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  • 1965-1969  (22)
  • 1
    Online Resource
    Online Resource
    Magnetic Moment and Susceptibility of MnCl2 as a Function of Field along the b Magnetic Axis to 95 kG from 1.3° to 4.2°K
    AIP Publishing ; 1965
    In:  The Journal of Chemical Physics Vol. 42, No. 1 ( 1965-01-01), p. 9-20
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 42, No. 1 ( 1965-01-01), p. 9-20
    Abstract: Values of magnetic moment, isothermal differential susceptibility, magnetic work and free energy change of single-crystal MnCl2 have been obtained by means of a digital voltmeter integrating the dc potential on a sensing coil surrounding a spherical sample. This substance becomes antiferromagnetic near 2°K. The sample was moved vertically along the measuring coil axis which coincided with the field direction in an accurately stabilized field in a long solenoid. The observations cover the range from 1.3° to 4.2°K and fields to 95 kG. The measurements show no signs of irreversibility over the above region. The sample was high purity anhydrous MnCl2 with its b magnetic axis (a crystallographic axis) parallel to the field. The saturation value of MnCl2 was found to be 27 988 G·cm3/mole corresponding to a g=2.004 for a 6S52 state. Problems connected with the accurate use of digital integrators for such measurements are discussed and illustrated by means of various experiments. Magnetic effects due to air, should leaks occur into a refrigerant under vacuum within a solenoid, are discussed and a method of removing solid air from the region near the magnetic sample during magnetic measurements is suggested.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1695732
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1965
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 2
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    NiSiF6·6H2O. Temperature and Other Thermodynamic Properties from Adiabatic Demagnetization without Low-Temperature Heat Introduction. H ∥ c Axis
    AIP Publishing ; 1967
    In:  The Journal of Chemical Physics Vol. 46, No. 5 ( 1967-03-01), p. 1804-1812
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 46, No. 5 ( 1967-03-01), p. 1804-1812
    Abstract: Values of field and magnetic moment have been measured on 40 magnetic isentropes of NiSiF6·6H2O. The field was directed along the crystallographic c axis of the 3.5-cm-diam spherical single crystal. Typical derived values of the magnetic work, differential isentropic susceptibility, relative heat content (enthalpy), and relative internal energy have been tabulated. A principal purpose of the measurements has been to investigate the evaluation of temperature and other thermodynamic properties in the presence of any available magnetic fields without heat introduction below 0.3°K. This avoids the difficulty of distributing heat under small temperature heads in poor thermal conductors. Absolute temperatures from the thermodynamic equation T = (∂H/∂S)H, where H, S, and H are heat content, entropy, and field, respectively, and values of heat capacity CH = T (∂S/∂T)H have been derived at representative fields. At entropies below 1 gibbs/mole and within about ±200 G of zero field, the adiabatic magnetic susceptibility remains constant at 34.3 cm3/mole. At the same time the limiting temperatures of the adiabatics varied from about 0.05°—0.15°K. There was some evidence that the system was beginning to develop irreversibility near 0.05°K but it appeared to be reversible at higher temperatures.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1840938
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1967
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 3
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    Online Resource
    Magnetothermodynamic Properties of MnCl2 from 1.3° to 4.4°K at 90 kG. A Zero Entropy Reference. The Magnetomechanical Process at Absolute Zero
    AIP Publishing ; 1965
    In:  The Journal of Chemical Physics Vol. 42, No. 1 ( 1965-01-01), p. 1-8
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 42, No. 1 ( 1965-01-01), p. 1-8
    Abstract: The heat capacity of single-crystal manganous chloride has been measured in a constant magnetic field, accurately stabilized at 90 000 G and parallel to the b magnetic axis (a crystallographic axis), over the range 1.4° to 4.35°K. The heat capacity approaches zero and magnetic saturation occurs near 1°K, thus providing a reference for the zero of electronic entropy which might otherwise be difficult to obtain due to possible irreversible behavior of this antiferromagnetic system below 1°K. It has been established that loss of magnetic moment from the saturated magnetic domain of the crystal occurs with increasing temperature through the loss of individual Bohr units of angular momentum. By extrapolating reversibly measured values of the magnetic moment, on isoerstedic paths to 0°K, the magnetomechanical process of magnetization at the absolute zero has been described in fairly complete detail. The magnetization