Magnetic Properties Of Alloys Research Articles

First-principles calculations and experimental studies on Cr2MnAl Heusler alloy nanoparticles for spintronics applications

In depth understanding of the magnetic, structural and electrical properties of Heusler alloys are crucial to achieve potential applications in spin-based device. Wherein, we report the synthesis of Cr2MnAl Heusler alloy nanoparticles (NPs) via co-precipitation method and also demonstrated their transport properties. Interestingly X-ray analysis confirms the cubic phase of the synthesized Heusler alloy NPs and transmission electron microscopy (TEM) analysis reveals that the Cr2MnAl as particle size of 10 ± 2 nm. Moreover, this particle size has adverse effect on symmetry of Cr2MnAl Heusler alloy due to their higher surface to volume ratio that significantly changes their magnetic and electrical properties. These NPs exhibit soft ferromagnetic properties with a Curie temperature (Tc) of 25 K. Besides, resistivity measurements indicate the semiconducting nature and also we report the observation of anomalous Hall effect. In addition, we support our experimental results by studying the electronic and magnetic properties of alloy using first principle calculations. This density functional theory reveals that Cr2MnAl has half metallic characteristics with high spin polarization. In light of above, this material can be used as intermediate layer to decouple the two ferromagnetic layers which acts as spin-polarized carriers in spin-based device.

Critical behavior, structural, electronic, and magnetic properties of the Heusler alloy: CoFeCrP

In this work, we study the equiatomic quaternary Heusler alloy (EQHA) CoFeCrP using two methods: density functional theory (DFT) and Monte Carlo simulations. The DFT method allowed us to illustrate the structural, electronic, and magnetic properties of this alloy. The ground state phase diagrams have been presented to show the stable configurations in different physical parameter planes. On the other hand, the Monte Carlo simulations, performed under the Metropolis algorithm, permitted to deduce the critical the behavior of the EQHA CoFeCrP. The structural properties results show that the phase of type I, of this alloy is the most stable configuration. In addition, the band structures and density of states calculations results show that this compound exhibits a half-metallic character with a 100% of spin polarization (SP) at the Fermi-level. The total magnetic moment of the Heusler compound is found to be 4.00 µB. Moreover, it is found that the Slater-Pauling is well described for this alloy. Our results show that this material is a potential candidate for the spintronic applications. This is due to its half-metallicity, its high spin moments, its complete SP polarization, and its high Curie temperature.

Magnetic Properties of a High-Pressure Torsion Deformed Co-Zr Alloy.

Co-Zr amorphous alloys exhibit soft magnetic properties, whereas the Co-rich crystalline magnetic phases in this alloy system displayed a hard magnetic behavior. In this study, an initial two-phase Co-Zr composite with an overall composition of 75 at.% Co and 25 at.% Zr was processed by high-pressure torsion (HPT), and the effects of severe plastic deformation and subsequent thermal treatment on the composite's structural evolution and its magnetic properties were investigated. HPT processing allowed us to achieve an amorphous microstructure with low coercivity in its as-deformed state. To further tune the alloy's magnetic properties and study its crystallization behavior, various annealed states were investigated. The microstructural properties were correlated with the magnetic properties, and a decreasing coercivity with increasing annealing temperatures was observed despite the onset of crystallization in the amorphous alloy. At higher annealing temperatures, coercivity increased again. The results appear promising for obtaining tuneable rare-earth free magnetic materials by severe plastic deformation.

Microstructural and magnetic properties of Mn2FeSi and Mn2FeAl alloys prepared in bulk form

Microstructural and magnetic properties of the Mn2FeSi and Mn2FeAl alloys prepared in the bulk form have been investigated. Cylinder-shaped ingots produced by induction melting technique were analyzed in as-quenched state and additionally annealed at 773 K for 5 days in the protective argon atmosphere. The results show that Si and Al have different effects on the microstructural and magnetic properties of the alloys. The Mn2FeAl ingots are single-phase both before and after annealing, and their diffractograms surprisingly correspond not to the Heusler (L21 or XA) but to the primitive cubic β-Mn structure. Conversely, Mn2FeSi alloys show a two-phase behavior in the as-quenched state. From results of X-ray diffraction it was not possible to judge whether Mn2FeSi alloy has the inverse-Heusler (XA) or full Heusler (L21) structure. Annealing of Mn2FeSi leads to the formation of multiple phases. The EDX chemical area analyses resulted in only slight deviations of compositions compared to the nominal ones. The lattice parameters of 0.5672 nm and 0.6339 nm were estimated for the Mn2FeSi and Mn2FeAl samples from X-ray diffraction measurements. From the magnetic viewpoint, all samples are paramagnetic at room temperature and transform into antiferromagnetic state at the N é el temperatures about 50 K and 36 K for Mn2FeSi and Mn2FeAl, respectively. The negative Curie temperatures determined at all samples by Curie-Weiss law indicate an antiferromagnetic ordering of spins. Positron annihilation investigations revealed that Mn2FeSi contains a high concentration of vacancies. The local chemical environment of vacancies characterized by coincidence Doppler broadening is compatible with L21 rather than with XA structure. In contrast vacancy concentration in Mn2FeAl is very low and almost all positrons are annihilated in the free state.

