Centre for Advanced Studies in Electronics Science and Technology

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  • Item
    Low temperature anomalous electrical resistivity behaviour of amorphous ferromagnetic Fe < inf > 40 < /inf > Ni < inf > 38 < /inf > Mo < inf > 4 < /inf > B < inf > 18 < /inf >
    ( 1983-01-01) Chandra, Girish ; Rajaram, G.
    The resistivity of the amorphous ferromagnet Fe40Ni38Mo4B18 has been measured from 3.6 to 300 K. The resistivity exhibits a minimum in the temperature interval 45-50 K. The data could be fitted to a log(T2 + Δ2) dependence below the minimum and to a T2-dependence above the minimum. © 1983.
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    Iron hyperfine field distribution in amorphous FeNiCrMoSiB
    ( 1983-10-03) Rajaram, G. ; Prasad, Shiva ; Chandra, Girish ; Shringi, S. N. ; Krishnan, R.
    The distribution of Fe hyperfine fields, P(H), has been studied for the amorphous ferromagnetic alloys Fe40- x 2Ni40- x 2CrxMo2Si10B8, x = 0, 1, 3, 4, 5 by Mössbauer measurements at room temperature. The results favour a bimodal distribution for P(H) as suggested earlier for METGLAS 2826A. The low field component is found to increase with x. © 1983.
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    MOESSBAUER STUDIES IN SPUTTERED a-Fe//8//0B//2//0 FOILS.
    ( 1984-01-01) Chandra, Girish ; Prasad, Shiva ; Rajaram, G. ; Srinivas, V. ; Shringi, S. N. ; Laridjani, M. ; Krishnan, R.
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    Mossbauer studies in sputtered a-Fe80B20 foils
    ( 1984-01-01) Chandra, Girish ; Prasad, Shiva ; Rajaram, G. ; Srinivas, V. ; Shringi, S. N. ; Laridjani, M. ; Krishnan, R.
    Mossbauer studies have been carried out on sputtered amorphous Fe80B20 foils in the temperature range of 4.4 K to 300 K. The results have been analysed using Window's method. The coefficients B and C in Bloch's law are evaluated from the data. One finds a smaller value of B in sputtered foils in comparison to the liquid quenched ribbons. There are indications that the mean square range of exchange interaction is larger in these foils. © 1984 IEEE
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    Low temperature resistivity studies in CR containing amorphous alloys Fe-Ni-Cr-Mo-Si-B
    ( 1984-01-01) Rajaram, G. ; Chandra, Girish ; Prasad, Shiva ; Srinivas, V. ; Shringi, S. N. ; Krishnan, R.
    Resistivity data on Fe40-x/2 Ni40-x/2CrxMo2Si10B8 samples with x = 0, 1, 3, 4, 5 in the temperature region 7 K - 300 K have been reported. A minimum is observed in the resistivity as a function of temperature at a temperature Tmin varying between 20 K to 80 K for the five samples. Attempts are made to fit the data with a sum of a T2 term and various functional forms predicted for the negative temperature coefficient region. © 1984 IEEE
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    LOW TEMPERATURE RESISTIVITY STUDIES IN Cr CONTAINING AMORPHOUS ALLOYS Fe-Ni-Cr-Mo-Si-B.
    ( 1984-09-01) Rajaram, G. ; Girish, Chandra ; Shiva, Prasad ; Srinivas, V. ; Shringi, S. N. ; Krishnan, R.
    Resistivity data on Fe//4//0// minus //x/////2Ni//4//0// minus //x/////2Cr//xMo//2Si//1//0B//8 samples with x equals 0,1,3,4,5 in the temperature region 7 K-300 K have been reported. A minimum is observed in the resistivity as a function of temperature at a temperature T//m//i//n varying between 20 K to 80 K for the five samples. Attempts are made to fit the data with a sum of a T**2 term and various functional forms predicted for the negative temperature coefficient region.