curve at 0°K consists of two nearly straight lines joined by a small deviation near 10 kG and approximating saturation at about 32 kG. The value of the quantity (Esat−EH=0)0∘K=10.80 cal/mole. It has been shown that (∂E/∂T)H for MnCl2 at 90 kG is a negative quantity, as would be expected for an antiferromagnetic substance near magnetic saturation. Magnetic work is by far the dominant effect in determining the size of the quanta absorbed near magnetic saturation. The initial increments of demagnetization, with increasing temperature, are assisted by withdrawal of stored internal energy. Thus, the quanta with the smaller energies are those connected with the loss of angular momentum from individual atomic centers, rather than proportionally from the entire cooperative system of electron spins. The limiting heat content at 90 kG is given by HH–Hlattice=20.3exp(−20.3/RT) cal/mole, and the limiting magnetic moment is represented by M=Msat−Ngβ/[exp(20.3/RT)−1] G·cm3/mole, where Msat=27 988 and Ngβ=11 194 G·cm3/mole, with g taken as 2.004. The abuse of the word ``point'' in thermodynamics is discussed and the word ``pernt'' is defined.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1695673
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1965
    detail.hit.zdb_id: 3113-6
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  • 4
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    Online Resource
    Magnetothermodynamics of Single-Crystal CuSO4·5H2O. III. Properties over the Range of 0.4°–4.2°K with Fields to 90 kG ‖ to the γ Magnetic Axis
    AIP Publishing ; 1968
    In:  The Journal of Chemical Physics Vol. 48, No. 9 ( 1968-05-01), p. 3906-3918
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 48, No. 9 ( 1968-05-01), p. 3906-3918
    Abstract: The heat capacity and magnetic moment of CuSO4·5H2O have been measured over the range 0.4°–4.2°K in stabilized magnetic fields of 0, 1, 3, 5, 10, 20, 30, 50, 70, and 90 kG. The field was directed along the γ magnetic axis of a 3.70-cm-diam spherical single crystal. A sensitive carbon thermometer was used to measure the change of temperature during demagnetizations at essentially constant entropy to connect the several isoerstedic heat-capacity series. Magnetic saturation, corrected for diamagnetism and an almost trivial temperature-independent paramagnetism, was used to evaluate the gyromagnetic ratio as gγ = 2.269, and as a zero entropy reference. Within the limit of accuracy of the estimated “tail” above 4°K the electronic entropy was found to be Rln2. All observations were uncorrected for the demagnetizing effect of the spherical sample. At 90 kG the heat-capacity observations show that the nuclear spin polarization is in thermal equilibrium down to 0.7°K.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1669715
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1968
    detail.hit.zdb_id: 3113-6
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  • 5
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    Online Resource
    Magnetothermodynamics of α -NiSO4·6H2O. IV. Heat Capacity, Entropy, Magnetic Moment, and Internal Energy from 0.4° to 4.2°K with Fields 0–90 kG along the a Axis
    AIP Publishing ; 1968
    In:  The Journal of Chemical Physics Vol. 49, No. 9 ( 1968-11-01), p. 4096-4107
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 49, No. 9 ( 1968-11-01), p. 4096-4107
    Abstract: The heat capacity and magnetic moment of a 4-cm-diam spherical single crystal of α-NiSO4·6H2O have been measured over the range 0.4°–4.2°K, with stabilized magnetic fields of 0, 5, 10, 15, 25, 40, 65, and 90 kG along the a crystallographic axis. Comparison with our previous data with the field along the bisector of the a, b axes confirms the observation of Bose and Schoenberg that the magnetic characteristics in the a, b plane of this tetragonal crystal are not isotropic. The heat capacity and entropy of the lattice and electronic system approach zero at the lower temperatures and all fields. These data and closely interlocked observations of temperature vs magnetic field on isentropes which crossed the heat-capacity curves enabled an accurate tabulation of the entropy as a function of field and temperature. The derived differential magnetic susceptibility, the internal energy, enthalpy, and magnetic work are tabulated. At 90 kG the proton spins were in good equilibrium with the lattice above 1.1°K and were essentially out of equilibrium below 0.9°K. Details of heat-capacity measurements, out of equilibrium, in partial equilibrium, and in rapid equilibrium with the nuclear spin system are presented. With minor deviations it was found possible to represent the heat-capacity observations at all fields by means of three-state Schottky functions. The separations of the three states combined with the change of enthalpy of the ground state W0 with field enabled evaluation of the Zeeman pattern for the W0, W1, and W2 states between 0 and 90 kG. The W1 and W2 states were found to be degenerate in zero field. All of the observations were found to be in excellent agreement with values calculated from the spin-Hamiltonian–molecular-field parameters derived by Fisher and Hornung from previous observations with the field along the c axis together with those obtained when the field was along the bisector of the a, b axes.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1670723
