Effect Of Fe Substitution Research Articles

Metallurgical origin of the effect of Fe doping on the martensitic and magnetic transformation behaviours of Ni 50Mn 40-xSn 10Fe x magnetic shape memory alloys

This study investigated the metallurgical origin of the effects of Fe substitution for Mn on the martensitic and the magnetic transformation behaviours of Ni 50Mn 40-xSn 10Fe x ( x = 0, 3, 4, 5, 6) alloys. Substitution of Fe for Mn at above 3 at% introduced an fcc γ phase in the microstructure. Formation of the γ phase influenced the composition of the bcc/B2 matrix, leading to decrease in martensitic transformation temperatures and transformation entropy change. The Curie temperature of the parent phase increased slightly, whereas the Curie temperature of the martensite increased rapidly with increasing Fe addition. Changes in the temperatures of the martensitic and magnetic transformations are confirmed to directly relate to the e/a ratio of the matrix caused by formation of γ phase. The minimum e/a ratio value for the occurrence of the martensitic transformation is estimated to be 8.045 for the alloy system studied. A narrow e/a ratio range of 8.113–8.137 is estimated for the occurrence of metamagnetic transformation M ( p a r a ) ⇔ A ( f e r r o ) . This metamagnetic reverse transformation was induced by a magnetic field at 225 K within a range of 3–7 T in the Ni 50Mn 35Sn 10Fe 5 alloy. The magnetic work required to induce the transformation is estimated to be ∼176 J/kg, comparable to the thermodynamic energy deficit for the transformation at the testing temperature estimated from thermal measurement. These findings clarify the origin of the effects of Fe doping in Ni 50Mn 40-xSn 10 alloys and provides reference on alloys design for this system.

Neutron-Scattering Study of Fe-Substitution Effect on the Static Spin Correlation in La2-xSrxNiO4

We have performed elastic neutron scattering measurements on the Fe-doped La 2- x Sr x NiO 4 (LSNO) with 0.12 ≤ x ≤0.50 to study the magnetic impurity effects on the static spin correlations. In the pristine LSNO system, it is well known that both spin and charge stripe orders are stabilized at low temperatures in the wide hole concentration range from 0.12 to 0.70. The incommensurability (e) increases upon Sr-doping and tends to saturate with e max ∼0.47 (r.l.u.) for x > 0.5. We found that 4% Fe-substitution for Ni ion reduces e at the fixed Sr concentration for the all measured samples with 0.12 ≤ x ≤0.5. The e in the Fe-substituted samples with x = 0.25, 0.33, 0.37, and 0.50 was 0.02–0.04 (r.l.u.) smaller than that in the pristine samples. Furthermore, we observed commensurate peak in the Fe-doped x = 0.12 sample. No well-defined incommensurate magnetic peaks were detected, unlike to the result for the pristine x = 0.12 sample. The effect of Fe-substitution on the magnetic ordering temperature ( T spin...

Effect of Fe substitution on magnetocaloric effect in La0.7Sr0.3Mn1−xFexO3 (0.05≤x≤0.20)

We have studied the effect of Fe substitution on magnetic and magnetocaloric properties in La0.7Sr0.3Mn1−xFexO3 (x=0.05, 0.07, 0.10, 0.15, and 0.20) over a wide temperature range (T=10–400K). It is shown that substitution by Fe gradually decreases the ferromagnetic Curie temperature (TC) and saturation magnetization up to x=0.15 but a dramatic change occurs for x=0.2. The x=0.2 sample can be considered as a phase separated compound in which both short-range ordered ferromagnetic and antiferromagnetic phases coexist. The magnetic entropy change (−ΔSm) was estimated from isothermal magnetization curves and it decreases with increase of Fe content from 4.4Jkg−1K−1 at 343K (x=0.05) to 1.3Jkg−1K−1 at 105K (x=0.2), under ΔH=5T. The La0.7Sr0.3Mn0.93Fe0.07O3 sample shows negligible hysteresis loss, operating temperature range over 60K around room temperature with refrigerant capacity of 225Jkg−1, and magnetic entropy of 4Jkg−1K−1 which will be an interesting compound for application in room temperature refrigeration.

