Identification of a high-temperature magnetic phase transition in ball-milled and compacted nanocrystalline Fe-Cu alloys (original) (raw)
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Magnetic Properties of Nanocrystalline Fe x Cu 1-x Alloys Prepared by Ball Milling
Hyperfine Interactions, 2000
X-ray diffraction, Mössbauer and magnetization measurements were used to study Fe x Cu 1−x alloys prepared by ball-milling. The X-ray data show the formation of a nanocrystalline Fe-Cu solid solution. The samples with x 0.8 and x 0.5 exhibit bcc or fcc phase, respectively. Both the bcc and fcc phases are principally ferromagnetic for x 0.2, but the sample with x = 0.1 remains paramagnetic down to 78 K. The influence of the local environment on the hyperfine parameters and the local magnetic moment are discussed using calculations based on the discrete-variational method in the local density approximation.
Journal of Magnetism and Magnetic Materials, 2004
Fe 1Àx Co x ) 86 Hf 7 B 6 Cu 1 (x ¼ 021) alloys were investigated as candidates for soft magnetic materials for elevated temperature applications. The lattice parameter of nanoscale precipitate decreases with the increasing of Co content because of the large Co solubility in the aða 0 Þ-Fe(Co) solid solution. However, it is a little larger than that of the crystalline phase in the Fe(Co) binary alloy. The Curie temperature of amorphous alloys studied monotonously increases with the increase of Co content. The nanocrystallized alloy with Co content of x ¼ 0:4 exhibits both the higher magnetization and lower coercivity at the elevated temperature, being the optimum alloy among the alloys studied for high temperature applications. r
Journal of Alloys and Compounds, 2010
The structure of annealed Sm(Co 0.6 Cu 0.4 ) 5 compounds, prepared with different Sm excess content, has been investigated by means of high resolution x-ray diffraction and scanning electron microscopy. The samples were also magnetically characterized by thermomagnetic analysis and M versus H curves at room temperature. Increasing Sm excess improves the compositional order of the 1 : 5 phase. The coercivity (H C ) and the Curie temperature (T C ) are both changed as a function of Sm excess content. The decrease in the structural defects density, resulting from the compositional order, is responsible for the observed magnetic behaviour.
International Journal of Materials Research, 2010
Fe 1Àx Co x (x = 0.1, 0.15, 0.2, 0.25, 0.3 and 0.5) powders were prepared by different milling-annealing treatments, and magnetic properties were investigated based on microstructure. Elevated heating times led to an increase in crystallite size, and decrease in lattice parameter. Up to 20 min annealing, series 3 powders showed a decrease in microstrain 2.5 times more than series 2. The coercivity (H C ) of 1-step milled and 60 min annealed Fe 50 Co 50 alloys decreased rigorously from 60 Oe to 19 Oe due to strain relief (from 0.3% to 0.08%) and grain growth (from 30 nm to 40 nm). For series 2 alloys, the H C (up to 60 min heating) increased from 72 Oe to 90 Oe, and decreased (up to 100 min heating) to 70 Oe. Compared to series 1, extra milling treatment of series 2 causes an increase in magnetization saturation (M S ) due to completion of alloying and grain refinement. Also, compared to series 2, extra annealing treatment for series 3 resulted in larger values of M S caused by stain relief.
High-temperature magnetic behavior of FeCo-based nanocrystalline alloys
Physical Review B, 2002
The soft magnetic response of nanocrystalline Fe 73.5Ϫx Co x Si 13.5 B 9 Cu 1 Nb 3 ͑xϭ0, 30, and 45͒ samples are analyzed above room temperature through the temperature evolution of the magnetic permeability and the associated loss factor. Moreover, the actual structure and composition of the crystalline phase is analyzed through neutron-diffraction studies. The results show that the inclusion of Co atoms give rise to an improvement in the soft magnetic behavior at high temperatures with respect to the Fe-based sample as a consequence of the increase in the Curie temperature of the precipitated crystallites. However, the role of the residual amorphous matrix cannot be disregarded and the decrease in its Curie temperature for the Co richest sample gives rise to a deterioration of the high-temperature soft magnetic response. The observed temperature evolution is analyzed within the framework of the random anisotropy model and associated with the temperature dependence of the magnetic coupling between the ferromagnetic crystals.
