“…. 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

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

Magnetic properties of the perovskite-type oxide LaMnO 3 were studied in detail, experimentally and theoretically. The properly stoichiometric LaMnO 3 had a weak ferromagnetic moment in addition to the antiferromagnetic character with a Neel temperature of 141°K. It was found to be a parasitic weak ferromagnet. These results can be successfully explained using a phenomenological approach or the Spin-Hamiltonian formalism. The theoretical results show that the antiferromagnetic spin axis should be along the b -axis of the orthorhombic crystal axes and the ferromagnetic moment along the c -axis. The relation between a layer-type ( A -type) antiferromagnetic superexchange interaction and the Jahn-Teller distortion of Mn 3+ ions is also discussed.

Study of (La 1− x Ca x )MnO 3 . I. Magnetic Structure of LaMnO 3

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.

Shin Yoneyama

Papers

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

A Simple Recording Magnetometer

Susceptibility Measurements on KCrF3

CPT Magnetometer with Atomic Energy Level Modulation