Crystallization processes and phase evolution in amorphous Fe–Pt–Nb–B alloys

Crisan, O.; Crisan, A.; Randrianantoandro, N.; Nicula, R.; Burkel, E.

doi:10.1016/j.jallcom.2006.08.331

Cited by 25 publications

(10 citation statements)

References 10 publications

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“…The as-deposited film and the film annealed at 650 ℃ for 20 min show patterns with broad Bragg lines, centred at about 42° (in 2θ). In most alloys, such patterns are characteristic of a material structure made of small nanocrystals [23][24][25] with topological disorder [26,27] and dominant amorphous-like structure [28]. The broad Bragg lines observed in the patterns suggest the existence of a Cr-Al-C solid solution.…”

Section: X-ray Diffraction Patternsmentioning

confidence: 99%

Incipient low-temperature formation of MAX phase in Cr–Al–C films

Crisan

2018

J Adv Ceram

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Ceramic-metallic MAX phase of chromium aluminium carbide ternary compounds was successfully obtained through deposition by DC sputtering onto Si substrates. A study of the influence of substrate temperature and in-air post-annealing on the film crystallinity and oxidation was undertaken. Scanning electron microscopy (SEM), wavelength-dispersive X-ray analysis (WDSX), and X-ray diffraction (XRD) were used for film characterization. It is shown that, at substrate temperature of about 450 ℃, as-deposited films are amorphous with small nanocrystals. Subsequent annealing in air at 700 ℃ leads to film crystallization and partial oxidation. WDSX spectroscopy shows that the films oxidise to a depth of around 120 nm, or 5% of total film thickness which amounts at around 2.68 µm. As a novelty, this demonstrates the possibility of in-air crystallization of Cr 2 AlC films without significant oxidation. Materials Analysis Using Diffraction (MAUD) software package for a full-profile analysis of the XRD patterns (Rietveld-type) was used to determine that, as a result of annealing, the average crystallite size changes from 7 to 34 nm, while microstrain decreases from 0.79% to 0.24%. A slight tendency of preferential growth along the (10 10) direction has been observed. Such texturing of the microstructure has the potential of inducing beneficial anisotropic fracture behaviour in the coatings, potentially interesting for several industrial applications in load-bearing devices.

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Section: X-ray Diffraction Patternsmentioning

confidence: 99%

Incipient low-temperature formation of MAX phase in Cr–Al–C films

Crisan

2018

J Adv Ceram

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“…Various chemical and physical synthesis methods, such as thermal decomposition using high-temperature boiling point solvents [ 7 ], polyol [ 8 ], microemulsions [ 9 ], microwave processing [ 10 ], sonochemistry [ 11 ], pulsed plasma in liquid [ 12 ], or inert gas condensation [ 13 ], have been used to obtain FePt nanoparticles with well-defined shape and controllable sizes. Various other reports deal with the specific link between synthesis methods and magnetic performances in a large range of magnetic materials [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ]. As a building block for various devices, FePt is also of interest.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Phase Coexistence and Hard–Soft Exchange Coupling in FePt Nanocomposite Magnets

et al. 2020

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With the aim of demonstrating phase coexistence of two magnetic phases in an intermediate annealing regime and obtaining highly coercive FePt nanocomposite magnets, two alloys of slightly off-equiatomic composition of a binary Fe-Pt system were prepared by dynamic rotation switching and ball milling. The alloys, with a composition Fe53Pt47 and Fe55Pt45, were subsequently annealed at 400 °C and 550 °C and structurally and magnetically characterized by means of X-ray diffraction, 57Fe Mössbauer spectrometry and Superconducting Quantum Interference Device (SQUID) magnetometry measurements. Gradual disorder–order phase transformation and temperature-dependent evolution of the phase structure were monitored using X-ray diffraction of synchrotron radiation. It was shown that for annealing temperatures as low as 400 °C, a predominant, highly ordered L10 phase is formed in both alloys, coexisting with a cubic L12 soft magnetic FePt phase. The coexistence of the two phases is evidenced through all the investigating techniques that we employed. SQUID magnetometry hysteresis loops of samples annealed at 400 °C exhibit inflection points that witness the coexistence of the soft and hard magnetic phases and high values of coercivity and remanence are obtained. For the samples annealed at 500 °C, the hysteresis loops are continuous, without inflection points, witnessing complete exchange coupling of the hard and soft magnetic phases and further enhancement of the coercive field. Maximum energy products comparable with values of current permanent magnets are found for both samples for annealing temperatures as low as 500 °C. These findings demonstrate an interesting method to obtain rare earth-free permanent nanocomposite magnets with hard–soft exchange-coupled magnetic phases.

