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Crystallisation Kinetics of Co75-xMxSi15B10 (M = Fe, Mn, Cr and x=0, 5) Amorphous Alloys
(Polish Acad Sciences Inst Physics, 2016) Bayri, N.; Kolat, V. S.; Izgi, T.; Atalay, S.; Gencer, H.; Sovak, P.
In this study, the effect of Fe, Mn and Cr substitution for Co on the crystallization kinetics of amorphous Co75-xMxSi15B10 (M = Fe, Mn and Cr; x = 0 and 5) alloys were investigated. The broad diffraction peaks in the X-ray diffraction patterns for as-quenched ribbons indicated that all of the samples exhibit an amorphous structure. The activation energies of the alloys were calculated from differential thermal analysis data using the Kissinger, Ozawa and Augis-Bennett models. The increased activation energy for Fe, Mn and Cr doped samples indicated that the thermal stability and the crystallization kinetics were improved in the doped samples. The value of the Avrami exponent indicated that the crystallization is typical diffusion controlled three-dimensional growth for all of the samples.
The crystallisation kinetics, magnetic and magnetocaloric properties of Gd55Co20Fe5Al20 - xSix (x=0, 5, 10, 15) alloys
(Elsevier, 2013) Gencer, H.; Izgi, T.; Kolat, V. S.; Bayri, N.; Kaya, A. O.; Atalay, S.
The effects of substituting Si for Al on the crystallisation kinetics and magnetic and magnetocaloric properties of Gd55Co20Fe5Al20 Si-- x(x) (x = 0, 5, 10, 15) alloys have been investigated in detail. The broad diffraction peaks in the XRD patterns indicated that all the samples have amorphous structures. The activation energies of the alloys were calculated using the Kissinger, Ozawa and Augis-Bennett models based on differential thermal analysis data. The Avrami exponent n was calculated from the Johnson-Mehl-Avrami equation. The increase in the activation energy as the Si content increased to x = 10 indicated that the addition of Si improves the thermal stability and slows the crystallisation kinetics of the samples. The value of the Avrami exponent showed that the nucleation and growth mechanisms of the crystallisation process depend on the Si concentration. The maximum entropy change reached a maximum value of 6.82 J/kg K for x = 5 and then decreased with further increases of Si. The refrigeration capacities are 558, 665,700 and 519 J/kg for x = 0, 5, 10 and 15, respectively. The increased thermal stabilities and large refrigeration capacities make these amorphous alloys attractive candidates for magnetic refrigeration applications. (C) 2013 Elsevier B.V. All rights reserved.
Crystallization kinetics of Fe73.5-xMnxCu1Nb3Si13.5B9 (x=0, 1, 3, 5, 7) amorphous alloys
(Elsevier Science Bv, 2009) Bayri, N.; Izgi, T.; Gencer, H.; Sovak, P.; Gunes, M.; Atalay, S.
In this study, we have investigated the effect of substituting Mn for Fe on the crystallization kinetics of amorphous Fe73.5-xMnxCu1Nb3Si13.5B9 (x = 1, 3, 5, 7) alloys. The samples were annealed at 550 degrees C and 600 degrees C for 1 h under an argon atmosphere. The X-ray diffraction analyses showed only a crystalline peak belonging to the alpha-Fe(Si) phase, with the grain size ranging from 12.2 nm for x = 0 to 16.7 nm for x = 7. The activation energies of the alloys were calculated using Kissinger, Ozawa and Augis-Bennett models based on differential thermal analysis data. The Avrami exponent n was calculated from the Johnson-Mehl-Avrami equation. The activation energy increased up to x = 3. then decreased with increasing Mn content. The values of the Avrami exponent showed that the crystallization is typical diffusion-controlled three-dimensional growth at a constant nucleation rate. (C) 2008 Elsevier B.V. All rights reserved.
