Resolved magnetic hyperfine spectra of Au-Fe alloys as a function of temperature

We have analyzed the Mössbauer hyperfine magnetic spectra of six compositions of Au-Fe from 10.5 to 33 at.% Fe at temperatures ranging from 4.2 K to the magnetic ordering temperature of each alloy. Only two elementary magnetic hyperfine spectra are required to fit the data, each of which has its own value of the magnetic hyperfine field, quadrupole coupling, isomer shift, and relative intensities. The intensity ratios of the two spectra for a given Fe concentration are essentially invariant with temperature. These results point to the existence of two chemically different Fe sites with all the Fe atoms magnetically coupled over the entire temperature regime below the upper magnetic ordering temperature. A relatively sharp increase in the local moment commences at both Fe sites, at ∼ 17 at.% Fe and continues to increase with Fe concentration.     

Magnetism and atomic clustering in Au-Fe alloys

a.c. magnetic susceptibility measurements are used to investigate atomic clustering in Au-Fe alloys near 15 at. pct. Fe. The highest degree of disorder is obtained by quenching from 550C. Quenching from higher temperatures leads to inhomogeneous states. Changing the degree of clustering has qualitatively the same effect on the magnetic properties as changing the chemical concentration.     

Polarized neutron diffuse scattering experiments on disordered Cr-rich Cr-Fe alloys

The results of polarized neutron elastic diffuse scattering measurements on disordered Cr-Fe alloys with 1.5 2.4, and 12 and 14.2 at % of Fe are reported and discussed. The measurements have been done using neutron wavelength of 4.25 A in the scattering vector range 0.2Å^?1 < K < 2Å^?1 and in function of temperature. The data show clustering effects in the alloys with iron concentration starting from 2.4 at%. At the iron concentration of 14.2 at% the clusters contain about 110 atoms and extend up to about 6.3 Å from a central atom. Above a characteristic temperature the iron-rich clusters behave as superparamagnetic entities and below this temperature they are magnetically frozen.At 4.6K the average iron moment within these clusters is found to be 2.0(2)μ_B in the alloys with 12 and 14.2 at % of Fe.     

Crystallization kinetics of amorphous FeB alloys by dta

The crystallization kinetics of amorphous FeB alloys was investigated by means of differential thermal analysis. The activation energy for the crystallization of amorphous FeB alloys was estimated. The concentration dependence of the activation energy, exhibiting a maximum at about 16 at.% B, has similarity to other physical properties.     

Magnetic properties and magnetic interactions in chromium-rich Cr-Fe alloys

The results of magnetization measurements on several disordered b.c.c. Cr-Fe alloys with 1, 1.5, 2.4, 5.3, 12 and 14.2 at % of Fe are reported. The measurements were done in pulsed magnetic fields up to 330 kOe and for the two last alloys also in static magnetic fields up to 44 kOe as in function of temperature. The data support the recently proposed model of magnetic interactions in these alloys by Friedel and Hedman. For the alloys with iron concentration equal to and greater than 2.4 at % we observe, at low temperature, the occurence of a ferromagnetic component in the magnetization curves saturating at an external field of about 140 kOe arising from ferromagnetic iron-rich cluster. At liquid helium temperature the localized iron moments within such iron clusters increase from 1.4μ_B to 1.8μ_b when the iron concentration changes from 2.4 at % to 14.2 at %. At higher iron concentrations we observe a spin glass like transition connected with a freezing of ferromagnetic clusters at very low temperature. Both phase boundaries connected with supermagnetic-paramagnetic and superamagnetis-spin glass like transitions are given.     

An investigation of the magnetic order in pseudo binary Co(Ga, Fe) alloys

The results of a Mössbauer effect and a low dc field magnetisation study of the pseudo binary Co₂Ga_2-xFe_x (0.01 x 1.00) alloy system are presented. As a concentration of x=1 is approached, the Fe atoms exhibits a preference for one of two apparently identical Ga sites, resulting in the doubly ordered Heusler structure of the L2₁ type. The critical concentration for the onset of long range ferromagnetic order is x=0.08, with superparamagntic clusters existing either side of this concentration. The size, shape, and interaction between these clusters is strongly dependent on the sample heat treatment. Alloys in the vicinity of this critical concentration, quenched from 830°C, show superparamagnetic behaviour with the magnetic clusters displaying a range of blocking temperatures; whereas alloys given a slow anneal exhibit typical spin-glass freezing.     

Residual resistivity in Ni-Fe-Cr/V alloys and the two-current model

The resistivity of a large number of Ni-Fe-Cr/V alloys has been measured at 77 K. An attempt has been made to explain the concentration dependence of resistivity in the light of Mott’s two-current model. It is seen that contrary to earlier observation, the model is applicable to a larger range of concentration for the Ni-Fe-Cr series. Appreciable deviation from the model starts for Fe concentration exceeding about 15 at. % and Cr about 7 to 8 at. %. However, for similar concentration range in Ni-Fe-V series, disagreement between the experimental and theoretical results is more pronounced.     