Magnetic and structural properties of as-milled and heat-treated bcc-Fe70Cu30 alloy
Journal of Magnetism and Magnetic Materials, 1995
A ferromagnetic solid solution with a nomina] atomic composition FeroCUr~ and a body-cen~ structure has been obtained by high-energy ball milling. The decomposition of the system is monitored by X-ray diffraction (XRD), measurements and M~ssbauer spectroscopy. According to XRDo for heating lcmpe.~tures below 723 K there is only a bcc ph.".~e in the material, while fvr heating temperatures above 723 K a new phase, with a fcc structure, appears, suggesting lha~ the solid solution has decomposc'd into bce-Fe and fcc-Cu. However, the magnetic behavior observed during the decomposition process indicates that this evolution is more complex than the simple deeomposition into the equilibrmm phases. This behavior can be summarized in two points: (1) a decrease in the ma~-tization at 5 K, and (2) dra~Ii¢ cha~'cs in the coercive field with the thermal treatment, soft magnetic behavior for the matc~"ial in the as-milled sta~e, ~a~g~ netism for low heating temperatures and a hardening of the mat~al ~ to above 723 K, for which the va|~es of the coercive field at room temperature are several times higher than those for the as-milled sampte. The Mtissbat~r st~ctrosc~y performed at room temperature shows thai for the heat-u~ated samples ~i~ Fe atoms are in two differem phases: a ferromagnetic phase, which evolves to bcc-Fe, and a paramag,~et~: phase.
Journal of Alloys and Compounds, 2010
The mechanical alloying process has been used to prepare nanocrystalline Fe70−xCuxCo30 (x = 0, 3, 6, and 10) alloy from powder mixture. The structure and magnetic properties were investigated through powder X-ray diffraction (XRD), electron microscopy and magnetization measurements. The XRD patterns show a bcc crystal structure with lattice constant 0.2865 nm and crystallite size (D) of 15 nm evolves on 60 h milling in the case of Fe–Co alloy. But it is found that Cu speeds up the formation of bcc phase with finer microstructure (D = 7 nm for x = 10). Increase in microstrain is observed with the milling time and also with Cu concentration. The magnetic measurements show a contrasting saturation magnetization and coercivity (HC) for the case of samples having lower (x ≤ 3) and higher (x > 3) Cu content in Fe–Co alloys. These variations are explained on the basis of crystallite size and strain variations in the samples during milling. Present results indicate that a nonmagnetic inc...
Journal of Magnetism and Magnetic Materials, 2014
Synthesis of Cu 1 À x Zn x Fe 2 O 4, (x ¼0.00, 0.02, 0.04 and 0.08) nanoparticles by a low-temperature combustion method is achieved and its structural and magnetic characterizations are performed. X-ray powder diffraction (XRD) study and high resolution transmission electron microscope (HRTEM) images confirm the formation of single cubic phase of nanocrystalline copper ferrite. The inter-planar spacing (d) and particle size increases with increasing Zn content. Cation distribution of mixed spinel Cu 1 À x Zn x Fe 2 O 4 nanoparticles are estimated by Fourier transformed infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and further verified by 57 Fe Mossbauer spectroscopy. Detailed magnetic properties are studied by means of Field Cooled (FC)-Zero Field Cooled (ZFC) magnetization measurements and hysteresis loops at various temperatures by the physical property measurement system (PPMS). A transition from superparamagnetic state to ferrimagnetic state is observed as the Zn concentration increases in Cu 1 À x Zn x Fe 2 O 4 nanoparticles. The temperature dependence of intrinsic magnetic parameters, i.e., coercivity (H C), saturation magnetization (M S), effective anisotropy constant (K eff) and paramagnetic susceptibility (χ p) of Cu 1 À x Zn x Fe 2 O 4 reveals the existence of low-temperature spin-glass-like state, which is more prominent for smaller particles and starts to disappear with increasing Zn concentration.
Journal of Applied Physics, 2015
Composition gradient and phase separation at the nanoscale have been investigated for arc-melted and solidified with equiatomic Fe-Cu. Diffraction studies revealed that Fe and Cu exhibited phase separation with no trace of any mixing. Microscopy studies revealed that immiscible Fe-Cu form dense bulk nanocomposite. The spatial distribution of Fe and Cu showed existence of two distinct regions, i.e., Fe-rich and Cu-rich regions. Fe-rich regions have Cu precipitates of various sizes and different shapes, with Fe forming meshes or channels greater than 100 nm in size. On the other hand, the matrix of Cu-rich regions formed strips with fine strands of nanosized Fe. Macromagnetic response of the system showed ferromagnetic behavior with a magnetic moment being equal to about 2.13 l B =Fe atom and a bulk like negligible value of coercivity over the temperature range of 5-300 K. Anisotropy constant has been calculated from various laws of approach to saturation, and its value is extracted to be equal to 1350 J/m 3. Inhomogeneous strain within the Cu and Fe crystallites has been calculated for the (unannealed) sample solidified after arc-melting. Annealed sample also exhibited local inhomogeneity with removal of inhomogeneous strain and no appreciable change in magnetic character. However, for the annealed sample phase separated Fe exhibited homogenous strain. V
Journal of Non-crystalline Solids, 2001
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