Current-induced dynamics in hybrid geometry MgO-based spin-torque nano-oscillators

Spin-torque nano-oscillators (STNOs) are prospective successors of transistor-based emitters and receivers of radio-frequency signals in commonly used remote communication systems. In comparison to the conventional electronic oscillators, STNOs offer the advantage of being tunable over a wide range of frequencies simply by adjusting the applied current, the smaller lateral size (up to 50 times) and the lower power consumption as the lateral size of the device is reduced. It has already been demonstrated that the output signal characteristics of STNOs are compatible with the requirements for applications: they can provide output powers in the µW range, frequencies of the order of GHz, quality factors Q (equal to df/f, where f is the frequency, and df is the linewidth) up to several thousands (e.g., 3 200), and can be integrated into Phase-Locked Loop (PLL) circuits. The most promising type of spin-torque oscillators is the hybrid geometry STNOs utilizing an in-plane magnetized fixed layer, an out-of-plane magnetized free layer and the MgO tunnel barrier as a spacer. This geometry maximizes the output power, since the full parallel-to-antiparallel resistance variation can be exploited in the limit of large magnetization precession angle (i.e., when the magnetization oscillates fully within the plane of the STNO stack). Moreover, the considered hybrid geometry allows for the reduction of the critical currents, enables functionality regardless of the applied magnetic or current history and requires a simplified fabrication process in comparison to the opposite hybrid geometry, consisting of an in-plane magnetized free layer and an out-of-plane reference layer, which requires an additional read-out layer. Simultaneously, the choice of the spacer material in considered STNOs is motivated by the increase of both the output power (via large magnetoresistance ratios) and the power conversion rate ('output power to input power' ratio), compared to their fully metallic counterparts. Despite the many advantages of MgO-based hybrid geometry STNOs, unexplained issues related to the physics behind their principle of operation remained. In this thesis, the main focus is put on the two key aspects related to the out-of-plane steady-state precession in hybrid STNOs: the precession mechanism (combined with the analysis of the influence of the bias dependence of the tunnel magnetoresistance) and the zero-field oscillations stabilized by an in-plane shape anisotropy. State-of-the-art theoretical studies demonstrated that stable precession in hybrid geometry STNOs can only be sustained if the in-plane component of the spin-transfer torque (STT) exhibits an asymmetric dependence on the angle between the free and the polarizing layer (which is true for fully metallic devices, but not for the MgO-based magnetic tunnel junctions (MTJs)). Nevertheless, recent experimental reports showed that spin-transfer driven dynamics can also be sustained in MgO-based STNOs with this particular configuration. In this thesis, a phenomenological and straightforward mechanism responsible for sustaining the dynamics in considered system is suggested. The mechanism is based on the fact that, in MgO-based MTJs, the strong cosine-type angular dependence of the tunnel magnetoresistance, at constant applied current, translates into an angle-dependent voltage component, which results in an angle-dependent spin-transfer torque giving a rise to the angular asymmetry of the in-plane STT and, thus, enabling steady-state precession to be sustained. Subsequently, the bias dependence of the tunnel magnetoresistance (TMR), which has been so far neglected in similar calculations, is taken into account. According to the results of analytical and numerical studies, the TMR bias dependence brings about a gradual quenching of the dynamics at large applied currents. The theoretical model