C and N effect on magnetic coupling and vibrational properties of bcc and fcc-FeMnCr alloys: DFT study

In this work we report, magnetic and thermal properties of the bcc-Fe0.52MnxCr0.28-xCu0.06Mo0.10C0.012N0.014 (xMn = 5.77, 11.51 and 17.22 wt%) and the fcc-Fe0.63MnxCr0.26-xCu0.03Mo0.05C0.006N0.007 (xMn = 8.98, 11.95 and 14.92 wt%) alloys, applying the pseudo-potential Density Functional Theory (PP-DFT). The obtained results show that magnetic properties of these alloys are governed by Mn concentrations and C, N additions. The magnetic moments at each atom depend strongly on Mn concentrations as well as on the presence of C, N atoms. The C, N or both CN additions into octahedral sites do not affect the magnetic coupling between atoms. The quasi-harmonic Debye model is successfully applied to predict thermal properties of these alloys. The bulk modulus, volume expansion and Gibbs free energy are significantly affected by temperature, Mn concentrations and C, N additions in both bcc and fcc alloys. Whereas, vibrational entropy is more affected by bcc–fcc phase transition than C, N addition and Mn concentration.

Effects of Heat Treatment and on Magnetic Properties of NdFeB Based Permanent Magnet Alloys

In this study, the effect of flash annealing heat treatment applied at 680 oC for 5 minutes on the magnetic properties of NdFeB-based permanent magnet alloys produced by melt spinning method, which is one of the fast solidification methods, was investigated by using a very fast heating and cooling rate of 300 K/s. The obtained results showed that there was a remarkable improvement in the magnetic properties of the alloys with the applied heat treatment. Mainly, the hard magnetic properties were optimized by enhancing magnetic remanence from 21.64 emu/g to 55.76 emu/g, magnetic coercivity from 1184.15 Oe to 9146.30 Oe, and maximum energy product from 4.06 kJ/m3 to 62.02 kJ/m3 respectively.

Microstructure and magnetic properties of anisotropic Mn-Bi powder prepared by low energy ball milling assisted with polyvinylpyrrolidone

The excellent anisotropic Mn55Bi45 powder was prepared by arc melting and surfactant-assisted low-energy ball milling (LEBM). The microstructure and magnetic properties of the alloy were investigated. The ionic polyvinylpyrrolidone (PVP) was selected as a surfactant. The results show that the addition of PVP can improve the low-temperature phase (LTP) content and magnetic properties of the Mn55Bi45 alloy. The coercivity (Hcj) of the anisotropic Mn55Bi45 powder is 14.7 kOe, the maximum energy product ((BH)max) is 7.1 MGOe and the saturation magnetization (Ms) is 57.5 emu/g when it is 10 wt% PVP and after 3 h ball milling. The angle dependence of coercivity shows that mechanism of anisotropic Mn-Bi alloy follows to the Stoner-Wohlfarth model.

