Reversible magnetization of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">MgB</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>single crystals with a two-gap nature

Kang, Byeongwon; Kim, Heon‐Jung; Park, Min-Seok; Kim, Kyung‐Hee; Lee, Sung‐Ik

doi:10.1103/physrevb.69.144514

Cited by 33 publications

(12 citation statements)

References 48 publications

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“…As shown in Fig. 4, H p2 tends to emerge at temperatures T < $20 K. In this temperature region, it has been estimated, as mentioned previously in this paper, that the value of k in MgB 2 is an order of 100 nm or less, whereas it shows an abrupt increase to $200 nm or more for temperatures above 25 K. 34 This allows us to expect that the length scale of the magnetic inhomogeneity is on the order of 100 nm, which is several times larger than the estimated (or averaged) size of the primary MgO crystallites ($20 nm) in the composite. This implies that the expected magnetic gradients are derived not from the individual primary MgO crystallites but from a certain collective effect of, for example, their aggregates with larger dimensions.…”

Section: Discussionsupporting

confidence: 71%

“…33 In the temperature region higher than 35 K, the value of k in MgB 2 has been estimated to be $250 nm or more. 34 Thus, the size of the present MgB 2 crystallites is considered to be on the order of $500 nm.…”

Section: B Magnetic Propertiesmentioning

confidence: 99%

“…Such an asymmetric M(H) hysteresis loop is commonly observed in the powder samples where the magnetic moment is determined by geometrical and Bean-Livingston surface barriers. 35,36 The value of k in bulk MgB 2 is estimated to be $70-$100 nm in the temperature range of $10-$25 K, 34 and hence 2k becomes comparable with or smaller than the size of the MgB 2 crystallites. Accordingly, surface pinning begins to operate in the composite in this temperature region.…”

Section: B Magnetic Propertiesmentioning

confidence: 99%

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Magnetic hysteresis behavior and magnetic pinning in a d ferromagnet/superconductor nanostructure

Uchino

Uenaka

Soma

et al. 2014

Journal of Applied Physics

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We investigate the interaction between superconductivity and defect-induced d0 ferromagnetism using a composite consisting of MgB2 and MgO nanocrystals. The composite exhibits a ferromagnetic hysteresis behavior in the temperature region from 40 to 300 K. Defective MgO nanocrystals (∼20 nm) embedded in the composite are considered to be responsible for the observed ferromagnetism. The zero field cool and field cool magnetization curves show that the superconducting transition occurs at Tc = 38.6 K, in agreement with Tc of pure MgB2. In the temperature region from Tc to 0.9Tc (∼35 K), the magnetization hysteresis curves show a superposition of ferromagnetic (F) and superconducting (S) signals. When the temperature of the system is decreased below 0.65Tc (∼25 K), the S signals dominate over the F signals. The resulting magnetic hysteresis loops are highly asymmetric and the descending filed branch is nearly flat, as predicted in the case of surface pinning. At temperatures below 0.5Tc (∼20 K), a sharp peak is developed near zero field in the magnetization hysteresis curves, implying an enhancement of superconducting vortex pinning. The observed pinning enhancement most likely results from magnetic pinning due to randomly distributed magnetic MgO grains, which yield the magnetic inhomogeneity and the related pinning potential in a length scale of ∼100 nm. Thus, the present ferromagnetic/superconducting composite provides an ideal model system that demonstrates the availability of d0 ferromagnetism as a source of magnetic potential for effective vortex pinning.

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Section: Discussionsupporting

confidence: 71%

Section: B Magnetic Propertiesmentioning

confidence: 99%

Section: B Magnetic Propertiesmentioning

confidence: 99%

See 1 more Smart Citation

Magnetic hysteresis behavior and magnetic pinning in a d ferromagnet/superconductor nanostructure

Uchino

Uenaka

Soma

et al. 2014

Journal of Applied Physics

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“…The upper critical field l 0 H c2 (0) at 0 K was determined from the Bardeen-Cooper-Schrieffer (BCS)-type function l 0 H c2 ðTÞ ¼ l 0 H c2 ð0Þ½1 À ðT=T c Þ a b , using the trilayer film's T c with l 0 H c2 (0) and a and b as fitting parameters. 30 We found l 0 H k c2 ð0Þ ¼ 23:2 T with a ¼ 1.26 and b ¼ 1.09 in the parallel magnetic field (blue line) and l 0 H ? c2 ð0Þ ¼ 16:2 T with a ¼ 1.26 and b ¼ 1.00 in the perpendicular magnetic field (red line).…”