Ac susceptibility studies in Fe doped La0.65Ca0.35Mn1−xFexO3: Rare earth manganites

The effects of Fe substitution on Mn sites in the colossal magnetoresistive compounds La0.65Ca0.35Mn1−xFexO3 with 0.00≤x≤0.10 have been studied. A careful study in the magnetic properties has been carried out by the measurement of magnetic ac susceptibility. The temperature range of colossal magnetoresistance (CMR) is greatly broadened with the addition of Fe. Substitution of Fe induces a gradual transition from a metallic ferromagnetic with a high Curie temperature (Tc=270 K) to a ferromagnetic insulator with low Tc=79 K. Increased spin disorder and decrease of Tc with increasing Fe content are evident. The variations in the critical temperature Tc and magnetic moment show a rapid change at about 4%–5% Fe. The effect of Fe is seen to be consistent with the disruption of the Mn-Mn exchange possibly due to the formation of magnetic clusters. An extraordinary behavior in the out of phase part (χ″) of ac susceptibility, characterized by double bump (shoulder), was observed around x=0.01 and 0.02. The shoulder in χ″ disappears at x≥0.04 Fe concentration. With increasing Fe concentration the χ″ peak shift to T<T1/2 (mid point of the transition temperature) and becomes broader. The χ″ peak moves to 8 or 10 K higher temperature on the application of a dc field, for 3 and 4% Fe samples. We observed that increasing the Fe, leads to increased spin disorder and dissipation at low temperature. The effects of the dc field are discussed in terms of the suppression of spin fluctuations close to Tc. The same ionic radii of Fe3+ and Mn3+ cause no structure changes in either series, yet ferromagnetism has been consistently suppressed by Fe doping. Doping with Fe bypasses the usually dominant lattice effects, but depopulates the hopping electrons and thus weakens the double exchange. The results were explained in terms of the formation of magnetic clusters of Fe ions.

Effect of Fe substitution on the phase stability and magnetic properties of Mn-rich Ni–Mn–Ga ferromagnetic shape memory alloys

The influence of Fe additions on the martensitic transformation and magnetic properties of Mn-rich Ni–Mn–Ga alloys was investigated by substituting either 1 at% Fe for each atomic species or by substituting Ni with varying amounts of Fe. The magnetic structure of the alloys was studied using 57Fe Mössbauer spectroscopy. Mössbauer spectra revealed typical paramagnetic features in Mn-rich Ni–Mn–Ga–Fe alloys owing to the preferential site occupancy of Fe atoms at Ni sites. The evolution of the magnetic properties and phase stability has been correlated with the chemical and atomic ordering in these alloys.

Effects of Fe substitution on structural and magnetic properties of the Nd 2Co 7− xFe x compounds

The structural and magnetic properties of the Nd 2Co 7− x Fe x compounds related to R m+ n T 2 m+5 n series (R = rare earth, T = transition metal) were investigated by means of X-ray diffraction and magnetic measurements. The compounds crystallize in the Ce 2Ni 7-type structure with the space group P6 3/ mmc between x = 0.0 and 2.1. For higher Fe content the Nd 2(CoFe) 7 either coexists with the Nd(CoFe) 3 phase ( x > 2.1) or decomposes to Nd(CoFe) 3 + Nd 2(CoFe) 17 ( x > 2.4). The single phase Nd 2Co 7− x Fe x compounds exhibit two spin-reorientation transitions (SRT) for x < 1.5. The substitution of Fe for Co elevates both the spin-reorientation transition temperatures for x < 1.5 and finally leads to a single ferromagnetism to paramagnetism transition for x ≥ 1.5. A magnetic phase diagram is constructed based on the magnetic measurements, thermogravimetry analysis under a low magnetic field and X-ray diffraction of magnetically aligned samples. The saturation magnetization of the compounds increases gradually first with the Fe content for x ≤ 0.20, substantially for 0.20 < x < 1.5, and then decreases for x > 1.5, which can be elucidated by a depletion effect of d band electrons due to the substitution of Fe for Co and the spin-flipping due to an enhanced d band splitting.