Microstructure and Properties of FeCoNiCuSix High Entropy Alloys

The microstructure morphology, hardness, corrosion resistance and magnetic properties of FeCoNiCuSix high entropy alloys prepared by vacuum arc melting at different Si content were studied. Found by multiple testing methods, the crystal structure of the FeCoNiCuSix high entropy alloy without Si has both FCC and BCC structures. After adding Si, all the structure of the alloy transforms to FCC, and there are differences between the alloys after adding Si, which mainly concentrates in the interdendritic areas and dendritic edges. At the same time, because of the addition of Si, the overall hardness of the alloy very significantly improves. When the content of Si < 0.2, the overall compressive property of the alloy decreases, but when the content of Si > 0.2, the alloy has a certain ductility and compressive strength. Due to the enrichment of Cu, the alloy is easy to form a primary cell at the enrichment of Cu, which reduces the corrosion resistance of the alloy. Meanwhile, a small amount of Si can form a solid solution in the Cu enrichment area, reduce the galvanic effect, and improve the corrosion resistance of the alloy. However, with the increase of Si content in the FeCoNiCuSix high entropy alloy, the corrosion resistance of the alloy will deteriorate and the corrosion rate will accelerate. At the same time, the addition of Si will also have a negative effect on the magnetic properties of the alloy.

Control of hysteretic properties in powder alloys based on the Fe–Cr–Co system

Hysteresis alloys based on the Fe–Cr–Co system are of scientific and practical interest, primarily due to their high manufacturability, high level and temperature stability of magnetic properties, which provide the required hysteresis magnet performance including residual magnetic induction, coercive force, and loop squareness ratio. The research was aimed to control and stabilize the Fe–Cr–Co ridge alloy magnetic properties using reageing. The 22Kh15K4MS hard magnetic powder alloy was investigated after quenching and multistage aging. Billets were obtained by cold pressing at a pressure of 600 MPa and subsequent sintering in vacuum. The samples obtained by sintering in the α phase in the presence of the liquid phase formed during contact melting had a porosity of up to 1 %. The concentration heterogeneity of chromium and cobalt distribution was 0.06–0.08. The alloy magnetic structure parameters were determined by electron microscopy. The relationship between the magnetic structure formation kinetics during aging and the level of magnetic properties was established. After aging, the fine structure of the 22Kh15K4MS alloy was represented by elongated α1 phase sections in the α2 phase matrix. The average particle sizes of the α1 phase were »124 nm in length and »44 nm in width after the first stage of aging, and they remained the same after final aging. It was shown that it is possible to control magnetic properties by reaging without repeated quenching. A slight change in the size and morphology of magnetic phase particles was observed during aging. The influence of the number of reaging cycles on the stability of magnetic properties over time was determined.

The Effects of La Doping on the Crystal Structure and Magnetic Properties of Ni2In-Type MnCoGe1-xLax (x = 0, 0.01, 0.03) Alloys.

In this experiment, a series of MnCoGe1−xLax (x = 0, 0.01, 0.03) alloy samples were prepared using a vacuum arc melting method. The crystal structure and magnetic properties of alloys were investigated using X-ray diffraction (XRD), Rietveld method, physical property measurement system (PPMS), and vibrating sample magnetometer (VSM) analyses. The results show that all samples were of high-temperature Ni2In-type phases, belonging to space group P63/mmc (194) after 1373 K annealing. The results of Rietveld refinement revealed that the lattice constant and the volume of MnCoGe1−xLax increased along with the values of La constants. The magnetic measurement results show that the Curie temperatures (TC) of the MnCoGe1−xLax series alloys were 294, 281, and 278 K, respectively. The maximum magnetic entropy changes at 1.5T were 1.64, 1.53, and 1.56 J·kg−1·K−1, respectively. The respective refrigeration capacities (RC) were 60.68, 59.28, and 57.72J·kg−1, with a slight decrease along the series. The experimental results show that the doping of La results in decreased TC, basically unchanged magnetic entropy, and slightly decreased RC.

Electronic, structural and magnetic properties of Mn(1+x)Pt(1-x)Sb

Electronic and magnetic properties of half-metallic Heusler alloys can be modified by tuning their chemical compositions. We have carried out a combined theoretical and experimental investigation of Mn(1+x)Pt(1-x)Sb (0 ≤ x ≤ 0.5) alloys. Our first-principles calculations indicate that the stoichiometric MnPtSb exhibits nearly half-metallic band structure, but a robust half-metallicity can be achieved in Mn-rich compositions Mn(1+x)Pt(1-x)Sb (0 ≤ x ≤ 0.5) with x = 0.25 and higher in their cubic structures. In addition, while MnPtSb exhibits ferromagnetic alignment, Mn(1+x)Pt(1-x)Sb are ferrimagnetic for all non-zero values of x. We have also synthesized cubic MnPtSb and Mn1.25Pt0.75Sb alloys using arc melting and annealing. The magnetic properties of these alloys are consistent with our theoretical predictions. These results indicate that the Mn-rich Mn(1+x)Pt(1-x)Sb alloys have potential for spin-transport-based devices.

