Mitesh Sarkar

Mössbauer studies of iron doped poly(methyl methacrylate) before and after ion beam modification

High-energy MeV ions from accelerators are known to produce drastic modifications in polymers. The typical effects include chain scissions, crosslinks, molecular emission and double bond formation. Poly(methyl methacrylate) was doped with Fe(III) and irradiated with 95 MeV O7+ ions.57Fe-Mössbauer studies were done on the doped samples before and after irradiation. Before irradiation, no Mössbauer absorption was observed. The irradiated samples showed a good Mössbauer absorption, which seems to indicate that there is a significant interaction between the metal ion and the polymer matrix. Two possibilities exist at these doses (∼ 22 × 1012 ions/cm): Fe(III) ions may be bridging the various polymer segments through crosslinking or amorphization of the sample leading to Fe-C bonding. Studies of FTIR, conductivity and glass transition temperatures on these samples support these observations.

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.

Room temperature magnetism and metal to semiconducting transition in dilute Fe doped Sb1?xSex semiconducting alloy thin films

The magnetism was observed in very dilute Fe doped alloy thin film Fe0.008Sb1?xSex, for x?=?0.01 to 0.10. These thin films were grown on silicon substrate using thermal evaporation technique. Structural, electrical, optical, charge carrier concentration measurement, surface morphology and magnetic properties were observed using glancing incidence x-ray diffraction (GIXRD), four probe resistivity, photoluminescence, Hall measurement, atomic force microscopy (AFM) and magnetic force microscopy (MFM) techniques, respectively. No peaks of iron were seen in GIXRD. The resistivity results show that activation energy increases with increase in selenium (Se) concentration. The Arrhenius plot reveals metallic behavior below room temperature. The low temperature conduction is explained by variable range-hopping mechanism, which fits very well in the temperature range 150?300 K. The decrease in density of states has been observed with increasing selenium concentration (x?=?0.01 to 0.10). There is a metal-to-semiconductor phase transition observed above room temperature. This transition temperature is Se concentration dependent. The particle size distribution ?47?61 nm is evaluated using AFM images. These thin films exhibit ferromagnetic interactions at room temperature.

Mössbauer Study of Multiple Substitutions in YBCO

Mössbauer studies of multiple substitutions in YBCO with general formula (Y1−ZCaZ)Ba2(Cu1−X−YFeYMX)3O7−δ are reported. XRD has been used to find out the lattice parameters. All the samples show a single tetragonal phase formation. Iodometric titration is done to estimate the oxygen content. The present study discusses the effect of multiple substitutions of 3d-ions like Ni, Zn, Co, Mn, Cr in YBCO and the effect of various substitutions on charge balancing, oxygen content and site occupancy.

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.

Effect of swift heavy ion irradiation on dilute Fe-doped Sb0.95Se0.05 magnetic semiconductor

ABSTRACT A thin film of dilute Fe (0.008)-doped Sb0.95Se0.05 alloy was grown on silicon substrate using the thermal evaporation technique. This film was irradiated with swift heavy ions (SHIs) Ag+15 having 200 MeV energy at ion fluences of 1 × 1012 and 5 × 1012 ions per cm2, respectively. The thickness of the thin film was ∼500 nm. We study the effect of irradiation on structural, electrical, surface morphology and magnetic properties of this film using grazing angle XRD (GAXRD), DC resistivity, atomic force microscopy (AFM) and magnetic force microscopy (MFM), respectively. GAXRD suggests that no significant change is observed in this system due to SHI irradiation. The average crystallite size increases with fluence, whereas the AFM image shows the rms roughness decreases due to irradiation with respect to the un-irradiated thin film. The MFM image shows that the magnetic interaction in irradiated film decreases due to the irradiation effect. Although the un-irradiated sample shows metal to semiconducting transition, but after irradiation with fluence of 5 × 1012 ions per cm2, the sharpness of the metal to semiconducting phase transition is observed to increase dramatically at ∼300 K. This characteristic of the thin film makes it a promising candidate for an electrical switching device after irradiation.

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.