Magnetoelastic Coupling and Possibility of Spintronic Electromagnetomechanical Effects

Nanoelectromangetomechanical systems (NEMMS) open up a new path for the development of high speed autonomous nanoresonators and signal generators that could be used as actuators, for information processing, as elements of quantum computers etc. Those NEMMS that include ferromagnetic layers could be controlled by the electric current due to effects related with spin transfer. In the present paper we discuss another situation when the current-controlled behaviour of nanorod that includes an antiferro- (instead of one of ferro-) magnetic layer. We argue that in this case ac spin-polarized current can also induce resonant coupled magneto-mechanical oscillations and produce an oscillating magnetization of antiferromagnetic (AFM) layer. These effects are caused by \emph{i}) spin-transfer torque exerted to AFM at the interface with nonmagnetic spacer and by \emph{ii}) the effective magnetic field produced by the spin-polarized free electrons due to $sd$-exchange.The described nanorod with an AFM layer can find an application in magnetometry and as a current-controlled high-frequency mechanical oscillator.Comment: 8 pages, 2 figures, submitted to Low Temp. Physic

Raman response of quantum critical ferroelectric pb-doped srtio3

A quantum paraelectric SrTiO3 is a material situated in close proximity to a quantum critical point (QCP) of ferroelectric transition in which the critical temperature to the ferroelectric state is suppressed down to 0 K. However, the understanding of the behavior of the phase transition in the vicinity of this point remains challenging. Using the concentration x of Pb in solid solution Sr1−x Pbx TiO3 (PSTx) as a tuning parameter and applying the combination of Raman and dielectric spectroscopy methods, we approach the QCP in PSTx and study the interplay of classical and quantum phenomena in the region of criticality. We obtain the critical temperature of PSTx and the evolution of the temperature-dependent dynamical properties of the system as a function of x to reveal the mechanism of the transition. We show that the ferroelectric transition occurs gradually through the emergence of the polar nanoregions inside the non-polar tetragonal phase with their further expansion on cooling. We also study the ferroelastic cubic-to-tetragonal structural transition, occurring at higher temperatures, and show that its properties are almost concentration-independent and not affected by the quantum criticality.Fil: Linnik, Ekaterina D.. Southern Federal University; RusiaFil: Mikheykin, Alexey S.. Southern Federal University; RusiaFil: Rubi, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Constituyentes | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Constituyentes; ArgentinaFil: Shirokov, Vladimir B.. No especifíca;Fil: Mezzane, Daoud. No especifíca;Fil: Kondovych, Svitlana V.. No especifíca;Fil: Lukyanchuk, Igor A.. No especifíca;Fil: Razumnaya, Anna G.. Southern Federal University; Rusi

Phase Diagram of a Strained Ferroelectric Nanowire

Ferroelectric materials manifest unique dielectric, ferroelastic, and piezoelectric properties. A targeted design of ferroelectrics at the nanoscale is not only of fundamental appeal but holds the highest potential for applications. Compared to two-dimensional nanostructures such as thin films and superlattices, one-dimensional ferroelectric nanowires are investigated to a much lesser extent. Here, we reveal a variety of the topological polarization states, particularly the vortex and helical chiral phases, in loaded ferroelectric nanowires, which enable us to complete the strain–temperature phase diagram of the one-dimensional ferroelectrics. These phases are of prime importance for optoelectronics and quantum communication technologie

Electrostatics of charges in thin dielectric and ferroelectric films

Nous explorons la variété des types d'interactions électrostatiques entre les charges dans des films minces à haute permittivité diélectrique, en analysant le cas particulier de l'interaction de Coulomb bidimensionnel logarithmique. Pour ce système, nous proposons une méthode de réglage du régime d'interaction à l'aide de l'électrode externe. Nous étudions ensuite les électrostatiques des charges étendues dans les matériaux diélectriques: des fils et des bandes chargés de manière homogène ou périodique. En s'appuyant sur les potentiels électrostatiques calculés de ces objets, nous abordons plusieurs applications possibles. Tout d'abord, nous suggérons la méthode non destructive pour mesurer la constante diélectrique des films minces déposés par un substrat par un condensateur à deux fils. Ensuite, nous étudions la formation des domaines dans des films ferroélectriques avec la polarisation dans le plan. L'apparition de la texture en domaines est causée soit par le bord chargé d'un échantillon de taille finie, soit par l'existence d'une paroi de domaine chargé dans le film. Les deux phénomènes augmentent l'énergie électrostatique de l'échantillon, ce qui stimule l'apparence des domaines pour minimiser l'énergie totale. Nous montrons que la taille équilibre du domaine dépend de la géométrie de l'échantillon et, pour les domaines dans le plan, elle viole la loi racine carrée de Kittel, étant inversement proportionnelle à l'épaisseur du filmWe explore the various types of electrostatic interaction between charges in thin films with high dielectric permittivity, including the special case of the two-dimensional logarithmic Coulomb interaction, and propose a method of tuning the interaction regime using the external gate electrode. Changing the gate-to-film distance, one may alter the electrostatic screening length of the dielectric sample and control the ranges of different interaction types. We investigate next the electrostatics of extended charges in dielectric media, modeling the electrostatic potential distribution for charged wires, stripes and domain walls, with either homogeneous or periodic linear charge density. Basing on the calculated dependencies of the potential on the system geometry and material parameters, we discuss several possible applications: i ) we suggest the non-destructive method for measuring the dielectric constant of substrate deposited thin films by a two-wire capacitor; ii ) we study the domain structure formation in ferroelectric films with in-plane polarization. We show that for the in-plane striped 180˚ domain structure, induced by the discontinuity of the order parameter at the film edge, the equilibrium domain width violates the Kittel's square root law, being instead inversely proportional to the film thickness. The calculations for the in-plane domains, generated by the microscope tip or charged domain wall in the ferroelectric slab, demonstrate the conformity of the optimal domain length to the characteristic electrostatic length of the sample, and accord with the experimental dat

