Magnetic properties of amorphous NiP alloys

Magnetization, NMR and coercive force measurements were performed on amorphous Ni_1?cP_c alloys for concentration ranging between 0.15 and 0.25. The experimental results show that the magnetism is not of the same nature below and above some critical concentration c₀ which determines the concentration ranges: the first one (0.15 < c < 0.18) presents the characters of a weak homogeneous ferromagnetism, while inhomogeneities dominate the magnetic properties of the second one (0.18 < c < 0.25).     

Magnetic and mechanical properties of amorphous Fe-Y alloys

The magnetic and mechanical properties of amorphous Fe_100−xY_x alloys (20 ≤ x ≤ 60) fabricated by rapid quenching have been measured. The dependence of the density, Young's modulus and magnetic moment per Fe atom on x shows a break point between x = 30 and 40, accompanied by a drastic change in the X-ray diffraction pattern. The spontaneous volume magnetostriction as well as the forced volume magnetostriction are a maximum at x = 20 and decrease rapidly with increasing x. The variation of the magnetic and mechanical properties with x is explained by a change of the local atomic arrangement in the amorphous state, reflecting the structure of corresponding crystalline compounds.     

Magnetic properties of amorphous rare-earth—Iron alloys

The magnetic properties of various amorphous alloys of the type R_1-xFe_x (R = Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu) have been determined in the concentration range 0.3 ? x ? 0.5. With the exception of the Gd and Lu alloys pronounced thermomagnetic history effects were observed in the temperature dependence of the magnetization. These effects are due to a strong temperature dependence of the coercive force (H_c) which is found to obey an exponential law of the form H_c ∞ exp(-αT). ⁵⁷Fe Mössbauer spectra were obtained on the alloys of a composition close to 40 at% Fe. From the combined results of the Mössbauer spectroscopy and magnetic measurements it is derived that the Fe moment decreases if one passes through the rare-earth series. It is postulated that this decrease is due to small differences in the compositional short-range order in the amorphous alloys caused by the heat of mixing becoming more negative in the same sense.     

Magnetic properties of rapidly quenched amorphous Fe-Sm alloys

The structural analysis and investigation of magnetic properties were carried out on rapidly quenched Fe_100−xSm_x (10.5 x 80) alloys. Amorphous alloys are fabricated in a wide composition range from x = 17 to 72.5. After heating the amorphous alloys up to 900 K, they transform into metastable phase I (T_c = 465 K)+ -Fe (x < 20), metastable phase II (T_c = 555 K)+-Fe (20 x 33.3) and Fe₂Sm+Sm (x40). The composition dependence of Curie temperature and magnetization is found to be similar to that of amorphous Fe-(Nd, Pr) alloys. A maximum coercive force of about 1.1 kOe at 300 K and 12 kOe at 77 K is obtained in the x = 40 alloy. The rapid decrease in coercive force with raising temperature can be explained by the wall pinning model proposed by Gaunt. The pronounced composition dependence of these magnetic properties for the amorphous Fe-Sm alloys can be considered to be caused by the change in the short-range atomic order with Sm concentration on the basis of the results of X-ray structural analysis.     

Magnetic and electrical properties of several Mn-based amorphous alloys

Magnetic and electrical properties of amorphous Mn-Y, Mn-Zr, and Mn-Nb alloys have been investigated. All these alloys have a temperature-dependent susceptibility which is well fitted by a Curie-Weiss law. This implies the existence of localized magnetic moments associated with the Mn atoms. In addition, amorphous Mn-Y alloys exhibit spin-glass characteristics at low temperature. The experimental results of the electrical resistivity show that the temperature coefficient of resistivity (TCR) of both Mn-Y and Mn-Zr are negative, while Mn-Nb has a positive TCR. On the other hand, the resistivity-temperature curves of Mn-Zr and Mn-Nb have nearly the same tendency but are different from that of Mn-Y.     