Short range ordering in electrochemically prepared Fe−P amorphous alloys

⁵⁷Fe Mössbauer spectroscopy was used to study electrodeposited Fe?P amorphous alloys with 12–16 at% P content. We have found that the Mössbauer parameters and the hyperfine field distributions of Fe?P samples depend on the preparation parameters (composition of electrolyte, temperature and current density of electrolysis). The Fe?P samples of nearly identical concentration and prepared under different conditions have different short range ordering.     

On the stability of bcc Co in Co/Fe superlattices an NMR and XRD study

While RHEED observations show that 10 to 11 As is the stability limit for an open bcc Co layer when grown on an Fe substrate, our XRD and NMR studies have shown that, in MBE grown Co/Fe superlattices, cobalt can be stabilised in a bcc structure up to a critical Co thickness of 21 Ås. In order to understand this apparent discrepancy, NMR experiments have been carried out in Co_x/Fe_y multilayers with thickness varying in the range 5 Å < x < 42 Å and 24 Å < y < 60 Å, grown on GaAs (1 1 0) as well as on MgO (1 0 0) substrates. The analysis of the chemical short range order by NMR concludes that the larger bcc Co thickness observed in superlattices results from the formation of a rather homogeneous CoFe_20% bcc alloy which contains the supplementary 10–11 As of Co and which coexists with pure Co grains. The concentration of about 20% Fe in the alloyed part of the Co layer happens to be close to the stability limit for a bcc structure in the equilibrium phase diagram of bulk CoFe alloys. However, while a mixture of bcc and fcc phases is observed in bulk alloys, the bcc structure is preserved in all phases under the MBE growth conditions and below the critical thickness. Above the critical thickness amixture of bcc Co, bcc CoFe and hcp Co is observed.     

Spin correlations in Au-Fe alloys

Measurements of the (111) Bragg peak of ferromagnetic Au-Fe alloys reveal a remarkable three-step increase to saturation with decreasing temperature. The final “RKKY step” around ≈ 50 K is accompanied by broadening of the Bragg peak resulting in the observed q-dependent maxima in the low-q intensity. Viewed with increasing temperature the results suggest a continuous process of de-freezing of magnetic clusters of spins accompanied by “dynamic narrowing” of the Bragg peak.     

Deformation hardening and the temperature dependence of the mechanical properties of ternary ordering alloys. Part II

Yield point, hardening factor, and elastic modulus are reported as functions of quenching and test temperatures for the alloys Ni₃(Fe + 3 at% Al), Ni₃(Fe + 3 at% Mn). A maximum is found in the mechanical properties near the critical temperature T_cr; this does not occur for alloys in the disordered state. The deformation aging under load is examined near this maximum and at 200 ° C. A range of linear hardening occurs up to e of 15–18% in ordered alloys, which is replaced by a range of decreasing hardening coefficient at higher . The results are discussed by reference to earlier ones for Ni₃Fe, Ni₃(FeCr). Ni₃(FeMo).     

Structural and Mössbauer studies of Fe1−xAlx alloys over the entire composition range

Metastable Fe_1?xAl_x alloys over the entire composition range have been investigated by X-ray diffraction and Mössbauer effect measurements. Alloys with x less than 0.55 are bec, whereas those with x>0.9 are fce, in between, the samples are amorphous. The Mössbauer spectra at 300 K for the bce alloys with x<0.5 consist of a broadened sextet and the spectra for the alloys with x≥0.5 are quadrupole-split doublets with a slight asymmetry. The magnetic hyperfine field at 4.2 K decreases monotonically with Al concentration from 340 kOe in pure Fe to zero at x=0.7. The isomer shift increases essentially linearly with Al concentration, and reaches a maximum at x=0.75. It is noted that at the boundary of x=0.55 separating the bce and the amorphous states, there is no discernible change in elther hyperfine field or lsomer shift.     

Magnetic cluster expansion simulation and experimental study of high temperature magnetic properties of Fe-Cr alloys

We present a combined experimental and computational study of high temperature magnetic properties of Fe-Cr alloys with chromium content up to about 20?at.%. The magnetic cluster expansion method is applied to model the magnetic properties of random Fe-Cr alloys, and in particular the Curie transition temperature, as a function of alloy composition. We find that at low (3-6?at.%) Cr content the Curie temperature increases with the increase of Cr concentration. It is maximum at approximately 6?at.% Cr and then decreases for higher Cr content. The same feature is found in thermo-magnetic measurements performed on model Fe-Cr alloys, where a 5?at.% Cr alloy has a higher Curie temperature than pure Fe. The Curie temperatures of 10 and 15?at.% Cr alloys are found to be lower than the Curie temperature of pure Fe.     

