“…. For the truth of the conclusions of physical science, observation is the supreme Court of Appeal….” (Sir Arthur Eddington, The Philosophy of Physical Science.) In this paper we shall review the theoretical and experimental results obtained on simple magnetic model systems. We shall consider the Heisenberg, XY and Ising type of interaction (ferro and antiferromagnetic), on magnetic lattices of dimensionality 1, 2 and 3. Particular attention will be paid to the approximation of these model systems in real crystals, viz. how they can be realized or be expected to exist in nature. A large number of magnetic compounds which, according to the available experimental information, meet the requirements set by one or the other of the various models are considered and their properties discussed. Many examples will be given that demonstrate to what extent experiments on simple magnetic systems support theoretical descriptions of magnetic ordering phenomena and contribute to their understanding. It will a...

Experiments on simple magnetic model systems

Publisher Summary There have been many reviews and books on electron spin resonance (ESR) and several on transition metal ions. Many of these publications have been written by physicists or theoreticians and are very comprehensive. This review is aimed at inorganic chemists, who have had no experience relating to electron spin resonance and who are becoming more and more likely either to use the technique or to need to appreciate the significance of the information available from the technique. The first part of the review gives an elementary account of the relevant theory. There are many good books for further reading for the inorganic chemist, who wishes to go deeper into the subject. The second part of the review is a comprehensive survey of the results of ESR studies on compounds of transition elements. Inevitably, there has had to be some selection of material, and the criteria for inclusion or rejection has been based upon the likely interest of an inorganic chemist might have in the species. This is particularly in the areas, where there is a lot of related work, e.g., the Mn2+ host-lattice data. In the case of copper dg complexes, there has been much duplication of work and papers devoted to the spectra of complexes where a minor substitutive change has been made to a bulky organic ligand.

Electron Spin Resonance of Transition Metal Complexes

The present situation in theoretical and experimental studies on one-dimensional magnetic systems is fully discussed. Equal-time as well as the dynamic properties are included with an emphasis on the latter. Four model systems are examined in detail: TMMC (Heisenberg antiferromagnet), CsNiF3 (planar ferromagnet), CoCl2. 2NC5H5 (Ising ferromagnet), CuCl2. 2NC5H5 (Heisenberg antiferromagnet with S = ½). The equal-time properties are quite well understood in theory and in experiment but the dynamical properties much less so. The open questions and possible investigations for the future are discussed.

Theoretical and experimental studies on one-dimensional magnetic systems

Magnetic properties of single crystal of CsCuCl 3 , CsNiCl 3 , RbNiCl 3 , CsCoCl 3 , and RbFeCl 3 were investigated by the measurements of magnetic susceptibilities, magnetic torques, ESR absorptions from liquid helium temperature to room temperature. The experimental results were interpreted in terms of linear antiferromagnetic chains, taking into account the effect of crystal field. The anisotropic exchange interaction energies between the neighboring magnetic inos along a chain were estimated to be J // / k =-7.0°K, -11.0°K, -14.1°K, -85°K, and -11.5°K, and J ⊥ / k =-6.0°K, -11.0°K, -14.1°K, -17.0°K, and -3.8°K, for CsCuCl 3 , CsNiCl 3 , RbNiCl 3 , CsCoCl 3 , and RbFeCl 3 , respectively by the comparison with the calculated susceptibilities for linear antiferromagnetic chains with Heisenberg and Ising spins by Bonner, Fisher et al. . Properties which appeared in short range magnetic order were studied for two nickelous compounds above T N , 4.5°K in CsNiCl 3 and 11°K in RbNiCl 3 . A qualitative discuss...

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Linear Antiferromagnetic Chains in Hexagonal ABCl3-Type Compounds (A; Cs, or Rb, B; Cu, Ni, Co, or Fe)

Spin exchange interactions and magnetic structures of extended magnetic solids with localized spins: theoretical descriptions on formal, quantitative and qualitative levels

KCuF 3 shows a broad peak of the magnetic susceptibility at ∼243°K and has been supposed to be an antiferromagnet. Scatturin et al. , on the other hand, have reported that the neutron diffraction shows no magnetic ordering in KCuF 3 even at temperatures as low as 4.2°K. In the discussion, they implies the existence of linear magnetic chains along the c -axis. In order to make sure of their conjecture, the measurements of susceptibility, its anisotropy and specific heat have been made. These measurements assure us that KCuF 3 is a one-dimensional antiferromagnet, with the exchange interaction along the chain being J / k =-190°K.

Formation of One-Dimensional Antiferromagnet in KCuF 3 with the Perovskite Structure

Large single crystals of Fe 7 Se 8 and Fe 3 Se 4 were prepared, and their magnetic properties below the Curie point were investigated by a torque magneto meter. The results obtained on Fe 7 Se 8 at room temperature show similar characterics to that of natural pyrhotite (Fe 7 S 8 ), i.e. the crystals can be magnetized only in the c -plane. As the temperature is lowered, however, the c -axis becomes the direction of easy magnetization. This change in direction seems to occur gradually. In the case of Fe 3 Se 4 , such a change in direction of easy magnetization does not take place. The obtained saturation magnetizations for Fe 7 Se 8 and Fe 3 Se 4 are respectively 68 and 80 gauss at the liquid air temperature.

The Magnetic Properties of Iron Selenide Single Crystals

Perovskite structure fluoride KCuF 3 is a one-dimensional antiferromagnet in which the magnetic coupling is very strong along the c -axis. No detectable magnetic interaction is found along any axis perpendicular to it. The nuclear magnetic resonance shifts of F 19 nuclei both on the a - and c -axes are determined separately from the measurements on the single crystal. From the observed shifts, it is found that the fractions of the unpaired spin on the 2 s and 2 p orbitals of the F - ions on the c -axis are f s =0.44% and f σ =4.93% respectively, whereas the fictitious f s ' and f σ ' of the F - ions on the a -axis are 0.16% and 2.34% respectively.

Kinshiro Hirakawa

Papers

Formation of One-Dimensional Antiferromagnet in KCuF 3 with the Perovskite Structure

The Magnetic Properties of Iron Selenide Single Crystals

Nuclear Magnetic Resonance in One-Dimensional Antiferromagnet KCuF3

On the Phase Transition in Tungsten Oxide

Observation of the Hyperfine Interaction Constants in KMnF 3