Electric‐Field‐Dependent Spin Polarization in GdN Spin Filter Tunnel Junctions

Pal, Avradeep; Senapati, Kartik; Barber, Z. H.; Blamire, M. G.

doi:10.1002/adma.201300636

Cited by 46 publications

(66 citation statements)

References 32 publications

(44 reference statements)

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“…The spin polarization at 15 K (P 15 K ) shown in Fig. 4e shows a similar trend with thickness as observed previously 9 .…”

Section: K)supporting

confidence: 86%

“…These distortions from the behaviour expected for a perfect Fraunhofer pattern are due to the fact that thin film GdN has a low coercivity of 20-50 Oe (ref. 9) and because of their large area, our devices have multiple magnetic domains, and micromagnetic structure plays an important role in multidomain devices in distorting the I c (H) patterns 10 , especially in the switching regions. Because GdN has a high remnant moment, the second lobe in Fig.…”

Section: Resultsmentioning

confidence: 99%

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Pure second harmonic current-phase relation in spin-filter Josephson junctions

et al. 2014

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Higher harmonics in current-phase relations of Josephson Junctions are predicted to be observed when the first harmonic is suppressed. Conventional theoretical models predict higher harmonics to be extremely sensitive to changes in barrier thickness, temperature, and so on. Here we report experiments with Josephson junctions incorporating a spin-dependent tunnelling barrier, revealing a current-phase relation for highly spin polarized barriers that is purely second harmonic in nature and is insensitive to changes in barrier thickness. This observation implies that the standard theory of Cooper pair transport through tunnelling barriers is not applicable for spin-dependent tunnelling barriers.

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“…The spin polarization at 15 K (P 15 K ) shown in Fig. 4e shows a similar trend with thickness as observed previously 9 .…”

Section: K)supporting

confidence: 86%

Section: Resultsmentioning

confidence: 99%

Pure second harmonic current-phase relation in spin-filter Josephson junctions

et al. 2014

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“…Ludbrook and co-workers [20] were able to achieve a tunneling magnetoresistance ratio (TMR) of 35%. Later, Pal et al and Senapati et al [21,22] reported observing a spin polarization of conductance reaching 90% in a GdN film sandwiched between NbN electrodes.…”

Section: Introductionmentioning

confidence: 95%

“…It was also shown that this feature of the crystal depends on the lattice constant. In recent works [20][21][22] transport properties of GdN films were investigated experimentally. Ludbrook and co-workers [20] were able to achieve a tunneling magnetoresistance ratio (TMR) of 35%.…”

Section: Introductionmentioning

confidence: 99%

Spin-polarized transport properties of GdN nanocontacts

2014

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Gadolinium nitride (GdN) nanocontacts were recently experimentally shown to be efficient spin filters. Our study is aimed at identifying and analyzing the physical processes responsible for the high spin polarization of the tunneling current in GdN nanostructures. By the example of planar contacts and atomic chains attached to Cu electrodes we assert, using first principle techniques, that a 100% spin-filtering effect can be indeed achieved in GdN nanocontacts. Our analysis shows that the spin filtering is due to the predominant role of nitrogen majority p states in the electron transport, while minority conductance decays exponentially with contact size due to the presence of a minority band gap at the Fermi level. Additionally, GdN zigzag infinite chains are found to be as efficient spin filters as their planar contact counterparts, also exhibiting a 100% spin-filtering effect, which is robust against chain geometry changes.

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“…Good candidates for the tunneling barriers are europium chalcogenides (EuO and EuS) for which values of P ranging from 80 up to almost 100% have been reported. [13][14][15][16][18][19][20][21] Also very high spin-filtering has been reported in GdN barriers [22][23][24] with polarizations as large as 97% at 15 K (even larger values are expected as T decreases).…”

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confidence: 96%

Proposal for a phase-coherent thermoelectric transistor

Giazotto

Robinson

Moodera

et al. 2014

Applied Physics Letters

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Identifying materials and devices which offer efficient thermoelectric effects at low temperature is a major obstacle for the development of thermal management strategies for low-temperature electronic systems. Superconductors cannot offer a solution since their near perfect electron-hole symmetry leads to a negligible thermoelectric response; however, here we demonstrate theoretically a superconducting thermoelectric transistor which offers unparalleled figures of merit of up to ∼ 45 and Seebeck coefficients as large as a few mV/K at sub-Kelvin temperatures. The device is also phasetunable meaning its thermoelectric response for power generation can be precisely controlled with a small magnetic field. Our concept is based on a superconductor-normal metal-superconductor interferometer in which the normal metal weak-link is tunnel coupled to a ferromagnetic insulator and a Zeeman split superconductor . Upon application of an external magnetic flux, the interferometer enables phase-coherent manipulation of thermoelectric properties whilst offering efficiencies which approach the Carnot limit.It is known that electron-hole symmetry breaking is essential for a material to posses a finite thermoelectric figure of merit 1,2 . In principle, conventional superconductors have a near perfect symmetric spectrum and therefore are not suitable for thermoelectric devices. However, if the density of states is spin-split by a Zeeman field a superconductor-ferromagnet hybrid device can provide a thermoelectric effect 3-5 with a figure of merit close to 1. Here we propose a multifunctional phase-coherent superconducting transistor in which the thermoelectric efficiency is tunable through an externally applied magnetic flux. A giant Seebeck coefficient of several mV/K and a figure of merit close to ∼ 45 is predicted for realistic materials parameters and materials combinations.The phase-coherent thermoelectric transistor is based on two building blocks. The first one is sketched in Fig. 1(a) and consists of a superconducting film (S R ) tunnel-coupled to a normal metal (N) by a ferromagnetic insulator (FI). The latter induces an exchange field (h) in S R which leads to a Zeeman spin-split superconducting DoS. The spectrum for spin-up (↑) and spin-down (↓) electrons is given bywhere| is the conventional Bardeen-Cooper-Schrieffer DoS in a superconductor, E is the energy, ∆ R is the order parameter, and Γ accounts for broadening. Due to the presence of the spin-splitting field, ∆ R depends on temperature (T ) and h. While the total DoS of S R , ν S R (E) = ν S R↑ (E) + ν S R↓ (E), is electron-hole symmetric [ Fig. 1(b)], the spin-dependent a) Electronic mail: giazotto@sns.it b) Electronic mail: jjr33@cam.ac.uk c) Electronic mail: sebastian bergeret@ehu.es ν S R↑(↓) (E) components are no longer even functions of the energy. This means that electron-hole imbalance can, in principle, be achieved using a spin-filter contact with a normal metal. This would yield a finite thermoelectric effect 3,4 in the N/FI/S R heterostructure shown in F...

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Electric‐Field‐Dependent Spin Polarization in GdN Spin Filter Tunnel Junctions

Cited by 46 publications

References 32 publications

Pure second harmonic current-phase relation in spin-filter Josephson junctions

Pure second harmonic current-phase relation in spin-filter Josephson junctions

Spin-polarized transport properties of GdN nanocontacts

Proposal for a phase-coherent thermoelectric transistor

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