Manganese Fluoride Research Articles

Far-Infrared Optical Absorption of Manganese Fluoride

Optical absorption in MnF2 in the region from 50 to 350 cm−1 was studied. A search was made in particular for multiple-magnon processes previously reported in the literature. While, for example, four-magnon processes can be obtained theoretically from an expansion of the Heisenberg spin Hamiltonion, we found no temperature dependent absorption in the region studied other than the well-known two-magnon peak at 100 cm−1. All the observed peaks above 100 cm−1 could be attributed to phonons.

Interaction of matrix-isolated nickel fluoride and nickel chloride with carbon monoxide, molecular nitrogen, nitric oxide, and molecular oxygen and of calcium fluoride, chromium(II) fluoride, manganese(II) fluoride, copper(II) fluoride, and zinc(II) fluoride with carbon monoxide in argon matrixes

Interaction of matrix-isolated nickel fluoride and nickel chloride with carbon monoxide, molecular nitrogen, nitric oxide, and molecular oxygen and of calcium fluoride, chromium(II) fluoride, manganese(II) fluoride, copper(II) fluoride, and zinc(II) fluoride with carbon monoxide in argon matrixes

Mass spectrometric and thermochemical studies of the manganese fluorides

Mass spectrometric, calorimetric, thermal analysis and X-ray diffraction studies have been performed on MnF 2, MnF 3 and MnF 4. The heat capacity of MnF 2 has been measured from 330°K to 770°K. D(MnF-F), D(MnF 2-F) and D(MnF 3-F) have been determined to be 126 ± 7, 79 ± 6 and 62.3 ± 2.4 kcal mole -1, respectively. The uncorrected electron impact ionization potentials of MnF, MnF 2, MnF 3, and MnF 4 are 8.41, 11.18, 12.25 and 13.15 eV, all ± 0.1 eV, respectively. Evidence for the phase Mn 2F 5(c) has been found. MnF 3 is far more volatile and stable than previously believed. The vapor pressure of MnF 3 (769-930°K) is given by ▪ MnF 4 exerts about 10 -9 atm for fluorine pressure at room temperature and about 10 -6 atm of sublimation pressure at 600°K. MnF 4(c) is 10.5 ± 2 kcal mole -1 more stable than MnF 3(c) at 298°K. Formation and atomization enthalpies for MnF, MnF 2, MnF 3 and MnF 4 have been derived from these new data and a critical review of existing data. No evidence was found for MnF 5, MnF 6 or MnF 7. A simple method of removing much of the ambiguity from the electron impact threshold measurements is reported.

The elastic constants of manganese fluoride

An audio-frequency resonance method has been applied to a set of single-crystal MnF2 rods to determine the elastic compliances. The derived elastic constants are in good agreement with published data.

Critical Magnetic Scattering in Manganese Fluoride

The angular dependence of the quasielastic magnetic scattering has been measured in Mn${\mathrm{F}}_{2}$ in the critical region $T>{T}_{N}$. The temperature dependence of the inverse correlation range and the staggered mode susceptibility for both transverse and longitudinal spin fluctuations were observed as a function of incident neutron energy over the range $56<{E}_{0}<134$ meV. The validity of the quasielastic approximation for this energy region was verified. The data for the longitudinal fluctuations were found to follow simple power laws with the critical exponents $\ensuremath{\nu}=0.634\ifmmode\pm\else\textpm\fi{}0.02$, $\ensuremath{\gamma}=1.24\ifmmode\pm\else\textpm\fi{}0.02$. An $\ensuremath{\eta}$ fitted to the data closest to ${T}_{N}$ gave $\ensuremath{\eta}=0.05\ifmmode\pm\else\textpm\fi{}0.02$. The transverse fluctuations are not divergent at ${T}_{N}$, although for $T>{T}_{N}$ they can be described by power-law fits taken with respect to a temperature ${T}_{\ensuremath{\perp}}\ensuremath{\approx}66\ifmmode^\circ\else\textdegree\fi{}$K by indices ${\ensuremath{\nu}}_{\ensuremath{\perp}}=0.63\ifmmode\pm\else\textpm\fi{}0.08$, ${\ensuremath{\gamma}}_{\ensuremath{\perp}}=1.47\ifmmode\pm\else\textpm\fi{}0.1$. The actual critical temperature is ${T}_{N}=67.458\ifmmode\pm\else\textpm\fi{}0.008$.

Neutron Scattering Verifies Dynamic Scaling

A Brookhaven group has observed the time‐dependent behavior of rubidium manganese fluoride near the critical point, and their results agree with dynamic‐scaling predictions made by Bertrand Halperin and Pierre Hohenberg (Bell Telephone Laboratories); the agreement is the latest in a series of successes that scaling laws have achieved in predicting critical‐point behavior.