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1968
    detail.hit.zdb_id: 3113-6
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  • 6
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    Thermodynamic Temperature and Heat Capacity of NiSiF6·6H2O without Heat Introduction below 0.35°K. Magnetic Moment and Internal Energy from 0.05° to 4.2°K. Fields 0–90 kG Perpendicular to the c Axis
    AIP Publishing ; 1967
    In:  The Journal of Chemical Physics Vol. 47, No. 8 ( 1967-10-15), p. 2685-2700
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 47, No. 8 ( 1967-10-15), p. 2685-2700
    Abstract: Values of the magnetic moment of a 3.5-cm-diam spherical single crystal of NiSiF6·6H2O have been determined over the range 0.3°—4.2°K and 0–90 kG. The field was perpendicular to the c crystallographic axis. The differential isothermal magnetic susceptibility and the isothermal work of magnetization are given. The data have been combined with our previous related measurements of heat capacity and entropy to evaluate the changes in internal energy and enthalpy. All of the data apply to a spherical crystal without correction for the demagnetizing effect. The temperature-independent magnetic moment was estimated as 3.4×10−4H G·cc/mole from the high-field observations. Using this value to correct the data, ga,b=2.233, and a similar correction of our previous data with H ∥ c axis gives gc=2.241 for the temperature-dependent moment. Measurements of magnetic moment as a function of field on 40 adiabatics have been used to extend the thermodynamic temperature and heat capacity below the region of heat introduction, thus avoiding problems of thermal contact and thermal conductivity at very low temperatures.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1712285
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1967
    detail.hit.zdb_id: 3113-6
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  • 7
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    Magnetothermodynamics of α -NiSO4·6H2O. III. Derivation of Spin-Hamiltonian–Molecular-Field Parameters from Experimental Data
    AIP Publishing ; 1968
    In:  The Journal of Chemical Physics Vol. 48, No. 9 ( 1968-05-01), p. 4284-4291
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 48, No. 9 ( 1968-05-01), p. 4284-4291
    Abstract: Magnetothermodynamic data for α-NiSO4·6H2O, with magnetic fields along two axes, the c crystallographic axis ([001] direction) and the [110] direction, have been interpreted using a spin-Hamiltonian–molecular-field model for the NI(H2O)6+ 2 complexes. Best values for the spin-Hamiltonian parameters are D = 4.741 cm− 1 (singlet–doublet separation for H = 0); gz = 2.2158, gxy = 2.2495 (principal values for the g tensor of the Ni(H2O)6+ 2 complexes); φ = 39.00° (angle the z magnetic axes of the four Ni(H2O)6+ 2 complexes per unit cell makes with the c tetragonal screw axis—the x magnetic axes are perpendicular to the tetragonal axis); γ = 0.272 mole / cm3 (molecular field constant representing an isotropic combined ferromagnetic exchange and dipole–dipole interaction between Ni+ 2 ions); and λ = − 281 cm− 1 (the spin–orbit coupling constant). For the c axis the temperature-independent susceptibility α was computed to be 0.75 × 104, while for the [110] direction it was 0.98 × 10− 4 cm3/mole. However, a best fit to the magnetic-moment data for the [110] axis was obtained using only the diamagnetic susceptibility, −1.25 × 10− 4 cm3/mole. A detailed analysis of the methods used in obtaining the parameters from the data is given. The over-all fit to all of the magnetothermodynamic data is excellent, constituting a “textbook” example of the spin-Hamiltonian–molecular-field method.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1669770
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1968
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  • 8
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    Heat Capacity and Entropy of NiSiF6·6H2O from 0.35° to 4.2°K with Magnetic Fields 0–90 kG Perpendicular to the c axis. The Use of 3He Gas Conduction in Calorimetry
    AIP Publishing ; 1967
    In:  The Journal of Chemical Physics Vol. 46, No. 1 ( 1967-01-01), p. 67-72
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 46, No. 1 ( 1967-01-01), p. 67-72
