Electric noise can be an important limitation for applications of conducting elements in the nanometer size range. The intrinsic electrical noise of prospective materials for opto-spintronics applications like ZnO has not yet been characterized. In this study, we have investigated the conductivity fluctuations in 10 nm thick current paths produced by proton implantation of ZnO microwires at room temperature. The voltage noise under a constant dc current bias in undoped, as well as in Li-doped microwires, is characterized by [Formula: see text] power spectra with [Formula: see text]. The noise intensity scales with the square of the bias current pointing to bias-independent resistivity fluctuations as a source of the observed noise. The normalized power spectral density appears inversely proportional to the number of carriers in the probed sample volume, in agreement with the phenomenological Hooge law. For the proton-implanted ZnO microwire and at 1 Hz we obtain a normalized power spectral density as low as [Formula: see text] Hz(-1).

Non-equilibrium magnetic properties of the near half-doped Sm0.43Ca0.57MnO3 nanoparticles with an average size as small as 15 nm have been investigated by measuring temperature dependence of zero field cooled (ZFC) magnetization, ac-susceptibility, time dependence of ZFC magnetization, relaxation of the remanent magnetization, and memory effects in ZFC magnetization. For the studied particles, charge ordering, characteristic for the bulk, is gradually suppressed with decreasing particle size and fully disappears in 15 nm particles, while the Neel temperature decreases slightly from 73 K for 60 nm to 58 K for 15 nm particles. It was found that dipolar interaction between 15 nm nanoparticles is enough to leads to the formation of a superspin glass state. Characteristic features of superspin glass state, such as aging and memory effects have been observed in 15 nm samples. In a difference to atomic spin glasses, no strong rejuvenation of magnetization has been observed at low temperatures. (C) 2014 Elsevier B. V. All rights reserved.

Conductivity of current-biased La0.82 Ca0.18 MnO3 low-doped manganite single crystals has been investigated in wide temperature and magnetic field ranges. Strong zero-bias anomalies in the form of conductance minima and maxima have been observed below the Curie temperature TC. Applied magnetic field and temperature strongly affect the anomaly and cause its transition from the conductance minimum to the conductance maximum. The observed anomalies are ascribed to Anderson localisation and combined Kondo and Fano effects.

Magnetic properties of compacted Sm0.1Ca0.9MnO3 particles with 25 and 60 nm average sizes have been investigated. Particular attention has been paid to Griffiths-like features at temperatures above magnetic transition temperature TC and to the system glassiness at low temperatures. Griffiths-like features in inverse magnetic susceptibility of Sm0.1Ca0.9MnO3 nanoparticles have been linked to the presence of short range ferromagnetically correlated spin clusters above TC. Glassy behavior has been revealed in temperature and frequency dependence of ac-susceptibility, temperature and field dependence of thermoremanent and isothermoremanent magnetization, and time decay of the remanent magnetization. Experiments revealed the major impact of the glassy component on magnetic properties of investigated nanoparticles. The magnetic relaxation associated with glassy features was found to be much more pronounced in smaller particles, where a formation of collective state in an ensemble of phase separated nanoparticles may take place. Thermomagnetic irreversibility found in Sm0.1Ca0.9MnO3 nanoparticles has been linked to martensitic strain effects.

Conductivity of current-biased La0.82Ca0.18MnO3 low-doped manganite single crystals has been investigated in wide temperature and magnetic field ranges. Strong zero-bias anomalies in the form of conductance minima and maxima have been observed below the Curie temperature T-C. Applied magnetic field and temperature strongly affect the anomaly and cause its transition from the conductance minimum to the conductance maximum. The observed anomalies are ascribed to Anderson localisation and combined Kondo and Fano effects. Copyright (C) EPLA, 2013

Magnetic properties of compacted Sm0.1Ca0.9MnO3 nanoparticles with average particle size of 25 and 60 nm have been investigated. It was found that the relative volume of the ferromagnetic phase decreases with decreasing particle size. Magnetization curves measured in field cooled and zero field cooled mode separate near the transition temperature TC and remain different even in magnetic field of 15 kOe. AC-susceptibility is strongly frequency dependent below TC, although the temperature of the maximum depends on frequency only slightly. Magnetization hysteresis loops exhibit horizontal and vertical shifts, relatively small in 60 nm and much larger in 25 nm particles, due to size-dependent exchange bias effect. The exchange bias field and the coercive field depend in a non-monotonic way on cooling magnetic field, while the asymmetry of remanence magnetization and magnetic coercivity increase monotonously with the increase of cooling field. Applied pressure enhances Curie temperature TC of nanoparticles with a pressure coefficient dTC/dP ≈ 0.6 K kbar−1, close to that of the bulk, suggesting that magnetic state of the core is similar to the bulk state. The thermoremanance and isothermoremanance curves provide fingerprints of irreversible magnetization originating from the presence of glassy component. We have ascribed the magnetic behavior of the nanoparticles to a core-shell scenario with phase separated core containing ferromagnetic clusters embedded in an antiferromagnetic matrix and partially disordered antiferromagnetic or paramagnetic shell. The suppression of the ferromagnetic phase in the core with decreasing particle size may account for the enhancement of the exchange bias effect seen in smaller particles.

Conductivity noise in dc current biased La0.82Ca0.18MnO3 single crystals has been investigated in different metastable resistivity states enforced by applying voltage pulses to the sample at low temperatures. Noise measured in all investigated resistivity states is of 1/f-type and its intensity at high temperatures and low dc bias scales as a square of the bias. At liquid nitrogen temperatures for under bias exceeding a threshold value, the behavior of the noise deviates from above quasi-equilibrium modulation noise and depends in a non monotonic way on applied bias. The bias range of nonequilibrium 1/f noise coincides with the range at which the conductance increases linearly with bias voltage. This feature is attributed to a broad continuity of states enabling indirect inelastic tunneling across intrinsic tunnel junctions. The nonequilibrium noise has been ascribed to indirect intrinsic tunneling mechanism while resistivity changes in metastable states to variations in the energy landscape for charge carriers introduced by microcracks created by the pulse procedures employed.

Low frequency noise in current biased La0.82Ca0.18MnO3 single crystals has been investigated in a wide temperature range from 79 to 290 K. Despite pronounced changes in the magnetic properties and dissipation mechanisms of the sample with changing temperature, the noise spectra were found to be always of the 1/f type, and their intensity (except for the lowest temperature studied) scaled as the square of the bias. At liquid nitrogen temperatures and under a bias exceeding some threshold value, the behavior of the noise deviates from the quasiequilibrium modulation noise and starts to depend in a nonmonotonic way on the bias. It has been verified that the observed noise obeys the Dutta and Horn model of 1/f noise in solids. The appearance of nonequilibrium 1/f noise and its dependence on bias have been associated with changes in the distribution of activation energies in the underlying energy landscape. These changes have been correlated with bias induced changes in the intrinsic tunneling mechanism dominating dissipation in La0.82Ca0.18MnO3 at low temperatures.

1 ∕ f noise in current biased La0.82Ca0.18MnO3 crystals has been investigated. The temperature dependence of the noise follows the resistivity changes with temperature, suggesting that resistivity fluctuations constitute a fixed fraction of the total resistivity, independently of the dissipation mechanism and magnetic state of the system. The noise scales as a square of the current as expected for equilibrium resistivity fluctuations. However, at 77K at bias exceeding some threshold, the noise intensity starts to decrease with increasing bias. The appearance of nonequilibrium noise is interpreted in terms of bias dependent multistep indirect tunneling.