Magnetic and electrical transport properties of amorphous Zr-Fe alloys

Amorphous Zr_1?xFe_x samples were prepared in the composition range 0.2 ? x ? 0.9 either by means of vapour deposition or melt spinning. The electrical resistivity was determined in the range 4.2–300 K. Negative temperature coefficients were observed in the whole concentration range. The extended Ziman theory (diffraction model) was found to be able to explain these results only if the effective valence of the Fe atoms involves not only s electrons but also d electrons. The magnetic properties and the ⁵⁷Fe Mössbauer effect of the Zr_1?xFe_x alloys were studied in the range 4.2–300 K. The Fe-rich alloys are ferromagnetic. The Fe moment vanishes in alloys of an Fe concentration lower than about 50 at%. In most alloys (x ? 0.8) the Curie temperature is below room temperature and continuously decreases with Zr concentration. By means of Mössbauer spectroscopy and magnetic measurements it is shown that compositional short-range order (CSRO) is present to a higher degree in melt-spun alloys than in vapour-deposited alloys. The effect of sign and magnitude of the heat of solution on CSRO and the magnetic properties is discussed.     

Severe plastic deformation of amorphous alloys: II. Magnetic properties

The influence of severe plastic deformation in a Bridgman cell on the magnetic properties of amorphous alloys of metal-metalloid type, Ni₄₄Fe₂₉Co₁₅Si₂B₁₀, Fe₇₄Si₁₃B₉Nb₃Cu₁, Fe_57.5Ni₂₅B_17.5, Fe_49.5Ni₃₃B_17.5, and Fe₇₀Cr₁₅B₁₅, obtained by melt spinning, has been investigated. It is found that the saturation magnetization significantly changes (increases or decreases), depending on the number of ferromagnetic and antiferromagnetic components in the alloy. It is suggested that very high shear stress causes internal phase decomposition in the amorphous matrix into nanoscale regions, enriched or depleted with ferromagnetic components.     

Magnetic clusters in amorphous metal alloys

The effect of thermal treatment in combination with an external magnetic field and/or elastic stress on the magnetic characteristics of amorphous metal alloys of the 2NSR type is studied. The complex behavior of the magnetization and coercivity values in dependence on the length of annealing at temperatures below crystallization is described. It is assumed that the observed changes in the macroscopic magnetic characteristics are associated with the formation of clusters with different degrees of exchange interaction.     

Magnetic and electrical properties of amorphous PdCoP alloys

Magnetic susceptibility and electrical resistivity measurements were performed (Pd_100?xCo_x)₈₀P₂₀ alloys where 15 < x < 50. The magnetic properties show that these alloys undergo a ferromagnetic transition between 272 and 399 K as the cobalt concentration increases from 15 to 50 atomic %. Below 20 atomic % Co the short-range exchange interactions which produce the ferromagnetism are unable to establish a long-range magnetic order and a peak in the magnetization shows up at the lowest temperature range under an applied field of 6.0 kOe. The electrical resistivity of these alloys has been measured from 4.2 K up to the vinicity of the melting point (900 K). The electrical resistivity data could be interpreted by the coexistence fo a Kondo-like minimum and ferromagnetism. The minimum becomes less important as the transition metal concentration increases. The coefficients of In T and T² become smaller and concentration dependent. The spin ordering in such alloys can be simulated as either the ordering due to an applied “external field” or as an increase in “internal fields”. These are due to an increase in transition metal concentration. The negative magnetoresistivity is a strong indication of the existence of localized moment.     

Magnetic phases of amorphous transition metal-metalloid alloys

Hysteresis loop and ac susceptibility measurements were performed on three series of amorphous alloys: (A_wB_1-w)₇₅P₁₆B₆Al₃, where (A, B) are (Fe, Ni), (Co, Ni) and (Fe, Mn). Upon cooling, low w alloys undergo paramagne t to spin glass transitions. Alloys with higher w first experience a Curie transition to a ferromagnetic state, and then a spin freezing transition to a spin glass state. the T dependence of the width of the ac hysteresis loop is used to determine the spin freezing transition temperature. A magnetic phase diagram is presented for each alloy series and the value of w required for ferromagnetism, w_C, is determined. When measured in the presence of small constant fields, the ac susceptibility of alloys with w just above w_C has maxima near both transition temperatures. The field and temperature dependences of the peaks are explained by scaling arguments, used to determine the critical exponent δ for the Curie transition, and suggest that a similar scaling law holds for the ferromagnet to spin glass transition.     