Effect of Fe substitution on the structure and properties of LnBaCo 2− xFe xO 5+ δ (Ln = Nd and Gd) cathodes

The effect of Fe substitution for Co on the crystal chemistry, thermal and electrical properties, and catalytic activity for oxygen reduction reaction of the layered LnBaCo 2− x Fe x O 5+ δ (Ln = Nd and Gd) perovskite has been investigated. The air-synthesized LnBaCo 2− x Fe x O 5+ δ samples exhibit structural change with increasing Fe content from tetragonal (0 ≤ x ≤ 1) to cubic (1.5 ≤ x ≤ 2) for the Ln = Nd system and from orthorhombic ( x = 0) to tetragonal (0.5 ≤ x ≤ 1) for the Ln = Gd system. The thermal expansion coefficient (TEC) and electrical conductivity decrease with increasing Fe content in LnBaCo 2− x Fe x O 5+ δ . While the substitution of a small amount of Fe ( x = 0.5) for Co leads to slightly improved performance in solid oxide fuel cells (SOFC), larger Fe contents ( x ≥ 1.0) deteriorate the fuel cell performance. In the Ln = Gd system, the better performance of the x = 0.5 sample is partly due to the improved chemical stability with the LSGM electrolyte at high temperatures. With an acceptable electrical conductivity of >100 S cm −1 at 800 °C, the x = 0.5 sample in the LnBaCo 2− x Fe x O 5+ δ (Ln = Nd and Gd) system offers promising mixed oxide-ion and electronic conducting (MIEC) properties.

Effects of Fe-substitution for cobalt on electrochemical properties of La-Mg-Ni-based alloys

In order to improve electrochemical properties, especially cycling stability, Co was partially substituted by Fe in A 2B 7-type La-Mg-Ni-based alloys. The La 0.74Mg 0.26Ni 2.55Co 0.65 –x Fe x ( x=0, 0.10, 0.20, 0.30) alloys were prepared by inductive melting, and their phase structure and electrochemical properties were studied. The XRD and SEM results showed that the alloys consisted mainly of (La, Mg) 2Ni 7 phase, (La, Mg) 5Ni 19 phase and LaNi 5 phase, except for absence of LaNi 5 phase in the non-substituted alloy. The (La, Mg) 5Ni 19 phase and LaNi 5 phase increased and the (La, Mg) 2Ni 7 phase decreased as Fe content increased. The partial Fe substitution for Co decreased the maximum discharge capacity to some extent; however, the cycling stability was improved and the self-discharge was remarkably suppressed by Fe substitution. The linear polarization and cyclic voltammetry measurements showed that the electro-catalytic activity and hydrogen diffusibility were both deteriorated by Fe substitution and thus the high rate dischargeability decreased.

The structural and magnetic properties of Mn2−xFexNiGa Heusler alloys

The effect of Fe substitution on the phase transformation and magnetic properties of Mn2NiGa has been studied. A single bcc phase was obtained in Mn2−xFexNiGa (x=0–0.6). With the substitution of Fe for Mn, the lattice constant decreases gradually. The martensitic transformation can be observed when x=0–0.3. Both the martensitic transformation and austenitic transformation temperatures decrease monotonically with increasing Fe content, which is different from common electron concentration dependence in Ni–Mn–Ga system. The saturation magnetizations Ms of Mn2−xFexNiGa in both austenitic and martensitic phases increase obviously with the doping of Fe, while the variation of TC shows an opposite tendency. Theoretical calculations indicate that both austenitic and martensitic phases are ferrimagnets. The Fe moment varies from positive to negative after the tetragonal distortion, which leads to the decrease of the saturation magnetization.

