Apparatus for nonresonant rf power absorption studies in high Tc superconductors and CMR materials using rf oscillators

Sarangi, S.; Bhat, S. V.

doi:10.1063/1.1841851

Cited by 6 publications

(5 citation statements)

References 9 publications

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“…The inductive methods for measuring magnetoresistance are advantageous since they are contactless and allow for the sample rotation in magnetic field. This is most easily realized using a cavity perturbation technique where conducting sample is mounted off-center the resonant cavity [2] or in the antinode of the microwave electric field [3,18,19]. We consider here a different setup where the sample is mounted in the antinode of the microwave magnetic field.…”

Section: Nonresonant Microwave Absorption and Magnetoresistancementioning

confidence: 99%

Nonresonant microwave absorption in epitaxialLa0.7Sr0.3MnO3films and its relation to colossal magnetoresistance

et al. 2007

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We study magnetic-field-dependent nonresonant microwave absorption and dispersion in thin La 0.7 Sr 0.3 MnO 3 films and show that it originates from the colossal magnetoresistance. We develop the model for magnetoresistance of a thin ferromagnetic film in oblique magnetic field. The model accounts fairly well for our experimental findings, as well as for results of other researchers. We demonstrate that nonresonant microwave absorption is a powerful technique that allows contactless measurement of magnetic properties of thin films, including magnetoresistance, anisotropy field and coercive field.

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Section: Nonresonant Microwave Absorption and Magnetoresistancementioning

confidence: 99%

Nonresonant microwave absorption in epitaxialLa0.7Sr0.3MnO3films and its relation to colossal magnetoresistance

et al. 2007

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“…As seen from equation (3), the power absorbed at a given frequency depends both on the total number of junctions going into the resistive state and the strength of the individual junction. In our earlier studies [21,22] we had observed that the loss in the superconducting state of ceramic YBCO increases with decreasing temperature. Even though the coupling energy of the intergranular extrinsic junctions of the ceramic sample was low, total power absorbed was large in the superconducting state, since the total number of such junctions was very large.…”

Section: Discussionmentioning

confidence: 89%

“…The crystal which is used for the studies had a nominal T c of ∼85 K with a narrow transition width ( T ∼ 1 K) as determined by ac susceptibility measurements. The present studies of ac losses are carried out using an rf oscillator fabricated in our laboratory [22]. The oscillator consists of a self-resonant LC tank circuit driven by a NOT gate.…”

Section: Methodsmentioning

confidence: 99%

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A new behaviour of ac losses in superconducting Bi₂Sr₂CaCu₂O₈single crystals

Chockalingam

Sarangi

Bhat

et al. 2009

J. Phys.: Condens. Matter

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A new ac loss behaviour is observed in the superconducting state of Bi(2)Sr(2)CaCu(2)O(8) single crystals using a novel technique of measuring dissipation at radio frequencies. It is found that the ac loss in the superconducting state is larger than that in the normal state. This counter-intuitive result is explained in terms of the cumulative effect of repetitive decoupling of intrinsic Josephson junctions in the crystals and analysed in the framework of Ambegaokar-Baratoff theory. The ac losses are studied as a function of temperature, rf amplitude and magnetic field applied at different orientations. A peak in ac losses is observed in the superconducting state along the temperature scale. The amplitude of the peak decreases and shifts towards lower temperature with increasing field and also when the field orientation with respect to the c axis of the crystal changes from the perpendicular to parallel direction. The origin of the peak and its behaviour are discussed in the context of coupling energy of Josephson junctions present in the sample. In the presence of a magnetic field another peak in ac losses arises at temperatures close to T(c), which is associated with the Lorentz-force-driven motion of vortices.

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“…So the AC loss in rf range is determined from the non-resonant power absorbed by the sample. The power absorption measurements were performed with using a standard Integrated Circuit Oscillator (ICO) [5]. This system consists of a self-resonant LC tank circuit of an oscillator driven by a NOT logic gate.…”

Section: Experimentmentioning

confidence: 99%

Frequent Josephson junction decoupling is the main origin of ac losses in the superconducting state

Sarangi

Chockalingam

Bhat

2005

Journal of Applied Physics

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The origin of AC resistivity in the high T c superconductors is not addressed adequately in literature. We found out, Josephson Junction (JJ) decoupling is the main origin of the AC resistivity in high T c superconductors. We have measured the AC resistivity in the superconductors in the low frequency range by measuring the complex AC impedance of superconducting YBa 2 Cu 3 O 7 (YBCO) polycrystalline samples. Our data shows that under certain conditions when the number density of Josephson Junctions (JJ) present in the sample and the JJ critical current crosses a threshold value, AC resistivity in the superconducting state keeps on increasing with lowering temperature. The underlying mechanism is an interesting interplay of JJ coupling energy, amplitude of the supply AC voltage and the current applied to the superconducting sample. The effect of the applied AC current of different frequencies and the variation of temperature were studied in detail. To find out the exact relation between the JJ coupling energy, JJ number density, applied AC frequency, the amplitude of AC current and the AC resistivity in the superconductors, we have studied samples of different grain sizes, pressurized with different pressure and sintered at different physical situations. These results have important implications for the understanding of the origin of AC resistivity and characterization of superconducting samples. In this paper we also extend the capability of the AC impedance studies in superconductors for the characterization of materials for device applications.

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Apparatus for nonresonant rf power absorption studies in high Tc superconductors and CMR materials using rf oscillators

Cited by 6 publications

References 9 publications

Nonresonant microwave absorption in epitaxialLa0.7Sr0.3MnO3films and its relation to colossal magnetoresistance

Nonresonant microwave absorption in epitaxialLa0.7Sr0.3MnO3films and its relation to colossal magnetoresistance

A new behaviour of ac losses in superconducting Bi₂Sr₂CaCu₂O₈single crystals

Frequent Josephson junction decoupling is the main origin of ac losses in the superconducting state

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Apparatus for nonresonant rf power absorption studies in high Tc superconductors and CMR materials using rf oscillators

Cited by 6 publications

References 9 publications

Nonresonant microwave absorption in epitaxialLa0.7Sr0.3MnO3films and its relation to colossal magnetoresistance

Nonresonant microwave absorption in epitaxialLa0.7Sr0.3MnO3films and its relation to colossal magnetoresistance

A new behaviour of ac losses in superconducting Bi2Sr2CaCu2O8single crystals

Frequent Josephson junction decoupling is the main origin of ac losses in the superconducting state

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A new behaviour of ac losses in superconducting Bi₂Sr₂CaCu₂O₈single crystals