Ferromagnetism and antiferromagnetism in Ni2+x+yMn1−xAl1−y alloys

The magnetic behavior of Ni_2+xMn_1−xAl alloys around the stoichiometric 2:1:1 composition was investigated with several experimental techniques. The results of low-temperature magnetization measurements indicate that a competition mechanism between ferromagnetism and antiferromagnetism is expected in off-stoichiometric alloys. Although the Curie temperature is strongly dependent on the composition, the saturation magnetization has an unsystematic variation for deviations from the stoichiometric Ni₂MnAl alloy. A reentrant-spin-glass behavior is observed below 50 K.     

Cation distribution by Rietveld,spectral and magnetic studies of chromium-substituted nickel ferrites

Ultrafine crystals of chromium-substituted nickel ferrite were prepared by wet chemical co-precipitation method using sulphates of respective metal ions. Formation of these materials has been confirmed by X-ray powder diffraction method. The fine crystal nature of these materials is evidenced from scanning electron microscope (SEM). Cation distribution has been investigated using X-ray diffraction technique. Cation distribution indicates that chromium occupy octahedral site for all the values of composition x. The saturation magnetization and magneton number both are decreasing with increase of chromium concentration x. The decrease in saturation magnetization and magneton number is attributed to the substitution of the Cr³⁺ ions. Curie temperature (T _C ) from susceptibility plot is found to decrease with Cr concentration x. Curie temperature of all the compositions are also obtained theoretically and it agrees with observed Curie temperature.     

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.     

Influence of the magnetic state on the chemical order-disorder transition temperature in Fe-Ni permalloy

In magnetic alloys, the effect of finite temperature magnetic excitations on phase stability below the Curie temperature is poorly investigated, although many systems undergo phase transitions in this temperature range. We consider random Ni-rich Fe-Ni alloys, which undergo chemical order-disorder transition approximately 100 K below their Curie temperature, to demonstrate from ab initio calculations that deviations of the global magnetic state from ideal ferromagnetic order due to temperature induced magnetization reduction have a crucial effect on the chemical transition temperature. We propose a scheme where the magnetic state is described by partially disordered local magnetic moments, which in combination with Heisenberg Monte Carlo simulations of the magnetization allows us to reproduce the transition temperature in good agreement with experimental data.     

High-field susceptibility and magnetization in Fe-Ni invar alloys

The high-field susceptibility of Fe-Ni Invar alloys does not give rise to a sudden increase at the Curie temperature. The decrease in magnetization with increasing temperature is attributed to the T² term as well as to the spin wave term for Fe-Ni Invar alloys.     

Pressure effect on curie temperature in (CoTm)90Zr10 (Tm = Cr,Mo) amorphous alloys

The forced volume magnetostriction in (CoTm)₉₀Zr₁₀ (Tm = Cr, Mo) amorphous alloys was measured by the 3-terminal capacitance method in the fields up to 18 kOe and in the temperature range of 77 K to the Curie temperature or crystallization temperature. From the temperature dependence of the forced volume magnetostriction, the pressure effects on magnetization and Curie temperature are estimated indirectly using the thermodynamical relation between the forced volume magnetostriction and the pressure effect on magnetization. The results obtained indirectly indicate that the pressure effect on Curie temperature approaches nearly zero in Co₉₀Zr₁₀ amorphous alloy, though it cannot be measured directly under pressure.     

Invar effects on some iron-base amorphous alloys

The thermal expansion and magnetic properties of Fe-B and Fe-P amorphous alloys prepared from melts have been investigated. These amorphous alloys show distinct Invar characteristics. heir magnetic properties are also very similar to those of Fe-Ni crystalline Invar alloys; that is, the high-field susceptability and forced-volume magnetostriction are remarkably large, the magnetic moment per Fe atom does not increase linearly, the Curie temperature decreases with a decrease in concentration of B or P, and their reduced their magnetization curves are much flatter than those of crystalline pure Fe.     

An influence of pressure on magnetic properties of some amorphous alloys

Abstract

The paper presents the results of measurements of of magnetic properties of some Fe based amorphous alloys. The magnetization curves B(H) have been investigated within the range of pressure up to 2.5 GPa showing considerable changes with pressure. The reduction of spontaneous magnetization has been observed due to the pressure shift of Curie temperature. In some cases the total disappearence of ferromagnetism with increase of pressure has been observed at isothermal conditions.     

