Academic literature on the topic 'Ordered L10-FePt phase'

FePt alloys are an important class of materials in permanent magnetic applications because of their large uniaxial magnetocrystalline anisotropy and good chemical stability. We have applied the pulsed plasma in liquid method to synthesis nanoparticles. Short duration of pulse and quenching effects of the surrounding liquid limit the size of crystal. That enable synthesis of small size and metastable nanoparticles. In this study, ferromagnetic FePt nanoparticles were successfully synthesized. Face-centered-cubic (FCC) A1-type phase was synthesized from FePt (Fe:PT=50:50, 55:45 in atomic %) alloy rod electrodes using the pulsed plasma in ethanol. The ordered face-centered-tetragonal (FCT) L10-type phase FePt was obtained by annealing the A1-type phase at 400oC for 1 h. The average diameter of L10-type FePt nanoparticles was less than 10 nm. Vibrating Sample Magnetometer (VSM) analysis showed that the coercivity of L10-type nanoparticles was much larger than that of the A1-type phase nanoparticles.

FePt binary alloy nanopowder has been synthesized by a chemical vapor condensation process using a mixture of iron acetylacetonate and platinum acetylacetonate. Particle size of the synthesized powder was less than 10 nm and the powder had very narrow size distribution with relatively high dispersivity. FePt nanopowder possessing L10 ordered phase was synthesized at the condition of well controlled precursor mixing ratio and reaction temperature with some disordered cubic phase.

Constant increase of magnetic recording density requires application of modern ferromagnetic materials with high value of magnetic anisotropy constant and coercivity. Thin films on the bases of L10-FePt ordered phase is one of such materials. However, practical application of such materials requires to solve a number of materials science problems such as decrease of ordered phase formation temperature, formation of its predominantly oriented grains and increase of coercivity. Factors that affect structure formation and properties of FePt based films have been examined in this study. A number of modern studies aimed on solving problems mentioned above have been analyzed.

L10 phase FePt alloy is regarded as one of the most promising materials for ultra high density magnetic recording media. However, structural point defects, which would reduce the media's signal to noise ratio, are inevitable in non-stoichiometric L10 FePt alloy. Hence, possible types of point defect (vacancy and anti-site defect) in non-stoichiometric ordered FePt alloy were fully studied using density functional theory. Investigation over vacancy shows the formation energy of Fe and Pt vacancy is respectively 2.58eV and 3.20eV. Geometry relaxation implies Fe vacancy has a stronger deformation force upon the original lattice. Meanwhile, anti-site defect study shows that the formation energy of Fe anti-site (Fe occupation in Pt sublattice) and Pt anti-site (Pt occupation in Fe sublattice) is respectively 1.05eV and 0.66eV. Therefore, for Fe-rich and Pt-rich alloy, the preferred structural point defects are both anti-site substitution rather than vacancy due to the much lower formation energy.

Multiwalled carbon nanotubes (MWCNTs) were used as nanotemplates for the dispersion and stabilization of FePt nanoparticles (NPs). Pre-formed capped FePt NPs were connected to the MWCNTs external surface via covalent binding through organic linkers. Free FePt NPs and MWCNTs-FePt hybrids were annealed in vacuum at 700 °C in order to achieve the L10 ordering of the FePt phase. Both as prepared and annealed samples were characterized and studied using a combination of experimental techniques, such as Raman and Mössbauer spectroscopies, powder X-ray Diffraction (XRD), magnetization and transmittion electron microscopy (TEM) measurements. TEM measurements of the hybrid sample before annealing show that a fine dispersion of NPs along the MWCNTs surface is achieved, while a certain amount of free particles attached to each other in well connected dense assemblies of periodical or non-periodical particle arrangements is also observed. XRD measurements reveal that the FePt phase has the face-centered cubic (fcc) disordered crystal structure in the as prepared samples, which is transformed to the face-centered tetragonal (fct) L10 ordered crystal structure after annealing. An increase in the average particle size is observed after annealing, which is higher for the free NPs sample. Superparamagnetic phenomena due to the small FePt particle size are observed in the Mössbauer spectra of the as prepared samples. Mössbauer and magnetization measurements of the MWCNTs-FePt hybrids sample reveal that the part of the FePt particles attached to the MWCNTs surface shows superparamagnetic phenomena at RT even after the annealing process. The hard magnetic L10 phase characteristics are evident in the magnetization measurements of both samples after annealing, with the coercivity of the hybrid sample over-scaling that of the free NPs sample by a factor of 1.25.