yields trends confirming our experimental results. The most important conclusion regarding to this part of the thesis is that, while the angular dependence of the tunnel magnetoresistance introduces an angular asymmetry for the in-plane spin transfer torque parameter (which helps maintain steady-state precession), the bias dependence of the resistance works to reduce this asymmetry. Thus, these two mechanisms allow us to tune the asymmetry of the in-plane STT as function of current and to control the dynamical response of the actual device. Except for the precession mechanism, the thesis is also focused on the issue of zero-field oscillations, which would be especially desirable from the point of view of potential applications. According to the state-of-the-art theoretical studies, for hybrid geometry devices with circular cross-section (i.e., exhibiting no other anisotropy terms), current-driven dynamics cannot be excited at zero applied field. Indeed, zero-field oscillations have only been experimentally observed for systems having the free layer magnetization slightly tilted from the normal to the plane, which has usually been achieved by introducing an in-plane shape anisotropy. In the thesis, the influence of the in-plane shape anisotropy of the MTJ on zero-field dynamics in the hybrid geometry MgO-based STNOs is analytically and numerically investigated. In agreement with the previous reports, no zero-field dynamics for circular nano-pillars is observed; however, according to the numerical data, an additional in-plane anisotropy smaller than the effective out-of-plane anisotropy of the free layer enables zero-field steady-state precession. Accordingly, the lack of an in-plane anisotropy component (e.g., for circular cross-section nano-pillars), or the presence of an in-plane shape anisotropy equal or greater than the out-of-plane effective anisotropy, inhibits the stabilization of dynamics in the free layer at zero field. The results of analytical and numerical studies and the general trends identified in the corresponding experimental data are found to be in excellent qualitative agreement.:1. Introduction 1.1. Short history of magnetotransport applications 1.2. Spin-transfer torque induced effects and devices 1.3. Goals of the thesis 2. Fundamentals 2.1. Electronic transport in single transition metal layers 2.2. Tunnel magnetoresistance (TMR) 2.2.1. Electronic transport in magnetic tunnel junctions 2.2.2. Tunnel magnetoresistance versus structural properties of the multilayer 2.2.3. Bias voltage and temperature dependence of tunnel magnetoresistance 2.2.4. Angular dependence of tunnel magnetoresistance 2.3. Spin-transfer torque in GMR/TMR structures 2.3.1. Spin-transfer torque 2.3.2. Landau-Lifshitz-Gilbert (LLG) equation 2.3.3. LLG equation and spin-transfer torques 2.3.4. Bias voltage dependence of spin-transfer torques in MTJs 2.3.5. Angular dependence of spin-transfer torque 2.4. Spin-torque-based phenomena 2.4.1. Current-induced switching 2.4.2. Current-induced dynamics 3. Experimental 3.1. General characteristics of MgO-based magnetic tunnel junctions 3.2. STNO samples 3.2.1. Samples by AIST (Tsukuba, Japan) 3.2.2. Samples by HZDR / SINGULUS (Dresden / Kahl am Main, Germany) 3.3. Magnetotransport measurements 3.3.1. Experimental setup and data analysis 3.3.2. Experimental results 3.4. Aspects to be explained 4 Numerical and analytical calculations 4.1 Out-of-plane steady-state precession in hybrid geometry STNO 4.1.1 Angular dependence of tunnel magnetoresistance as a mechanism of stable precession 4.1.2. Influence of the bias dependence of tunnel magnetoresistance 4.1.3. Comparison with the experimental data 4.1.4. Comparison with the GMR-type counterpart 4.1.5. Summary 4.2. Zero-field dynamics in hybrid geometry STNO stabilized by in-plane shape anisotropy 4.2.1. Effect of the in-plane shape anisotropy 4.2.2. Zero-field dynamics 4.2.3. Summary 5. Conclusions 6. Outlook Appendix Bibliograph

