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...

Organic molecules have recently revolutionized ways to create new spintronic devices. Despite intense studies, the statistics of tunneling electrons through organic barriers remains unclear. Here we investigate conductance and shot noise in magnetic tunnel junctions with PTCDA barriers a few nm thick. For junctions in the electron tunneling regime, with magnetoresistance ratios between 10 and 40\%, we observe superpoissonian shot noise. The Fano factor exceeds in 1.5-2 times the maximum values reported for magnetic tunnel junctions with inorganic barriers, indicating spin dependent bunching in tunneling. We explain our main findings in terms of a model which includes tunneling through a two level (or multilevel) system, originated from interfacial bonds of the PTCDA molecules. Our results suggest that interfaces play an important role in the control of shot noise when electrons tunnel through organic barriers

We calculate shot noise and the corresponding Fano factors in magnetic double-barrier tunnel junctions. Two situations are analyzed: (i) the central metallic layer is nonmagnetic while the external ones are ferromagnetic, and (ii) all of the metallic layers are ferromagnetic. In the latter case, the number of various magnetic configurations of the junctions is larger, which improves the functionality of such devices. The corresponding shot noise and Fano factor are shown to depend on the magnetic configuration of the junctions. The effect of spin relaxation in the central layer is also taken into account. The theoretical results are compared with experimental data on the shot noise in Fe/MgO/Fe/MgO/Fe structures.

We analyze shot noise in a magnetic tunnel junction with a two-level quantum dot attached to the magnetic electrodes. The considerations are limited to the case when some transport channels are suppressed at low temperatures. Coupling of the two dot's levels to the electrodes are assumed to be generally different and also spin dependent. To calculate the shot noise we apply the approach based on the full counting statistics. The approach is used to account for experimental data obtained in magnetic tunnel junctions with organic barriers. The experimentally observed Fano factors correspond to the super-Poissonian statistics, and also depend on relative orientation of the electrodes' magnetic moments. We have also calculated the corresponding spin shot noise, which is associated with fluctuations of spin current.

Vacuum metal deposition was introduced in the process of visualization of latent fingermarks already in the 20th century. However, due to the requirement of using specialist equipment to ensure appropriate conditions for the development process, which would have generated significant costs, the method was not available in Poland. Technological developments, however, made it possible to create compact devices with smaller dimensions and lower parameters, which, nowadays, can be used in virtually every forensic fingerprint identification laboratory. The article describes the theoretical basis of the process of developing fingerprints by means of the vacuum metal deposition method with the use of sequential deposition of gold, zinc and silver on the tested surfaces. The device used for the VMD method is also presented along with sample effects of treating fingerprints on various surfaces, including registration in the range of reflected infrared light and with recovering marks on lifting foils. The final part deals with the issue of accrediting forensic service providers performing fingerprint examinations, including problems related to the implementation of vacuum metal deposition in the range of accredited fingerprint visualization techniques.