Relaxation phenomena in amorphous Co75−x Mn x B25 induced by stress annealing

The change of the magnetization direction in amorphous ferromagnets by the application of a magnetic field and a tensile stress is investigated by magnetoresistivity measurements. Attention is focussed on permanently remaining influences on the domain structure induced by stress annealing treatments. To observe any dependence on the sign of the magnetostrictionλ _s, we investigated the amorphous Co_75?x Mn _x B₂₅ system where the sign ofλ _s changes from negative to positive values with increasing Mn content. Surprisingly the stress-annealed samples showed a similar behavior independent of the sign of the magnetostriction.     

The magnetostriction of aluminum substituted nickel ferrites

The room temperature magnetostriction constant λ₁₁₁ of the system NiFe_2?xAl_x0₄ is determined for 0<x<0.3. An unconventional system is used for the magnetostriction measurements. The growth, composition and saturation magnetization of the crystals are discussed. The values of x = 0 are in good agreement with those given in the literature. The saturation magnetostriction decreases with increasing aluminum content.     

Magnetostriction and other magnetic properties of Co-Ni based amorphous alloys

The magnetostriction coefficients λ_s of (Co_1−xNi_x)₇₅Si₁₅B₁₀ amorphous alloys have been determined in the range 0 ⩽ x ⩽ 0.41. The dependence of the magnetostriction on temperature T has been related to that of the magnetic polarization J_s in a phenomenological way as λ_s(T) = α[J_s(T)]³ + β[J_s(T)]². The compositional dependence of the coefficients α and β has been obtained.From the studies of the magnetostriction in the region close to the Curie temperature it has been possible to evaluate the magnetostriction critical exponent K.     

Magnetic moment and high-field susceptibility of amorphous FeB Invar-type alloys

The saturation magnetization and high-field susceptibility of amorphous Fe_100?xB_x (11 ? x ? 22) alloys have been measured at 4.2 K, 77 K and room temperature in magnetic fields up to 100 kOe. The concentration dependence of the saturation moment per iron atom shows a maximum around 14% boron, while the high-field susceptibility increases remarkably with decreasing boron content. The features are similar to those of crystalline FeNi Invar alloys.     

Magnetic transitions and magnetostrictive properties of Laves compounds Sm0.88Nd0.12(Fe1−xCox)1.93

The structure, magnetic and magnetostrictive properties of Sm_0.88Nd_0.12(Fe_1−xCo_x)_1.93 (0≤x≤1.0) alloys have been investigated. The alloys have the cubic MgCu₂ structure over the whole composition range and the lattice parameter a decreases with increasing x. For 0≤x≤0.2, substitution of Co for Fe slightly increases the saturation magnetization M_s and Curie temperature T_c, while further substitution causes a decrease in both M_s and T_c. The spin reorientation is observed, and a phase diagram for the spin configurations of the Sm_0.88Nd_0.12(Fe_1−xCo_x)_1.93 system is determined. The spontaneous magnetostriction λ₁₁₁ increases as x is increased, while a monotonic decrease of the saturation magnetostriction λ_s with x originates from the increase of λ₁₀₀ with opposite sign to that of λ₁₁₁, which may be caused by the filling of the d band due to Co substitution.     

Nanocrystals and amorphous matrix phase studies of Finemet-like alloys containing Ge

Two simple models were developed in order to determine the chemical composition of both nanocrystals and intergranular amorphous phases in nanocrystallized Fe_73.5Si_13.5B₉Nb₃Cu₁ containing Ge using data from X-ray diffraction and Mössbauer spectroscopy techniques. Saturation magnetization of the amorphous intergranular matrix (M_s^am) was calculated considering the contribution of the α-Fe(Si,Ge) nanocrystals and saturation magnetization of the alloys. The behavior of M_s^am with the iron content of the matrix was obtained and discussed. The exchange stiffness constant for the nanograins and for the amorphous phases was determined. The increment in the coercive field (H_c) with increasing Ge content was evaluated using two theoretical models for the random magnetocrystalline anisotropy constant (〈K₁〉). Results show that the magnetic hardening observed could not be attributed to an increase in 〈K₁〉 but mainly to an important increment of the magnetostriction constant of the α-Fe(Si,Ge) nanocrystals (λ_s^cr). Values for λ_s^cr are proposed.     

X-ray and Mössbauer studies of the Tb<Subscript>0.3</Subscript>Dy<Subscript>0.7</Subscript>Fe<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> system alloys

A complex study of the phase composition, atomic and crystalline structure, magnetic properties, and superfine interactions of the Tb_0.3Dy_0.7Fe_{2 ? x} Co _x system alloys (x = 0?1.3) has been performed. The synthesized alloys are isotypic with the cubic Laves phase (C15 type), their cell parameter monotonically decreases with an increase in the Co content and, hence, the saturation magnetostriction also does. However, the concentration dependences of the Curie temperature, saturation magnetization, and superfine magnetic field strength measured in the Mössbauer experiment display a nonmonotonic (dome-like) character.     

