The ternary spinel-type compounds CdCr2Se4, CdCr2S4, HgCr2Se4, and CuCr2Se4 with Cr as transition metal form a special group of ferromagnetic semiconductors with Curie temperatures up to 430 K. They have particular perspectives in spintronics due to the coexistence of semiconducting and ferromagnetic properties. In this work the ferromagnetic semiconductors were investigated by the hyperfine interactions of implanted nuclear probes using the PAC (perturbed angular correlations) spectroscopy. In such compounds both magnetic hyperfine fields (Bhf) and electric field gradients (efg) allow a detailed study of the behavior of probes, which can additionally represent essential doping atoms in these substances. Besides the popular 111In(111Cd), also 111mCd, 111Ag(111Cd), 77Br(77Se), 117Cd(117In), 199mHg, and 100Pd(100Rh) probes were used exploiting the unique possibilities at the ISOLDE on-line separator and implanter (CERN, Geneva, Switzerland). The main objective of these investigations was to examine the lattice site occupation and the behavior of the implanted probes. In addition, the experimental hyperfine fields were used as test quantities for modern ab initio calculations of the electronic and spin structure (WIEN97).

The ternary spinel-type compounds CdCr2Se4, CdCr2S4, HgCr2Se4, and CuCr2Se4 with Cr as transition metal form a special group of ferromagnetic semiconductors with Curie temperatures up to 430 K. They have particular perspectives in spintronics due to the coexistence of semiconducting and ferromagnetic properties. In this work the ferromagnetic semiconductors were investigated by the hyperfine interactions of implanted nuclear probes using the PAC (perturbed angular correlations) spectroscopy. In such compounds both magnetic hyperfine fields (Bhf) and electric field gradients (efg) allow a detailed study of the behavior of probes, which can additionally represent essential doping atoms in these substances. Besides the popular 111In(111Cd), also 111mCd, 111Ag(111Cd), 77Br(77Se), 117Cd(117In), 199mHg, and 100Pd(100Rh) probes were used exploiting the unique possibilities at the ISOLDE on-line separator and implanter (CERN, Geneva, Switzerland). The main objective of these investigations was to examine the lattice site occupation and the behavior of the implanted probes. In addition, the experimental hyperfine fields were used as test quantities for modern ab initio calculations of the electronic and spin structure (WIEN97).