Effect of Quaternary Element (Ni and Mn) Additions on Structural and Magnetic Properties of Cu-Based Alloys

We investigated the quaternary Cu-25.49%Zn-7.68%Al-3.44%Ni and Cu-26.03%Zn-6.31%Al-2.73%Mn (wt. %) alloys according to their structural and magnetic properties. For structural observations, we employed X-ray diffraction (XRD), scanning electron microscope (SEM), and electron dispersion spectroscopy (EDS) techniques to study. The magnetic properties of alloys were characterized as a function of temperature (T) and applied external magnetic field (H) by using Physical Properties Measurement System (PPMS) magnetometry. According to SEM and XRD observations, the existing microstructures consist of two types of precipitates that are namely α and intermetallic κ-phases in CuZnAlNi alloy. We also observed the austenite phase in CuZnAlMn alloy. The M-H magnetization curves exhibited obvious paramagnetic behavior for the examined alloys. Although Ni and Mn elements have similar magnetic nature, they show different magnetic characteristics with different structures.

Investigation into Effect of Cooling Rate on Magnetic Properties of Alloys that Are Based on FeCoB Matrix

Investigation into Effect of Cooling Rate on Magnetic Properties of Alloys that Are Based on FeCoB Matrix

Effects of Nb and Mo additions on thermal behavior, microstructure and magnetic property of FeCoZrBGe alloy* *Project supported by the National Natural Science Foundation of China (Grant No. 51301075) and supported by Sinoma Institute of Materials Research (Guang Zhou) Co., Ltd.

Both Nb and Mo additions play a vital role in FeCo-based alloys and it is crucial to understand their roles and contents on thermal behavior, microstructural feature and magnetic property of alloys. Nanocrystalline alloy ribbons Fe40Co40Zr9 – y M y B10Ge1 (y = 0–4; M = Nb, Mo) were prepared by crystallizing the as-quenched amorphous alloys. The effects of Nb and Mo additions on structures and properties of the Fe40Co40Zr9B10Ge1 alloy are investigated systemically and compared. With increasing Nb or Mo content, the primary crystallization temperature, grain size of α-Fe(Co) phase and coercivity H c all decrease. Moreover, the effect of Mo addition on thermal behavior, microstructure and magnetic properties of the FeCoZrBGe alloy is greater compared to Nb addition. The gap between primary and secondary crystallization peaks of Mo-containing alloys is wider than that of Nb-containing alloys. Both grain size and H c of Mo-containing alloys are smaller than those of Nb-containing alloys. For Fe40Co40Zr9B10Ge1 alloy, high Mo addition proportion is better compared to high Nb addition proportion.

Thermal and magnetic properties of Fe(Co)BCCu amorphous alloys with high saturation magnetization of 1.77 T

The effects of partial substitution of Fe by Co on the thermal behaviors, Curie temperature and magnetic properties of Fe83.2-xCoxB10C6Cu0.8 amorphous alloys were investigated. Thermodynamic analysis revealed that Co doping expands the crystallization window of alloys and inactivates the annealing sensitivity of Fe(Co)–B/C compounds, although the first onset crystallization temperature slightly drops. The doping of Co can effectively regulate the Curie temperature and magnetic properties of alloys. The former increases from 327 to 476 °C and the later shows first increase and then decrease, and the maximum value of 1.77 T is achieved with 6 at.% Co doping, which is higher than that of most as-quenched Fe-based amorphous alloys reported so far. The theoretical calculation is consistent well with the experimental result that the magnetic moment per magnetic atom and exchange stiffness constant support the variation of saturation magnetization. Moreover, the coercivity of alloys was investigated by the magnetic domain structure.

Soft magnetic cobalt based amorphous alloys with low saturation induction

The influence of the concentration of alloying components on thermal stability, magnetic and electrical properties of amorphous alloys of Co73-66Fe4,6-3Cr0-9(B,Si)22-29 system was studied by methods of differential scanning calorimetry, XRD, resistometry and magnetometry. The crystallization of several alloys with advanced magnetic characteristics was studied. At continuous heating of the ribbons, either primary or eutectic crystallization was observed depending on the chemical composition of these alloys. Certain tendencies in the anomalous behavior of temperature dependence of electrical resistance of ribbons were revealed. By increasing chromium and metalloids concentrations, we obtained the alloys with relatively low saturation induction and large difference between the Curie temperature and the temperature of crystallization onset. The heat treatment regimes to obtain the best magnetic properties of these alloys were found. Prospective applications of Co73-66Fe4,6-3Cr0-9(B,Si)22-29 amorphous ribbons for fabrication of high sensitive sensors of magnetic field were discussed.

