The microwave surface impedance of MgB<sub>2</sub>thin films

Purnell, A.; Жуков, А. А.; Nurgaliev, T.; Lamura, G.; Bugoslavsky, Y.; Lockman, Zainovia; MacManus‐Driscoll, Judith L.; Zhai, H. Y.; Christen, H. M.; Paranthaman, M.; Lowndes, D. H.; Jo, Moon‐Ho; Blamire, M. G.; Líu, Hao; Gallop, J.C.; Cohen, L. F.

doi:10.1088/0953-2048/16/1/301

Cited by 28 publications

(11 citation statements)

References 41 publications

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“…with γ = 3 − T / T c , describing the weak coupling regime [18]. The use of this equation is justified by previous results [19] on the effective gap measurement in our MgB 2 thin films at microwave frequencies, where attempts to use γ = 4 (strong coupling regime and two fluid approximation) or γ = 2 (dwave superconductivity) [20] did not lead to any reasonable results. The result of the iterated calculation converges to a value of 0.24 mm 2 for the effective area and of 200 nm for λ(0).…”

Section: Resultsmentioning

confidence: 64%

MgB₂magnetometer with a directly coupled pick-up loop

Portesi

Mijatovic

Veldhuis

et al. 2006

Supercond. Sci. Technol.

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In this work, we show the results obtained in the fabrication and characterization of an MgB 2 magnetometer with a directly coupled pick-up loop. We used an all in situ technique for fabricating magnesium diboride films, which consists of the co-evaporation of B and Mg by means of an e-gun and a resistive heater respectively. Consequently, we realized the superconducting device, which incorporates two nanobridges as weak links in a superconducting loop. The nanobridges were realized by focused ion beam milling; they were 240 nm wide and had a critical current density of 10 7 A cm −2 . The magnetometer was characterized at different temperatures and also measurements of the noise levels have been performed. The device shows Josephson quantum interference up to 20 K and the calculated effective area at low temperatures was 0.24 mm 2 . The transport properties of the magnetometer allow determining fundamental materials properties of the MgB 2 thin films, such as the penetration depth.

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Section: Resultsmentioning

confidence: 64%

MgB₂magnetometer with a directly coupled pick-up loop

Portesi

Mijatovic

Veldhuis

et al. 2006

Supercond. Sci. Technol.

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“…Using different measurement apparatus several groups reported n values ranging from n = 1 to 4 [21][22][23][24]. For the m(T) fit we used n = 1, 1.5 and 2, evaluating several λ 0 value: 85, 110, 180 nm found in the literature [23,[25][26][27]].…”

Section: Squid Magnetometer Measurementsmentioning

confidence: 99%

Size determination of superconducting MgB₂powder from magnetization curve, image analysis and surface area measurements

Vignolo¹,

Bovone²,

Bernini³

et al. 2014

Supercond. Sci. Technol.

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The present article reports a method for the average grain size evaluation of superconducting nanoparticles through their magnetic properties. The use of SQUID magnetometry to determine the average MgBB 2 particle size was investigated and the results compared with those achieved through other techniques. In particular the data obtained from zero field cooled magnetization measurement as function of the temperature were compared with the results obtained by scanning electron microscopy and Brunauer-Emmett-Teller techniques. The particle magnetization was measured by a commercial SQUID magnetometer in magnetic field (1 mT) and temperatures ranging from 5 to 50 K dispersing the powders in a grease medium. The grain size is obtained by fitting the data taking into account the Ginzburg-Landau temperature dependence of the London penetration depth. Variations on typical modeling parameters were explored in order to gain a better picture of the average grain size and the effectiveness of various measurement techniques. We find that it is possible to use the magnetization measurements to determine the average grain size even if the SEM image analysis allows extracting more information about the grain size distribution. Furthermore a Matlab routine has been developed in order to get automatic analysis of SEM images.

