Bohr Magneton Number Research Articles

Magnetic Susceptibility of Orthopyroxenes

Magnetic properties of a series of orthopyroxenes, x FeSiO3⋅(1-x) MgSiO3 separated from various kinds of rocks were examined. Paramagnetic susceptibility of the orthopyroxenes was determined from the slope of the straight line part of the magnetization curve, generally expressed as σ=σ0+χH. The following empirical formula was obtained at the room temperature for the molecular magnetic susceptibility of the orthopyroxenes with varying x, i.e. χmol=1.12x×10-2e.m.u/mol. Using this experimental value and assuming that the Fe2+ ions are embedded isolately without any interaction between them in the orthopyroxene crystal, the effective Bohr magneton number of the Fe2+ ion was estimated to be 5.14 from the Curie's law. That this value is within the range of the accepted values of the ferrous ions in the crystal (5.1-5.55) seems to justify the above simple calculation.

The magnetic properties of alloys having the compositions Mn60AlxZn20-xC20and Mn60GaxZn20-xC20

Abstract In the alloys Mn60Al20C20 and Mn60Zn20C20 the Bohr magneton number per manganese atom for the ferromagnetic state differs by 0.32, being greater in the zinc alloy. It was thought that this difference could be accounted for by the difference in valencies between Al and Zn, the extra valency electron of the aluminium atom over that of zinc causing a reduction of one Bohr magneton per unit cell, corresponding to 0.33 Bohr magneton per manganese atom. If this were the case then a simple variation of Bohr magneton number might be expected in the alloy system Mn60Al x Zn20-xC20. In addition, since the alloy Mn60Zn20C20 possesses a transformation at -42°c (when it becomes an antiferromagnetic substance with a complex magnetic structure) whereas the aluminium alloy shows no such transition, measurements on the quaternary alloys should illustrate how this transition is dependent on the electron concentration of the corner atom in the unit cell. The results show a complex behaviour which points against any...

On Magnetic Susceptibility of Olivines

The magnetic susceptibility of several olivines, xFe2SiO4⋅(1-x)Mg2SiO4 with varying x has been measured. The results showed that the olivines are paramagnetic and that their molecular magnetic susceptibility χmol can be expressed empirically by χmol=2x× 10-2emn/mol at the room temperature. Using the accepted values of the Bohr magneton number of Fe+2 ion, and assuming that the Fe+2 ions are embedded isolatedly in the crystal, the paramagnetic susceptibility of olivines at the room temperature can be calculated as χmol=2.2x∼2.6x×10-2emn/mol, provided that the other constituents such as Mg+2 and SiO4 are only diamagnetic. The comparison of the empirical and the calculated values seems to justify the above simple calculation. We expect such calculation will also valid for other rock-forming paramagnetic minerals.

Structure and magnetic properties of Co3O4 and ZnCo2O4

AbstractMeasurements are described of the paramagnetic susceptibilities of Co3O4, ZnCo2O4, and mixed crystals of ZnAl2O4‐ZnCo2O4 and the results are given in a table of X‐values and two plots of 1/X against absolute temperature.To explain the very low value of the mean Bohr magneton number, found for these compounds, the assumption is made that Co3+ in these spinel structures is situated at octahedral interstices and covalently bonded as in the other complex compounds of CoIII, thus not contributing to the paramagnetism.This assumption gives the reasonable, although somewhat high value of 4.7 μB for the Co2+ ion in Co3O4. This high value of μ for Co2+ and the weak paramagnetism of ZnCo2O4 may be caused by a slight oxygen deficiency of the compounds or a small energy difference between the diamagnetic and paramagnetic states of Co3+ in octahedra.

CI.The structure and magnetic properties of the alloyMn3AlC

Abstract An alloy of composition close to Mn3AlC was prepared by induction melting. In the as-cast state the alloy was feebly magnetic at room temperature and the magnetic property was retained after homogenization at 1000°c. This alloy was composed of a single phase possessing an ordered face centred cubic structure with lattice parameter 3·869 å. The ordered structure is similar to that found in the alloy Mn3ZnC, the properties of which have been described elsewhere. The alloy Mn3AlC, is strongly magnetic at low temperatures having a saturation moment at 0°k of 99·6 ergs/g/oersted equivalent to a Bohr magneton number 1·20 per Mn atom, the Curie temperature being 15°c. The paramagnetic susceptibility measured over the temperature range 65–800°c, was found to vary with temperature in a manner different from a normal ferromagnetic material, the 1/X-T graph possessing pronounced curvature concave to the temperature axis.

Magnetic Properties of FeTe

Susceptibility-temperature relation for the compound FeTe was measured over a range of temperatures between liquid air and 1150°C. Evidence was found of an antiferromagnetic character in the region of temperatures below 500°C, the molal magnetic susceptibility having been expressed by χ=0.92/( T +220). The effective number of Bohr magnetons was estimated to be 2.72. The susceptibility dependence on temperature in the region beyond 600°C showed evidences of the feeble constant paramagnetism and an anomaly at 815°C, which is the melting point of this compound. A tentative interpretation of these magnetic properties is given in terms of an electronic configuration of Fe.

Measurement of the Magnetic Susceptibility of Manganese Nitride Mn5N2 by a Microvibration Method

The susceptibility-temperature relationship of carefully prepared manganese nitride Mn5N2 was measured over the temperature range —180°C to 530°C. The Curie-Weiss law χ=C/(T—θ) was found to hold, with θ=—1070 and C=0.0316 emu deg/g. The effective Bohr magneton number is 3.94 per Mn, and is in reasonable agreement with the theoretical value 3.87 for 3 unpaired electrons. This suggests that Mn5N2 behaves as a coordination compound with 4 electron-pair bonds. A new microvibration technique, particularly suitable for susceptibility investigations of materials available in small amounts, has been developed for the present work. The underlying principle is to modulate the magnetic field and to translate the periodic force on the material into a periodic displacement of an elastic strip. The force is measured dynamically in terms of a compensating electrostatic force, an electronic circuit being used as a null detector. Accuracy to 10—4 dyne is claimed.