On the Role of Aluminum in Finemet

The role of aluminum with respect of its influence on some intrinsic magnetic properties of the nanocrystalline Finemet, such as saturation magnetization, Curie temperature, spin-wave stiffness constant and hyperfine magnetic fields was investigated. The strengthening effect of Al on the exchange interaction was observed for the alloys with small Al content (up to 3 at.%). Higher concentration of Al (5-7 at.%) led to considerably suppressed exchange interaction.     

Some magnetic characteristics of monocrystalline nickel-germanium alloy

The magnetic characteristics of monocrystalline nickel-germanium alloy are investigated. The temperature dependence of the saturation magnetization, the coercive force, the magnetic reversal hysteresis losses, and the Curie point are examined for alloys with various germanium contents.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, Vol. 12, No. 1, pp. 42–47, January, 1969.     

Electric and magnetic properties of binary Ni-Ge alloys

Results of measurements of the temperature dependence of the resistivity and of the temperature coefficient of the electrical resistivity of Ni-Ge alloys with the concentrations of Ge up to 16 wt.% (13.27 at.%) are stated in this paper. The absence of ferromagnetism and the presence of a maximum of the temperature coefficient of electrical resistivity, corresponding to the Curie points of the alloys, are indicated. In addition, the temperature-dependent data of the magnetization of the above-mentioned alloys are cited.     

MAGNETIC PROPERTIES OF NEW SERIES R-Mo-Fe NITRIDES WITH THE ThMn12-TYPE STRUCTURE AT A LOWER Mo CONTENT

A systematic study has been made on formation condition, crystallographic structure and magnetic properties of RMo_1.5Fe_10.5N_x, where R=Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er. The interstitial nitrogen atom effects on Curie temperature, saturation magnetization and magneto-crystalline anisotropy have been investigated. Two important preliminary results have been obtained. (1) A single phase crystallized in the ThMn₁₂-type structure was stabilized with a smaller content of molybdenum, thus, the compounds possess a higher Curie temperature and a larger spontaneous magnetization. (2) A complete system of compounds with 1:12 type structure containing the light rare earth cerium and praseodymium was synthesized, which will be favorable for developing new rare earth hard magnetic materials.     

In-Situ Alignment of MnBi Crystals Induced by High Magnetic Field above Curie Temperature

Above Curie temperature, MnBi crystals are aligned in situ along the c-axis in a Bi matrix by a high fabrication magnetic field H f of 10 T. Magnetic testing shows a pronounced anisotropy in magnetization in directions normal and parallel to the fabrication field, resulting from the alignment. The successful alignment m v result from the fact that the easy magnetization direction is along the c-axis of MnBi and the high fabrication field of 10 T is large enough to rotate the ）MnBi crystal to this direction even though the temperature is above the Curie temperature.     

Monte Carlo simulation of the reorientation transition in Heisenberg model with dipole interactions

The change of magnetic states in ultrathin films with temperature have been simulated by Monte Carlo method. A Heisenberg model with long-range dipole interactions was adopted in our calculations. The results were qualitatively in good agreement with the experimental phenomena. That is at low temperatures the magnetization is perpendicular to the plane, and at higher temperatures but below the Curie point, the magnetization is mostly within the plane. In between these two regions, the magnetization seems to be suppressed. The simulations show that the loss of magnetization is a consequence of the special magnetic states in which the local domains orientations are reverse with the neighbor ones.     

Magnetism in gold-iron alloysbelow 14 at.% Fe

The dependence of the magnetization on temperature and on magnetic field for Au alloys with 5, 10 and 13·8 at.% Fe has been measured. The gradual freezing of the spin orientations on cooling, time dependence, and thermomagnetic history effects characteristic of mictomagnetism are found. This magnetic behavior, occurring in disordered alloys, can be described in terms of a “spin glass” matrix with magnetic clusters. Metallurgical treatment strongly affects the cluster sizes and concentrations and the magnetization. The “Curie temperatures” observed by earlier Mössbauer measurements apparently correspond to the freezing of the “spin glass” matrix.     

