Richard L. Carlin

Magnetic properties of transition metal compounds

I. Paramagnetism: The Curie Law.- A. Introduction.- B. Diamagnetism and Paramagnetism.- C. Magnetic Moment of a Magnetic Ion Subsystem.- D. Some Curie Law Magnets.- E. Susceptibilities of the Lanthanides.- F. Temperature Independent Paramagnetism.- References.- II. Thermodynamics and Relaxation.- A. Introduction.- B. Thermodynamic Relations.- C. Thermal Effects.- D. Adiabatic Demagnetization.- E. Relaxation Time and Transition Probability.- F. Spin-lattice Relaxation Processes.- G. Susceptibility in Alternating Fields.- H. Adiabatic Susceptibilities.- References.- III. Paramagnetism: Zero-Field Splittings.- A. Introduction.- B. Schottky Anomalies.- C. Adiabatic Demagnetization.- D. Van Vlecks Equation.- E. Paramagnetic Anisotropy.- F. Effective Spin.- G. Direct Measurement of D.- H. Electron Paramagnetic Resonance (EPR).- References.- IV. Dimers and Clusters.- A. Introduction.- B. Energy Levels and Specific Heats.- C. Magnetic Susceptibilities.- D. Copper Acetate and Related Compounds.- E. Some Other Dimers.- F. EPR Measurements.- G. Clusters.- H. The Ising Model.- References.- V. Long-Range Order.- A. Introduction.- B. Molecular Field Theory of Ferromagnetism.- C. Thermal Effects.- D. Molecular Field Theory of Antiferromagnetism.- E. Ising, XY, and Heisenberg Models.- F. Critical Point Exponents.- G. Cu(NO3)2*21/2H2O.- H. Dipole-Dipole Interactions.- I. Exchange Effects on Paramagnetic Susceptibilities.- J. Superexchange.- References.- VI. Short-Range Order.- A. Introduction.- B. One-Dimensional or Linear Chain Systems.- C. Two-Dimensional or Planar Systems.- D. Long-Range Order.- References.- VII. Special Topics: Spin-Flop, Metamagnetism, Ferrimagnetism and Canting.- A. Introduction.- B. Phase Diagrams and Spin-Flop.- C. Metamagnetism.- D. Ferrimagnetism.- E. Canting and Weak Ferromagnetism.- References.- VIII. Selected Examples.- A. Introduction.- B. Some Single Ion Properties.- 1. Ti3+.- 2. V3+.- 3. VO2+.- 4. Cr3+.- 5. Mn2+.- 6. Fe3+.- 7. Fe2+ and Cr2+.- 8. Co2+.- 9. Ni2+.- 10. Cu2+.- 11. Lanthanides.- C. Some Examples.- 1. Iron(III) Methylammonium Sulfate.- 2. CaCu(OAc)4*6H2O.- 3. Hydrated Nickel Halides.- 4. Hydrated Nickel Nitrates.- 5. Tris Dithiocarbamates of Iron(III).- 6. Spin-3/2 Iron(III).- 7. Manganous Acetate Tetrahydrate.- 8. [M(C5H5NO)6]ClO4)2.- 9. NiX2L2.- 10. [(CH3)3NH]MX3*2H2O.- References.- Append.- A. Physical Constants.- B. Hyperbolic Functions.- Formula Index.

ESR Studies of Coordination to the Sixth Position of Vanadyl Acetylacetonate

The electron spin resonance spectra of vanadyl acetylacetonate (VOacac2) and a number of its adducts have been examined in benzene solution at ambient temperatures. It is found that the magnitude of the vanadium nuclear hyperfine splitting constant decreases from 108.19 to 105.3 G as amine adducts are formed, while the g value increases from 1.9695 to 1.9699. The anisotropies of the axially symmetric g and hyperfine tensors, Δg and b, and the rotational correlation time τR have been calculated from the linewidths of VOacac2, VOacac2·pyridine, and VOacac2·piperidine in benzene solution. The correlation time increases from 2.4×10−11 to 3.0×10−11 sec, |b| increases from 2.1×109 to 2.3×109 rad/sec, and |Δg| decreases from 0.034 to 0.029 on coordination of pyridine. Although the g values calculated from the electronic spectra using the theories of Ballhausen and Gray or Kivelson and Lee decrease slightly on adduct formation rather than increase as observed experimentally, the calculated anisotropies Δg follow ...

