Isothermal defect annealing in semiconductors investigated by time-delayed Mössbauer spectroscopy: application to ZnO

The theory for so-called Time-Delayed-Measurements is outlined. This method allows for isothermal annealing studies in emission Mössbauer spectroscopy utilizing radioactive beams. The usefulness of this method is illustrated by the example of the annealing of a magnetic defect in ZnO.     

Local nuclear orientation using defect-induced electric field gradients in cubic lattices

It is demonstrated that the detection of low temperature nuclear orientation by Mössbauer spectroscopy, rather than by the observation of the angular distribution of the emitted radiation, allows to determine nuclear quadrupole interaction strengths generated by randomly oriented defect-induced electric field gradients in cubic lattices. Also the cooling behaviour of radioactive nuclei implanted in semiconductors is studied.     

The characterization of FeH molecules by mössbauer spectroscopy

Mössbauer emission spectroscopy performed with ⁵⁷Co implanted in solid hydrogen reveals a single quadrupole-split component assigned to an FeH molecule. This molecular bond is characterized by a temperature-independent quadrupole splitting ΔE_Q of 2.4 (1) mm/s and an isomer shift with respect to α-Fe of 0.59(5) mm/s. The FeH is formed following dissociation of the H₂ molecule due to the highly energetic electron-capture, decay process. The molecule persists at least up to 70 K, long after evaporation of the H₂ matrix. These results are discussed in connection with previous attempts to observe the formation of FeH by conventional rare-gas-matrix isolation.     

Magnetic hyperfine structure of 119Sn in ferromagnetic Pd2MnSb

A magnetic hyperfine field of H = + 210 ± 5 kOe has been observed at Sn in Pd₂MnSb_0.99Sn_0.01 by Mössbauer spectroscopy on ¹¹⁹Sn. The significance of this measurement with respect to other hyperfine fields and theoretical calculations is discussed.     

Anomalies generated by extrinsic curvature

On the classical level, the embedding of a two-dimensional string in ad-dimensional space induces a natural Weyl operator. It is shown, however, that ford≧4 the corresponding quantum theory is ill-defined. The anomalies of the effective action require the presence of additional degrees of freedom—the theory cannot be specified exclusively in terms of the embedding.     

Interlayer exchange coupling,crystalline and magnetic structure in Fe/CsCl–FeSi multilayers grown by molecular beam epitaxy

Crystalline and magnetic structure as well as the interlayer exchange coupling in MBE grown Fe/FeSi multilayers are investigated. From conversion electron Mössbauer spectroscopy and ion beam channeling measurements the spacer FeSi material is found to be stabilized in a crystalline metastable metallic FeSi phase with the CsCl structure. Strong non-oscillatory interlayer exchange coupling is identified with magnetometry and synchrotron Mössbauer reflectometry. From the fits of the time spectrum and the resonant ?—? scans a model for the sublayer magnetization of the multilayer is deduced.

     

Step-induced canting of magnetization in Fe/Ag superlattices

We have investigated the reorientation of the easy axis of magnetization in (0 0 1) Fe/Ag superlattices using vibrating sample magnetometry, Mössbauer spectroscopy and nuclear resonance scattering of synchrotron radiation. Clear evidence is found that the Fe-layer magnetization can be oriented considerably out of the plane of the sample at room temperature, even for Fe-layer thicker than 6 ML at which the spin-reorientation transition usually occurs in Fe/Ag. The spin canting is attributed to frustration and a strong contribution of a step-induced anisotropy.     

Ion implantation

The extreme sensitivity of Mössbauer Spectroscopy to the local atomic and electronic configuration around ion implanted Mössbauer probes is demonstrated in a number of recent defect configuration studies in semiconductors and metals. A surge of interest is observed towards Mössbauer studies on high dose implantations connected with materials research: recent studies are reviewed dealing with ion beam synthesis, ion beam modification and ion beam mixing of materials.