Effect of Fe Substitution on Magnetic and Magnetocaloric Properties of La0.94Bi0.06Mn1-xFexO3 (x=0, 0.05, 0.075 and 0.1) Compounds
(Korean Magnetics Soc, 2017) Gencer, H.; Kolat, V. S.; Bayri, N.; Izgi, T.; Atalay, S.
The effects of Fe doping on structural, magnetic and magnetocaloric properties of La0.94Bi0.06Mn1-xFexO3 (x = 0, 0.05, 0.075, 0.1) compounds were investigated. X-ray analyses showed that the substitution of Mn by Fe produced no major structural change. It was found that the saturation magnetization, Curie temperature and maximum value of magnetic entropy change decrease with increasing Fe content. The decrease in magnetic entropy change was attributed to the decrease in saturation magnetization and the nature of phase transition transforms from first-order to second-order. The refrigeration capacities were determined to be 259 and 230 J/kg for the x = 0 and 0.075 samples, respectively at a field change of 5 T.
Effects of Ru substitution on the structural, magnetic and magnetocaloric properties of Pr0.68Ca0.22Sr0.1Mn1-xRuxO3(x=0, 0.05, 0.1 and 0.2) compounds
(Springer, 2020) Pektas, M.; Izgi, T.; Gencer, H.; Atalay, S.; Kolat, V. S.; Bayri, N.
The structural, magnetic and magnetocaloric properties of polycrystalline Pr0.68Ca0.22Sr0.1Mn1-xRuxO3(x = 0, 0.05, 0.1 and 0.2) compounds were studied. All the samples crystallized in an orthorhombic symmetry. A significant increase in the lattice parameters in the doped samples was attributed to the existence of Ru with a the mixed-valence state (Ru3+/Ru4+). The increase in the Curie temperature (T-c) with increasing Ru content was interpreted as Ru doping promoting the ferromagnetic interactions between Ru4+-Mn(3+)and Ru4+-Mn(4+)pairs. The decrease in saturation magnetisation was attributed to an AFM interaction between the Ru3+-Mn(3+)and Ru3+-Mn(4+)pairs and smaller magnetic moments of Ru than those of Mn. The decrease in |Delta S-M| (from 4.66 J kg(-1) K(-1)forx = 0.05 to 2.32 J kg(-1) K(-1)forx = 0.2 at 5 T) was attributed to the nature of phase transition (from a first-order to second-order transition) and a decrease in the saturation magnetisation.
Electrical Transport and Magnetoresistance of La0.67Ca0.33MnO3: Agx (x=0, 0.1, 0.2, 0.3, 0.4) Composites
(Korean Magnetics Soc, 2012) Gencer, H.; Pektas, M.; Babur, Y.; Kolat, V. S.; Izgi, T.; Atalay, S.
The structural, magnetic and magnetotransport properties of La0.67Ca0.33MnO3: Ag-x (x = 0, 0.1, 0.2, 0.3 and 0.4) composites were investigated systematically. X-ray and EDX analysis indicated that Ag is not substituted into the main La0.67Ca0.33MnO3 phase and remains an additive to the second phase at the grain boundary. The Curie temperature first decreased from 269 K for x = 0 to 257 K for x = 0.1 and then remained nearly unchanged with increasing Ag content. For the x > 0.1 samples, a second transition temperature (T-M12) was observed in the resistance curves. At temperatures below 150 K, a significant enhancement in MR was observed while high temperature MR decreased with increasing Ag content. The maximum MR was observed to be 55% in the x = 0.4 sample at 10 K and a 6T magnetic field, this value is larger than that of pure La0.67Ca0.33MnO3 (53% at 265 K and 6 T). In addition, at low fields (H < 1T), a sharp increase in the MR was observed.
Electrical transport and magnetoresistance properties of La0.67Ca0.33Mno3 film coated on pyrex glass substrate
(World Scientific Publ Co Pte Ltd, 2008) Gencer, H.; Goktas, A.; Gunes, M.; Mutlu, H. I.; Atalay, S.
