Thermal Expansion, Electrical Resistance and the Effect of Hydrostatic Pressure on the Neel Temperature in Fe-Mn Alloys

Thermal expansion, temperature change of electrical resistance and its change due to hydrostatic pressure, and magnetic susceptibility were measured with some antiferromagnetic Fe-Mn alloys containing 30 to 40 at% Mn. It was found that an additional magnetic volume expansivity, δV/V, due to an antiferromagnetic spin ordering is as large as 10^?10^, and the change of the Neel temperature with pressure, ∂T_N/∂P is about -2.5×10^ deg. Kg^・cm^2 in 30 at% Mn alloy. With these values, the volume dependence of the molecular field constant, ∂A/∂ω) is estimated to be positive by the molecular field theory with the localized moment model. The results are discussed in comparison with Bethe-Slater\u27s and Weiss\u27 theories and with the similar behavior in some ferromagnetic invar-type alloys

On the Magnetic and Electric Properties of (Fe_<1-x>Co_x)_<0.89>Cr_<0.11> Alloys

To make clear the mechanism of the appearance of large spontaneous volume magnetostriction of fcc (Fe_Co_x)_Cr_ alloys, their magnetization and elctrical resistivity were measured and the following results were obtained : (1) The dependences of the mean magnetic moments and the Curie point on the concentration, x, and the outer electron concentration, n, of the alloys were similar to those in the Fe-Ni and Fe-Pd Invar alloy systems. That is, the alloys in these three systems are ferromagnetic on the Co- and Ni-rich sides and their ferromagnetic moments disappeared at the n of about 8.2～8.4 which corresponds to the concentration containing Fe more than it in Invar alloys. (2) The magnetization-temperature curve of the Invar alloys mentioned above did not follow Brillouin\u27s function. (3) The electrical resistivity-temperature curves of the Invar alloys showed an anomalous broad maximum near the Curie point. And the residual resistivity were very large. These phenomena may be explained by the co-existence of the ferromagnetic and antiferromagnetic states. It may be considered that the co-exsistence of the two magnetic states is closely connected with the sharp drop of the ferromagnetic moments near the concentration of Invar type alloys

SOFT MAGNETIC PROPERTIES OF AMORPHOUS Fe-Co-Ni BASE ALLOYS WITH Si AND B

Amorphous alloys of Fe-Co-Ni-Si-B system with a wide composition have been produced by a conventional rapid quenching method, and their soft magnetic properties have been examined. The Fe-rich alloys having a high saturation magnetization (～ 1.6×10^4 G) exhibit a rectangular-type B-H hysteresis loop with low coercive force of about 0.01 Oe when the alloys are subjected by a magnetic field cooling. On the other hand, the Co-rich non-magnetostrictive alloys exhibit a high effective permeability ( 50 - 100×10^3 ) at the initial magnetization and audio frequency range. The detailed compositions and heattreatments in obtaining the best soft magnetic properties, and the characteristics which may be interest in engineering applications will be reviewed

Magnetic Properties of h.c.p. Fe-Ru Alloys

X-ray diffraction experiments at room temperature and magnetization measurements from 4.2 to about 1000°K have been performed on the whole composition range of Fe-Ru alloys. The magnetic susceptibility, χ, in the ε phase of 100 at% Ru to 13 at% Ru-Fe alloy shows a Pauli-paramagnetic temperature dependence at high temperatures with small negative and positive temperature coefficients for the alloys less than and more than 30 at% Ru, respectively. The value of χ at room temperature increases with increasing Fe concentration from 100 at% Ru ; the extrapolated value of χ, that is χ of the ε Fe, is as large as 10^/Oe/mole. The Fe-rich alloys in the ε phase shows some decrease in χ at low temperatures, suggesting the occurrence of metallic antiferromagnetic ordering. The reason for the variation in χ with Fe concentration may be attributed to the change in the density of states at the Fermi level due to the change of the width of the d-band, relative position of the Fermi level being unchanged because of the fixed number of outer electrons

Magnetic Domain Structure of an Amorphous Fe-P-C Alloy

The domain structure of an amorphous Fe_P_C_7 alloy ribbon produced by the centrifugal solidification technique was investigated using the magnetic powder pattern technique. Two different types of domains (a maze domain and a 180°-domain) were observed on the specimen surface. The relationship between the domain structure and the magnetization process was also investigated. The results showed that some of the 180°-walls, which ran nearly parallel to the long axis of the ribbon, caused the hysteresis in the magnetization curve, while the maze domain was responsible for the difficulty in obtaining the saturation in magnetization. The maze domain arises probably from the uniaxial magnetic anisotropy having the direction of easy magnetization perpendicular to the surface. This anisotropy seems to be caused by the magnetoelastic coupling between positive magnetostriction and internal stress in the specimen