Électrostatique des charges dans les couches minces diélectriques et ferroélectriques

We explore the various types of electrostatic interaction between charges in thin films with high dielectric permittivity, including the special case of the two-dimensional logarithmic Coulomb interaction, and propose a method of tuning the interaction regime using the external gate electrode. Changing the gate-to-film distance, one may alter the electrostatic screening length of the dielectric sample and control the ranges of different interaction types. We investigate next the electrostatics of extended charges in dielectric media, modeling the electrostatic potential distribution for charged wires, stripes and domain walls, with either homogeneous or periodic linear charge density. Basing on the calculated dependencies of the potential on the system geometry and material parameters, we discuss several possible applications: i ) we suggest the non-destructive method for measuring the dielectric constant of substrate deposited thin films by a two-wire capacitor; ii ) we study the domain structure formation in ferroelectric films with in-plane polarization. We show that for the in-plane striped 180˚ domain structure, induced by the discontinuity of the order parameter at the film edge, the equilibrium domain width violates the Kittel's square root law, being instead inversely proportional to the film thickness. The calculations for the in-plane domains, generated by the microscope tip or charged domain wall in the ferroelectric slab, demonstrate the conformity of the optimal domain length to the characteristic electrostatic length of the sample, and accord with the experimental dataNous explorons la variété des types d'interactions électrostatiques entre les charges dans des films minces à haute permittivité diélectrique, en analysant le cas particulier de l'interaction de Coulomb bidimensionnel logarithmique. Pour ce système, nous proposons une méthode de réglage du régime d'interaction à l'aide de l'électrode externe. Nous étudions ensuite les électrostatiques des charges étendues dans les matériaux diélectriques: des fils et des bandes chargés de manière homogène ou périodique. En s'appuyant sur les potentiels électrostatiques calculés de ces objets, nous abordons plusieurs applications possibles. Tout d'abord, nous suggérons la méthode non destructive pour mesurer la constante diélectrique des films minces déposés par un substrat par un condensateur à deux fils. Ensuite, nous étudions la formation des domaines dans des films ferroélectriques avec la polarisation dans le plan. L'apparition de la texture en domaines est causée soit par le bord chargé d'un échantillon de taille finie, soit par l'existence d'une paroi de domaine chargé dans le film. Les deux phénomènes augmentent l'énergie électrostatique de l'échantillon, ce qui stimule l'apparence des domaines pour minimiser l'énergie totale. Nous montrons que la taille équilibre du domaine dépend de la géométrie de l'échantillon et, pour les domaines dans le plan, elle viole la loi racine carrée de Kittel, étant inversement proportionnelle à l'épaisseur du fil

Vortex states in a PbTiO3 ferroelectric cylinder

The past decade's discovery of topological excitations in nanoscale ferroelectrics has turned the prevailing view that the polar ground state in these materials is uniform. However, the systematic understanding of the topological polar structures in ferroelectrics is still on track. Here we study stable vortex-like textures of polarization in the nanocylinders of ferroelectric PbTiO3, arising due to the competition of the elastic and electrostatic interactions. Using the phase-field numerical modeling and analytical calculations, we show that the orientation of the vortex core with respect to the cylinder axis is tuned by the geometrical parameters and temperature of the system

Gate-tunable electron interaction in high-κ dielectric films

The two-dimensional (2D) logarithmic character of Coulomb interaction between charges and the resulting logarithmic confinement is a remarkable inherent property of high dielectric constant (high-kappa) thin films with far reaching implications. Most and foremost, this is the charge Berezinskii-Kosterlitz-Thouless transition with the notable manifestation, low-temperature superinsulating topological phase. Here we show that the range of the confinement can be tuned by the external gate electrode and unravel a variety of electrostatic interactions in high-k films. We find that by reducing the distance from the gate to the film, we decrease the spatial range of the 2D long-range logarithmic interaction, changing it to predominantly dipolar or even to exponential one at lateral distances exceeding the dimension of the film-gate separation. Our findings offer a unique laboratory for the in-depth study of topological phase transitions and related phenomena that range from criticality of quantum metal- and superconductor-insulator transitions to the effects of charge-trapping and Coulomb scalability in memory nanodevices

Phase Diagram of a Strained Ferroelectric Nanowire

Ferroelectric materials manifest unique dielectric, ferroelastic, and piezoelectric properties. A targeted design of ferroelectrics at the nanoscale is not only of fundamental appeal but holds the highest potential for applications. Compared to two-dimensional nanostructures such as thin films and superlattices, one-dimensional ferroelectric nanowires are investigated to a much lesser extent. Here, we reveal a variety of the topological polarization states, particularly the vortex and helical chiral phases, in loaded ferroelectric nanowires, which enable us to complete the strain–temperature phase diagram of the one-dimensional ferroelectrics. These phases are of prime importance for optoelectronics and quantum communication technologies