Ising-type antiferromagnets. Models systems in statistical physics and in the magnetism of exchange bias. (Q1420205)

The book deals with selected modern aspects of artificially layered structures and bulk materials involving antiferromagnetic long-range order. The book contains two parts. The first part deals with the impact of insulating ionic compounds with localized magnetic moments in the field of statistical physics. They are perfect realizations of anisotropic Heisenberg systems which, in the case of strong single-ion anisotropy, enable the realization of Ising-type model systems. Such compounds involving strong direct ferromagnetic exchange and additional weak antiferromagnetic interaction turn out to be among the best available model systems of low-dimensional Ising ferromagnets. \(\text{FeCl}_2\) is a representative of these prototypical systems which provides experimental access to fundamental thermodynamic properties in general and the statistical theory of Lee and Yang in particular. Starting with a brief introduction of the Lee-Yang theory from an experimentalist's point of view, density functions of the complex zeros of the partition function as well as the gap exponent of the two-dimensional Ising ferromagnet on a triangular lattice are determined from isothermal magnetization data. Finally, modern approaches beyond the Lee-Yang theory are briefly discussed. Fisher's zeros in the complex temperature plane are introduced. A possible simple basis underlying the circle theorem is motivated and implications from the Lee-Yang in the field of nonequilibrium systems are briefly discussed. The second part of the book deals with the exchange-bias phenomenon in prototypical magnetic heterostructures. Special emphasis is laid on model systems where the limited number of spin degrees of freedom minimizes the complexity of the problem. A generalization of the phenomenological Meiklejohn Bean approach is presented which takes into account, e.g., finite anisotropy and thickness of the antiferromagnetic pinning layer. Mechanisms which create the antiferromagnetic interface magnetization are investigated and discussed. Special attention is paid to piezomagnetism. This is a well-known bulk phenomenon, e.g. has been overlooked so far as a significant contribution to the antiferromagnetic interface magnetization of exchange-bias heterostructures.