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    MOSSBAUER STUDIES IN SPUTTERED A-Fe//8//0B//2//0 FOILS.
    ( 1984-09-01) Chandra, Girish ; Prasad, Shiva ; Rajaram, G. ; Srinivas, V. ; Shringi, S. N. ; Laridjani, M. ; Krishnan, R.
    Mossbauer studies have been carried out on sputtered amorphous Fe//8//0B//2//0 foils in the temperature range of 4. 4 K to 300 K. The results have been analyzed using Window's method. The coefficients B and C in Bloch's law are evaluated from the data. One finds a smaller value of B in sputtered foils in comparison to the liquid quenched ribbons. There are indications that the mean square range of exchange interaction is larger in these foils.
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    Low temperature Mössbauer study of amorphous Fe-Ni-Cr-Mo-Si-B
    ( 1985-01-01) Prasad, Shiva ; Chandra, Girish ; Rajaram, G. ; Srinivas, V. ; Shringi, S. N. ; Krishnan, R.
    Chromium containing amorphous alloys of composition Fe40- x 2Ni40- x 2CrxMo2Si10B8, x=0,1,3,4,5, have been studied by Mossbauer effect at 4.4 K. The results indicate that the large reductions in the saturation magnetisation observed in these alloys on addition of Cr may be largely due to the reduction of the Fe moment in the neighbourhood of Cr. © 1985.
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    Temperature dependence of hyperfine parameters in Fe-Ni-Cr-Mo-Si-B
    ( 1986-01-01) Prasad, Shiva ; Chandra, Girish ; Rajaram, G. ; Srinivas, V. ; Shringi, S. N. ; Krishnan, R.
    The temperature dependence of the average and width of the hyperfine field distribution, isomer shift and the intensity ratio I2,5/I3,4 are reported for amorphous Fe40-x/2Ni40-x/2CrxMo2Si10B8, x = 0-5. The spin-wave constant, B, determined from the temperature dependence of the average hyperfine field is larger than that determined from net magnetization data for x = 5. The hyperfine field distribution in the crystallised alloys are reported. © 1986.
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    Crystallisation studies in Fe < inf > 37.5 < /inf > Ni < inf > 37.5 < /inf > Cr < inf > 5 < /inf > Mo < inf > 2 < /inf > Si < inf > 10 < /inf > B < inf > 8 < /inf >
    ( 1986-03-01) Chandra, Girish ; Rajaram, G. ; Prasad, Shiva ; Srinivas, V. ; Shringi, S. N. ; Krishnanc, R.
    The distribution of hyperfine fields (HF) is obtained at room temperature for Fe37.5Ni37.5Cr5Mo2Si10B8 annealed at temperatures between 641 K and 744 K. P(H,T) is also derived for samples annealed at 744 K for over 70 hours. Three steps are noted in the evolution of the crystalline phases: (1) separation of ∼ 35% of Fe atoms into environments with low and high HF's, with increase in Tc for the remainder (2) nearly complete separation of the P(H) into these two components on further annealing at a higher temperature and (3) at yet higher annealing temperatures, conversion of the high field phase into one with a lower HF. The observations are tentatively explained in terms of preferential presence of Cr in one of the phases and its subsequent migration into the other phase. © 1986 J.C. Baltzer A.G., Scientific Publishing Company.
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    ELECTRICAL TRANSPORT STUDIES IN AMORPHOUS Fe//8//0// minus //xCr//xB//1//2Si//8 ALLOYS.
    ( 1986-12-01) Srinivas, V. ; Rajaram, G. ; Prasad, Shiva ; Chandra, Girish ; Shringi, S. N. ; Krishnan, R.
    Electrical resistivity has been measured from 1. 5 K to 300 K on a-Fe//8//0// minus //xCr//xSi//8 samples for x equals 0,2,. . . ,12. For x greater than 6 of a second minimum is observed at a temperature lower than the principal minimum. An attempt has been made to fit various functions to the resistivity data in temperature range where temperature coefficient of resistance is positive.