Crystal Structure of Pyroelectric Paramagnetic Barium Manganese Fluoride, BaMnF4

BaMnF4, pyroelectric at room temperature and paramagnetic above 30°K, crystallizes in the orthorhombic system with space group A21am and lattice constants a = 5.9845 ± 0.0003, b = 15.098 ± 0.002, and c = 4.2216 ± 0.0003 Å at 298°K. The integrated intensities of 5085 reflections within a reciprocal lattice hemisphere of radius (sinθ) / λ = 1.02 Å−1 were measured using pexrad. The crystal structure has been solved and refined by a combination of Patterson and Fourier series and the method of least squares, using 455 independent and significantly nonzero F(meas). The final agreement factor R, for atoms with anisotropic temperature coefficients, is 0.0466. The structure consists of MnF6 octahedra sharing corners to form puckered sheets parallel to (010). These sheets are linked by Ba2+ ions only, giving rise to excellent (010) cleavage. Within the sheets there are nearly linear –Mn–F–Mn–F– chains parallel to c. Parallel to a there is a second set of planar zigzag –Mn–F–Mn–F– chains, formed by adjacent shared fluorine atoms with Mn–F–Mn angles of 138.6°. The F–Mn–F angles in this chain are 98.3°. The remaining two fluorine atoms in each octahedron are adjacent. These atoms, on the outside of the sheets, are bonded to one Mn atom only. The octahedra are distorted with Mn–F distances ranging from 2.037 to 2.151 Å, with an average of 2.098 Å. Each barium ion is surrounded by a distorted trigonal prism of fluorine atoms, with two more located in the equatorial plane through rectangular prism faces, all Ba–F distances being less than 2.88 Å. A model is presented to account for the observed ferroelectricity in BaZnF4 and the absence of ferroelectricity in isomorphous BaMnF4, based on the separation of the Zn or Mn atoms in the puckered sheets. The experimental absolute polarization sense is in agreement with that calculated. The theoretical polarization for BaMnF4 of 11.5 ± 1.5 μC cm−2 may be compared with the average value of 8.0 μC cm−2 for the ferro-electric members of the BaMF4 series.

Cobalt-Doped TlMnF3, a Zero Anisotropy Cubic Antiferromagnet

Single crystals of cobalt-doped thallium manganese fluoride (TlMn1−xCoxF3) have been studied by antiferromagnetic resonance for cobalt concentrations of 0≤x≤0.001. In this range the antiferromagnet remains cubic at 4.2°K, with its crystalline anisotropy varying linearly with cobalt concentration from K1/M = −5.1 Oe for pure TlMnF3 to +8.2 Oe, passing through zero for x=0.0004. Other magnetic properties, such as Néel temperature and exchange field, are unaffected by the small cobalt concentrations. Multiple non-equivalent equilibrium spin-orientation states, which have been observed in spin-flopped resonance in the 〈100〉 and 〈110〉 crystal planes when K1/M is greater than zero, are described.

Optical Absorption of Cobalt in Manganese Fluoride

The polarized crystal spectra of cobalt-doped MnF2 have been measured down to near 4.2°K. Three broad, anisotropic bands near 7200, 14 000, and 20 000 cm−1 are seen that are presumably due to the spin-allowed 4T1g(F)→4T2g(F), 4A2g(F), and 4T1g(P) transitions of substitutional Co2+, 3d7 ions. The D2h symmetry provided by the rutile structure of the MnF2 lattice produced marked orthorhombic splitting of about 3000 cm−1 in the 4T1g(P) band. Several weak spin-forbidden bands are also seen. The observed anisotropy indicates that the 4T2g(F) band is largely magnetic dipole while the other two are electric dipole. These latter parity-forbidden transitions are aided by coupling with odd lattice vibrations. Application of the appropriate selection rules allows tentative identification of several of the states involved.

Observation of a spin-wave sideband in the optical spectrum ofmnf2

Spin wave sideband in absorption spectrum at low temperatures for transition of manganese ion in antiferromagnetic manganese fluoride

Mass Spectrometric Studies at High Temperatures. V. The Sublimation Pressure of Manganese(II) Fluoride and the Dissociation Energy of Manganese(I) Fluoride

Mass Spectrometric Studies at High Temperatures. V. The Sublimation Pressure of Manganese(II) Fluoride and the Dissociation Energy of Manganese(I) Fluoride

331. A Langmuir measurement of the sublimation pressure of manganese (II) fluoride: R. G. Bautista and J. L. Margrave, J. Phys. Chem., 67, July 1963, 1564–1565

331. A Langmuir measurement of the sublimation pressure of manganese (II) fluoride: R. G. Bautista and J. L. Margrave, J. Phys. Chem., 67, July 1963, 1564–1565

X-ray studies on the thermal expansion of zinc fluoride, manganous fluoride and cobaltous fluoride

A precision determination of the lattice parameters of zinc fluoride (ZnF2), manganous fluoride (MnF2) and cobaltous fluoride (CoF2) has been made in the temperature range 25 to 600° C., using a Unicam 19 cm. high temperature powder camera. From these data the coefficients of thermal expansion α| and α⊥ have been evaluated by a graphical method. For zinc and manganous fluorides, α| is greater than α⊥ as in the case of other crystals of rutile type of structure, whereas cobaltous fluoride is anomalous in its behaviour having a greater value for α⊥.