L10 ordered FePt and FePtCu nanoparticles (NPs) with a good dispersion were successfully fabricated by a simple, green, one-step solid-phase reduction method. Fe (acac)3, Pt (acac)2, and CuO as the precursors were dispersed in NaCl and annealed at different temperatures with an H2-containing atmosphere. As the annealing temperature increased, the chemical order parameter (S), average particle size (D), coercivity (Hc), and saturation magnetization (Ms) of FePt and FePtCu NPs increased and the size distribution range of the particles became wider. The ordered degree, D, Hc, and Ms of FePt NPs were greatly improved by adding 5% Cu. The highest S, D, Hc, and Ms were obtained when FePtCu NPs annealed at 750 °C, which were 0.91, 4.87 nm, 12,200 Oe, and 23.38 emu/g, respectively. The structure and magnetic properties of FePt and FePtCu NPs at different annealing temperatures were investigated and the formation mechanism of FePt and FePtCu NPs were discussed in detail.

Chemical ordering kinetics in L10- and B2-ordered AB binary intermetallics was simulated by means of Monte Carlo (MC) technique implemented with vacancy mechanism of atomic migration. While vacancy concentration is usually much lower than the antisite defect concentration in L10-ordered systems, triple defects are generated in particular B2–ordered systems. The latter definitely affects the chemical ordering process and requires that full thermal vacancy thermodynamics is involved in B2-ordering simulations. The study on L10-ordered binaries was dedicated to FePt thin layers considered as a material for ultra-high-density magnetic storage media. Metastability of the L10 c-variant with monoatomic planes parallel to the layer surface and off-plane easy magnetization was revealed. Thermal vacancy formation in B2-ordered binaries was modelled by implementing a mean-field Hamiltonian with a specific formalism of phase equilibria in a latticegas composed of atoms and vacancies. It was demonstrated that for particular pair-interaction energetics, equilibrium concentrations of vacancies and antisites result mutually proportional in well-defined temperature ranges. The MC simulations of B2-ordering kinetics involved the modelled equilibrium vacancy concentration and reproduced the experimentally observed low rate of the process.

