G. Lengaigne

Magnetoresistive effects in perpendicularly magnetized Tb-Co alloy based thin films and spin valves

Tb-Co ferrimagnetic alloy thin films and spin valves have been grown to study their magnetoresistance response in various geometries. The studied Tb-Co alloys show strong perpendicular anisotropy and tunable magnetization by several orders of magnitude. Magnetoresistance signals such as giant magnetoresistance (GMR), anisotropic magnetoresistance (AMR), extraordinary Hall effect (EHE), and magnon magnetoresistance (MMR) have been studied. The angular dependence of those magnetoresistive effects is also investigated. Finally we demonstrate that by adjusting the Tb-Co layer composition in a spin valve structure, the sign and the amplitude of the GMR and EHE signal can be tuned.

Magnetic properties of postoxidized Pt∕Co∕Al layers with perpendicular anisotropy

The magnetic properties of ultrathin Co layers sandwiched between Pt and Al layers are studied as a function of the Al layer oxidation time. The association of three batches of complementary experiments (extraordinary Hall effect, x-ray photoelectron spectroscopy, and tunneling magnetoresistance) allows the authors to finely characterize their samples both magnetically and chemically. The authors show that their oxidation process reduces the coercive field of ultrathin Co layers with perpendicular anisotropy (case of short oxidation time) and can even induce transition from a ferromagnetic to a superparamagnetic state (lengthy oxidation time).

Spin-orbit coupling effect by minority interface resonance states in single-crystal magnetic tunnel junctions

Symmetry dependent scattering effect by minority interface resonance states (IRS) has been evidenced in full-epitaxial Fe/MgO/Fe magnetic tunnel junctions (MTJs). Two types of samples with and without carbon doped bottom Fe/MgO interface were fabricated to represent two different types of IRS in the minority channel in the vicinity of the Fermi level. By analysis of the first- principles calculated local density of states (LDOS) and the temperature dependence of conductance in parallel configuration at low bias, we show that the IRS in the carbon free sample is dominated by the delta5 symmetry. This has a major contribution on the majority deltai to delta5 channel scattering and explains the enhancement of the delta5 conductance in the parallel configuration at low temperature. Furthermore, the spectral composition of the IRS in the carbon doped interface is found to be dominated by the delta1 symmetry, which is responsible for the suppression of delta5 channel in the parallel conductance.

Long-Range Phase Coherence in Double-Barrier Magnetic Tunnel Junctions with a Large Thick Metallic Quantum Well

Double-barrier heterostructures are model systems for the study of electron tunneling and discrete energy levels in a quantum well (QW). Until now resonant tunneling phenomena in metallic QWs have been observed for limited thicknesses (1-2 nm) under which electron phase coherence is conserved. In the present study we show evidence of QW resonance states in Fe QWs up to 12 nm thick and at room temperature in fully epitaxial double MgAlO_{x} barrier magnetic tunnel junctions. The electron phase coherence displayed in this QW is of unprecedented quality because of a homogenous interface phase shift due to the small lattice mismatch at the Fe-MgAlO_{x} interface. The physical understanding of the critical role of interface strain on QW phase coherence will greatly promote the development of spin-dependent quantum resonant tunneling applications.

Local Magnetic Anisotropy Induced by a Nano-Modulated Substrate and Application to Two-Dimensional Magnetic Sensors

Topological modulation of magnetic thin films can induce a magnetic anisotropy of magnetostatic origin. In this paper, we report on the magnetic properties of NiFe layers deposited on wavy Si substrates. Without modulation, the film posses an intrinsic anisotropy. We unambiguously show that patterning the substrate overcomes the intrinsic anisotropy and establishes a new easy axis of magnetization. By choosing the patterning appropriately, orthogonal easy axes can be established at different locations of the same sample. We demonstrate the advantage of this approach in the fabrication of bidimensional magnetic sensors.

Interfacial trapping for hot electron injection in silicon

We have evidenced a new interfacial trapping phenomenon for hot electron injection in silicon by studying magnetic tunnel transistors (MTTs) with a MgO tunneling barrier emitter and a Cu/Si Shottky barrier collector. Transport measurements on hot electrons indicate that an interfacial charge trapping and a backscattering-induced collector current limitation take place with the MTT spin-valve base both in parallel and antiparallel states when the temperature is lower than 25 K, which results in a rapid decrease of the magnetocurrent ratio from ∼2000% at 25 K to 800% at 17 K. The binding energy of the trapped electron is estimated to be about 1.7 meV, which is also found to increase with the magnetic field. A simple analytic model considering the interfacial electron trapping and releasing is proposed to explain the experimental results.

Fe/MgO/Fe (100) textured tunnel junctions exhibiting spin polarization features of single crystal junctions

Crystallographic and spin polarized transport properties of (100) textured and (100) epitaxial Fe/MgO/Fe magnetic tunnel junctions are compared. Strong similarities in the transport properties show that structural coherence and magnetic quality at the 25 nm grain scale in textured junctions are sufficient to issue signatures of the spin polarized transport specific to a single crystal junction. This demonstrates that the lateral coherence of the Bloch tunneling wave function is identically limited in both systems. Our analysis leads to model the textured tunnel junction as a juxtaposition of nanometer sized single crystal junctions, placed in parallel.

Electrical control of interfacial trapping for magnetic tunnel transistor on silicon

We demonstrate an electrical control of an interfacial trapping effect for hot electrons injected in silicon by studying a magnetic tunnel transistor on wafer bonded Si substrate. Below 25 K, hot electrons are trapped at the Cu/Si interface, resulting in collector current suppression through scattering in both parallel and antiparallel magnetic configurations. Consequently, the magneto-current ratio strongly decreases from 300% at 27 K to 30% at 22 K. The application of a relatively small electric field (∼333 V/cm) across the Cu/Si interface is enough to strip the trapped electrons and restore the magneto-current ratio at low temperature. We also present a model taking into account the effects of both electric field and temperature that closely reproduces the experimental results and allows extraction of the trapping binding energy (∼1.6 meV).

Publisher's Note: Long-Range Phase Coherence in Double-Barrier Magnetic Tunnel Junctions with a Large Thick Metallic Quantum Well [Phys. Rev. Lett. 115, 157204 (2015)].

This corrects the article DOI: 10.1103/PhysRevLett.115.157204.