Polish Family and Fertility Survey: a user's guide

"This working paper is a result of the collaboration between researchers of the Sfb-project B6 'Household Dynamics and Social Inequalities - an International Comparison' and the Institute of Statistics and Demography, Warsaw School of Economics, Poland. This paper has several purposes. First, it should provide basic information on the goals of the PFFS survey and explain the data collection principles. Second, special attention will be given to the longitudinal nature of the PFFS and the methods that allow analyzing this type of data. Third, and most important, this User's Guide should provide help in practical research work with the PFFS. The reader will be introduced to the computer program TDA, designed by Götz Rohwer, which makes the use of a broad range of event history analysis techniques simple and convenient."Der polnische Fertilitäts- und Familiensurvey (PFFS) enthält retrospektive Longitudinaldaten über eine Anzahl von Prozessen im Lebenslauf der Individuen, der Familien und der Privathaushalte. Die national repräsentativen Daten enthalten weiterhin Angaben zur Bildung und Erziehung, dem Beschäftigungsstatus, der Migration, der Partnerschaftswahl, dem Wandel von Familienstrukturen und der Zusammensetzung der Haushalte. Die Erhebung ist in Umfang und der Qualität dem Sozioökonomischen Panel der Bundesrepublik Deutschland vergleichbar. Das Arbeitspapier liefert zunächst einige Grundinformationen zu den Zielen, zum Aufbau und zu den Prinzipien der Datenerhebung und -aufbereitung. Der primäre Zweck ist es, den Nutzern für Sekundäranalysen dieses Datenpools die entsprechenden institutionellen und technischen Hinweise zu liefern. (pre

Małoletni więźniowie obozów specjalnych NKWD (1939–1940)

Pomimo bogatej literatury, opracowań naukowych i publikacji źródłowych zbrodnia katyńska to wciąż zagadnienie, które kryje w sobie wiele niepodjętych przez badaczy aspektów. Jednym z nich jest los małoletnich więźniów trzech obozów specjalnych NKWD: w Starobielsku, Kozielsku i Ostaszkowie. W artykule spróbowano znaleźć odpowiedzi na podstawowe w tej kwestii pytania: kim byli chłopcy przebywający w tych obozach, dlaczego się w nich znaleźli, jak liczna to była grupa, jaki los ich spotkał. Despite the rich literature, scientific studies and source publications, the Katyn Massacre is still an issue that hides many aspects not taken up by researchers. One of them is the fate of juvenile prisoners of three NKVD special camps: at Starobilsk, Kozelsk and Ostashkov. The article tries to answer to the basic questions in this matter: who were the boys staying in these camps, why were they in, how large was the group, and what happened to them?Pomimo bogatej literatury, opracowań naukowych i publikacji źródłowych zbrodnia katyńska to wciąż zagadnienie, które kryje w sobie wiele niepodjętych przez badaczy aspektów. Jednym z nich jest los małoletnich więźniów trzech obozów specjalnych NKWD: w Starobielsku, Kozielsku i Ostaszkowie. W artykule spróbowano znaleźć odpowiedzi na podstawowe w tej kwestii pytania: kim byli chłopcy przebywający w tych obozach, dlaczego się w nich znaleźli, jak liczna to była grupa, jaki los ich spotkał. Despite the rich literature, scientific studies and source publications, the Katyn Massacre is still an issue that hides many aspects not taken up by researchers. One of them is the fate of juvenile prisoners of three NKVD special camps: at Starobilsk, Kozelsk and Ostashkov. The article tries to answer to the basic questions in this matter: who were the boys staying in these camps, why were they in, how large was the group, and what happened to them

A Successful Pyloromyotomy In A Child With COVID-19 Infection

Infantile Hypertrophic Pyloric Stenosis (IHPS) is the most common cause of gastric outlet obstruction in children, usually manifesting between 2 and 6 weeks of age by non-bilious vomiting. Although the COVID-19 pandemic has dominated the world since the beginning of 2020 causing the restructuring of healthcare delivery, patients still require high-quality medical care concerning other diseases. We report a 6-week infant with confirmed COVID-19 infection, who developed mild symptoms after a successful pyloromyotomy. Our aim is to encourage other professionals not to delay the necessary treatment in asymptomatic COVID-19 patients, considering the proper use of personal protective equipment, as it may worsen the course of the underlying disease

The study of phenylboronic acid optical properties towards creation of a glucose sensor