MAGNETIC SUSCEPTIBILITIES OF IRON GROUP SALTS AT LOW TEMPERATURES

A magnetic balance of the Sucksmith ring type has been constructed. It is capable of a precision of 0.5 to 1% in measurements of displacement. The estimated maximum error in susceptibility measurements is 2%. This apparatus has been used to measure the temperature variation of the susceptibilities of chromium sulphate, hydrated and anhydrous, and of the nitrates of chromium, cobalt, and nickel. Measurements were made at several values of the magnetic field strength, so that a correction for small amounts of ferromagnetic impurity could be obtained. The reciprocals of the corrected specific susceptibilities were plotted against the absolute temperature. The intercepts on the temperature axis of the resulting straight lines gave the values of the Curie–Weiss constant. These values have been compared with those for other salts of the same ions. The effective Bohr magneton numbers were calculated and compared with theoretical values given by van Vleck.

The structure and properties of the alloy Cu2MnIn

The ferromagnetic Heusler alloy Cu2MnAl has a body-centred cubic structure with an ordered arrangement of the atoms. Considerations of valency and atomic diameters suggested that if the aluminium were replaced by indium the superlattice would be more stable, and that a homogeneous alloy would be obtained if the indium content were slightly less than that required by the formula Cu2MnIn. An alloy of composition Cu2.057Mn0.975In0.965was prepared and was ferromagnetic in the as-cast state, and also after a variety of heat treatments. The intensities of magnetization were measured in field strengths between 7250 and 17,150 oersteds at temperatures between — 183° C and the Curie point. X-ray powder photographs show that the indium alloy has the same structure as the aluminium Heusler alloy but with a larger lattice spacing. This increase in the size of the unit cell means an increase in theR/rvalue for the closest approach of manganese atoms from 2.84 in Cu2MnAl to 2.98 in Cu2MnIn, and corresponds with a fall in Curie point of 97° C. The two alloys are strictly analogous as regards structure and valencies, and the results suggest that in the indium alloy the critical value ofR/ris being approached at which ferromagnetism will disappear. Reasons are given for supposing that the ferromagnetism is due to interaction between manganese atoms, in which case the Bohr magneton number per atom of manganese is approximately 4, and manganese behaves as a univalent element, in agreement with conclusions reached independently from the study of phase-boundaries in ternary Cu-Mn-Al alloys.

The Application of the Bethe-Peierls Method to Ferromagnetism

The method introduced by Bethe and Peierls for treating the problem of order-disorder in alloys is applied to the problem of ferromagnetism. The method is first applied to the Ising model of the spin in which case the treatment is much the same as it is for the alloy problem, as has already been pointed out by Peierls. The correct treatment of the spin is used for spin values of \textonehalf{} and 1 per atom. The critical temperatures of different types of lattices are investigated. The method gives results in agreement with the rigorous results of the Bloch spin-wave theory in that only three-dimensional lattices are found to be ferromagnetic. The values of the critical temperatures of these lattices are found to lie between the values predicted by the two Heisenberg approximations. The discontinuity of the specific heat at the critical temperature is computed for a body-centered lattice and for the two values of the spin. The magnitude of the discontinuity is larger than that predicted by Heisenberg's first approximation. The magnitude for the spin 1 is 3.4 $3.4k$ per atom and compares favorably with the experimental value for iron. The susceptibility is computed as a function of the temperature above the critical point. The variation of the susceptibility with temperature does not obey the Curie-Weiss Law but displays some curvature. This curvature explains qualitatively the difference between the paramagnetic and ferromagnetic critical temperatures and also helps remove some of the discrepancy between the number of Bohr magnetons per atom as measured at high and low temperatures.

The wave-length of the Green Auroral line

Mixed ferrites with nominal chemical compositions LixNi0.2Mn0.8−2xFe2+xO4 ranging from x=0 to 0.4 in the steps of 0.1 have been prepared by the auto combustion technique. The X-ray diffraction patterns consist of major cubic spinel LixNi0.2Mn0.8−2xFe2+xO4 phase with minor impurity phases (Fe2O3 and MnO) and with Li substitution phase purity has increased, such that for x=0.4 pure phase spinel structure has been obtained. The lattice parameter has decreased with the increase in Li content obeying Vegard’s law. Both the bulk density and theoretical density have decreased with Li content and with sintering temperature (Ts) up to 1300 °C ρB has increased and beyond that it has decreased. Morphological studies have performed by a high resolution optical microscope and observed that average grain size noticeably dependent on Li substitution. The initial permeability (μi′′) has found to decrease with Li substitution. The Curie temperature (TC) has determined from the temperature dependent μi′′ and found to increases with Li content. From the room temperature magnetization measurement, it has observed that all samples are in ferrimagnetic state at room temperature. The number of Bohr magneton has been obtained from the observed saturation magnetization. Dielectric constant, dielectric loss tangent, ac conductivity and complex impedance are studied in the frequency range 20 Hz–10 MHz. Frequency dependence of dielectric constant in lower frequencies indicates a usual dielectric dispersion due to the Maxwell-Wagner type interfacial polarization. Dielectric loss tangent shows similar behavior like dielectric constant. The complex impedance analysis has been used to study the effect of grain and grain boundary on the electrical properties and with Li content both grain and grain boundary resistance show an increasing trend. The ac conductivity shows frequency independent behavior at the low frequency side and with increasing frequency the conductivity increases.