mentioning

confidence: 82%

Epitaxial contact Andreev reflection spectroscopy of NbN/Co2FeSi layered devices

Shigeta

Kubota

Sakuraba

et al. 2018

Applied Physics Letters

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We investigated the spin polarization P of Co-based Heusler alloy Co2FeSi by epitaxial contact Andreev reflection (ECAR) spectroscopy using epitaxially grown superconductor NbN and Heusler alloy Co2FeSi layered devices. Ferromagnetic Co2FeSi possesses the highest Curie temperature (TC ≈ 1100 K) and the largest spontaneous magnetic moment (ps ≈ 6 μB) in the class of Heusler alloys. The ECAR measurements revealed that the P value of Co2FeSi was 54 ± 2% with a finite barrier parameter Z, indicating that an intrinsic P value in ECAR spectroscopy would exceed reported values in point-contact Andreev reflection spectroscopy. We therefore established not only the epitaxial integration of ferromagnetic Co2FeSi with superconductor NbN on an MgO substrate but also the fabrication and evaluation techniques of their ECAR devices. This highly versatile superconducting spintronic system enables fundamental superconducting spintronic studies, and it is also a candidate for practical superconducting spintronic devices.

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“…Also from [20] we determine M 1 = K 2 /K 1 ≈ 1.06. For the GL parameter κ, we have used the experimentally determined value of κ = 6.4 [22,28]. The only free parameter in the formalism is thus the linear interband coupling parameter γ which is determined by fitting the reversible magnetization results obtained by our model with the corresponding experimental data.…”

Section: Theoretical Formalism and Numerical Calculationsmentioning

confidence: 99%

Effect of two length scales on the properties of MgB₂for arbitrary applied magnetic field

Karmakar

Dey²

2010

J. Phys.: Condens. Matter

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Experiments carried out on the intermetallic superconducting material MgB(2) have shown anomalous magnetic field dependence of upper critical field, small angle neutron scattering form factor, specific heat, critical current etc. Similarly, scanning tunnelling microscopy (STM) experiments on vortex structures have shown unusually large vortex core size and two different magnetic and spatial field scales. Also, whereas the specific heat measurements and isotope shift experiments have shown Bardeen-Cooper-Schrieffer-like (BCS-like) behaviour, the temperature dependences of the penetration depth experiments have shown non-BCS-like behaviour. These anomalous behaviours have been attributed to the multiband superconductivity of this material and the nature of the local spatial behaviour of the magnetic induction and the order parameter components having two length scales. We report an analytical investigation of the effect of two length scales on the temperature and the applied magnetic field dependence of several properties of MgB(2), such as, the penetration depth, single vortex and vortex lattice structure, vortex core radius, reversible magnetization, critical current, small angle neutron scattering form factor and the shear modulus of the vortex lattice within the framework of two-order parameter Ginzburg-Landau theory. We solve the corresponding nonlinear Ginzburg-Landau equations numerically exactly using an iterative method for arbitrary applied field H(c1) < H < H(c2), the Ginzburg-Landau parameter and vortex lattice symmetry. This enables us to compute the local spatial behaviour of the magnetic induction and the order parameters accurately for arbitrary applied field and a wide range of temperature. Comparison of the analytical results with experiments on MgB(2) gives very good agreement.

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Reversible magnetization ofMgB2single crystals with a two-gap nature

Cited by 33 publications

References 48 publications

Magnetic hysteresis behavior and magnetic pinning in a d ferromagnet/superconductor nanostructure

Magnetic hysteresis behavior and magnetic pinning in a d ferromagnet/superconductor nanostructure

Epitaxial contact Andreev reflection spectroscopy of NbN/Co2FeSi layered devices

Effect of two length scales on the properties of MgB₂for arbitrary applied magnetic field

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Reversible magnetization ofMgB2single crystals with a two-gap nature

Cited by 33 publications

References 48 publications

Magnetic hysteresis behavior and magnetic pinning in a d ferromagnet/superconductor nanostructure

Magnetic hysteresis behavior and magnetic pinning in a d ferromagnet/superconductor nanostructure

Epitaxial contact Andreev reflection spectroscopy of NbN/Co2FeSi layered devices

Effect of two length scales on the properties of MgB2for arbitrary applied magnetic field

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Product

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Effect of two length scales on the properties of MgB₂for arbitrary applied magnetic field