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“…However, a reduction of the ordering temperature required for L1 0 phase formation can be obtained via suitable modulation of the stoichiometry, for example by adding other elements to the composition. In the case of the FePt system, noble metals such as Au, Ag or Nb have been considered as suitable additions, having the role of promoting early ordering by segregation to the (Fe,Co)Pt grain boundaries [7][8][9][10][11][12][13][14] while a glass-forming element such as boron has been added to FePt to allow synthesis by out-of-equilibrium techniques such as rapid solidification from the melt [15][16][17][18][19][20][21].Chang et al [22] have studied the effect of Co substitution on the magnetic properties of melt-spun (Fe,Co)-Pt-B nanocomposite ribbons and found that Co substitution enhances the coercivity and energy product due to the formation of ordered L1 0 -(Fe,Co)Pt phase with higher anisotropy field. Makino et al [23] obtained the crystalline ordered L1 0 -FePt phase, with high coercivity, directly formed by rapid quenching of the melt in (Fe,Co)-Pt-Zr-B system, in the compositional range of 2-5 at.…”

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confidence: 99%

“…However, no L1 0 phase has been obtained due to low Pt concentration in that alloy and amorphous as-cast state was obtained due to the presence of two glass-forming elements (B and Si) with an abundance of 22 at. %.Additional elements have been introduced in the alloy stoichiometry of FePt-based systems [8,9], to diminish the temperature of the phase transformation and to provide a fine tuning of the as-obtained microstructure. The subsequent purpose is to enhance both the magnetic and structural features.…”

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Annealing-Induced High Ordering and Coercivity in Novel L10 CoPt-Based Nanocomposite Magnets

Crisan

Vasiliu

Mercioniu

et al. 2018

Metals

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A novel class of quaternary intermetallic alloys based on CoPt is investigated in view of their interesting magnetic properties induced by the presence of hard magnetic L1 0 phase. A Co 48 Pt 28 Ag 6 B 18 alloy has been prepared by rapid solidification from the melt and subjected to various isothermal annealing procedures. The structure and magnetism of both as-cast and annealed samples as well as the phase evolution with temperature are investigated by means of thermal analysis, X-ray, and selected area electron diffraction, scanning and high-resolution electron microscopy, and magnetic measurements. The X-ray diffraction (XRD) analysis shows that both the as-cast alloy and the sample annealed at 400 • C (673 K) have a nanocrystalline structure where fcc CoPt phase predominates. Annealing at 473 • C promotes the formation of L1 0 phase triggered by the disorder-order phase transformation as documented in the differential scanning calorimetry results. The sample annealed at 670 • C (943 K) shows full formation of L1 0 CoPt as revealed by XRD. Magnetic measurements showed coercivity values ten times increased compared to the as-cast state. This confirms the full formation of L1 0 CoPt in the annealed samples. Moreover, detailed atomic resolution HREM images and SAED patterns show the occurrence of the rarely seen (003) superlattice peaks, which translated into a high ordering of the L1 0 CoPt superlattice. Such results spur more interest in finding novel classes of nanocomposite magnets based on L1 0 phase.at 675 • C (948 K) does the disorder-order phase transformation take place in CoPt and the strong remanence enhancement effect is due to the multiple phase character of the samples, as it originates from exchange coupling between the face-centered-tetragonal (fct)-ordered hard magnetic phase and the face-centered-cubic (fcc)-disordered soft magnetic matrix.The high ordering temperature is regarded as an obstacle for future utilization of such alloys as the next class of nanocomposite magnets. However, a reduction of the ordering temperature required for L1 0 phase formation can be obtained via suitable modulation of the stoichiometry, for example by adding other elements to the composition. In the case of the FePt system, noble metals such as Au, Ag or Nb have been considered as suitable additions, having the role of promoting early ordering by segregation to the (Fe,Co)Pt grain boundaries [7][8][9][10][11][12][13][14] while a glass-forming element such as boron has been added to FePt to allow synthesis by out-of-equilibrium techniques such as rapid solidification from the melt [15][16][17][18][19][20][21].Chang et al. [22] have studied the effect of Co substitution on the magnetic properties of melt-spun (Fe,Co)-Pt-B nanocomposite ribbons and found that Co substitution enhances the coercivity and energy product due to the formation of ordered L1 0 -(Fe,Co)Pt phase with higher anisotropy field. Makino et al. [23] obtained the crystalline ordered L1 0 -FePt phase, with high coercivity, directly formed by rapid q...

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Crystallization processes and phase evolution in amorphous Fe–Pt–Nb–B alloys

Cited by 25 publications

References 10 publications

Incipient low-temperature formation of MAX phase in Cr–Al–C films

Incipient low-temperature formation of MAX phase in Cr–Al–C films

Magnetic Phase Coexistence and Hard–Soft Exchange Coupling in FePt Nanocomposite Magnets

Annealing-Induced High Ordering and Coercivity in Novel L10 CoPt-Based Nanocomposite Magnets

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