Druckstudien zu strukturellen und magnetischen Eigenschaften molekularer und molekülbasierter Magnete (English shop)

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For the simplest magnetic applications (e.g. the kitchen magnet that decorates many people’s refrigerators), the magnetic properties of the solid do not need to be altered during use, but in more complex applications it is necessary to change the characteristics of a material in order, for example, to write or erase data on a computer hard disk. Changes in the magnetic properties of a solid can be achieved by a wide variety of methods, e.g. by optical effects or, as described in this work, by the application of external pressure. Some of the compounds investigated here responded to the applied pressure as was to be expected according to the current state of solid-state physics, but there were also completely unexpected effects whose causes can only be clarified by further investigations.

Chapter 1 provides an overview of the experimental techniques mainly used in this work; for example, pressure cells for measuring the magnetic susceptibility and the specific heat are presented.

Chapter 2 contains the treatises on the chain compound MnNi(NO2)4(en)2, which, despite its relatively small bulk modulus, responds only weakly to the applied hydrostatic pressure with regard to its magnetic properties.

Chapter 3 deals with the sample system XCl2(PM)2. Here X stands for the transition metal atoms iron (Fe), cobalt (Co) and nickel (Ni), and PM for pyrimidine (C4H4N2). The samples investigated exhibit antiferromagnetism and behave exemplarily under external pressure, which means that the compression of the unit cell leads to an increase in the magnetic transition temperature.

The investigations on Cu2Te2O5Br2 are presented in Chapter 4. After the preparation of this sample it was hoped that the magnetism of isolated spin-frustrated copper tetrahedra could be studied, but to this day the magnetic dimensionality of this compound has not been clarified. The frustration of the Cu spins in the tetrahedra, already present in any case, is further enhanced by the external pressure and leads to a weakened magnetism.