K. C. Sebastian

Magnetic hyperfine fields in the room-temperature dilute magnetic semiconducting alloy Fe:Sb1−xSex

A dilute quantity of Fe (0.008) was doped into V-VI (Sb1−xSex) for X=0 to 0.50 alloys based on Sb semimetal. Hall measurements showed that the materials were n-type semiconductors for X=0.01 to 0.10 and the charge carrier densities increased from 4.2×1019cm−3 to 1.142×1021cm−3 in this region. For higher concentration of Se (X=0.50), the charge carrier densities decreased dramatically to 2.1×1015. For X=0, Fe showed no magnetic moment. For X=0.01 to 0.1 two magnetic sites (A and B) were observed at room temperature by Mossbauer measurement. Site A appears to be an SeFeSb, type ternary alloy. p-d interaction and carrier-induced polarization seem to be responsible for the magnetic interaction at this site (A). Tc (for Site A) was measured to be ∼573K. Similar behavior was observed for Fe(0.002). Site B Mossbauer parameters coincide with those of Fe7Se8.

Electric field gradient studies in SnSe

The EFG in IV–VI compound semiconductor SnSe was studied using two hyperfine interaction techniques, namely, TDPAC and Mössbauer spectroscopy. The EFG in this material increases sharply up to 300 K and thereafter at higher temperatures it gets saturated. However, the conductivity increases steadily at all the temperatures. The conductivity curve has two slopes. The first portion is due to the population of shallow Cd acceptor levels. Thus, in SnSe also the variation of the EFG with temperature is complex, as in other medium-gap semiconductors.

Quadrupole interaction at181Ta in BaHfO3

BaHfO3 is prepared by sintering a mixture of BaCO3 and HfO2 giving the same heat treatments as for YBa2Cu3O7−δ (YBCO). X-ray diffraction analysis confirms the formation of cubic BaHfO3 along with some unreacted HfO2. A181Ta TDPAC study of the sample, prepared using neutron-irradiated HfO2 and BaCO3, shows a relaxation process to be present in the sample. The value of the relaxation constantλ≅0.26 ns is unusually large and temperature independent.

Mössbauer Study of Magnetic FeSb Dilute System

Mössbauer study of semimetals is of great importance in understanding the origin of hyperfine interactions in these materials. A concentration dependence study in FexSb1−x for x=0.0025, 0.005, 0.01, 0.05, 0.10 and 0.20 is reported. It was found that for 0.0025<x<0.1 FeSb2 compound formation is inevitable. For x=0.0025 a magnetic interaction is observed along with a Quadrupole doublet whose value corresponds to the FeSb2 compound phase.

Perturbed angular correlation study of radiation-induced defects in Rh metal

Radiation-induced defects are studied in cubic rhodium metal, using the local probe technique ‘Time differential perturbed angular correlation’ (TDPAC) at liquid N2 temperature. Isochronal annealing was done at 300, 1073 and 1473 K temperatures. The irradiated sample showed two quadrupole interaction frequencies at 1150 and 93 MHz. The low frequency disappeared at room-temperature annealing, which was assigned to In trapped at a vacancy, whereas the higher frequency remained up to high temperatures and was attributed to In trapped at Rh–C complexes in the Rh matrix.

EFG Studies at 111Cd in InBi Systems

TDPAC study of InBi1−xTex with x=0.0, 0.01, 0.05, 0.1 and 0.2 as a function of temperature is done. Both pure and Te-doped samples show a semi-metallic character up to around room temperature. Above room temperature a steep transition to semiconducting state was observed, which is independent of the doping concentrations. Hence Te may be in the interstitial sites. Conductivity measurement of the above samples showed the same trend as observed in the EFG studies. Thus the importance of the conduction electron density is prominently seen in these systems.

Interaction of repulsive impurity pairs in silver

Probe-impurity interactions of In–Cd and In–Zn pairs in silver matrix have been studied using 111In-TDPAC measurements. The interactions are repulsive for both the pairs. For 3% alloys, the interaction energy of In–Cd pairs in Ag is 51± 2 meV and that of In–Zn pairs is 19± 1 meV. The Electric Field Gradient (EFG) at 111Cd due to a single Cd nn impurity to the In probe is found to be 0.83± 0.04× 1021 V/m2 while for a Zn impurity is 1.50± 0.05× 1021 V/m2. Cd–Cd contact interaction in silver is also found to be repulsive.

Quadrupole interaction at181Ta in selenium

The nuclear quadrupole interaction of Ta-181 in selenium was measured using perturbed angular correlation technique. The electric field gradient at room temperature is 4.56(32) × 1017 V/cm2. The temperature dependence of EFG follows the usual T3/2 behaviour.