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“…14 Attempts to use γ = 4 (strong coupling regime and two fluid approximation) or γ = 2 (d-wave superconductivity) 15 did not lead to any reasonable result. It has to be noted that (2) …”

Section: Determination Of Penetration Depth Surface Resistance and Mmentioning

confidence: 99%

“…with γ = 3-T/T c , describing the weak coupling regime. 14 Attempts to use γ = 4 (strong coupling regime and two fluid approximation) or γ = 2 (d-wave superconductivity) 15 did not lead to any reasonable result. It has to be noted that (2) applies only to homogeneous superconductors with a single isotropic gap.…”

Section: Determination Of Penetration Depth Surface Resistance and Mi...mentioning

confidence: 99%

Effective gap at microwave frequencies inMgB2thin films with strong interband scattering

et al. 2005

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The microwave properties of polycrystalline MgB 2 thin films prepared by the so-called in-situ method are investigated. The characterization of the films at microwave frequencies was obtained by a coplanar resonator technique. The analysis of the experimental data results in the determination of penetration depth, surface impedance and complex conductivity. The aim of this work is to set the experimental results in a consistent framework, involving the two-band model in the presence of impurity scattering. The energy gaps are calculated and the contribution of intra-and inter-band scattering is considered. From the comparison between the calculated gap values and the experimental data it turns out that the temperature dependence of the penetration depth 1 can be accounted for by an effective mean energy gap, in agreement with the predictions of Kogan et al. [Phys. Rev. B 69, 132506 (2004)]. On the other hand, the temperature dependence of the real part of the microwave conductivity and of the surface resistance is accounted for by the single smaller gap, in agreement with the work of Jin et al. [Phys. Rev. Lett. 91, 127006 (2003)]. Since these findings rely on the same calculated gap structure, the required consistency is fulfilled.74.70. Ad, 74.25.Nf IntroductionSince the discovery of its superconducting properties, magnesium diboride (MgB 2 ) has generated a great deal of interest because of its simple structure, relatively high critical temperature and two-gap nature. The Fermi surface of MgB 2 consists of two threedimensional sheets, from the π bonding and antibonding bands, and two nearly cilindrical sheets from the two-dimensional σ bands. 1 Many physical properties of MgB 2 are reasonably described within a model with two separated energy gaps, ∆ π and ∆ σ . 2,3 Nevertheless, the role of interband and intraband scattering has to be considered: 2,3 it is still not completely clear, also due to the wide spread quality of samples used in different experiments. In fact, a significant scattering between the different Fermi sheets may reduce the effective gap structure to a single isotropic gap. Recently, the expected 2 observation of single-gap superconductivity at high impurity level has been observed in C-substituted MgB 2 single crystals by point-contact spectroscopy. 4 When the level of impurities is high enough, the two gaps merge into a single gap with a ratio 2∆/k B T c close to the standard BCS value.The role of the two bands in determining the microwave conductivity in MgB 2 thin films is controversial as well. The temperature dependence of the microwave conductivity in caxis oriented films was interpreted by Jin et al. 5 in terms of a dominant contribution of the π band. They deduced this argument from the observation of a single anomalous peak around t=T/T c =0.6. The presence of such a peak can be explained in the framework of the BCS theory. When the superconducting state is entered and the gap opens, a singularity appears in the density of states at the gap edges, increasing the microwave ...

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The microwave surface impedance of MgB₂thin films

Cited by 28 publications

References 41 publications

MgB₂magnetometer with a directly coupled pick-up loop

MgB₂magnetometer with a directly coupled pick-up loop

Size determination of superconducting MgB₂powder from magnetization curve, image analysis and surface area measurements

Effective gap at microwave frequencies inMgB2thin films with strong interband scattering

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The microwave surface impedance of MgB2thin films

Cited by 28 publications

References 41 publications

MgB2magnetometer with a directly coupled pick-up loop

MgB2magnetometer with a directly coupled pick-up loop

Size determination of superconducting MgB2powder from magnetization curve, image analysis and surface area measurements

Effective gap at microwave frequencies inMgB2thin films with strong interband scattering

Contact Info

Product

Resources

About

The microwave surface impedance of MgB₂thin films

MgB₂magnetometer with a directly coupled pick-up loop

MgB₂magnetometer with a directly coupled pick-up loop

Size determination of superconducting MgB₂powder from magnetization curve, image analysis and surface area measurements