Electron-electron interactions in nano-patterned La 0.3 Sr 0.7 MnO 3 thin films

International audienceUnderstanding the transport in ultra-thin epitaxial La0.3Sr0.7MnO3 (LSMO) is a topic widespread current interest. Here we explore electron-electron interactions in low temperature magneto-transport in straight and zigzag nanowires fabricated from ultra-thin epitaxial LSMO films grown to different thicknesses on STO(100) substrates. We find that three-dimensional electron-electron interactions can explain the resistivity upturn, including many of the changes observed with film thickness, nano-patterning, and magnetic field

Spin electronic magnetic sensor based on functional oxides for medical imaging

8th Spintronics Symposium , AUG 09-13, 2015 , San Diego, CAInternational audienceTo detect magnetic signals coming from the body, in particular those produced by the electrical activity of the heart or of the brain, the development of ultrasensitive sensors is required. In this regard, magnetoresistive sensors, stemming from spin electronics, are very promising devices. For example, tunnel magnetoresistance (TMR) junctions based on MgO tunnel barrier have a high sensitivity. Nevertheless, TMR also often have high level of noise. Full spin polarized materials like manganite La0.67Sr0.33MnO3 (LSMO) are attractive alternative candidates to develop such sensors because LSMO exhibits a very low 1/f noise when grown on single crystals, and a TMR response has been observed with values up to 2000%. This kind of tunnel junctions, when combined with a high Tc superconductor loop, opens up possibilities to develop full oxide structures working at liquid nitrogen temperature and suitable for medical imaging. In this work, we investigated on LSMO-based tunnel junctions the parameters controlling the overall system performances, including not only the TMR ratio, but also the pinning of the reference layer and the noise floor. We especially focused on studying the effects of the quality of the barrier, the interface and the electrode, by playing with materials and growth condition

Magneto-ionic control of spin polarization in multiferroic tunnel junctions

Magnetic tunnel junctions (MTJs) with Hf0.5Zr0.5O2 barriers are reported to show both tunneling magnetoresistance effect (TMR) and tunneling electroresistance effect (TER), displaying four resistance states by magnetic and electric field switching. Here we show that, under electric field cycling of large enough magnitude, the TER can reach values as large as 10^6%. Moreover, concomitant with this TER enhancement, the devices develop electrical control of spin polarization, with sign reversal of the TMR effect. Currently, this intermediate state exists for a limited number of cycles and understanding the origin of these phenomena is key to improve its stability. The experiments presented here point to the magneto-ionic effect as the origin of the large TER and strong magneto-electric coupling, showing that ferroelectric polarization switching of the tunnel barrier is not the main contribution

Magneto-optical properties of textured La2/3_{2/3}Sr1/3_{1/3}MnO3_3 thin films integrated on silicon via a Ca2_2Nb3_3O10_{10} nanosheet layer

We demonstrate the possibility of growing textured La$_{2/3}$Sr$_{1/3}$MnO$_3$ (LSMO) thin films on silicon substrates with magneto-optical and optical properties comparable to high-quality epitaxial layers grown on bulk SrTiO$_3$ (STO). The pulsed laser deposition growth of LSMO is achieved by a two-dimensional nanosheet (NS) seed layer of Ca$_2$Nb$_3$O$_{10}$ (CNO) inducing epitaxial stabilization of LSMO films. The resulting layers possess a higher Curie temperature and a lower overall magnetization than samples of LSMO on STO. Spectra of the full permittivity tensor were calculated from optical and magneto-optical measurements. Spectral dependencies of both the diagonal and off-diagonal elements share many similarities between the LSMO/NS/Si and LSMO/STO samples. These similarities indicate comparable electronic structures of the layers and demonstrate comparable optical quality of textured LSMO on NS/Si and epitaxial LSMO on STO

A rhombohedral ferroelectric phase in epitaxially strained Hf0.5Zr0.5O2 thin films

Hafnia-based thin films are a favoured candidate for the integration of robust ferroelectricity at the nanoscale into next-generation memory and logic devices. This is because their ferroelectric polarization becomes more robust as the size is reduced, exposing a type of ferroelectricity whose mechanism still remains to be understood. Thin films with increased crystal quality are therefore needed. We report the epitaxial growth of Hf0.5Zr0.5O2 thin films on (001)-oriented La0.7Sr0.3MnO3/SrTiO3 substrates. The films, which are under epitaxial compressive strain and predominantly (111)-oriented, display large ferroelectric polarization values up to 34 mu C cm(-2) and do not need wake-up cycling. Structural characterization reveals a rhombohedral phase, different from the commonly reported polar orthorhombic phase. This finding, in conjunction with density functional theory calculations, allows us to propose a compelling model for the formation of the ferroelectric phase. In addition, these results point towards thin films of simple oxides as a vastly unexplored class of nanoscale ferroelectrics.</p

The T-381C SNP in BNP gene may be modestly associated with type 2 diabetes: an updated meta-analysis in 49 279 subjects

A recent study reported an association between the brain natriuretic peptide (BNP) promoter T-381C polymorphism (rs198389) and protection against type 2 diabetes (T2D). As replication in several studies is mandatory to confirm genetic results, we analyzed the T-381C polymorphism in seven independent case-control cohorts and in 291 T2D-enriched pedigrees totalling 39 557 subjects of European origin. A meta-analysis of the seven case-control studies (n = 39 040) showed a nominal protective effect [odds ratio (OR) = 0.86 (0.79-0.94), P = 0.0006] of the CC genotype on T2D risk, consistent with the previous study. By combining all available data (n = 49 279), we further confirmed a modest contribution of the BNP T-381C polymorphism for protection against T2D [OR = 0.86 (0.80-0.92), P = 1.4 × 10−5]. Potential confounders such as gender, age, obesity status or family history were tested in 4335 T2D and 4179 normoglycemic subjects and they had no influence on T2D risk. This study provides further evidence of a modest contribution of the BNP T-381C polymorphism in protection against T2D and illustrates the difficulty of unambiguously proving modest-sized associations even with large sample size