Magnetic relaxations in amorphous soft magnetic alloys

The paper reviews selected results of the extended experimental investigations of magnetic properties, time–temperature stability and workability of the soft magnetic amorphous alloys controlled by structural magnetic relaxation. Complex approach to the magnetic relaxations in multicomponent amorphous alloys is presented. The transition from magnetic after-effect to a new MAE spectrometry is illustrated on ternary amorphous CoSiB alloy.     

Magnetic annealing in electrodeposited Co-P amorphous alloys

The different diffusion processes that occur in electrodeposited Co-P amorphous alloys when they are subjected to magnetic annealing at different temperatures are studied by Coercive field measurements. Different processes are identified with different activation energies: 0.19 eV (stress relaxation): 0.75 eV (directional order); 2.9 eV (crystallization process). The low value of the activation energy for the first mechanism is identified with the diffusion of H, and that of the second with the diffusion of P.     

Mechanical properties of Co-Si-B amorphous alloys

The ternary amorphous systems Co_xSi₅B_95?x with 7070Si _y B_30?y with 5<y<18 were studied for their mechanical properties at room temperature. Structure sensitive parameters as density, Young's modulus, micro-hardness and crystallization temperature were investigated as a function of Co and Si contents. The value of density increases with higher Co content but not linearly as for Co-B. Young's modulus, micro-hardness and crystallization temperature decrease with increasing Co concentration. The packing fractionη was calculated using 12-coordinated Goldschmidt atomic radii. It is shown that changes in the proportions of metalloids contents in the alloys have more significant influence on the atomic structure and therefore on the mechanical properties than changes of Co content. The maximum tensile elastic strain for the Co-Si-B system was estimated. Influence of magnetic moment on Young's modulus is discussed.     

Magnetic properties and large magnetocaloric effects in amorphous Gd-Al-Fe alloys for magnetic refrigeration

A series of the amorphous Gd75-55Al25-5Fe0-40 alloy ribbons were prepared by melt spinning.The structure,magnetic properties and magnetocaloric effect(MCE) of these alloys were investigated.The prepared samples have shown the characteristics of a second-order phase transition with zero hysteresis loss and the Tc can be tuned by changing the Fe contents.For the different compositions,the magnetic entropy change(--Sm) for a field change of 0-5 T reached a maximum value of 7.14 J kg-1 K-1 in the Gd70Al20Fe10 a...     

Magnetic and structural features of amorphous FeMo-based alloys

NANOPERM-type FeMoCuB alloys are studied using magnetic and Mössbauer measurements in the as-prepared amorphous state. It is shown that the Fe₇₆Mo₈Cu₁B₁₅ (A) and Fe₇₄Mo₈Cu₁B₁₇ (B) alloys exhibit the magnetic dipole and electrical quadrupole interactions well detected in the room-temperature Mössbauer spectra. The thermomagnetic measurements above the room temperature indicate a vanishing of the magnetic interactions at approximately 310 K (A) and at 340 K (B), respectively. The low-temperature DC magnetic measurements show an anomaly around 200 K which is also a boundary at which zero-field Mössbauer measurements of both samples reflect the gradual “vanishing” of the electrical quadrupole interactions and appearance of another magnetically ordered component. The Mössbauer measurements in the field of 4 MA/m yield a survival of quadrupole and an enhancement of magnetic dipole interactions.     

Magnetic properties of CuRh alloys

By means of rapid quenching techniques single phased samples of Cu_xRh_1?x(0?x?1) were obtained. For these alloys the Knight shift of ⁶³Cu and ¹⁰³Rh has been determined employing pulsed NMR at low temperatures, furthermore the magnetic susceptibility was measured for temperatures between 4.2 and 300 K. While the Knight shift of ¹⁰³Rh is dominated by s-electron contributions in spite of a high density of d-states at the Fermi level, for the susceptibility, however, the d-electron contributions prevail. In addition the susceptibility shows a pronounced maximum at about 10 at.% Cu. Using the extrapolated Knight shift of copper (x→0) we estimate a net copper hyperfine field of — 15 T in close agreement with the corresponding values for CuPd and CuPt.     

Weak ferromagnetic properties of amorphous FeGe alloys

Magnetization measurements of amorphous FeGe alloys containing 20 and 30 at.% iron have been made under high field and high pressure. These alloys possess a weakly itinerant ferromagnetic character although large inhomogeneous effects are superposed.