Abstract:Spin-transfer torques (STTs) can be exploited in order to manipulate the magnetic moments of nanomagnets, thus allowing for new consumer-oriented devices to be designed. Of particular interest here are tuneable radio-frequency (RF) oscillators for wireless communication. Currently, the structure that maximizes the output power is an Fe/MgO/Fe-type magnetic tunnel junction (MTJ) with a fixed layer magnetized in the plane of the layers and a free layer magnetized perpendicular to the plane. This structure allows… Show more
“…2(c). Reversing the bias polarity results in a much weaker STO signal and broader linewidth (not shown), similarly to other reports 21 .Figure 2( a ) STO power (expressed in dB over the noise floor) measured in different magnetic fields applied at 65° with respect to the sample plane, ( b ) bias current dependence on the STO signal. The STO frequency and power extracted from ( b ) are presented as a function of the bias current ( c ).…”
Modulation of a microwave signal generated by the spin-torque oscillator (STO) based on a magnetic tunnel junction (MTJ) with perpendicularly magnetized free layer is investigated. Magnetic field inductive loop was created during MTJ fabrication process, which enables microwave field application during STO operation. The frequency modulation by the microwave magnetic field of up to 3 GHz is explored, showing a potential for application in high-data-rate communication technologies. Moreover, an inductive loop is used for self-synchronization of the STO signal, which after field-locking, exhibits significant improvement of the linewidth and oscillation power.
“…2(c). Reversing the bias polarity results in a much weaker STO signal and broader linewidth (not shown), similarly to other reports 21 .Figure 2( a ) STO power (expressed in dB over the noise floor) measured in different magnetic fields applied at 65° with respect to the sample plane, ( b ) bias current dependence on the STO signal. The STO frequency and power extracted from ( b ) are presented as a function of the bias current ( c ).…”
Modulation of a microwave signal generated by the spin-torque oscillator (STO) based on a magnetic tunnel junction (MTJ) with perpendicularly magnetized free layer is investigated. Magnetic field inductive loop was created during MTJ fabrication process, which enables microwave field application during STO operation. The frequency modulation by the microwave magnetic field of up to 3 GHz is explored, showing a potential for application in high-data-rate communication technologies. Moreover, an inductive loop is used for self-synchronization of the STO signal, which after field-locking, exhibits significant improvement of the linewidth and oscillation power.
Here, we present an analytical and numerical model describing the magnetization dynamics in MgO-based spin-torque nano-oscillators with an in-plane magnetized polarizer and an out-of-plane free layer. We introduce the spin-transfer torque asymmetry by considering the cosine angular dependence of the resistance between the two magnetic layers in the stack. For the analytical solution, dynamics are determined by assuming a circular precession trajectory around the direction perpendicular to the plane, as set by the effective field, and calculating the energy integral over a single precession period. In a more realistic approach, we include the bias dependence of the tunnel magnetoresistance, which is assumed empirically to be a piecewise linear function of the applied voltage. The dynamical states are found by solving the stability condition for the Jacobian matrix for out-of-plane static states. We find that the bias dependence of the tunnel magnetoresistance, which is an inseparable effect in every tunnel junction, exhibits drastic impact on the spin-torque nano-oscillator phase diagram, mainly by increasing the critical current for dynamics and quenching the oscillations at high currents. The results are in good agreement with our experimental data published elsewhere.
“…[53,66,93,110,111,113,141,155] Figure 12a-d shows the possible defects inside junctions. [2] Although the role of defects has been investigated in detail in the context of, for instance, tunnel magnetoresistance [156][157][158] and perovskite solar cells, [159,160] how such defects affect the electrical characteristics of molecular junctions has only been occasionally studied. [93,[110][111][112][113][161][162][163] Line "B" corresponds to the "long" time of ≈2.5 min, measured at low frequency (f = 10 Hz).…”
Section: Role Of Defects and Self-repair Of Samsmentioning
workings of charge transport in exquisite detail in areas including molecular plasmonics, [9] spintronics, [10,11] bioelectronics, [12] sensing, [13] catalysis, [14,15] energy storage, [12,16] memory, [17][18][19] and flexible electronics. [2,3,[20][21][22] Control over the dielectric behavior of nanoscale systems is important for a wide range of applications including supercapacitors, [23] organic field effect transistors (OFETs), [24][25][26][27] flexible and stretchable electronics, [25,28] optoelectronics, [29] and memory. [30] For example, for OFETs, it is important to develop gate materials with high dielectric constants yet with low leakage (via tunneling) currents. [24,25] In principle, molecular junctions are interesting because they allow us to study the dielectric properties of materials at the molecular length scale, but their dielectric behavior remains, to date, virtually unexplored despite promising features. [31][32][33][34] For instance, it has been predicted that, due to their well-organized nature, self-assembled monolayers (SAMs) can have very high relative dielectric constants ε r of ≈20, [32] while usually bulk organic materials have values of ε r in the range of 2-4. [35,36] Theoretically it has been shown that ε r can increase with the thickness of SAMs helping to avoid the adverse decrease of the capacitance in OFETSs with increasing gate dielectric thickness [26,31,34,35] which, in turn, can be used to reduce leakage currents. The dielectric behavior of SAMs are also important to modulate work functions, [37][38][39][40] or to reduceThe dielectric behavior of organic materials at molecular dimensions can be vastly different than their bulk counterparts and therefore it is important to investigate and control the dielectric response of molecular-scale materials for a large variety of applications. Large-area molecular junctions are explored to study the charge transport mechanisms with unprecedented detail and to demonstrate novel functionalities. Therefore, large-area molecular junctions are, in principle, a promising platform to study the dielectric effects at the molecular scale. This review summarizes recent progress on the measurements and understanding of the dielectric behavior of molecular systems and how they behave differently from their bulk properties. This review introduces, briefly, the concepts of impedance spectroscopy (IS) and how this technique can be applied to study the dielectric response of solid-state large-area molecular junctions. This analysis gives new insights in the factors that determine the dielectric constant of monolayers (including collective electrostatic effects and how the dielectric constant increases with monolayer thickness), how IS gives new insights into the role of defects, and the factors that contribute to the molecule-electrode contact resistance. This review ends with an outlook highlighting interesting future directions.
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