Antiferromagnetic metal phase in an electron-doped rare-earth nickelate

Long viewed as passive elements, antiferromagnetic materials have emerged as promising candidates for spintronic devices due to their insensitivity to external fields and potential for high-speed switching. Recent work exploiting spin and orbital effects has identified ways to electrically control and probe the spins in metallic antiferromagnets, especially in noncollinear or noncentrosymmetric spin structures. The rare earth nickelate NdNiO3 is known to be a noncollinear antiferromagnet where the onset of antiferromagnetic ordering is concomitant with a transition to an insulating state. Here, we find that for low electron doping, the magnetic order on the nickel site is preserved while electronically a new metallic phase is induced. We show that this metallic phase has a Fermi surface that is mostly gapped by an electronic reconstruction driven by the bond disproportionation. Furthermore, we demonstrate the ability to write to and read from the spin structure via a large zero-field planar Hall effect. Our results expand the already rich phase diagram of the rare-earth nickelates and may enable spintronics applications in this family of correlated oxides.Comment: 25 pages, 4 figure

Modelling human choices: MADeM and decision‑making

Research supported by FAPESP 2015/50122-0 and DFG-GRTK 1740/2. RP and AR are also part of the Research, Innovation and Dissemination Center for Neuromathematics FAPESP grant (2013/07699-0). RP is supported by a FAPESP scholarship (2013/25667-8). ACR is partially supported by a CNPq fellowship (grant 306251/2014-0)

25th annual computational neuroscience meeting: CNS-2016

The same neuron may play different functional roles in the neural circuits to which it belongs. For example, neurons in the Tritonia pedal ganglia may participate in variable phases of the swim motor rhythms [1]. While such neuronal functional variability is likely to play a major role the delivery of the functionality of neural systems, it is difficult to study it in most nervous systems. We work on the pyloric rhythm network of the crustacean stomatogastric ganglion (STG) [2]. Typically network models of the STG treat neurons of the same functional type as a single model neuron (e.g. PD neurons), assuming the same conductance parameters for these neurons and implying their synchronous firing [3, 4]. However, simultaneous recording of PD neurons shows differences between the timings of spikes of these neurons. This may indicate functional variability of these neurons. Here we modelled separately the two PD neurons of the STG in a multi-neuron model of the pyloric network. Our neuron models comply with known correlations between conductance parameters of ionic currents. Our results reproduce the experimental finding of increasing spike time distance between spikes originating from the two model PD neurons during their synchronised burst phase. The PD neuron with the larger calcium conductance generates its spikes before the other PD neuron. Larger potassium conductance values in the follower neuron imply longer delays between spikes, see Fig. 17.Neuromodulators change the conductance parameters of neurons and maintain the ratios of these parameters [5]. Our results show that such changes may shift the individual contribution of two PD neurons to the PD-phase of the pyloric rhythm altering their functionality within this rhythm. Our work paves the way towards an accessible experimental and computational framework for the analysis of the mechanisms and impact of functional variability of neurons within the neural circuits to which they belong

Application of ionic liquids and various carbon materials in reference electrodes with carbon paste-based transducers

In this article it is proved that carbon pastes with ionic liquids (ILs) are a promising material for transducers of reference electrodes, which favors their miniaturization. Two ILs were used: 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (IL1) and 1-(2-methoxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (IL2). They acted both as a binder of carbon paste and potential-determining component. ILs were also used in polymeric membrane of reference electrodes what ensured continuity of IL phase between carbon paste and the polymeric membrane and resulted in enhancement of electrode potential stability. It was shown that application of IL as a carbon paste binder is superior to conventional plasticizer and allows for significant increase of reference electrode potential stability. Different types of carbon materials were also tested during research: commercialy available graphite powder and graphene oxide obtained from waste biomass – palm kernel shells. It was observed that both the type of carbon paste material and IL influences reference electrode work parameters. Utilization of IL with less lipophilic cation resulted in higher potential stability of the reference electrodes. Application of graphite paste-based transducers resulted in higher potential stability of reference electrodes in sodium perchlorate and TMA chloride solutions while using palm kernel shell graphene oxide paste – based transducers caused enhancement of reference electrode long-term potential stability. The results indicate biomass-derived graphene oxide can be successfully applied as a construction material of reference electrode