Fe substitution effect on the magnetic properties of SmMn2−xFexGe2 studied by NMR

We have carried out 55Mn and 149Sm NMR measurements on SmMn2−xFexGe2 (0.05 ≤ x ≤ 0.6) at 4.2 K in order to elucidate the Fe substitution effect on the magnetic properties of SmMn2−xFexGe2. The NMR signals of Mn have been observed in the frequency range 180 – 210 MHz. The resonance frequency plotted against the Fe concentration shows an abrupt change between x = 0.3 and 0.4. This discontinuity suggests that the magnetic structure changes around x = 0.35 in the low temperature range where Sm and Mn sublattices order magnetically.

Magnetism, magnetocaloric effect and positive magnetoresistance in Fe-doped antipervoskite compounds SnCMn 3−xFe x ( x=0.05–0.20)

The effects of Fe substitution on the structure, magnetic properties, magnetocaloric effect and positive magnetoresistance (MR) effect in antipervoskite compounds SnCMn 3− x Fe x ( x=0.05–0.20) have been investigated systematically. Partial substitution of Fe for Mn leads to the monotonic reduction in both the Curie temperature T C and saturated magnetization ( M S ). It can be attributed to the reduction of electronic density of state at the Fermi energy by Fe-doping. The maximum values of magnetic entropy change (−Δ S M ) and positive MR gradually decrease as x increases, due to the broadening of magnetic phase transition. The refrigerant capacity increases initially with x≤0.05, then decreases gradually as x increases further, which is suggested to originate from the competition between the decreasing −Δ S M and broadening temperature span. Our result indicates that the chemical doping on Mn site is an effective method for manipulating the properties of antiperovskite compounds AXMn 3.

Structural and Mössbauer spectroscopic investigation of Fe substituted Ti–Ni shape memory alloys

In the present investigation the effect of Fe substitution in Ti 51Ni 49 alloy has been studied. The alloys were synthesized through radio frequency induction melting. The alloy was characterized through X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Mössbauer spectroscopy and positron annihilation techniques. It was found that the Fe substitution stabilized the TiNi type cubic ( a = 2.998 Å) phase. The microstructure and presence of the oxide phase in Ti 51Ni 45Fe 4 alloy have been investigated by scanning electron microscopy. The positron annihilation measurements indicated a similar bulk electron density in both the as-cast and annealed (1000 °C for 30 h) alloys, typically like that of bulk Ti. Mössbauer spectroscopy studies of as-cast and annealed iron substituted samples showed regions in the samples where nuclear Zeeman splitting of Fe levels occurred and an oxide phase was found to be present in as cast Ti 51Ni 45Fe 4 alloy, while annealed sample indicated the presence of bcc iron phase.

Preparation and Characterization of Li [Mn&lt;sub&gt;2-x&lt;/sub&gt;Fe&lt;sub&gt;x&lt;/sub&gt;]O&lt;sub&gt;4&lt;/sub&gt; (x = 0.0-0.6) Spinel Nanoparticles as Cathode Materials for Lithium Ion Battery

Nanosized powders in the system LiMn2−xFexO4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) have been synthesized by sol-gel technique using citric acid as chelating agent. The effect of Fe substitution on the structure and surface morphology of spinel LiMn2O4 has been examined by X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM) and Electrochemical characteristics. The materials for all the compositions except x = 0.6 exhibit a phase pure cubic spinel structure as evident from the XRD analyses. Doping with Fe increases the crystallinity in the materials and decreases the average particle size. The surface morphology of the synthesized particles is spherical and polygonal type. Average particle size lies in the range of 60 to 400 nm. Improved capacity retention in rechargeable 4 V Li/LiMn2-xFexO4 cells has been observed when a small amount of manganese in the spinel cathode is replaced with iron. The first discharge capacities of LiMn2−xFexO4 (x = 0.0, 0.1, 0.2, 0.3) in a voltage range of 3 V to 4.3 V decreases as the x increases, however, the cyclic performance improves.