The electrical transport and magnetoresistance properties of the polycrystalline La0.67Ca0.33MnO3 film produced on a Pyrex substrate were investigated for the first time. X-ray powder diffraction indicated that the film sample has a perovskite structure. Scanning electron microscope indicated that La0.67Ca0.33MnO3 film thickness is approximately 500 nm, and the average grain size of this sample varies between 40 and 50 nm. La0.67Ca0.33MnO3 film showed a phase transition from paramagnetic to ferromagnetic at (T-C) 80 K and a metal insulator transition at (T-MI) 77.5 K and at 2 mT magnetic field. The upturn of the resistance observed at low temperatures (<36 K) was attributed to the Coulomb blockade, and the strong structural disorder is due to the large lattice mismatch and strain relaxation. A large magnetoresistance ratio [MR %] of 780% was observed at 100 K and 6 T magnetic field.
Field Induced Unusual Magnetic Behavior at Low Temperature in Pr0.67Ca0.33MnO3
(Polish Acad Sciences Inst Physics, 2014) Pektas, M.; Gencer, H.; Izgi, T.; Kolat, V. S.; Atalay, S.
In this study, magnetic properties of Pr0.67Ca0.33MnO3 compound were investigated in detail. The magnetization versus temperature (M-T) curve showed that this material undergoes a charge order transition at 200 K. A more pronounced FM phase appeared below 56 K. At T = 5 K, a field induced sharp step like magnetisation transition associated with phase separation was observed. However, after application of 7 T magnetic field at 5 K, the magnetic behaviour of sample was changed completely and full FM behaviour was observed. The more interesting is that the sample remains in the FM state and does not retrieve the initial magnetic state until warmed up to charge order transition temperature. Large negative magnetic entropy change (-26.18 J/(kg K) at 38 K and 5 T) was attributed to step like magnetisation transition.
Influence of Ge and Bi substitution on the magnetic and magnetocaloric properties of LaFe11.4Si1.6
(Natl Inst Optoelectronics, 2010) Kolat, V. S.; Kaya, A. O.; Izgi, T.; Gencer, H.; Bayri, N.; Atalay, S.
In this work, the magnetic and magnetocaloric properties of LaFe11.4S1.6-xGex (x = 0.05, 0.1 and 0.2) and La1-xBixFe11.4Si1.6 (x = 0, 0.1 and 0.2) compounds have been investigated. X-ray results indicate that the samples with lower Ge and Bi contents mainly consist of the NaZn13-type phase with a small amount of alpha-Fe impurity phase. The alpha-Fe impurity phase increases with increasing concentrations of Ge and Bi. The Curie temperature of the samples also increases slightly with increasing Ge and Bi contents. The spin-wave dispersion coefficient D, exchange constant J and average mean-square range of exchange interaction ()(1/2) have been calculated. The increase in Curie temperature is attributed to an increase in the average Fe-Fe distance and ferromagnetic interactions. The peak values of the magnetic entropy change vertical bar Delta S-m vertical bar are found to decrease with increasing Ge and Si contents. This is attributed to a change of the phase transition from first order to second order. The peak values of vertical bar Delta S-m vertical bar are 22.38 J/kg K for LaFe11.4Si1.6, 12.58 J/kg K for LaFe11.4Si1.5Ge0.1 and 14.25 J/kg K for La0.9Bi0.1Fe11.4Si1.6 at a magnetic field of 6 T.
Influence of Si substitution on the structural, magnetic and magnetocaloric properties of Gd55Co20Fe5Al20-xSix alloys
(Elsevier, 2013) Atalay, S.; Gencer, H.; Kaya, A. O.; Kolat, V. S.; Izgi, T.