    Abstract: The heat capacity of nickel fluosilicate hexahydrate has been measured over the range 0.35–4.2°K in stabilized magnetic fields of 0, 1, 5, 10, 20, 40, 60 and 90 kG. The field was perpendicular to the crystallographic c axis of the 3.5-cm-diam single crystal. The entropy changes in NiSiF6·6H2O have been accurately tabulated over the ranges 0.35°—4.2°K and 0–90 kG, by combining the heat-capacity data and the change in temperature with field on isentropics. The temperature was measured by means of a carbon thermometer which was also used to introduce calorimetric heat. The total electronic entropy removed to magnetic saturation was Rln3. The substance gave no indication of hysteresis at any field or temperature. At the higher fields and lower temperatures it was necessary to consider a small entropy change due to nuclear magnetization of the hydrogen and fluorine atoms. As a practical rule it has been shown that a 2 mtorr pressure of 3He, which is sufficient to cause liquefaction near 0.3°K, is acceptable in a calorimeter over the range 0.4°—4°K, provided that the ratio of sample surface to volume is small, as, e.g., with a very large spherical single crystal.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1840431
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1967
    detail.hit.zdb_id: 3113-6
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  • 9
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    Magnetothermodynamics of α-NiSO4·6H2O. I. Heat Capacity, Entropy, Magnetic Moment, and Internal Energy, from 0.4° to 4.2°K, with Fields 0–90 kG along the c Axis
    AIP Publishing ; 1967
    In:  The Journal of Chemical Physics Vol. 46, No. 12 ( 1967-06-15), p. 4945-4958
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 46, No. 12 ( 1967-06-15), p. 4945-4958
    Abstract: The heat capacity and magnetic moment of single-crystal α-NiSO4·6H2O have been measured over a range of about 0.4°—4.2°K in stabilized fields of 0–90 kG. The field was parallel to the c crystallographic axis of the 4-cm-diam spherical sample. Although magnetic saturation was not attained even at 90 kG and 0.4°K, there was essentially no temperature coefficient of the magnetic moment below 0.7°K at any field. The heat capacity approached zero for all fields except for a small calculable contribution due to nuclear polarization at high fields. At 90 kG it was found that the nuclear-spin heat capacity at 0.95°K and above was in general equilibrium. At 0.90°K equilibrium was quite slow indicating a rather rapid increase in relaxation time with decreasing temperature. Each heat capacity series provided a zero-entropy reference, above that due to nuclear spin. These references agreed with precise measurements of the temperature change with field on adiabatics joining the various isoerstedic heat capacity series. The entropy changes, in combination with the work and free energy of magnetization, enabled the evaluation of the changes of internal energy and enthalpy as a function of field and temperature. With very minor deviations it was found possible to represent the heat capacity data at all fields by means of three state Schottky functions. At zero field the two upper states are degenerate and are 4.74 cm−1 (13.55 cal/mole) above the ground state. The variation of the enthalpy of each of the individual levels with field is given. A detailed description of the magnetocalorimeter is included.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1840659
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1967
    detail.hit.zdb_id: 3113-6
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  • 10
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    Online Resource
    Entropy, Internal Energy, and Heat Capacity of MnCl2 between 0° and 4.2°K in Magnetic Fields to 100 kG
    AIP Publishing ; 1965
    In:  The Journal of Chemical Physics Vol. 42, No. 3 ( 1965-02-01), p. 835-851
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 42, No. 3 ( 1965-02-01), p. 835-851
    Abstract: The thermodynamically reversible isothermal change of entropy of MnCl2 with magnetic field directed along the b magnetic axis has been measured calorimetrically. At 1.498°K (∂S/∂H)T is positive below 7.5 kG, then negative to magnetic saturation. At 1.333°K, (∂S/∂H)T is negative below 4.5 kG, then positive to 9.25 kG, after which it is negative to saturation. The isothermal entropy change with field has also been measured by a two-step process, in which: (1) the internal-energy change was obtained by combining calorimetric measurements with irreversible magnetic work; (2) combining the internal-energy change with reversible measurements of magnetic work. Measurements of heat capacity in constant fields have been repeated to improve accuracy and to apply a severe test of magnetothermodynamic reversibility by series of measurements made after varied approaches to the starting conditions. The entropy, internal energy, and heat content have been given over the range 0–4.2°K and 0–100 kG, and there are evidently no transition points in the entire area investigated, although gradual changes in magnetic structural types undoubtedly occur. Some values of the heat capacity at constant magnetic moment have been calculated.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1696069
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1965
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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