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Öğe 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.Öğe 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.Öğe 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.Öğe 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.Öğe 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.Öğe 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 contentÖğe 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.Öğe One-Dimensional Magnonic Crystal for Magnetic Field Sensing(Springer, 2015) Atalay, S.; Kaya, A. O.; Kolat, V. S.; Gencer, H.; Izgi, T.Magnetic field sensor capacity of one-dimensional magnonic crystals was investigated. The surface of YIG film was modulated by periodic Cu stripes and magnet array in one dimension. The surface modulations of YIG film form sharp band gaps, since magnetostatic surface wave (MSSW) propagates through the surface of a magnetic material. It was found that a very small magnetic field change leads to a large change in the peak value of band gap frequency. A 1-Oe change in the field caused nearly 2.7 and 2.6 MHz shift in the band gap frequency for magnonic crystals modulated by periodic Cu stripes and magnet array, respectively, which means that a very low magnetic field change could be detected. Such a large shift in the band gap frequency makes these one-dimensional magnonic crystals attractive candidates for magnetic field sensing.Öğe Production of LaFe11.4Si1.6 compound at high temperature with a very short annealing time(Natl Inst Optoelectronics, 2009) Kolat, V. S.; Izgi, T.; Gencer, H.; Kaya, A. O.; Bayri, N.; Atalay, S.In this work, LaFe11.4Si1.6 compound was prepared by arc-melting method and annealed at temperature of 1473 K for 5, 10, 30, 60, 180 and 7200 min. X-ray results indicated that as-cast compound mainly consists of alpha-Fe and LaFeSi phases. After 5 min annealing time at 1473 K, the mixture of a-Fe and LaFeSi was gradually transformed into cubic NaZn13 type phase of LaFe11.4Si1.6. X-ray result indicated that the sample annealed for 30 min crystallized in a single phase with a cubic NaZn13 structure. The magnetic characterizations of the samples were carried out at various temperatures and magnetic fields. The maximum magnetic entropy change (vertical bar Delta S-m vertical bar) of the sample annealed at 1473 K for 30 min is 22.7 J/kg K at a magnetic field change of 5 T. It was shown that magnetic and magnetocaloric properties for short high temperature annealing of LaFe11.4Si1.6 compound are in a good agreement with previously reported values.Öğe Surface modification of YIG by magnet array(Elsevier Science Bv, 2015) Atalay, S.; Kolat, V. S.; Bakir, H. G.; Izgi, T.; Kaya, A. O.; Kaya, O. A.; Gencer, H.In this work, magnetostatic surface spin waves (MSSW) were propagated along the single crystal YIG (Y3Fe5O12) film grown on GGG substrate. In order to obtain magnonic crystals, unlike the conventional methods, the surface of YIG films were magnetically modulated by magnet array in one and two-dimensions. The surface modulated YIG films formed sharp band gaps at approximately 6.55 GHz and 6.58 GHz at 1600 Oe magnetic field for one and two-dimensional magnonic crystals, respectively. It was found that a very small magnetic field change leads a large change in the peak value of band gap frequency. (C) 2015 Elsevier B.V. All rights reserved.Öğe YIG Film for Magnetic Field Sensor(Polish Acad Sciences Inst Physics, 2015) Kaya, A. O.; Atalay, S.; Gencer, H.; Kaya, O. A.; Kolat, V. S.; Izgi, T.Single crystal Y3Fe5O12 (YIG) film was grown onto (111) oriented gadolinium gallium garnet (GGG) substrate by the liquid phase epitaxy (PLD) technique. The X-ray diffraction measurements showed that epitaxial growth of the film along its (111) axis. The surface characteristic was investigated by atomic force microscopy (AFM) measurement. The magnetic field sensor consisted of a rectangular shape with 5 mm wide, 15 mm long and 5 mu m thick YIG film and a pair of identical 50 mu m wide microstrip copper transducers elements separated by 6 mm. The filter was tested by measuring reflection S-11 characteristic at various bias magnetic fields. The results have showed that when the bias field increased from 0 to 2.5 kOe, the frequency value corresponding to S-11 maxima increased from 1 GHz to 9 GHz. This suggests that the wide range magnetic field sensing and the highly sensitive field sensing are simultaneously fulfilled with the YIG film.