The structural, magnetic and magnetocaloric properties of Gd55Co20Fe5Al20-xSix (x=0, 2, 5, 10, 15, 20) alloys have been investigated in detail for the first time. The broad diffraction peaks for x=0 and 2 indicated that the samples have amorphous structures. For higher Si content (x >= 5), some diffraction peaks revealed that the Si substitution increases the crystallinity of the alloys. While the magnetization curves showed only one magnetic transition for low Si content, for the higher concentrations a second magnetic transition was observed due to the crystallization of the samples. The maximum entropy change of 8.01 J/kg K was observed in a 5 T magnetic field for the x=0 sample and decreased with further increase of Si concentration. The refrigerant capacities vary from 913 J/kg for x=0 to 596 J/kg for x=15. (C) 2013 Elsevier B.V. All rights reserved.
Influence of Ti substitution on magnetic and magnetocaloric properties of Pr2Fe17-xTix intermetallic compounds
(Springer, 2023) Cengiz, N. E.; Pektas, M.; Kaya, A. O.; Bayri, N.; Izgi, T.; Gencer, H.; Kolat, V. S.
The structural, magnetic, and magnetocaloric properties of the Pr2Fe17-xTix (x = 0, 0.2, 0.4, 0.6) intermetallic compounds prepared by the arc-melting process were investigated. X-ray analyses indicated that all samples are single phase with the rhombohedral Th2Zn17-type structure. The unit-cell volume was determined to increase with the increasing Ti content. The magnetic measurements revealed that the Curie temperature increases with Ti content from 286 K for x = 0 to 337 K for x = 0.6. The maximum value of |Delta Sm| tends to decrease from 5.63 J/kg.K for x = 0 to 4.28 J/kg.K for x = 0.6 with increasing Ti content at 5 T magnetic field change. At the same magnetic field change, the relative cooling power (RCP) ranges from 425.17 J/Kg for x = 0 to 385.62 J/Kg for x = 0.6. The critical exponents (beta, gamma, and delta) determined from magnetocaloric data for x < 0.2 belong to mean-field model with long-range ferromagnetic interaction. A small deviation in the critical exponents of gamma and delta for x > 0.4 samples was attributed to inhomogeneous magnetic state of the samples. From the phase analysis, it was concluded that all samples showed a second-order magnetic phase transition.
LaBaMnO films produced by dip-coating on a quartz substrate
(Elsevier Science Sa, 2008) Gencer, H.; Gunes, M.; Goktas, A.; Babur, Y.; Mutlu, H. I.; Atalay, S.
The electrical transport and magnetoresistance properties of the polycrystalline La0.67Ba0.33MnO3 film produced on a quartz substrate were investigated first time. X-ray powder diffraction indicated that film sample has perovskite structure. Scanning electron microscope indicated that La0.67Ba0.33MnO3 film thickness is approximately 20 mu m and the average grain size of this sample varies between 8 and 10 mu m. La0.67Ba0.33MnO3 film showed a phase transition from paramagnetic to ferromagnetic at (Tc) 130 K and a metal-insulator transition at (T-MI) 137 K at 2 mT magnetic field. The upturn of the resistance observed at low temperatures (<49 K) was attributed to the Coulomb blockade and the strong structural disorder due to the large lattice mismatch and strain relaxation. A large magnetoresistance ratio (MR(%)) of 230% was observed at 125 K and 6 T magnetic fields. (C) 2007 Elsevier B.V. All rights reserved.
Magnetic and Magnetocaloric Properties of (Gd1-xCex)Al2 (x=0, 0.25, 0.5, 0.75) Compounds
(Korean Magnetics Soc, 2011) Gencer, H.; Izgi, T.; Kolat, V. S.; Kaya, A. O.; Atalay, S.
The magnetic and magnetocaloric properties of Gd1-xCexAl2 (x = 0, 0.25, 0.5, 0.75) intermetallic compounds alloys have been investigated in detail for the first time. XRD patterns indicated that all the samples were crystallized in a single phase with MgCu2-type structure (Laves phase). Ce substitution for Gd increased the lattice parameters and decreased the Curie temperature from 163 K for x = 0 to 37 K for x = 0.75. A maximum entropy change of 3.82 J/kg K was observed when a 2 T magnetic field was applied to the x = 0 sample. This entropy change decreased with increasing Ce content to 2.04,J/kg K for the x = 0.75 sample.