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    ROOM TEMPERATURE MOSSBAUER STUDY OF AMORPHOUS Fe-V-B-Si ALLOYS.
    ( 1986-12-01) Vadnere, R. V. ; Srinivas, V. ; Prasad, Shiva ; Shringi, S. N. ; Rajaram, G. ; Nigam, A. K. ; Chandra, Girish ; Krishnan, R.
    A room temperature Mossbauer study of a-Fe//8//0// minus //xV//xSi//8 (0 less than equivalent to x less than equivalent to 12) is being reported. The results were analyzed using Window's technique. Various hyperfine parameters obtained from this study are reported and compared with those obtained for a-Fe//8//0// minus //xCr//xB//1//2Si//8 (0 less than equivalent to x less than equivalent to 12) which contains same metalloid concentration.
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    Remarkable change in resistivity minimum temperature in the presence of Ni in a-Fe-Cr-B-Si alloys
    ( 1987-01-01) Prasad, Shiva ; Srinivas, V. ; Chandra, G. ; Rajaram, G. ; Shringi, S. N. ; Krishnan, R. ; Rougier, P.
    Resistivity studies have been carried out on a-Fe76-xCr4NixB12Si8 for x = 0, 5, 10, 20, 30 in the temperature range of 1.5 K to 300 K. It is found that the temperature at which resistivity shows a minimum (Tmin) is a strong function of Ni concentration. By the addition of 5 to 10 at % Ni, the change caused in Tmin by Cr is compensated, and its value is found to be ∼20 K similar to Fe80B12Si8 alloy. © 1987.
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    Anisotropic spin glass behaviour of FeMnTiO < inf > 5 < /inf > system
    ( 1987-03-01) Srivastava, J. K. ; Ramakrishnan, S. ; Rajaram, G. ; Chandra, G. ; Marathe, V. R. ; Vijayaraghavan, R. ; Srinivas, V. ; Kulkarni, J. A. ; Darshane, V. S.
    Mössbauer effect, d.c. magnetisation (temperature variation, irreversibility, hysteresis and field dependence), a.c. susceptibility and x-ray measurements in FeMnTiO5 (4.2 ≤ T < - 500 K) show it to be an anisotropic reentrant ferrimagnet where magnetic ordering and spin freezing occur only along the c-axis. This is a consequence of the f- and c- site chemical disorder, and orthorhombic c-axis distortion. © 1987 J.C. Baltzer A.G., Scientific Publishing Company.
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    Effect of Cr on hyperfine parameters in a-Fe-Cr-Si-B alloys
    ( 1987-03-01) Srinivas, V. ; Rajaram, G. ; Prasad, Shiva ; Chandra, Girish ; Shringi, S. N. ; Krishnan, R. ; Rougier, P.
    Mössbauer studies on a-Fe80-xCrxSi8B12 (x = 0,2,...12) at 5K have been reported. The average hyperfine field and width of P(H) distribution have been analysed by a model which assumes a random distribution of Cr atoms. On assumption that the hyperfine field distribution of Fe atom with r number of Cr nearest neighbours is given by a gaussian with a mean field Hr =Ho - rC1 + r2C2; C and C2 being constants; broad features of Mössbauer spectra are explained. © 1987 J.C. Baltzer A.G., Scientific Publishing Company.
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    Temperature dependence of longitudinal magnetoresistance in amorphous FeCrSiB alloys
    ( 1988-01-01) Chandra, Girish ; Nigam, A. K. ; Srinivas, V. ; Prasad, Shiva ; Shringi, S. N. ; Krishnan, R. ; Rajaram, G.