Elastic properties of manganese fluoride

Abstract The elastic constants and compressibility of manganese fluoride have been measured between 4·2°K and 300°K. Analysis of these data give a Debye temperature (elastic) of 214°K ± 2°K. The compressibility data indicates that the magnetic ordering effects the compressibility at least 100°K above the Neel temperature. This can be interpreted as indicating short range ordering well above the Neel temperature. The elastic data, in conjunction with existing expansivity and specific heat data, is used to evaluate the Gruneisen factor as a function of temperature. These data will be discussed with reference to the crystal structure.

Measurement of the Covalent Spin Distribution in Manganous Fluoride Using Polarized Neutrons

The spatial distribution of the covalent spin density in MnF2 has been obtained from a measurement of the ``forbidden'' magnetic scattering in the nuclear reflections using polarized neutrons. A partial Fourier map of the projected covalent spin on the basal plane was prepared. A model representing the covalent spin by isolated spherical charges that is consistent with the experimental data indicates that the covalent spin density for a single bond undergoes a change in sign as we proceed from the Mn2+ to the F− ion. That part closest to the 3d unpaired electrons carries the same sign as the magnetic ion. The results are discussed in terms of the existing theory.

Some Effects observed by Electron Spin Resonnce of the Diffusion of Manganese into the Calcium and Strontium Fluoride Lattices

The x-band electron spin resonance spectra of calcium or strontium fluoride powder mechanically mixed with manganese fluoride, manganese ammonium fluoride, or manganese dioxide powder were observed immediately after nofixing, after periods of time, and after heating at various temperatures in an argon stream or in air. The proportion of manganese to calcium or strontium was 0.5%. The spectrum immediately after mixing is that of the manganese compound alone. Subsequent spectra depended on the grain size of the alkaline earth fluoride powder. (L.N.N.)

Antiferromagnetism of Mixed Crystals of Zinc and Manganese Fluoride

An attempt has been made to measure the Neel temperature of mixed crystals of various composition by finding the temperature Tc at which the nuclear magnetic resonance of the fluorine nuclei disappears on cooling from room temperature. The dependence of Tc upon concentration of manganese is compared with theoretical predictions. Measurements of the variation of line-width with temperature above Tc are also discussed.

原料の選択が半炭化ケイ素さやの耐久性に及ぼす影響

A heat-resistant semi silicon carbide sagger body could be produced by using black silicon carbide. Experiments were made to examine the effects of kinds of aggregate, combining clays and other additives on thermal shock resistance and oxidation of silicon carbide.The results obtained are as follows:(1) On thermal shock resistance, “Kibushi” clay of high plasticity both as an aggregate and as combining clay gives good effects. Burned “Kibushi” clay used as an aggregate gives better effects at S.K. 14 than S.K. 9, but fused “Kibushi” clay such as corhart is not effective as an aggregate.(2) Effects of other additives on oxidation of black silicon carbide by short-time heating are investigated through D.T.A., weight increase of black silicon carbide after burning and X-ray analysis. Copper carbonate and manganese fluoride increase the oxidation of silicon carbide, and borax which shows lower melting point prevents the oxidation. These results can be explained by the partial pressure of oxygen and their eutectic points with silica.(3) Borax as an additive gives better effects not only on the above physical properties but also on preventing the oxidation of silicon carbide.

The Optical Absorption in Manganese Zinc Fluoride Single Crystals near the N el Temperature

The visible and ultra-violet absorption spectra of single crystals of manganese fluoride, and of two manganese zinc fluoride mixtures, have been measured down to 62°K. The sharp lines arising from the level complexes {4Eg 4A1g} (4G) and 4Eg(4D), which are insensitive to the magnitude of the crystalline electrostatic field, show a non-linear shift with temperature, which varies with composition, and is correlated with the temperatures at which long-range antiferromagnetic order becomes appreciable. A separation of the exchange interaction effect from that due to the thermal expansion of the lattice can be made with some certainty in the material of medium dilution, except in the immediate neighbourhood of the ordering temperature where effects due to the lattice expansion anomaly may be appreciable. The magnitude of the antiferromagnetic interaction shift aids the identification of the transitions, and is interpreted as giving a measure of the variation of short-range spin order with temperature. Measurements of line width and oscillator strength have been made for several absorption lines, and the data for the magnetically dilute materials can be interpreted on simple vibrational models, but for pure manganese fluoride these models seem less satisfactory.

Thermal Expansion Coefficients of Manganese Fluoride

The expansivity ($\frac{\ensuremath{\Delta}l}{{l}_{273.2}}$) and linear thermal expansion coefficient [${l}^{\ensuremath{-}1}{(\frac{\mathrm{dl}}{\mathrm{dT}})}_{p}$] have been measured for the $a$ and $c$ axes of manganese fluoride. There is a marked anomaly in the linear thermal expansion coefficients at the N\'eel temperature; the N\'eel temperature was found to be 67\ifmmode^\circ\else\textdegree\fi{}\ifmmode\pm\else\textpm\fi{}1\ifmmode^\circ\else\textdegree\fi{}K. The anomaly has the characteristic shape associated with order-disorder transformations.