Magnetic and magnetocaloric properties of GdB2 compound
(Natl Inst Optoelectronics, 2012) Gencer, H.; Izgi, T.; Kolat, V. S.; Atalay, S.
In this study, magnetic and magnetocaloric properties of GdB2 compound were first time investigated.GdB2 compound was prepared by arc-melting method. The magnetic characterizations of the samples were defined at various temperatures and magnetic fields. Saturation magnetization value is 19.5 emu/g at 275 K. The magnetic entropy change of the GdB2 compound was calculated from the isothermal magnetization curves under the different magnetic fields. The peak value of vertical bar Delta S-m vertical bar is 1.89 J/kg K under the applied field changing from 0 T to 4 T. The adiabatic temperature change was calculated from heat capacity. The peak value of Delta T-ad is 0.49 K at 1 T magnetic field.
Magnetic and Magnetocaloric Properties of La0.94Bi0.06Mn1-xCrxO3 (x=0, 0.05, 0.1, 0.15, 0.2, 0.25) Samples
(Polish Acad Sciences Inst Physics, 2019) Gencer, H.; Ozkan, U.; Bayri, N.; Izgi, T.; Kolat, V. S.
The effects of Cr doping on structural, magnetic and magnetocaloric properties of La0.94Bi0.06Mn1-xCrxO3 (x = 0, 0.05, 0.1, 0.15, 0.2, 0.25) samples were investigated. It has been observed in X-ray analyses that the substitution of Mn by Cr produced no remarkable structural change and only the diffraction peaks for orthorhombic symmetry were obtained for all samples. The decrease in the Curie temperature and saturation magnetization with Cr content could be due to weakening of the ferromagnetism in Cr doped samples. The decrease in magnetic entropy change was attributed to the decrease in saturation magnetization with increasing Cr content.
Magnetic and Magnetocaloric Properties of Pr2Fe17-xCux Intermetallic Compounds
(Korean Magnetics Soc, 2021) Cengiz, N. E.; Pektas, M.; Kolat, V. S.; Izgi, T.; Gencer, H.; Bayri, N.; Atalay, S.
In this study, Cu-doped intermetallic compounds with the chemical composition of Pr2Fe17-xCux, (x = 0, 0.1, 0.2) were prepared by the arc-melting process. SEM analysis revealed that the samples consist of irregularly shaped and strongly connected micron-scale particles range from 0.5 mu m to 4 mu m. EDX analysis showed that all the samples consist of a single phase. The magnetic measurements revealed that all the samples exhibit a ferromagnetic to the paramagnetic phase transition. The Curie temperature was determined to increase linearly with increasing Cu substitution from 286 K for x = 0 to 303 K for x = 0.2. The maximum value of magnetic entropy change vertical bar Delta S-m vertical bar was estimated from isothermal magnetization curves and it decreases with increasing Cu content from 5.63 J/kg.K for x = 0 to 4.21 J/kg.K for x = 0.2 at 5 T magnetic field change. At the same magnetic field change, the relative cooling power values range from 404.8 J/Kg for x = 0 to 248.3 J/Kg for x = 0.2. Arrott plots and Landau analyses revealed that all the samples show second-order magnetic phase transition.
Magnetic and magnetoimpedance properties of Mn-doped FINEMET
(Elsevier Science Bv, 2009) Kolat, V. S.; Bayri, N.; Michalik, S.; Izgi, T.; Sovak, P.; Atalay, F. E.; Gencer, H.