The article presents influence of pH and glucose concentration on phenylboronic acid (PBA) fluorescence studied by steady-state and time-resolved measurements. Fluorescence of PBA decreases with growing pH. These changes reflected acid-base equilibrium of PBA and allowed to estimate value of pKd as 9.2, which is comparable with literature data. Fluorescence intensity of phenylboronic acid is quenched in presence of glucose. The effect of quenching is more pronounced with increasing pH. At pH 7 quenching can be described by Stern-Volmer equation, at pH 8 and 9 by modified one. The obtained quenching constants are growing with pH increase. The quenching of phenylboronic acid fluorescence by glucose is a static one, which is confirmed by time-resolved measurements. Two lifetimes were found for fluorescence decay of phenylboronic acid. The lifetimes are practically independent on pH and glucose concentration and also fraction of both lifetimes are nearly the same. The obtained Stern-Volmer constants can be interpreted as apparent equilibrium constants of ester formation between acid and glucose

Pomoc Jointu i Agro-Jointu dla ludności żydowskiej na obszarze Białorusi radzieckiej

The Soviet state that emerged after 1917 became the heir of the Russian Empire and its geopolitical situation, which the Bolsheviks intended to preserve and consolidate in order for different communities to adopt one common Soviet system of values, norms and opinions. The resettlement of the Jewish community into rural areas was one of the aspects of the eth­nic integration policies. The operation, launched by the Central Committee of the RCP(b) in 1924, aimed to facilitate the formation of a peasant stratum in the Jewish society, which would transform its culture in a way to merge the Jews with the multinational population of the USSR. Considering the lack of state funds, the implementation of the top-down plan was made possi­ble by financial aid from external sources, the American organisation Agro-Joint in particular.Powstałe po 1917 r. państwo radzieckie stało się spadkobiercą imperium carskiego, którego przestrzeń geopolityczną bolszewicy zamierzali utrzymać. Zespolić tak, by poszczególne społeczności przyjęły jeden, wspólny, radziecki system wartości, norm i ocen. Fragmentem inte­gracyjnej polityki narodowościowej była rolnicza akcja osiedleńcza ludności żydowskiej. Postano­wiona przez Komitet Centralny RKP w 1924 r. akcja kolonizacyjna miała sprzyjać uformowaniu się w tej społeczności warstwy chłopskiej, a więc transformacji jej kultury w kierunku zespolenia z wielonarodowym społeczeństwem radzieckim. W związku z brakiem państwowych środków pieniężnych, wykonanie odgórnie ustalonych planów stało się możliwe dzięki pomocy finanso­wej pochodzącej z zewnątrz, zwłaszcza od amerykańskiej organizacji Agro-Joint

Estymacja przedziałowa, jako wymiar wartości niematerialnej

Written by the author, the system of creating values equally includes individual and integrated chains of values of individual links, which on the one hand have to be flexible and respond quickly to changes in demand, and at the same time create a value on both the local markets, as well as globally. This paper analyzes the impact of behaviour patterns of links with the value and quality created in the network of cooperating links. With its issues the paper touches upon the aspects of quality management on macro-scale and interprets the phenomena of quality influence on the added value in the network. The research novelty here is the constitution of the quality criterion as intangible and subjected values. Written by the author, while determining ways to solve a problem you need to define the problem, identify the need for changeas well as its solution, defining alternatives. The paper touches upon the problems of identifying the function of an object, selecting its sets and cancelling such characteristics - so as to categorize properly the scope of a decision. The novelty of the analysis is selecting the estimated value and its impact on the extent of target optimization within the sensitivity areaAutorka pracy podjęła się próby zdefiniowania przestrzeni decyzji w oparciu o rozkład nieparametryczny. Kwantyfikacja nieparametryczna i identyfikacja funkcji celu stanowi kanwę wywodów polemizujących. Celem pracy jest zdefiniowanie pola szacowań i określenie sposobów tworzenia struktur klasterowych w oparciu o założone funkcje celu. Artykuł ma charakter konceptualny i poglądowy, łączy filozofię i elementy matematyki intuicjonistycznej, które stają się obszarem, myślą, a może metodyką zarządzania logistyczneg