A survey on the effect of vanadium content on the magnetoelastic properties of YFe12−xVx alloys

Experimental results on the thermal expansion and magnetostriction of YFe_12−xV_x (1.5≤x≤3.5) alloys are reported. The results show that the anisotropic magnetostriction (Δλ) at a finite field (1.5 T) increases with increasing vanadium content in the range of x<2. But for x>2, a decrease in the magnetic anisotropy with increasing vanadium content causes a decrease in the saturation values of Δλ. In addition, the thermal expansion coefficient becomes a minimum for x≈2. Experimental curves exhibit that the forced volume magnetostriction (ΔV/V) is positive and increases linearly with the applied field at high fields. But in the low field region (≤0.5 T), a minimum appears in the isothermal curves of ΔV/V around the saturation field. The results are explained by considering the influence of vanadium content on the magnetization anisotropy of YFe_12−xV_x compounds.     

Ferromagnetic resonance in amorphous systems: Dependence of the relaxation parameter on temperature (magnetization)

We have studied the uniform mode ferromagnetic resonance in the amorphous systems Metglass 28226A, 2826B, 2826 over the temperature range 77–430 K. The data have been analysed in terms of the Gilbert Equation. The g-values are very similar to those of crystalline permalloy. The relaxation parameters λ, are of the order of 10⁸ s^?1 and exhibit an interesting temperature dependence. In particular, for $\text{T}\text{T}{}_{\mathrm{c}}\text{?0.5, λ}$ is simply proportional to the static saturation magnetization M_s. The present results are compared with those obtained on crystalline samples of the 3-d transition metals and their alloys.     

Long range interactions and spin wave excitations in FexPd82−xSi18 metallic glasses

The low temperature magnetization of amorphous Fe_xPd_82?xSi₁₈, 2 ? x ? 25, approaches saturation like 1/H. RKKY-type cluster-cluster interactions and single impurity effects are indicated. The effective strength of the RKKY interaction decreases with increasing x. The magnetization of both spin glass-like and weakly ferromagnetic alloys exhibits Bloch's T^{$\text{3}\text{2}$} dependence. The spin wave stiffness constants increase linearly with 2 ? x ? 25. The range of exchange interactions decreases with increasing x.     

Magnetization and NMR study of amorphous Ni-P alloys in the paramagnetic concetration range

The temperature- and field-dependence of magnetization, and the ³¹P NMR linewidth and Knight shift of some amorphous Ni_100?xP_x alloys with 18? x ? 22 prepared by melt-quenching and electrodeposition were studied below room temperature. Although all the alloys investigated contain magnetic inhomogeneities, the amount and nature of which depend on impurities and on the details of sample preparation, it could be established that the amorphous matrix of Ni_100?xP_x alloys with x ? 18 exhibit Pauli paramagnetism and the Pauli susceptibility was found to decrease rapidly with P content. From the results, a similarity of the electronic structure and the short-range order in amorphous Ni-P alloys and in the crystalline Ni₃P compound is deduced.     

Invar-type new ferromagnetic amorphous Fe-B alloys

Measurements of magnetization, electrical resistivity, thermal expansion and differential thermal change were made on amorphous Fe_100-xB_x (9 ≦ X ≦ 21) alloys prepared by rapid quenching from the liquid state.With decreasing boron content in the alloys, the Curie temperature falls remarkably, while the magnetic moment increases sluggishly. The thermal expansion curves exhibit the invar characteristics below the Curie temperature due to a large positive spontaneous volume magnetostriction, and the reduced magnetization curves decrease much more rapidly with increasing temperature than those of other ferromagnetic amorphous alloys.     

Structure,magnetic properties and magnetostriction of laves compounds Nd1−xPrx(Fe0.35Co0.55B0.1)2

The C15 Laves phases with composition Nd_1−xPr_x(Fe_0.35Co_0.55B_0.1)₂ (0?x?1) have been synthesized by arc melting and subsequent annealing. The Curie temperature T_c and the saturation magnetizations M_s at 5 and 295 K decrease with increasing Pr content. The linear anisotropic magnetostriction λ_a=λ_∥−λ_⊥ at room temperature for Nd_1−xPr_x(Fe_0.35Co_0.55B_0.1)₂ alloys with 0?x?0.4 initially reaches a negative minimum, then increases and changes its sign with increasing magnetic field H, and the λ_a for the alloys with x?0.6 is positive and increases as magnetic field H increases.     