Effect of Fe-substitution on microstructure, hysteresis behaviour and magnetocaloric effect in Gd 5Si 2Ge 2 Alloys

Effect of Fe-substitution on the phase formation, partitioning behaviour of Fe in the co-existing phases, magneto-structural transition, magnetic entropy change and associated hysteresis losses has been investigated in Gd 5Si 2Ge 2 alloy. The virgin alloy crystallizes in monoclinic Gd 5Si 2Ge 2-type phase, while Fe-substituted alloys form mixed monoclinic Gd 5Si 2Ge 2-type and orthorhombic Gd 5Si 4-type phases. Electron probe microanalysis reveals that Fe does not dissolve in the matrix, but influences the magneto-structural transitions. Magneto-structural characterization of the Fe-containing alloys reveals that the Fe-substitution suppresses the structural transition observed at 273 K in virgin alloy. A maximum magnetic entropy change, Δ S M of 6.5 J/kg-K at 273 K was observed for a field change of 2 T in Gd 5Si 2Ge 2 alloy. The Fe-substituted alloys exhibit lower value of Δ S M but with reduced hysteresis losses.

Effect of Fe substitution on the magnetic properties of half-Heusler alloy CoCrAl

The effect of Fe substitution for the vacant site in half-Heusler alloy CoCrAl is studied. A series of single phase CoFe x CrAl ( x=0.0, 0.25, 0.5, 0.75 and 1.0) alloys has been successfully synthesized. The lattice constant is found to increase almost linearly with increasing Fe content, indicating Fe atoms enter the lattice of CoCrAl instead of existing as a secondary phase. When Fe entering the vacant site, spin polarization occurs and the alloy turns from a semimetal in CoCrAl to a half-metallic ferromagnet (HMF) in CoFeCrAl. This is due to the reconstruction of the energy band with Fe substitution. The Curie temperature and saturation magnetic moments are enhanced and increase monotonically with increasing Fe content. The variation of the spin moment follows the Slater–Pauling curve and agrees with the theoretical calculation as well.

Spin polarization tuning in Mn5−xFexGe3

Experimentally, the intermetallic compound Mn4FeGe3 has been recently shown to exhibit enhanced magnetic properties and spin polarization compared to the Mn5Ge3 parent compound. The present ab initio study focuses on the effect of Fe substitution on the electronic and magnetic properties of the compound. Our calculations reveal that the changes on the Fermi surface of the doped compound are remarkable, and provide explanations for the enhanced spin polarization observed. Finally, we show that it is indeed possible to tune the degree of spin polarization upon Fe doping, thus making the Mn5−xFexGe3 intermetallic alloy very promising for future spintronic applications.

Out-of-equilibrium Sm–Fe based phases

Structure and magnetic properties of nanocrystalline P6/mmm out-of-equilibrium precursors of hard magnetic R-3m Sm2(Fe,M)17C (M=Ga,Si,) and I4/mmm Sm(Fe,Co,Ti)11 equilibrium phases, are presented. Their structure is explained with a model ground on the R1 − s T5 + 2s formula (R=rare-earth, s=vacancy rate, T=transition metal) where s Sm atoms are statistically substituted by s transition metal pairs. The Rietveld analysis (RA) provides the stoichiometry of the precursors, 1:9 and 1:10, respectively precursor of 2:17 and 1:12 phases. The interpretation of the Mossbauer spectra of the 1:9 and 1:10 phases, is based on the correlation between δ and the Wigner–Seitz Cell volumes, calculated from the structural parameters. The δ behaviour of each crystallographic site versus Co content, defines the Co location while it confirms that of Si and Ga obtained by RA. Substitution occurs in 3 g site, whatever Co or M. The Sm(Fe,Co,Ti)10 and Sm(Fe,M)9C Curie temperature (Tc) are compared to those of the equilibrium phases, the effects of Fe substitution and C addition are discussed. The maximum μ 0Hc is obtained for low M or Co content, for auto-coherent diffraction domain size ∼30 nm. SmFe8.75Ga0.25C and SmFe8.75Si0.25C with Tc of 680 and 690 K, show respectively Mr and μ 0Hc of 58 emu/g, 27 kOe and 95 emu/g, 15 kOe, values higher than those obtained for Sm2(Fe,M)17 carbides.