X-ray photoelectron spectroscopy and magnetism of Mn1−x Al x alloys

X-ray photoelectron spectroscopy (XPS), magnetization and magnetic susceptibility of Mn_1−x Al _x (x = 0.0, 0.2, 0.4, 0.5, 0.6, 0.7) alloys are reported. X-ray diffraction measurements showed that all investigated samples have the same crystallographic structure as the parent compound (AuCu₃-structure type). The alloys are disordered for x ≤ 0.5, but become almost crystallographically ordered for higher Al concentration. This change in the crystallographic order is reflected both in the magnetization and Curie temperature values. The exchange interaction is ferromagnetic between the pairs of the near-neighbour Mn-Ni and Ni-Ni magnetic moments and antiferromagnetic for Mn-Mn pairs. The last one is present only in the disordered alloys, which leads to smaller values of the magnetization of these alloys in comparison with the ordered ones. The Mn magnetic moment has the fully ordered value of 3.2 μB in all investigated alloys. The decrease of the Ni magnetic moment as the Al concentration increases may be explained by the hybridization of the Ni 3d and Al 3sp states, which leads to a partial filling of the Ni 3d band. The magnetic susceptibility measurements pointed out the existence of spin fluctuations on Ni sites.      

MAGNETIC PROPERTIES OF NEW SERIES R-Mo-Fe NITRIDES WITH THE ThMn12-TYPE STRUCTURE AT A LOWER Mo CONTENT

A systematic study has been made on formation condition, crystallographic structure and magnetic properties of RMo_1.5Fe_10.5N_x, where R=Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er. The interstitial nitrogen atom effects on Curie temperature, saturation magnetization and magneto-crystalline anisotropy have been investigated. Two important preliminary results have been obtained. (1) A single phase crystallized in the ThMn₁₂-type structure was stabilized with a smaller content of molybdenum, thus, the compounds possess a higher Curie temperature and a larger spontaneous magnetization. (2) A complete system of compounds with 1:12 type structure containing the light rare earth cerium and praseodymium was synthesized, which will be favorable for developing new rare earth hard magnetic materials.     

Magnetoelastic and elastocaloric effects in rare-earth metals,their alloys and compounds in the region of magnetic phase transitions

This article discusses experimental data and their theoretical interpretation concerning the volume magnetostriction, spontaneous magnetostriction, variation of magnetization under the action of pressure, and elastocaloric effects in rare-earth metals, as well as their alloys and compounds. Particular attention is paid to the region of phase transitions. The volume magnetostriction ω of true magnetization was investigated near the Curie temperature Θ as a function of magnetization and determined from the change of magnetostriction under the action of pressure. From these data we obtained the dependence of the exchange integrals on the unit cell volume. Giant volume magnetostriction and magnetoelastic elastocaloric effects were discovered in the rare-earth metals and alloys in the region of their magnetic phase transitions. It was established that giant volume magnetostriction in RCo₂ compounds is caused by a critical increase of the magnetic moment of the 3d sublattice of cobalt in magnetic fields that exceeds the critical field at T > Θ. Giant volume magnetostriction in R₂Fe₁₇ compounds near the temperature Θ is shown to occur due to strong deformational dependences of exchange interaction and the value of the 3d electron bandwidth.     

The magnetic and magnetocaloric effect of (Mn0.5Co0.5)65Ge35 alloy in low magnetic field

The crystal structure and magnetocaloric effect (MCE) of water-quenched and annealed (Mn_0.5Co_0.5)₆₅Ge₃₅ alloys were studied in this paper. A CoMnGe-single phase was formed in the water-quenched alloy, and mixture phases of CoMnGe and Mn+2O in the annealed alloy. The annealed alloy has a smaller crystal parameter than the water-quenched alloy. The Curie temperature is 275 and 298 K for the water-quenched and annealed alloys, respectively, which means that the magnetic-transition temperature in this material can be controlled by anneal. In addition, the same magnetic entropy change was found in these two alloys, even though their Curie temperatures have a significant difference.     

First observation of ferromagnetism and ferromagnetic domains in a liquid metal

80 Pd₂₀ alloy below the Curie temperature T_C(l)=1257 K of the liquid state. The magnetization of the undercooled liquid sample has been measured as a function of temperature using a modified Faraday balance. Below T_C(l), the magnetization of the liquid metal shows a plateau in the weak external field of μ₀H_z=5.6 mT. The effect is comparable to the behaviour of the corresponding solid phase, indicating the onset of spontaneous magnetization with ferromagnetic domains. T_C(l) is about 20 K lower than the Curie temperature of the solid phase T_C(s). Received: 24 February 1997/Accepted: 16 May 1997