In this study, the effect of substituting Mn for Fe on the magnetic and magnetoimpedance (MI) properties of amorphous and nanocrystalline Fe73.5-xMnxCu1Nb3Si13.5B9 (x = 1, 3, 5, 7) alloys has been investigated. A higher Mn content causes a decrease in the saturation magnetization and Curie temperature. For as-received Fe73.5-xMnxCu1Nb3Si13.5B9 (x = 0, 1, 3, 5, 7) ribbons, the measured values of the MI are 11%, 12%, 16%, 12% and 15% for x = 0, 1, 3, 5, 7, respectively. The magnitude of the MI ratio increases in annealed samples, indicating that they are magnetically softened by nanocrystallisation. The change in MI is found to be similar to 70% for the x = 3 sample annealed at 550 degrees C. It is also found that replacing a small amount of Fe by Mn improves the magnetic softness of Fe73.5-xMnxCu1Nb3Si13.5B9 alloys. (C) 2009 Elsevier B.V. All rights reserved.
Magnetocaloric effect in CeCo4B compound
(Elsevier Science Sa, 2008) Gencer, H.; Kervan, N.; Gencer, A.; Gunes, A.; Atalay, S.
Polycrystalline CeCo4B compound was prepared by arc melting under argon atmosphere. The magnetic and magnetocaloric properties of CeCo4B were investigated. The magnetic measurements show that CeCo4B is ferrimagnetically ordered. The Curie temperature was determined to be 291 K. It was found that the maximum value of the magnetic entropy change |Delta S-m| has reached the highest value of 0.361 J/(kg K) at 1 T. Using the Landau expansion of magnetic free energy and Arrott plots, it was found that the phase transition in CeCo4B is of second order. (C) 2007 Elsevier B.V. All rights reserved.
Magnetotransport and magnetoresistance properties of Pr0.68Ca0.32-xSrxMnO3 (x=0, 0.1, 0.18, 0.26 and 0.32) manganites
(Natl Inst Optoelectronics, 2011) Izgi, T.; Kolat, V. S.; Bayri, N.; Kaya, A. O.; Gencer, H.; Atalay, S.
In this study, the magnetotransport and magnetoresistance properties of Pr0.68Ca0.32-xSrxMnO3 (x= 0, 0.1, 0.18, 0.26 and 0.32) compounds were investigated. The system illustrate an evolution from a charge-ordered manganite at x = 0, with an insulating-like resistivity and low magnetization values, towards to a completely ferromagnetic metallic state for x = 0.32. Above the metal-insulator transition temperature T-MI, the resistance curves were fitted to the small polaron popping model. The activation energy (E-a) was found to decrease with increasing Sr content. In the phase separated (PS) state, due to the coexistence of ferromagnetic (FM) metallic and charge order (CO) insulating phases, the magnetoresistance (MR) was found to be maximum. The MR ratio of 6.3x10(8) for the sample x = 0 at 60 K is one of the largest MR change has been reported in manganites. The MR values decreases considerably with increasing Sr content and the activation energy decreases with the increase of Sr content
Metamagnetic transition and magnetocaloric effect in charge-ordered Pr0.68Ca0.32-xSrxMnO3 (x=0, 0.1, 0.18, 0.26 and 0.32) compounds
(Elsevier, 2010) Kolat, V. S.; Izgi, T.; Kaya, A. O.; Bayri, N.; Gencer, H.; Atalay, S.
In this study, magnetic and magnetocaloric properties of Pr0.68Ca0.32-xSrxMnO3 (x=0, 0.1, 0.18, 0.26 and 0.32) compounds were investigated. X-ray results indicated that all the samples have a single phase of orthorhombic symmetry. The orthorhombic unit cell parameters increase with the increase in Sr content. Large negative magnetic entropy changes (-26.2 J/kg K at 38 K and 5 T for x=0 and -6.5 J/kg K at 83 K and 6 T for x = 0.1) were attributed to ultrasharp metamagnetic transitions. The peak value of Delta S-m decreased from -4.1 J/kg K for x=0.18 sample to -2.4 J/kg K for x=0.32 at 1 T magnetic field. (C) 2009 Elsevier B.V. All rights reserved.

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