Long-Range Order

We now expand the concept of exchange to include interactions throughout a three-dimensional (3-d) crystalline lattice. The interactions are not necessarily long-range, and probably are important only for first through fourth nearest neighbors, but the effects are observed over large distances in a sample. Transitions to such long-range order are characterized by both characteristic specific heat anomalies and susceptibility behavior quite different from what has been described above. In other words, the transition to an ordered state is in fact a phase transition.

Electronic Structure of Hexaquo Metal Ions. I. Chromium (III)

The optical spectra of the hexaquochromium (III) ion in the host crystals of C(NH2)3Al(SO4)2·6 H2O and several isomorphs, and in AlCl3·6 H2O, are presented and discussed. The broad‐band spectra have been analyzed to determine trigonal field parameters, and these results are confirmed by the analysis of the fine‐line spectra. The off‐diagonal element of the trigonal field, v′, is shown to be as large in magnitude as v, and therefore to be of considerable importance in the interpretation of polarized spectra. Evidence confirming the dependence of the ground‐state splitting D on the parameter v′ is also presented.

Two anisotropic Heisenberg linear chain manganese compounds

Abstract The specific heat and zero-field magnetic susceptibilities of [(CH 3 ) 3 NH] MnX 3 .2H 2 O (X=Cl Br) are reported. The isotropic Heisenberg model for linear chains offers a reasonable fit to the data, but a substantial anisotropy is also observed. For the chloride, T N = 0.98 K, J/k = -0.36 K, and zJ′/k = -0.55 K; for the bromide, T N = 1.56 K, J/k = -0.41 K, and zJ′/k = -0.74 K. A canted antiferromagnetic structure is proposed.

Magnetochemistry of Ions in the 4A2 Electronic State.

Each of the following ions with spin S = 3/2, octahedral chromium(III), five-coordinate iron(III), and tetrahedral cobalt(II), possesses a 4A2 ground state. The theory describing their paramagnetic properties is therefore the same, though some of the parameters change appreciably from ion to ion. This theory is described along with examples of experimental data. The implications of the paramagnetic properties for the magnetic ordering phenomena exhibited by complexes of these ions are also described.

Low‐temperature magnetic characteristics of tetrahedral CoCl42−. III. Magnetic exchange in paramagnetic Cs2CoCl4

The results of low‐temperature studies of the magnetic characteristics of Cs2CoCl4 are reported. Single‐crystal principal‐axes magnetic susceptibility measurements between 1.5 and 20 K have been fit to an exchange‐modified spin‐3/2 single‐ion model. Heat capacity measurements between 1 and 30 K on Cs2CoCl4 and between 4 and 25 K on Cs2ZnCl4 have been used with a corresponding states procedure to obtain the magnetic heat capacity of Cs2CoCl4. All the results generally indicate a large zero‐field splitting of 14 to 16 K with the possibility of a rhombic distortion of the CoCl42− ion. Both the susceptibility and heat capacity measurements indicate the presence of significant magnetic exchange. At the lower temperatures the heat capacity results appear to be describable by an XY linear chain model, in agreement with structural considerations in conjunction with the theoretically expected behavior of tetrahedral cobalt(II).

The first experimental evidence of a field-induced magnetic phase transition in an S = 1 singlet ground state system

Abstract A magnetic phase transition to a long range ordered state is observed in Ni(C 5 H 5 NO) 6 (ClO 4 ) 2 in external fields 26.4 kOe H

Low‐Temperature Paramagnetism in Calcium Copper(II) Acetate Hexahydrate

Single‐crystal magnetic‐susceptibility measurements have been made on CaCu(OAc)4·6H2O between 1.5 and 20°K. The present data cannot be fitted to Fishers linear chain model with J / k = − 1.4°K as had been previously reported for data taken at higher temperatures. However, the Curie–Weiss law with a value of θ = − 0.18°K describes both the present data and the previous results. In addition, the low‐temperature results are equally well fitted by the linear chain model with J / k = − 0.095°K.

Field‐induced magnetic ordering in uniaxial nickel systems: A second example

The zero‐field susceptibilities parallel and perpendicular to the tetragonal axis of NiCl2⋅4SC(NH2)2 have been measured between 1.2 and 30 K and fitted to the usual spin Hamiltonian. The resulting parameters are D/kB = 7.6±0.4 K, z0J/kB = −4.5±0.3 K, g∥ = 2.26±0.03 and g⊥ = 2.34±0.03. The susceptibility has also been measured parallel to the tetragonal axis at constant temperatures between 0.3 and 2 K as a function of external field. Magnetic ordering is found to occur, and portions of the phase boundary between paramagnetic and antiferromagnetic states have been determined.