Hall Effect and Magnetoresistance in Ferromagnetic Amorphous Fe-Co and Fe-Ni Alloys

The magnetoresistance over the temperature range from 77 K to the crystallization temperature and the Hall resistivity at room temperature were measured for the rapidly quenched amorphous alloys (Fe_Co_x)_Si_B_ and (Fe_Ni_x)_Si_B_. The anisotropic magnetoresistance ratio Δρ/ρ in both systems was roughly one order of magnitude smaller than that of crystalline Fe, Co and Ni metals and their alloys, and the normal and anomalous Hall coefficients R_0 and R_s were roughly one or two order of magnitude greater than those of the crystalline metals and alloys. The values of Δρ/ρ and R_0 and R_s monotonically changed with composition x at room temperature. The changes in Δρ/ρ and R_s with composition were compared with those for the Ni-based crystalline alloys on the basis of Berger\u27s theory

Magnetic Properties of Bulk Amorphous La-Fe Alloys

We have prepared three bulk amorphous La_Fe_x alloys (x=69.4, 76.7 and 82.5 at.% Fe) by a high rate dc-triode sputtering. All of the samples are found to be amorphous by neturon diffraction measurements. The amorphous Fe alloys with nonmagnetic Y and Lu are reported to have spin-glass characteristics, while the La-Fe alloys are found to be ferromagnetic. In the latter alloys, the magnetizations are easily saturated in low applied fields, and their values suggest that the Fe moments are completely aligned. Furthermore it has been found that the saturation magnetic moment has a maximum value 1.7μB per Fe atom at around x=75, while the Curie temperature tends to decrease gradually with increasing Fe concentration. The temperature dependence of the magnetization for these alloys follows the spin-wave relation M(T)=M_0(1-BT^-CT^). Using the values of B and C obtained, we have estimated the mean range of the Fe-Fe exchange interaction (). The range of the exchange increases sharply from ～2A^2 to ～100A^2 with increasing Fe concentration and exceeds that of crystalline Fe

High Permeability Properties of Amorphous Co-Fe Base Alloys

Amorphous alloys of (Fe_Co_x)_P_C_7 and (Fe_Co_x)_Si_B_ were prepared by rapid quenching from the melt by using two solidification techniques of centrifugal and roller types. Specimens were ribbons in form. Measurements were made of B-H hysteresis loop, effective permeability at high frequencies, longitudinal magnetostriction, electrical resistance, Vickers hardness and tensile strength. The magnetostriction is zero at a composition near x=0.94, being positive in the range of 0x>0.94. The alloy of Fe_Co_Si_B_ having a nearly zero magnetostriction exhibits the best soft magnetic properties ; the coercive force is 0.006 Oe and the maximum permeability is about 820×10^3 after annealing at 150℃ in a magnetic field. In addition, this alloy has a high effective permeability at higher frequencies up to about 100 kHz, high hardness and high tensile strength

New Co-Fe Amorphous Alloys as Soft Magnetic Materials

Amorphous alloys of (Fe_Co_x)_P_C_7 and (Fe_Co_x)_Si_B_ Were prepared by quenching from the melt by using the centrifugal type and roller type solidification techniques. Specimens were all ribbons in form. Measurements were made of B-H hysteresis loops, effective permeabilities at high frequencies, longitudinal magnetostrictions, electrical resistances, specific gravities and Vickers hardnesses. These alloys are magnetically very soft. The magnetostriction is zero at a composition near x=0.94, being positive in the range of 0≤x0.94. The coercive force and the permeability depends on the absolute value of magnetostriction. The alloy (x=0.94) having a vanishingly small magnetostriction exhibits the best soft magnetic properties : the coercive force is 0.006 Oe, the maximum permeability is 7.0×10^5 and the effective permeability is about 7×10^3 at higher frequencies up to about 100 KHz. In addition to these, this alloy has a high Vickers hardness of 910. Possible applications of this alloy are discussed

On the Magnetization Process in an Iron-Phosphorus-Carbon Amorphous Ferromagnet

The B-H hysteresis loop and the magnetic domain structure have been examined for an amorphous Fe_P_C_7 ribbon alloy produced by the centrifugal solidification technique. The as-quenched alloy exhibits soft-ferromagnetic properties which are characterized by a rectangular type loop with the large Barkhausen jumps and low coercive force of about 0.12 Oe. Magnetic domain structure consists of the 180°-domain and the maze-domain. By annealing for 350 mins at 300℃, the coercive force decreases to 0.06 Oe. An additional annealing increases again the coercive force by transformation of the amorphous to the b. c. c. crystalline phase