Maciej Misiorny

Magnetic switching of a single molecular magnet due to spin-polarized current

Magnetic switching of a single molecular magnet (SMM) due to spin-polarized current flowing between ferromagnetic metallic leads (electrodes) is investigated theoretically. Magnetic moments of the leads are assumed to be collinear and parallel to the magnetic easy axis of the molecule. Electrons tunneling through the barrier between magnetic leads are coupled to the SMM via exchange interaction. The current flowing through the system, as well as the spin relaxation times of the SMM, are calculated from the Fermi golden rule. It is shown that spin of the SMM can be reversed by applying a certain voltage between the two magnetic electrodes. Moreover, the switching may be visible in the corresponding current-voltage characteristics.

Spin polarized transport through a single-molecule magnet : Current-induced magnetic switching

Magnetic switching of a single molecule magnet (SMM) due to spin polarized current is investigated theoretically. The charge transfer between the electrodes takes place via the lowest unoccupied molecular orbital (LUMO) of the SMM. Generally, the double occupancy of the LUMO level, and hence a finite on-site Coulomb repulsion, is allowed. Owing to the exchange interaction between electrons in the LUMO level and the SMMs spin, the latter can be reversed. The perturbation approach (Fermi golden rule) is applied to calculate current-voltage characteristics. The influence of Coulomb interactions on the switching process is also analyzed.

Spin effects in transport through single-molecule magnets in the sequential and cotunneling regimes

We analyze the stationary spin-dependent transport through a single-molecule magnet weakly coupled to external ferromagnetic leads. Using the real-time diagrammatic technique, we calculate the sequential and cotunneling contributions to current, tunnel magnetoresistance, and Fano factor in both linear and nonlinear response regimes. We show that the effects of cotunneling are predominantly visible in the blockade regime and lead to enhancement of tunnel magnetoresistance (TMR) above the Julliere value, which is accompanied with super-Poissonian shot noise due to bunching of inelastic cotunneling processes through different virtual spin states of the molecule. The effects of external magnetic field and the role of type and strength of exchange interaction between the LUMO level and the molecules spin are also considered. When the exchange coupling is ferromagnetic, we find an enhanced TMR, while in the case of antiferromagnetic coupling we predict a large negative TMR effect.

Spin diode behavior in transport through single-molecule magnets

We study transport properties of a single-molecule magnet (SMM) weakly coupled to one nonmagnetic and one ferromagnetic lead. Using the diagrammatic technique in real time, we calculate transport in the sequential and cotunneling regimes for both ferromagnetic and antiferromagnetic exchange coupling between the molecules LUMO level and the core spin. We show that the current flowing through the system is asymmetric with respect to the bias reversal, being strongly suppressed for particular bias polarizations. Thus, the considered system presents a prototype of a SMM spin diode. In addition, we also show that the functionality of such a device can be tuned by changing the position of the molecules LUMO level and strongly depends on the type of exchange interaction.

Spintronic magnetic anisotropy

Superparamagnetism (preferential alignment of spins along an easy axis) is a useful effect for spintronic applications as it prevents spin reversal. It is now shown that high-spin quantum dots can become magnetically anisotropic when coupled to nearby ferromagnets—‘artificial’ superparamagnets.

Interplay of the Kondo effect and spin-polarized transport in magnetic molecules, adatoms, and quantum dots.

We study the interplay of the Kondo effect and spin-polarized tunneling in a class of systems exhibiting uniaxial magnetic anisotropy. Using the numerical renormalization group method we calculate the spectral functions and linear conductance in the Kondo regime. We show that the exchange coupling between conducting electrons and localized magnetic core generally leads to suppression of the Kondo effect. We also predict a nontrivial dependence of the tunnel magnetoresistance on the strength of exchange coupling and on the anisotropy constant.

Effects of intrinsic spin-relaxation in molecular magnets on current-induced magnetic switching

Current-induced magnetic switching of a single magnetic molecule attached to two ferromagnetic contacts is considered theoretically, with the main emphasis put on the role of intrinsic spin-relaxation processes. It is shown that spin-polarized current can switch magnetic moment of the molecule, despite the intrinsic spin-relaxation in the molecule. The latter processes increase the threshold voltage (current) above which the switching takes place.

Probing transverse magnetic anisotropy by electronic transport through a single-molecule magnet

By means of electronic transport, we study the transverse magnetic anisotropy of an individual Fe4 singlemolecule magnet (SMM) embedded in a three-terminal junction. In particular, we determine in situ the transverse anisotropy of the molecule from the pronounced intensity modulations of the linear conductance, which are observed as a function of applied magnetic field. The proposed technique works at temperatures exceeding the energy scale of the tunnel splittings of the SMM. We deduce that the transverse anisotropy for a single Fe4 molecule captured in a junction is substantially larger than the bulk value.

Underscreened Kondo effect in S=1 magnetic quantum dots: Exchange, anisotropy, and temperature effects

We present a theoretical analysis of the effects of uniaxial magnetic anisotropy and contact-induced exchange field on the underscreened Kondo effect in S=1 magnetic quantum dots coupled to ferromagnetic leads. First, by using the second-order perturbation theory we show that the coupling to spin-polarized electrode results in an effective exchange field

Effects of Transverse Magnetic Anisotropy on Current-Induced Spin Switching

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