Magnetic and electrical transport properties of La0.87Mn1−xFexO3 (0 ⩽ x ⩽ 0.15): coexistence of ferromagnetic and glassy magnetic states

We report on the effect of Fe substitution in the self doped manganite, La0.87Mn1−xFexO3 in the composition range 0 ⩽ x ⩽ 0.15. The electrical resistivity (ρ) and dc magnetization were measured as a function of temperature, field and time. The metal to semiconducting transition is clearly observed for x ⩽ 0.02, while a semiconducting temperature dependence of resistivity is noticed for x ⩾ 0.08. The compound with x = 0.05 shows interesting features of ρ in field-cooled (FC) condition such as bifurcation in the zero-field cooled and FC temperature dependence, weak thermal hysteresis and memory effect. We observe the enhancement of colossal magnetoresistance by the Fe substitution in the low substitution range. The paramagnetic to ferromagnetic transition (Tc) is found to decrease with increasing x. The large thermal hysteresis in magnetization under FC condition is noticed for x ⩽ 0.02, which is different in character for the composition range 0.05 ⩽ x ⩽ 0.15. The relaxation of magnetization indicates the ferromagnetic (FM) character for x = 0, while the coexistence of FM and glassy components is observed for x ⩾ 0.02. The glassy magnetic phase increases with the increase in Fe substitution. The inhomogeneous phase separation between FM and glassy magnetic phases has been proposed to explain the magnetic and electrical transport properties of La0.87Mn1−xFexO3.

Superconductivity and magnetism in R(Ni1−xFex)2B2C (R = Er and Tm) systems

The effect of Fe substitution on structure, superconductivity and magnetism in the R(Ni1−xFex)2B2C (R=Er and Tm) systems are systematically studied by means of X-ray diffraction, transport properties and heat capacity measurements. The crystal structure is almost unchanged upon the iron substitutions. A rapidly decrease of Tc is observed in both the systems, and disappeared around x=0.06 for R=Er, and x=0.08 for R=Tm. TN almost unchanged in the concentration range from x=0 to x=0.1 for R=Er. The effective magnetic moments μeff which were obtained by the Curie–Weiss law from the magnetic temperature dependence data were almost unchanged with x, respectively. Based on the results of susceptibility, specific heat and previous reported, it can be concluded that the substitution of Fe for Ni maybe similar to that of Co case which can be treated as non-magnetic impurities and the decreases of N(EF) is the main reason for the decrease of Tc.

A Raman spectroscopic investigation of Fe-rich sphalerite: effect of fe-substitution

A Raman spectroscopic study of Fe-rich sphalerite (Zn1 − x Fe x S) has been carried out for six samples with 0.10 ≤ x ≤ 0.24. Both the intensities and frequencies of the TO and LO modes of sphalerite are approximately independent of Fe concentration. However, the substitution of Zn by Fe results in five additional bands with frequencies between the TO (271 cm−1) and LO (350 cm−1) modes. Three of these bands are attributed to resonance modes (i.e. Y 1, Y 2 and Y 3 modes). The fourth band (B mode) is assigned to a breathing mode of the nearest-neighbor sulfur atoms around the Fe atoms. The band at 337 cm−1 is attributed to the presence of Fe3+. The excellent correlations between the normalized intensities of these five different modes and x Fe show that these modes depend on Fe-content. Another extra mode at 287 cm−1 is assigned to the presence of Cd in sphalerite.