Magnetostriction Constants of Face-Centered Cubic Nickel-Copper and Nickel-Cobalt Alloys

The magnetostriction constants, λ_ and λ_ of face-centered cubic Ni-Cu and Ni-Co alloys have been determined at room temperature, using single-crystal disc specimens and the strain gauge technique. In Ni-Cu alloys, both constants are negative irrespective of the composition and their absolute values decrease monotonously with increasing copper content. In Ni-Co alloys, the concentration dependence is quite different for λ_&tl;100> and λ_ ; λ_ is negative irrespective of the composition, showing a flat minimum centered at about 30% Co, while λ_ increases almost linearly with increasing cobalt content, passing through zero at about 20 % Co, and eventually reaches to a large value of 116×10^ at 55 % Co. It has been found that the experimental results on the concentration dependence of the magnetostriction constants of face-centered cubic Ni-Co alloys agree quite well with the Vonsovsky-Neel formula for binary cubic solid solutions consisting of two types of magnetic atoms A and B, which is of the form λ=C(N_A^2E_+2N_AN_BE_+N_B^2E_), where λ is λ_ or λ_, C the constant, N_A and N_B the concentrations of the A and B atoms, respectively, and E_, E_ and E_ the energies of magnetic interaction between A and A atoms, between A and B atoms, and between B and B atoms, respectively. For binary cubic solid solutions consisting of magnetic and non-magnetic atoms such as Ni-Cu alloys, it is shown theoretically and experimentally that the following relations hold approximately among the magnetostriction constants, saturation magnetization, I_s, and concentration of non-magnetic atoms, N : λ_∝ I_s^2∝ (1 -N/N_c)^2, where N_c is the concentration where the spontaneous magnetization disappears

Composition, Temperature, and Ordering Dependence of Magnetostriction Constants in Nickel-Manganese Alloys

Magnetostriction constants, λ_ and λ_&lt111>, in the state quenched from 700℃ of nickel and 3.1, 7.0, 14.2, 18.7 and 25.1 at.% Mn-Ni alloys and those in well-annealed state of 25.1 at.% Mn-Ni alloy have been determined in the temperature range between room and liquid air temperatures. In the quenched state, both constants decrease in magnitude roughly monotonically with increasing Mn content in this temperature range. It seems, however, that each of the magnetostriction constants vs. composition curves at temperatures near liquid air temperature has an inflection point at about 5 at.% Mn. The temperature dependence of the magnetostriction constants in the quenched state is roughly the same irrespective of the composition. A well-annealed Ni_3Mn alloy has fairly large negative magnetostriction constants, which decrease in magnitude rather rapidly with rising temperature, suggesting the occurrence of the change in their signs well below the Curie temperature. The composition dependence of the magnetostriction constants in disordered Ni-Mn alloys and the magnitude of the magnetostriction constants of an ordered Ni_3Mn alloy are discussed in terms of atom pair interactions, of which the magnitudes are assumed to depend on the atomic magnetic moments

Electrical Resistivity of Laves Phase Compounds Containing Transition Elements : I. Fe_2A (A=Sc, Y, Ti, Zr, Hf, Nb, and Ta)(Physics)

The electrical resistivity of a series of Fe_2A Laves phase compounds was measured in order to investigate its mutual correlation with their magnetic properties. In the ferromagnetic or antiferromagnetic Fe_2A compounds (A=Sc, Y, Ti, Zr, Hf, and U), a linear relation between the magnetic resistivity at temperatures above the Curie or Neel point and the localized magnetic moment was found, which means that the magnetic resistivity of these compounds is governed by the magnitude of magnetic moments. The electrical resistivity in the Pauli-paramagnetic Fe_Nb_ and Fe_Ta_ compounds with x≈0 shows a fairly large temperature variation, which seems to be due to the paramagnon scattering, whereas ρ-T curves in the iron-rich compounds suggest that the appearance of ferromagnetism is caused by the existence of the excess iron atoms occupying the wrong atomic sites

On the NMR Satellites in the X_2(Y_<1-v>η_v)Z Type Heusler Alloys

In the development of Niculescu et al.\u27s idea, the general expression of the hyperfine field of the nucleus in the Heusler alloy, X_2(Y_η_v)Z containing the impurity η is derived on the basis of the phenomenological relation between the moment and the local environment variable indicating the impurity arrangement around the nucleus. The expression is applied to several NMR experimental results and gives a satisfactory interpretation of the NMR satellites as well as the phenomenological coefficients in Fe_V_xSi and Fe_Mn_xSi alloy systems. The coefficients are in good agreement with those obtained independently in Fe_3Z and CO_2MnZ alloy systems. The analysis of the NMR spectrum of Mn_2V_Al_ alloy suggests that V atom should have the magnetic moment in addition to Mn in this alloy

