The phase relations of the GdCo 13−x Si x system have been studied by means of scanning microscopy, microprobe analysis and x-ray diffraction. Single-phase samples GdCo 9±δ Si 4∓δ (structure type LaFe 9 Si 4 with space group I 4/mcm) are formed in a narrow composition range |δ| 0.2, where GdCo 9 Si 4 forms as a fully ordered ternary compound. The magnetic properties of GdCo 9 Si 4 have been investigated by ac susceptibility, magnetization, specific heat and resistivity measurements. These experiments reveal ferrimagnetism below about 47 K, which is analysed in terms of a two-sublattice molecular field model with a local moment Gd subsystem coupling antiparallel to the itinerant ferromagnetic Co 3d sublattice. The 3d-3d exchange of the latter is the driving force for the onset of long range magnetic order. The validity of the twosublattice model is demonstrated by high field measurements, showing that the ferrimagnetic coupling starts to break up at a lower critical field µ 0 H l 27 T. The magnetic ground state of GdCo 9 Si 4 has been analysed on a microscopic basis via LSDA electronic structure calculations.

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A measurement method for studying the magnetoelectric effect in pulsed magnetic fields was developed. Besides magnetization, the system allows the measurement of magnetostriction (using strain gauges) and the magnetoelectric effect. For measuring the magnetoelectric effect a special sample holder with fixed contacts and compensation coils was developed to ensure the reproducibility of the measurements. The magnetoelectric effect can be measured by two different methods: (i) During the application of a magnetic field pulse when the voltage appearing on the sample is directly recorded and (ii) As a function of a high frequency (f=10kHz) ac field superimposed to the main field pulse. In this way an ac voltage appears in the sample which is proportional to the charge change ΔQ=Q0sin(wt+Φ). This voltage is measured using a fast analog lock-in amplifier. A detailed description of the total system is provided. The magnetoelectric effect on well known composites of cobalt ferrite and barium titanate was measured at room temperature. A maximum magnetoelectric coefficient of 1.5mV∕cmOe was obtained for a composite with a composition of 50wt% ferrite sintered at 1200°C. A model to explain the results obtained by this measurement method is discussed.

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