原子吸收光谱法测定血清中不同化学形态的铜、铁、锌

融合分子生物学技术与原子吸收光谱对血清中元素铜、铁和锌的化学形态进行研究。用60%乙醇低温(4℃)沉淀血清蛋白的方法将血清中的铜,铁,锌分为结合态和非结合态,原子吸收分光光度计分别测定血清中Cu,Fe和Zn三种元素的总量及非结合态含量,通过减差法求出血清中结合态元素含量,从而建立了Cu,Fe和Zn元素这两种化学形态的分离分析方法,并讨论了有关的实验条件。该方法铜、铁和锌的检出限分别为9·84×10-3μg·mL-1,2·76×10-2μg·mL-1,1·06×10-3μg·mL-1,相对标准偏差为0·30%～2·31%,回收率为95·0%～104·0%。该法已应用于SD大鼠血清中Cu,Fe和Zn三种元素不同化学形态的测量。     

Structure, spin reorientation and M(o)ssbauer effect studies of Tb0.3Dy0.7(Fe1-xAlx)1.95 alloys

The effect of Al substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb0.3Dy0.7(Fe1-xAlx)1.95 alloys (x = 0, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35) at room temperature and 77 K was investigated systematically. It was found that the primary phase of Tb0.3Dy0.7(Fe1-xAlx)1.95 is the MgCu2-type cubic Laves phase structure when x < 0.4 and the lattice constant a of Tb0.3Dy0.7(Fe1-xAlx)1.95 increases approximately and monotonically with the increase of x. The substitution of Al leads to the fact that the magnetostriction ( inceases slightly in a low magnetic field (H ≤ 40 kA/m), but decreases sharply and is easily close to saturation in a high applied field as x increases, showing that a small amount of Al substitution is beneficial to a decrease in the magnetocrystalline anisotropy. It was also found that the spontaneous magnetostriction (ζ)111 decreases greatly with x increasing. The analysis of the M(o)ssbauer spectra indicated that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry with the changes of composition and temperature, namely spin reorientation. A small amount of non-magnetic phase exists for x = 0.15 in Tb0.3Dy0.7(Fe1-xAlx)1.95 alloys and the alloys become paramagnetic for x > 0.15 at room temperture, but at 77 K the alloys still remain magnetic phase even for x = 0.2. At room temperature and 77 K, the hyperfine field decreases and the isomer shifts increase with Al concentration increasing.     

First principles study on the electronic structure and magnetism of Fe1-xCoxSi alloys

Electronic and magnetic properties of Fe1-xCoxSi alloys were investigated by using a full-potential linear augmented-plane-wave method based on density functional theory. Electronic structure calculation demonstrates that half-metallic property appears in the Fe-rich region of 0 〈 x ≤ 0.25, while the alloys turn out to be a magnetic metal for x 〉 0.25. The concentration dependence of the magnetic moment of the alloys can be understood by the fixed Fermi level at minority band in Fe-rich region, as well as at the majority band in Co-rich region. In Fe-rich alloys, the electronic structure and the magnetic properties at Fe site depend mainly on the spin-polarization of nearest neighbouring Co atoms, while in Co-rich alloys, these features at Co site arise mainly from the neighbours of Fe atoms.     

XPS study of the valence band spectrum of amorphous Fe-B alloys

XPS spectra of Fe 3s and Fe 3p levels and Fe 3d valence band of amorphous iron-boron alloys were measured as a function of boron concentration over the range from 12 to 25 at% B. It was found that a characteristic hump appeared at lower energy region in Fe 3d band spectrum of every amorphous Fe-B alloy. The origin of the hump was discussed in terms of the formation of a new bonding state between Fe and B atoms in amorphous Fe-B alloys.     

Tricritical phenomena at the gamma-->alpha transition in Ce0.9-xLaxTh0.1 alloys

The gamma-->alpha isostructural transition in the Ce0.9-xLaxTh0.1 system is measured as a function of La alloying using specific heat, magnetic susceptibility, resistivity, thermal expansivity or striction measurements. A line of discontinuous transitions, as indicated by the change in volume, decreases exponentially from 118 K to close to 0 K with increasing La doping, and the transition changes from being first-order to continuous at a critical concentration, x(c) approximately 0.14. At the tricritical point, the coefficient of the linear T term in the specific heat gamma and the magnetic susceptibility increase rapidly near x(c) and approach large values at x=0.35 signifying that a heavy Fermi-liquid state evolves at large doping. The Wilson ratio reaches a value above 2 for a narrow range of concentrations near x(c), where the specific heat and susceptibility vary most rapidly with the doping concentration.     

Magnetization of gold-iron alloys

Magnetization measurements have been made on Au-Fe alloys containing from 0·05 to 12·5 at. % Fe at temperatures below the magnetic ordering temperature. In combination with Mössbauer spectroscopy a qualitative explanation is derived for the complex mictomagnetic behavior observed.     

Pressure-induced Invar effect in Fe-Ni alloys

We have measured the pressure-volume (P-V) relations for cubic iron-nickel alloys for three different compositions: Fe 0.64Ni (0.36), Fe 0.55Ni (0.45), and Fe 0.20Ni (0.80). It is observed that for a certain pressure range the bulk modulus does not change or can even decrease to some minimum value, after which it begins to increase under still higher pressure. In our experiment, we observe for the first time a new effect, namely, that the Fe-Ni alloys with high Ni concentrations, which show positive thermal expansion at ambient pressure, become Invar system upon compression over a certain pressure range.