Theory of magnetostriction in amorphous and polycrystalline ferromagnets: II. Numerical results

Using the basic equations derived in part I of the paper it is shown that magnetostriction of amorphous and polycrystalline ferromagnets is determined by the conventional mechanism via the strain derivative of the local magnetic anisotropy tensor as in crystalline materials, whereas the reorientation mechanism due to the stiff rotation of structural units most probably plays only a negligibly small role. The effective magnetostriction constant λ^eff_s is calculated and conditions for zero magnetostriction are discussed, as well as changes of λ^eff_s during annealing or application of external stress.     

A magnetic, magnetostrictive and Mössbauer study of Tb0.3Dy0.7−xPrx(Fe0.9Al0.1)1.95 alloys

The effect of Pr substitution for Dy on the magnetization, magnetostriction, anisotropy and spin reorientation of a series of Tb_0.3Dy_0.7−xPr_x(Fe_0.9Al_0.1)_1.95 alloys (x=0, 0.1, 0.20, 0.25, 0.30, 0.35) at room temperature has been investigated. It was found that the magnetization and magnetostriction of the homogenized Tb_0.3Dy_0.7−xPr_x(Fe_0.9Al_0.1)_1.95 alloys decreases drastically with increasing x and the magnetostrictive effect disappears for x>0.2, but the spontaneous magnetostriction λ₁₁₁ increases approximately linearly with increasing x. Moreover, the magnetostriction exhibits slightly bigger value at x=0.1 than the free alloys and is saturated more easily with the magnetic field H, showing that a small amount of Pr substitution is beneficial to a decrease in the magnetocrystalline anisotropy. The analysis of the Mössbauer spectra indicated that the easy magnetization direction in the {1 1 0} plane deviates slightly from the main axis of symmetry with Pr concentration x, namely spin reorientation. Comparing with the Al substitution, the effect of Pr substitution for Dy on the spin reorientation is smaller.     

Giant forced volume magnetostriction of Fe-rich iron-cobalt-zirconium amorphous alloys

The forced volume magnetostriction has been measured as a function of composition and temperature in amorphous (Fe_1?xCo_x)₉₀Zr₁₀ alloys. The maximum value of $\text{δω}\text{δH}$ (T = 0 K), equal to 285 × 10^-10 Oe^-1, has been observed for Fe₉₀Zr₁₀ alloys. The effect of pressure on the magnetization σ₀ at T = 0 K was calculated from $\text{δω}\text{δH}$ data. The pressure dependence of the Curie temperature T_c and σ₀ behaves in a similar way as those observed for crystalline NiPd and NiRh alloys.     

Magnetic properties of amorphous Ge–Fe thin films

Thin films of Ge_100−xFe_x (x in at%) alloys, fabricated by thermal co-evaporation, have an amorphous structure at compositions x<∼40, although an unidentified crystalline phase with an FCC symmetry also exists at low Fe content. Magnetization versus temperature curves show that saturation magnetization is non-zero (1 to 2.5 emu/cm³) and remains nearly unchanged up to the highest measured temperature of 350 K. Magnetic hysteresis loops at room temperature show a typical ferromagnetic shape, complete saturation occurring by 1–2 kOe. These results may indicate ferromagnetic ordering at room temperature. No definite tendency is observed in the compositional dependence of saturation magnetization.     

Stress effect on the magnetoresistance of amorphous ferromagnets

To investigate the magnetization in amorphous ferromagnetic alloys we measured the change in the magnetoresistance (H⊥j and H 6j) simultaneously applying a tensile stress along the direction of the ribbons. With increasing stress we observed a complete alignment of the magnetic domain vectors M_s parallel andantiparallel (for λ_s > 0) or perpendicular (for λ_s < 0) to the stress axis. It is found that on average a value of σ_s = 10 kg/mm² is sufficient in all measured samples to produce this effect. The change in the magnetoresistance by stress annealing indicates that a preferred domain orientation in stress direction is induced.     

Magnetic Properties of Amorphous and Nanocrystalline Fe-Zr-B-Al Alloys

We have investigated the influence of aluminium substitution for iron on the magnetic properties of amorphous and nanocrystalline Fe_88-x Zr₇B₅Al _x alloys (x = 0, 1, 3, 5, 7 and 9 at.%). Thermomagnetic curves show an increase of Curie and crystallization temperature of amorphous phase with the increase of the content of aluminium in the alloy. The increase of aluminium content up to 3 at.% Al does not cause the decrease of a saturation magnetization in the as-quenched sample. In addition, magnetostriction of the annealed alloys has been studied. Also, the increase of aluminium content in the alloy causes an increase of the magnetostriction constant.     

Magnetoelastic behaviour in amorphous FePGa alloys

Temperature dependences of Young's modulus and saturation magnetization, linear and forced volume magnetostriction were measured for FePGa amorphous alloys. A discussion concerning the influence of linear magnetostriction, forced volume magnetostriction and magnetic ordering on the changes of E(T) function was made. It was found that annealing of the sample decreases the linear magnetostriction contribution increasing the other two contributions at the same time.