“…. 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 status of the temperature dependence of magnetocrystalline anisotropy, and the l(l+1)2 power law

The electronic structure of V-centers

The many theoretical studies of the various magnetic, thermal and magnetoelastic properties for paramagnetic and ferromagnetic transition metals and alloys in the simple itinerant electron model are reviewed. The important amendments to the simple itinerant electron model or Stoner model of magnetism due to the spin wave excitations and spin fluctuations are explained.

https://iopscience.iop.org/article/10.1088/0034-4885/44/4/001/pdf

Itinerant electron magnetism

In this paper, we review a large set of experimental data acquired over the past decade by several groups, and demonstrate how it can be used to construct a detailed picture of the low-temperature metallic state of the unconventional superconductor Sr2RuO4. We show how the normal state properties can be consistently and quantitatively explained in terms of Landau quasi-particles moving on a quasi-two-dimensional Fermi surface. Besides presenting our full and extensive data sets, we explain the details of some novel data analysis tools that can be used within the general context of quasi-two-dimensional metals. We then use the experimental Fermi surface and band dispersion to reassess several issues relevant to the unconventional superconductivity in Sr2RuO4, such as the spin-fluctuation spectrum, quasi-particle renormalization, interlayer dispersion and pressure dependence.

Quasi-two-dimensional Fermi liquid properties of the unconventional superconductor Sr2RuO4

Although the orbital magnetic moments of the electrons in metals are “ quenched ” by the crystal field, their contribution to the paramagnetic susceptibility for partly filled degenerate bands is shown to be of the same order of magnitude as the Pauli spin paramagnetism. This contribution corresponds to the so-called “ temperature independent high frequency term ” in the theory of the paramagnetic susceptibility of atoms. Due to this contribution, the gyromagnetic ratio is reduced by an appreciable amount.

Note on the Paramagnetic Susceptibility and the Gyromagnetic Ratio in Metals

based on Heisenberg model is developed by a method which is much more directly the analogue of the original B~the method than Weiss-Li's. By the present method, the calculations can be carried out over all temperatures. Especially, the situation at lower temperatures which is obscure in Weiss·U's papers is made dear. Thus we can see that an anti·Curie point which Anderson has proposed, does not occur, if we calculate the density matrix of a duster exactly without the perturbation method. By considering only a small cluster, being characteristic of the Bethe approxi· mation, the long wavelength spin waves, which are important at lower temperatures, are excluded, so that the magnetization of the sublattice is completely saturated at OOK in just the same way as in the Ising model. It is shown that, in the Bethe approximation, Curie point of antiferromagnet is higher than that of ferromagnet, for the same magnitude of I J I·.

/pdf/a-theory-of-antiferromagnetism-1xl5cakukn.pdf

A Theory of Antiferromagnetism

Nuclear magnetic relaxation rates due to dipolar and orbital interactions are calculated for cubic metals with partly filled p - or d –bands, using the tight-binding approximation. For p –band metals the ratio of two relaxation rates is 3:10. For d –band metals this ratio is a function of the degree of admixture of \(\varGamma_{5}\) and \(\varGamma_{3}\) atomic functions at the Fermi surface. It is shown that the orbital relaxation mechanism is almost always more effective than the dipolar one.

Nuclear Magnetic Relaxation in Transition Metals

The effect of the magnetic ions of those paramagnetic salts whose spin degeneracy is completely lifted by the combined action of the spin-orbit coupling and the crystalline electric field, on the magnetic resonance of nuclear spins and electronic spins of other kind of ions such as Cu 2+ , Co 2+ , Mn 2+ substituted for the host ions are studied theoretically. General formulas for the resonance field shift, line width and the thermal relaxation time in nuclear (or electron) spin resonance in magnetic substances are given. T 1 and T 2 are here related to the difference between isothermal and isolated susceptibilities. Temperature dependence of T 1 and T 2 as well as magnetic field dependence of them are studied. At low temperatures they become longer rapidly (exponentially) as temperature is lowered while at high temperatures they are independent of temperature. Field dependence of the line width is of the type of H 0 2 + H i 2 when the line is narrowed by spin-spin interaction among the host ion spins, or ...

Yukio Obata

Papers

Note on the Paramagnetic Susceptibility and the Gyromagnetic Ratio in Metals

A Theory of Antiferromagnetism

Nuclear Magnetic Relaxation in Transition Metals

Spin Quenching and Magnetic Resonance

Note on the Electron Spin Resonance of the V1-center – Calculation of the Electronic g-value –