Дисертаційна робота присвячена визначенню закономірностей формування фазового складу, структури і магнітних властивостей в нанорозмірних плівках Fe50Pt50-Au та багатошарових композиціях [Pt/Fe]n (n = 1, 4, 8) на підкладках SiO2(100 нм)/Si(001) та Al2O3 (1010) при термічних відпалах. Встановлено, що контролюючи рівень механічних напружень та їх знак у шарі Fe50Pt50 зміненням товщини, розташування, кількості додаткових шарів Au, швидкості нагріву та атмосфери при відпалі (вакуум, азот, водень), можна керувати процесами упорядкування та формуванням фазового складу, структури та магнітними властивостями в плівкових композиціях. Застосування водневої термообробки прискорює процеси упорядкування в плівках Fe50Pt50/Au/Fe50Pt50 порівняно з відпалом у вакуумі за рахунок створення додаткових стискаючих напружень при втіленні атомів водню у пустоти кристалічної гратки фази L10-FePt. При цьому вісь легкого намагнічування c у зернах фази L10-FePt розташовується у площині плівки. Швидкий термічний відпал плівкових композицій [Pt/Fe]n (де n=4, 8) на підкладках SiO2(100 нм)/Si(001) в атмосфері азоту призводить до орієнтованого росту зерен фази L10-FePt з віссю легкого намагнічування c, розташованою в напрямку [001], перпендикулярному площині плівки.
The work is devoted to definition of the phase composition formation regularities, structure and magnetic properties in nanoscale Fe50Pt50-Au films and multilayered [Pt/Fe]n (n = 1, 4, 8) compositions on SiO2(100 nm)/Si(001) and Al2O3 (1010) substrates at thermal annealings. It is established that by supervising of mechanical stresses level and their sign in Fe50Pt50 layer by change of a thickness, location, quantity of additional Au layers and annealing conditions (temperature, duration, speed of heating and atmosphere  vacuum, nitrogen, hydrogen) one can operate by ordering processes and phase compound formation, structure and magnetic properties of film compositions The variations in residual stresses/strains level and sign in the FePt layer of as-deposited films influense the change in the ordered L10-FePt phase formation temperature, structure and the coercivity in the film compositions. Increasing the level of compressive stresses in the Fe50Pt50 layer causes a decrease in the ordering temperature and improvement of the magnetic properties. It is established that oriented grain growth with c-axis of easy magnetization in the [001] direction perpendicular to the film plane at annealing in vacuum occurs in films with a smaller thickness of the intermediate Au(7.5 nm) layer due to the higher level of compressive strains in the deposited films. Increasing the thickness of the Au layer to 15 nm and reducing the level of compressive deformations contributes to the growth of FePt grains with the c-axis of easy magnetization in the plane of the film. The same orientation can be achieved by increasing the thickness of the intermediate Au layer to 30 nm. It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates It is revealed, that application of hydrogen heat treatment accelerates ordering ordering ordering ordering ordering ordering ordering ordering proceproce proce sses in Fesses in Fesses in Fesses in Fesses in Fesses in Fesses in Fesses in Fesses in Fe 50 Pt 50 /Au/Fe/Au/Fe/Au/Fe/Au/Fe/Au/Fe 50 Pt 50 fi lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with lms in comparison with annealing annealingannealingannealing annealingannealingannealing in vacuum at in vacuum at in vacuum at in vacuum at in vacuum at in vacuum at in vacuum at in vacuum at in vacuum at in vacuum at in vacuum at the costthe costthe cost the cost the costthe cost of creation additional compressiof creation of additional compressi of creation additional compressi of creation additional compressiof creation of additional compressiof creation of additional compressiof creation of additional compressiof creation of additional compressiof creation of additional compressiof creation of additional compressi of creation additional compressiof creation of additional compressiof creation of additional compressiof creation of additional compressiof creation of additional compressiof creation of additional compressiof creation of additional compressiof creation of additional compressiof creation of additional compressi of creation additional compressiof creation of additional compressiof creation of additional compressiof creation of additional compressiof creation of additional compressiof creation of additional compressi of creation additional compressiof creation of additional compressive stressesve stresses ve stressesve stressesve stressesve stresses ve stressesve stresses caused by caused bycaused bycaused bycaused bycaused bycaused bycaused by introduction of introduction of introduction of introduction of introduction of introduction of introduction of introduction of introduction of introduction of introduction of introduction of introduction of introduction of introduction of hydrogenhydrogenhydrogenhydrogen hydrogenhydrogenhydrogen atoms atoms atoms atoms atoms in to L10-FePt phase crystal lattice FePt phase crystal latticeFePt phase crystal latticeFePt phase crystal latticeFePt phase crystal latticeFePt phase crystal lattice FePt phase crystal lattice FePt phase crystal lattice FePt phase crystal latticeFePt phase crystal latticeFePt phase crystal lattice FePt phase crystal latticeFePt phase crystal latticeFePt phase crystal latticeFePt phase crystal latticeFePt phase crystal latticeFePt phase crystal latticeFePt phase crystal lattice voidsvoidsvoidsvoidsvoids. Thus the c-axis of easy magnetization in L10-FePt phasephasephase phase grains is located in the film plane. Hydrogen treatment allows to obtain higher values of coercivity (27.3 kOe) in Fe50Pt50/Au/Fe50Pt50 film compositions at a lower annealing temperature of 700 °C than at annealing in vacuum (900 °C), due to the intensive penetration of hydrogen atoms into the film. It was determined that due to the action of the compressive stress during the diffusion of gold along the grain boundaries and the increase in the number of interfaces in films with an intermediate Au(7.5 nm) layer, the ordered L10-FePt phase formation temperature the can be reduced compared to the other Au layer location. In the films with various Au layer location (top, intermediate, under-) separated from the substrate, the same tendency of the A1→ L10 phase transformation temperature changing as in the films on the substrate is remained: the ordering temperature is lower in film with intermediate Au(7.5 nm) layer then in Au/FeAu/FeAu/FeAu/Fe 50 Pt 50 and and and and Fe 50 Pt 50 /Au filmsfilmsfilmsfilmsfilms. In this work it is also shown that the increase in the number of interfaces in [Pt/Fe]n film compositions, where n = 1, 4, 8, while maintaining the total film thickness, promotes the activation in diffusion processes and the formation of the disordered phase A1-FePt in the composition [Pt/Fe]4 and partially ordered regions with tetragonal distortions in the [Pt/Fe]8 composition already during deposition. Rapid thermal annealing of [Pt/Fe]n film compositions (where n = 4, 8) on SiO2(100 nm)/Si(001) substrates in nitrogen atmosphere leads to the oriented growth of L10-FePt phase grains with a c-axis of easy magnetization, located in [001] direction, perpendicular to film plane. The recommendations for controlling the stress state, the reduction of the temperature of the ordered L10-FePt phase formation, the obtaining of c-axis of easy magnetization oriented perpendicular or parallel to the film plane in the film based on FePt, application of which by thermal activated method will allow to increase the magnetic recording density and storage information were developed
Диссертационная работа посвящена определению закономерностей формирования фазового состава, структуры и магнитных свойств в наноразмерных пленках Fe50Pt50-Au и многослойных композициях [Pt/Fe]n (n = 1, 4, 8) на подложках SiO2(100 нм)/Si(001) и Al2O3 при термических отжигах. Установлено, что контролируя уровень механических напряжений и их знак в слое Fe50Pt50 изменением толщины, расположения, количества дополнительных слоев Au, скорости нагрева и атмосферы при отжиге можно управлять процесами упорядочения и формированием фазового состава, структуры и магнитными свойствами в пленочных композициях. Применение водородной термообработки ускоряет процессы упорядочения в пленках Fe50Pt50/Au/Fe50Pt50, по сравнению с отжигом в вакууме, за счет создания дополнительных сжимающих напряжений при внедрении атомов водовода в пустоты кристаллической решетки фазы L10-FePt. При этом ось легкого намагничиваня c в зернах фази L10-FePt располагается в плоскости пленки. Быстрый термический отжиг пленочных композиций [Pt/Fe]n (где n=4, 8) на подложках SiO2(100 нм)/Si(001) в атмосфере азота приводит к ориентированному росту зерен фазы L10-FePt с осью легкого намагничивания c, расположенной в направлении [001], перпендикулярном плоскости пленки.

