Room-temperature ferromagnetism has been induced within ZnO single crystals by implant-doping with Fe ions. For an implantation temperature of 620 K and an ion fluence of 4x10^16 cm^-2, very tiny Fe particles, formed inside the host matrix, are responsible for the ferromagnetic properties. They were identified using synchrotron X-ray diffraction and Moessbauer spectroscopy. On the other hand, Fe ions implanted at a temperature of 253 K and an ion fluence of 4x10^15 cm^-2 are incorporated into the host matrix and develop a room temperature diluted magnetic semiconductor (DMS).Comment: 13 pages, 2 figs, to be published in Appl. Phys. Let

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The discovery of superconductivity in polycrystalline boron-doped diamond (BDD) synthesized under high pressure and high temperatures [Ekimov, et al. (2004) Nature 428:542-545] has raised a number of questions on the origin of the superconducting state. It was suggested that the heavy boron doping of diamond eventually leads to superconductivity. To justify such statements more detailed information on the microstructure of the composite materials and on the exact boron content in the diamond grains is needed. For that we used high-resolution transmission electron microscopy and electron energy loss spectroscopy. For the studied superconducting BDD samples synthesized at high pressures and high temperatures the diamond grain sizes are Ϸ1-2 m with a boron content between 0.2 (2) and 0.5 (1) at %. The grains are separated by 10-to 20-nm-thick layers and triangular-shaped pockets of predominantly (at least 95 at %) amorphous boron. These results render superconductivity caused by the heavy boron doping in diamond highly unlikely. superconductivity ͉ transmission electron microscopy A fter the discovery of superconductivity in boron-doped diamond (BDD) (1), numerous theoretical and experimental studies (2-10) confirmed the phenomenon and went along with its explanation. Superconductivity in group IV semiconductors with diamond structure-such as silicon, germanium, and their alloys-was already predicted in the early 1960s to occur at very low temperatures (11). Except for diamond (1-3, 8, 10), there was a report on experimentally observed superconductivity in boron-doped silicon (9). For diamond, Ekimov et al.(1) suggested that the superconducting transition temperature (T c ) increases with heavy boron doping (T c Ϸ 4 K at 2.6 at % B). However, further investigations of superconducting BDD prepared by the high-pressure-high-temperature (HPHT) technique and by chemical vapor deposition (CVD) revealed strong inhomogeneities in these materials (1,3,7,10,12). In particular, B-rich phases [such as B 4 C (1, 7, 10, 12), used as a reactant, and B 50 C 2 (10, 12)] were found in HPHT BDD samples. In BDD prepared by CVD sp 2 -bonded carbon is unavoidable (3), and one cannot exclude that sp 2 -bonded amorphous or graphite-like carbon accumulates some amount of boron. The presence of extra phases and large discrepancies in the B content determined by various methods (1-3, 7-10, 13, 14) (such as secondary ion-mass spectroscopy, Hall-effect measurements, correlations with diamond lattice parameters, infrared spectroscopy, and microprobe analysis) and the absence of a clear correlation between T c and the B concentration (10) raise the question of how much boron indeed is incorporated into the diamond structure of superconducting samples. It is remarkable that, although measurements of the temperature dependence of the resistance have been conducted on BDD single crystals with boron content ranging from Ϸ10 19 to 2.7 ϫ 10 21 cm Ϫ3 (i.e., up to 1.53 at % B), no evidence of superconductivity was found down to 0.5 K (15,16). This is ...

[Cu(HF2)(pyz)2]BF4 consists of rare mu(1,3) bridging HF2- anions and micro-pyrazine ligands leading to a 3D pseudo-cubic framework that antiferromagnetically orders below 1.54(1) K.

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