Crossover from diffusive to tunneling regime in NbN/DyN/NbN ferromagnetic semiconductor tunnel junctions

Abstract

We have investigated NbN-DyN-NbN junctions with 1 to 10 nm thick DyN barriers. A crossover from diffusive (hopping) to tunneling-type transport was found in these junctions as the DyN thickness is reduced below ∼4 nm. We have also made a detailed study of magnetic and electrical properties of thicker DyN thin films deposited under similar conditions; DyN films were found to be ferromagnetic with T Curie ∼ 35 ± 5 K. Electrical transport of the junctions with ∼10 nm DyN was understood in terms of Shklovskii-Efros (SE)-type variable range hopping (VRH) at low temperature between 90 and 35 K. We estimated localization length ξ = 5.6 nm in this temperature range. Temperature dependence of resistance was found to deviate from SE-VRH below 35 K along with large suppression of resistance with magnetic field. This is correlated with onset of magnetism below 35 K. Large butterfly-shaped MR up to ∼40% was found for the ∼10 nm thick DyN junction at 2 K. In the tunneling regime, barrier height of the tunnel junction was estimated ∼50 meV from the Simmons model. Signatures of spin filtering was found in temperature dependence of resistance in tunnel junction with ∼3 nm thick DyN. Cooper pair tunneling in these junctions below T C (∼10.8 K) of NbN was understood according to S-I-S tunneling current model. We found coherent tunneling of Cooper pairs through a ∼1 nm thick DyN tunnel barrier with critical current I C ∼ 12 μA. The critical current also showed modulation with magnetic field.

Carrier-controlled anomalous Hall effect in an intrinsic ferromagnetic semiconductor

“…9 Their wide-ranging magnetic and coupled magnetic-electronic responses have seen them included in a number of device structures. [10][11][12][13] The series includes at least one supercon- ducting member, 14 and ab initio calculations support the suggestion that they may show both ferroelectric 15 and topological insulator 16 phases. GdN lies in the center of the series with a purely spin magnetic moment of 7 Bohr magnetons (µ B ) per primitive cell that is sited primarily in the Gd 3+ 4f shell.…”

On the ferromagnetic ground state of SmN

“…SmN is especially unique among the series, with a vanishingly small ordered moment arising from the near-cancellation of spin and orbital moments [4,5] fixed antiparallel by strong spin-orbit coupling. So far the spintronic potential of the RENs remains largely untapped, though GdN has been integrated within spinfilters [11,12] and field effect transistors [13] while DyN has been incorporated into a magnetic tunnel junction [14]. However, SmN has quite recently displayed remarkable phenomena in magnetization and transport studies.…”

YbN: An intrinsic semiconductor with antiferromagnetic exchange

“…Modern experimental studies have corroborated the earlier magnetic and crystallographic measurements, but have highlighted the fact that many of the early studies which found rare earth nitrides to be semimetallic were probably compromised by poor stoichiometry. It is now widely accepted that most of the series are in fact semiconductors [6,[11][12][13][14][15][16][17][18][19][20].…”