Low Temperature Specific Heat of Amorphous (Co_<1-x>Mn_x)_<100-y>B_y Alloys

The low temperature specific heat (C_p) for the (Co_Mn_x)_B_y amorphous alloy series has been studied in the temperature range between 0.4 and 50K using a pumped ^3He-cryostat. Below about 10K, C_p for all the present samples can be well fitted to the ordinary expression C_p=γT+βT^3. The linearly temperature-dependent coefficient γ depends strongly on Mn concentration, that is, with increasing Mn concentration, γ values remarkably increase, for example γ of Co_B_ is 5.9mJmol^K^, while that of (Co_Mn_)_B_ is 15.6mJmol^K^. This rather large γ value cannot be explained only by the electronic term and must be attributed to the large magnetic contribution presumably due to the frustration in the spin system. The large γ values also have been obtained in the other amorphous spin glass alloys such as Fe-Ni-P-B, Fe-Zr and Co-Y. On the other hand, Mn concentration dependence of Debye temperature has a discontinuity at certain Mn concentration which corresponds to the same Co/Mn ratio at which the martensitic phase change occurs in the crystalline Co-Mn alloy. This discontinuity reflects a change in phonon behavior which must arise from substantial differences in the amorphous microstructure

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

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

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

Magnetic Moment and Curie Temperature of Amorphous (Co_<1-x>Mn_x)_<100-y>B_y Alloys

Measurements have been made of the magnetic moment and the Curie temperature of Co-Mn-B amorphous alloys with wide Mn and B concentrations. The magnetic moment decreases monotonically with increasing Mn concentration for the alloys with low B concentrations, while it increases initially and then decreases for the alloy with high B concentrations. Ferromagnetic moment vanishes at about Mn/(Co+Mn)=0.4 irrespective of B concentration. The Curie point also reaches zero absolute temperature near the same Mn concentration. The upwards convex curves of magnetic moment vs. Mn concentration in the present amorphous alloys are very different from that of the crystalline Co-Mn alloys, but rather similar to that of the (Co, Mn)_2B intermetallic compound. These composition dependences are analyzed in terms of the local environment effect

Ferromagnetic Tunneling Effect in NiFe/GdO_x/Co and NiFe/AlO_x/Co Junctions made by Electron Beam Deposition

Ferromagnetic tunneling effect has been investigated experimentally on the ferromagnetic-ferromagnetic metal junctions with insulator barrier such as 80NiFe/GdO_x/Co and 80NiFe/AlO_x/Co sandwich films fabricated by an electron beam deposition method under various conditions. Results of measurements of magnetization and magnetoresistance for several samples as a function of external magnetic field show the typical behavior for the ferromagnetic tunneling effect. The largest value of magnetoresistance ratio obtained in the present samples is 1.3%. This value is of about one-third compared to that by obtained by Miyazaki et al and far smaller than the theoretically expected value (about 10%). One of the reason of this small value may come from the quality of the barrier

New Amorphous Ferromagnets with Low Coercive Force

Soft-ferromagnetic properties have been studied for two amorphous alloy systems of (Fe_Co_x)_P_C_7 and (Fe_Co_x)_Si_B_ by means of the X-ray diffraction, thermo-electrical resistance, thermo-magnetization and B-H loop. The B-H loops measured using straight samples were highly rectangular for the as-quenched state. The ratio of the remanence to the saturation magnetization are small (0.4～0.6) for all the alloys. The alloy of Fe_5Co_Si_B_ has a very small value of coercive force, 0.01 Oe, and the high value of the maximum permeability, 120,000. The magnetic field annealing has been found to be very effective in improving the low-field magnetic properties. These excellent soft-magnetic properties may be attributed to the zero-magnetostriction and the isotropic nature of the amorphous structure