    Longitudinal magnetoresistance measurements on amorphous Fe80-xCrxB12Si8 (x = 0, 2, ..., 12) alloys have been carried out in order to study the effect of chromium and external magnetic fields on these iron-based amorphous alloys. The measurements were taken in external fields up to 45 kOe in various temperatures from 4.41 to 300 K. The slope of the longitudinal magnetoresistance at 4.4 K is found to change sign from negative to positive as x increases and then tends to saturate. We have discussed various possibilities to explain this behaviour and compared our data with those from other chromium-containing amorphous alloys. © 1988.
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    Resistivity and longitudinal magnetoresistance studies in amorphous FeNiCrMoSiB
    ( 1988-01-01) Rajaram, G. ; Prasad, Shiva ; Chandra, Girish ; Nigam, A. K. ; Srinivas, V. ; Shringi, S. N. ; Krishnan, R.
    With a view to study the effect of Cr on the transport properties of FeNi based amorphous magnetic materials, electrical resistivity and magnetoresistance measurements have been carried out on α-Fe40-x/2Ni40-x/2CrxMo2Si10B8 (0 < x < 5) samples from 1.5 to 300 K. The longitudinal magnetoresistance studies have been carried out in fields up to 45 kOe in varying temperatures from 4.2 to 100 K. Resistivity has been observed to show only a single minimum as a function of temperature in contrast with Fe based Cr containing alloys. The longitudinal magnetoresistance is found to show significant temperature dependence in the alloys of the present series, unlike α-FeCrB alloys. On the basis of fittings to various models, it is found that the functional form in the positive temperature coefficient of resistivity (TCR) region undergoes a change as Cr concentration increases. © 1988.
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    Mössbauer studies in a-Fe < inf > 76-x < /inf > Ni < inf > x < /inf > Cr < inf > 4 < /inf > B < inf > 12 < /inf > Si < inf > 8 < /inf >
    ( 1988-02-01) Vadnere, R. V. ; Srinivas, V. ; Nigam, A. K. ; Rajaram, G. ; Chandra, Girish ; Prasad, Shiva ; Shring, S. N. ; Krishnan, R.
    Room temperature Mössbauer studies on a-Fe76-xNixCr4B12Si8 alloys (0≤x≤30) are reported. The average hyperfine field is observed to remain constant. P(H) shows a low hyperfine field component which is found to be nearly absent for 2≤x≤4 samples. An attempt has been made to understand the correlation of this to the low temperature resistivity behaviour of Cr containing Fe-based amorphous alloys. © 1988 J.C. Baltzer A.G., Scientific Publishing Company.
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    Structural and optical properties of zirconia thin films
    ( 1990-12-01) Krishna, M. Ghanashyam ; Rao, K. Narasimha ; Mohan, S.
    Thin films of zirconia have been deposited using reactive electron beam evaporation in neutral and ionized oxygen media. The variation in optical properties and structure with post-deposition annealing temperature in the range 300-850°C has been studied. It has been found that the refractive index decreases and the extinction coefficient increases with increasing annealing temperature. Phase transitions have been characterized using IR absorption in conjunction with X-ray diffraction. The effect of ambient background ions on optical properties is not as marked as that on structure.
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    Optical and structural characterization of evaporated zirconia films
    ( 1990-12-01) Krishna, M. Ghanashyam ; Rao, K. Narasimha ; Mohan, S.
    Thin films of zirconia have been deposited using a reactive electron beam evaporation technique onto unheated alumina and fused silica substrates. The films were post annealed in the range 300-850°C. The influence of post-deposition conditions on the optical properties like refractive index and absorption and nonoptical properties like structure have been studied. The structural transitions were determined using infrared (IR) absorption and x-ray diffraction. Preliminary results of studies on the correlation between x-ray diffraction and IR absorption data for structural characterization are reported. It has been shown that the refractive index values change considerably with each structural transition, although the optical absorption does not seem to be very adversely affected by post-deposition annealing. Post-deposition annealing resulted in the formation of the cubic phase at 500°C which transformed to the tetragonal phase at 700°C and finally monoclinic phase at 800°C. The above-mentioned phases were only the major phases and post-deposition annealing did not result in single-phase material.