Magnetic frustration effects in artificial kagome arrays of nanomagnets are investigated using x-ray photoemission electron microscopy and Monte Carlo simulations. Spin configurations of demagnetized networks reveal unambiguous signatures of long range, dipolar interaction between the nanomagnets. As soon as the system enters the spin ice manifold, the kagome dipolar spin ice model captures the observed physics, while the short range kagome spin ice model fails.

We demonstrate that shot noise in Fe=MgO=Fe=MgO=Fe double-barrier magnetic tunnel junctions is determined by the relative magnetic configuration of the junction and also by the asymmetry of the barriers. The proposed theoretical model, based on sequential tunneling through the system and including spin relaxation, successfully accounts for the experimental observations for bias voltages below 0.5 V, where the influence of quantum well states is negligible. A weak enhancement of conductance and shot noise, observed at some voltages (especially above 0.5 V), indicates the formation of quantum well states in the middle magnetic layer. As solid-state electronic devices shrink in size, further advances essentially depend on the understanding and control of spontaneous off-equilibrium fluctuations in charge and/or spin currents. Being a consequence of the discrete nature of charge carriers, shot noise (SN) is the only contribution to the noise which survives at low temperatures. Moreover, SN is an excellent tool to investigate the correlations and coherency at the nanoscale, well beyond the capabilities of electron transport [1][2][3][4][5][6][7][8][9]. In the absence of correlations, SN is Poissonian (full shot noise) and its noise power is given by S full ¼ 2eI, where I is the average current and e the electron charge. The Fano factor, F ¼ S exp =S full , represents the experimental SN normalized by the full SN value. It is generally suppressed (F < 1) by electron correlations [1] (quantum and/or Coulomb), but it can also be enhanced (F > 1), e.g., due to tunneling via localized states [10].After the observation of spin dependent transport in Fe=MgO=Fe magnetic tunnel junctions (MTJs) [11,12], MgO-based junctions became important elements of spintronic devices. Moreover, the recent implementation of MgO for an effective spin injection [13,14] revealed a new road for reducing the spin relaxation due to conductivity mismatch [15,16]. The efforts aimed at understanding spin coherency and SN, limited up to now to MTJs, revealed suppressed SN with Al 2 O 3 barriers (0:7 < F < 1) due to sequential tunneling [17] and also in serial MTJ arrays [18]. As for MTJs with MgO barriers, full SN (F ¼ 1) independent of the magnetic state was observed in epitaxial Fe=MgO=Fe [19]. Then, the noise was examined for ultrathin (less than 1 nm) MgO barriers, where F ' 0:92 was observed in the parallel state [20,21]. Double-barrier magnetic tunnel junctions (DMTJs), with either nanoparticles [22,23] or a continuous magnetic layer as the central electrode [24], have some advantages in comparison with MTJs. First, they show an enhanced tunnel magnetoresistance (TMR) [24,25], which additionally reveals oscillations induced by quantum well states (QWSs) [23,26]. Second, spin accumulation in the central layer is expected to substantially enhance spin torque [27,28]. The investigation of the statistics of spin tunneling events in hybrid spintronic devices is of great potential interest also beyond the spintronics community. From a general point o...

Spin-orbit coupling (SOC) related to the minority interface resonance states (IRSs) of Fe(001) has been evidenced in full-epitaxial Fe(001)/MgO/Fe magnetic tunnel junctions (MTJs) from magnetotransport experiments correlated to theoretical ab initio calculations. We show that the SOC effect strongly depends on the symmetry composition of the IRS, which has been skillfully engineered via the interfacial chemical structure in the Fe(001)/MgO stack. The SOC scattering is enhanced between the majority 1 and minority 5 band near the Fermi level when presenting a 5 symmetry dominant IRS at the Fe/MgO interface. Our results validate the interplay between SOC and IRSs, which gives further understanding of the mechanisms responsible for the tunneling anisotropic magnetoresistance and the large perpendicular magnetic anisotropy at the Fe/MgO interface.