This work has been devoted to the study of phase transformations involving chemical ordering and magnetic properties evolution in bulk Fe-Pt alloys composed of nanometer-sized grains. A comprehensive study of phase transformations and ordering in Fe-Pt alloys is performed by a combination of in-situ neutron powder diffraction and thermal analysis. The dependence of ordering processes on the alloy composition and initial microstructure (homogeneous A1 phase or multilayer-type) is established. Through the use of mechanical alloying and subsequent heat treatment it has been possible to achieve the formation of chemically highly ordered L10 FePt and, in the case of the Fe-rich and Pt-rich compositions, L12 Fe3Pt and FePt3 phases, respectively. Whereas in Pt-rich alloys the decoupling effect of the FePt3 phase leads to coercivity improvement, in Fe-rich nanocomposites a peculiar nanometer scale multilayer structure gives rise to remanence enhancement due to large effects of exchange interactions between the crystallites of the phases. The structure, magnetic properties and magnetisation reversal processes of these alloys are investigated. Experimentally observed phenomena are understood on the basis of a simple two-particle interaction model. Neutron diffraction has also been used for the investigation of the magnetic structure of ordered and partially ordered nanocrystalline Fe-Pt alloys. It has been shown that the magnetic moment of Fe atoms in L10-type Fe Pt alloys is sensitive to the compositional order. The results are compared to density functional calculations.

This work has been devoted to the study of phase transformations involving chemical ordering and magnetic properties evolution in bulk Fe-Pt alloys composed of nanometer-sized grains. A comprehensive study of phase transformations and ordering in Fe-Pt alloys is performed by a combination of in-situ neutron powder diffraction and thermal analysis. The dependence of ordering processes on the alloy composition and initial microstructure (homogeneous A1 phase or multilayer-type) is established. Through the use of mechanical alloying and subsequent heat treatment it has been possible to achieve the formation of chemically highly ordered L10 FePt and, in the case of the Fe-rich and Pt-rich compositions, L12 Fe3Pt and FePt3 phases, respectively. Whereas in Pt-rich alloys the decoupling effect of the FePt3 phase leads to coercivity improvement, in Fe-rich nanocomposites a peculiar nanometer scale multilayer structure gives rise to remanence enhancement due to large effects of exchange interactions between the crystallites of the phases. The structure, magnetic properties and magnetisation reversal processes of these alloys are investigated. Experimentally observed phenomena are understood on the basis of a simple two-particle interaction model. Neutron diffraction has also been used for the investigation of the magnetic structure of ordered and partially ordered nanocrystalline Fe-Pt alloys. It has been shown that the magnetic moment of Fe atoms in L10-type Fe Pt alloys is sensitive to the compositional order. The results are compared to density functional calculations.