Interpretation of the Antiferromagnetic Magnetostriction in CoO Single Crystals

The magnetization process in an antiferromagnet and its contribution to the magnetostriction are theoretically treated. In a domain, the rotation of the antiferromagnetic axis and the change in the mutual inclination between up- and down-spins from the antiparallel alignment cause a homogeneous magnetostriction through the whole domain. The domain wall displacement also gives a change to specimen length. They are all proportional to the square of the applied field strength. However, the anisotropy in the former as calculated (a function of the direction of applied field) is much different from the experimental results. The calculated value is less than 10^ of the observed one. On the other hand, the calculated magnetostriction due to the latter shows satisfactory dependence on the applied field as well as on the direction of the magnetostriction : the sign and the magnitude are in good agreement with the experiment previously reported. It is concluded that the domain wall displacement plays the leading role in the magnetostriction of CoO single crystals

Magnetic Properties of Cobalt-Titanium Alloys with the CsCl-Type Structure

X-ray diffraction and magnetic studies have been made on the intermetallic compound CoTi. X-ray diffraction studies indicate that Co_Ti_with the CsCl-type structure has the single-phase ranging from about 44.5 (x=0.110) to 50.0 at.%Ti(x=0) . According to magnetic measurements, the stoichiometric CoTi appears to be Pauli paramagnetic, whereas in nonstoichiometric cobalt-excess composition an appreciable increase in magnetic susceptibility is observed at low temperatures, which may be attributed to the appearance of magnetic moment in this composition range. The magnetic moment estimated from the observed Curie constant is nearly proportional to x, therefore it may be concluded that the magnetic moment belongs to the excess cobalt atom, which is assumed to be substituted with the titanium atom in the equiatomic composition

Magnetic Properties of the Stoichiometric Laves Phase Compound in Cobalt-Titanium System

It has been confirmed by X-ray diffraction and magnetic studies that the cubic Laves phase Co_2Ti exists in a composition range of less than one atomic percent around the stoichiometric composition. Magnetic measurements, made in the temperature range from 4.2° to 800°K, indicates that this cubic Laves phase compound is antiferromagnetic with the Neel temperature of 43°K. The reciprocal magnetic susceptibility vs. temperature curve in the paramagnetic state is strongly concave towards the temperature axis. The curve is described by a modified Curie-Weiss law, in which the effective magnetic moment of the cobalt atom is 0.45μ_B

Ferromagnetic Properties of the Intermetallic Compound with the Hexagonal Laves-Phase Structure in Cobalt-Titanium System

The homogeneous composition range and magnetic properties of the hexagonal Laves-Phase compound. Co_Ti_ (x<0), have been determined by X-ray diffraction and magnetic studies. X-ray diffraction studies show that the MgNi_2-type structure is stable in a narrow composition range from about 29 to 31.3 at.% Ti at room temperature. Magnetic measurements made at temperatures from 4.2°to 1, 000°K indicate that these MgNi_2 phase compounds are ferromagnetic with Curie points lower than 44°K, showing a conspicuous concave toward the temperature axis in every reciprocal magnetic susceptibility vs. temperature curve above the Curie point. It is shown that magnetic data can be interpreted under the assumption that excess cobalt atoms behave as impurity atoms with a localized moment located in the matrix of a paramagnetic compound, similarly to the case of the analysis of the magnetism of dilute magnetic alloys

Magnetic Properties of the Stoichiometric Laves Phase Compound in Cobalt-Titanium System

It has been confirmed by X-ray diffraction and magnetic studies that the cubic Laves phase Co_2Ti exists in a composition range of less than one atomic percent around the stoichiometric composition. Magnetic measurements, made in the temperature range from 4.2° to 800°K, indicates that this cubic Laves phase compound is antiferromagnetic with the Neel temperature of 43°K. The reciprocal magnetic susceptibility vs. temperature curve in the paramagnetic state is strongly concave towards the temperature axis. The curve is described by a modified Curie-Weiss law, in which the effective magnetic moment of the cobalt atom is 0.45μ_B