Magneto-structural correlations in a systematically disordered B2 lattice

Ferromagnetism in certain B2 ordered alloys such as Fe60Al40 can be switched on, and tuned, via antisite disordering of the atomic arrangement. The disordering is accompanied by a ∼1 % increase in the lattice parameter. Here we performed a systematic disordering of B2 Fe60Al40 thin films, and obtained correlations between the order parameter (S), lattice parameter (a0), and the induced saturation magnetization (Ms). As the lattice is gradually disordered, a critical point occurs at 1 − S = 0.6 and a0 = 2.91 Å, where a sharp increase of the Ms is observed. DFT calculations suggest that below the critical point the system magnetically behaves as it would still be fully ordered, whereas above, it is largely the increase of a0 in the disordered state that determines the Ms. The insights obtained here can be useful for achieving tailored magnetic properties in alloys through disordering.

Investigation into the Effect of Thermal Treatment on the Obtaining of Magnetic Phases: Fe5Y, Fe23B6, Y2Fe14B and αFe within the Amorphous Matrix of Rapidly-Quenched Fe61+xCo10−xW1Y8B20 Alloys (Where x = 0, 1 or 2)

The paper presents the results of research on the structure and magnetic properties of Fe61+xCo10−xW1Y8B20 alloys (where x = 0, 1 or 2). The alloys were produced using two production methods with similar cooling rates: Injection casting and suction casting. The alloy samples produced were subjected to isothermal annealing at 940 K for 10 min. The structure of the materials was examined using X-ray diffraction. Isothermal annealing has led to the formation of various crystallization products depending on the chemical composition of the alloy and the structure of the alloy in a solidified state. In two cases, the product of crystallization was the hard magnetic phase Y2Fe14B. However, the mechanism of this phase formation was different in both cases. The magnetic properties of alloys were tested using a vibrating sample magnetometer and a Faraday magnetic balance. It is found that the grain crystallite size of the crystalline phases have a decisive influence on the value of the coercive field (especially in the case of hard magnetic phases). It has been shown that privileged areas can already be created during the production process. Their presence determines the crystallization process.

Evolution of Microstructure, Magnetic Properties, and Thermal Stabilities of Isotropic Alnico Ribbons

The magnetic properties of alnico alloys are highly dependent on the spinodally decomposed nanostructure. In this article, we report the fabrication of alnico nanoribbons and the effects of various heat treatments on the magnetic properties, spinodal decomposition, microstructure, and temperature stability. It is found that the spinodal decomposition occurs in a wider range of temperatures from 800 °C to 860 °C. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses of the microstructure confirmed that the nanostructure phases develop in a wide temperature range. Aspect ratio of the order of ~20 is obtained by optimizing the heat treatment conditions. Magnetic properties of H cj = 815 Oe, B r = 6.70 kG, and (BH) max = 1.88 MGOe are obtained after simplified heat treatment. The magnetic properties of the alloys are measured at low (10 K) and at high (800 K) temperature, and it is shown by calculating temperature coefficient of remanence (α) and temperature coefficient of coercivity (β) that alnico ribbons possess extraordinary temperature stability at low and high temperatures.

Calculation of the exchange integrals for Co1-xNix alloy by Korring-Kohn-Rostoker method

In this work we investigate the cobalt-nickel alloy magnetic properties. Calculations of lattice constants for Co, Ni and Co1-xNix alloy with different concentrations were performed with the VASP framework. Calculations of the exchange integrals were carried out using the SPR-KKR package (spin-polarized relativistic Korring-Kohn-Rostoker method). For pure ferromagnets, the Co exchange interaction is ferromagnetic. For Ni, the exchange interaction of the nearest neighbors also is ferromagnetic, but the exchange interaction of the next nearest neighbors has a very weak antiferromagnetic character. In the Co1-xNix alloy, the exchange interaction of the nearest neighbors JNi–Co1 and JCo–Co1 increases with increasing nickel concentration. The next nearest neighbors exchange interaction at a concentration of Ni x ≥ 0.5 has an antiferromagnetic character.