3 (Fe,Ti) 29 -type structure with monoclinic symmetry (space group A2/m). The unit cell volume is decreasing as the Co content increases; the cell parameters show anisotropic decrease with the Co content.

The magnetocrystalline anisotropy of the compounds with stoichiometry Y3Fe27. 5V1. 5 (Y (Fe, V) 9... more The magnetocrystalline anisotropy of the compounds with stoichiometry Y3Fe27. 5V1. 5 (Y (Fe, V) 9.66) and Y3Fe27. 5V1. 5Nx (Y (Fe, V) 9.66 Nx) with a CaCu5-type structure has been studied by magnetization measurements in the temperature range 5–300K, analyzed by the Sucksmith–Thompson method, and by torque measurements at room temperature on powder samples oriented in a rotating magnetic field.

Alloys with starting stoichiometry RCo7− xMnx (R= Sm, Gd; x= 0.1–1.4) were prepared by arc meltin... more Alloys with starting stoichiometry RCo7− xMnx (R= Sm, Gd; x= 0.1–1.4) were prepared by arc melting. The effect of Mn doping on the formation of the TbCu7-type structure and magnetic properties are studied. The SmCo7− xMnx as cast alloys with x< 0.4 present uniaxial anisotropy along the c-axis as determined by X-ray diffraction on magnetically oriented samples.

The structural and magnetic characteristics of Nd 3−x Dy x (Fe,Ti) 29 (0.1<x<3) based ternary all... more The structural and magnetic characteristics of Nd 3−x Dy x (Fe,Ti) 29 (0.1<x<3) based ternary alloys have been investigated. For each value of x, the optimum annealing temperatures were found in relation to the highest 3:29 phase content. Despite an extensive search concerning the annealing temperatures and the Dy content, no new phase was precipitated. The room temperature anisotropy field increases from 3.7 T for x=0 to 6.7 T for x=2.5.