Induced four fold anisotropy and bias in compensated NiFe/FeMn double layers

A vector spin model is used to show how frustrations within a multisublattice antiferromagnet such as FeMn can lead to four-fold magnetic anisotropies acting on an exchange coupled ferromagnetic film. Possibilities for the existence of exchange bias are examined and shown to exist for the case of weak chemical disorder at the interface in an otherwise perfect structure. A sensitive dependence on interlayer exchange is found for anisotropies acting on the ferromagnet through the exchange coupling, and we show that a wide range of anisotropies can appear even for a perfect crystalline structure with an ideally flat interface.Comment: 7 pages, 7 figure

Robust antiferromagnetic coupling in hard-soft bi-magnetic core/shell nanoparticles

The growing miniaturization demand of magnetic devices is fuelling the recent interest in bi-magnetic nanoparticles as ultimate small components. One of the main goals has been to reproduce practical magnetic properties observed so far in layered systems. In this context, although useful effects such as exchange bias or spring magnets have been demonstrated in core/shell nanoparticles, other interesting key properties for devices remain elusive. Here we show a robust antiferromagnetic (AFM) coupling in core/shell nanoparticles which, in turn, leads to the foremost elucidation of positive exchange bias in bi-magnetic hard-soft systems and the remarkable regulation of the resonance field and amplitude. The AFM coupling in iron oxide manganese oxide based, soft/hard and hard/soft, core/shell nanoparticles is demonstrated by magnetometry, ferromagnetic resonance and X-ray magnetic circular dichroism. Monte Carlo simulations prove the consistency of the AFM coupling. This unique coupling could give rise to more advanced applications of bi-magnetic core/shell nanoparticles

Magnetic multilayer interface anisotropy

Ni/Mo and Ni/V multilayer magnetic anisotropy has been investigated as a function of Ni layer thickness, frequency and temperature. Variable frequency ferromagnetic resonance (FMR) measurements show, for the first time, significant frequency dependence associated with the multilayer magnetic anisotropy. The thickness dependence allows one to extract the interface contribution from the total anisotropy. Temperature dependant FMR (9 GHz) and room temperature magnetization indicate that strain between Ni and the non-magnetic layers if contributing significantly to the source of the interface anisotropy and the state of the interfacial magnetization. In order to examine the interface properties of other transition metal multilayer systems, investigations on Fe/Cu are underway and CoCr/Ag is being proposed. ESR measurements have been reported on Gd substituted YBaCuO superconductors and a novel quasi-equilibrium method has been developed to determine quickly and precisely the transition temperature. During the next project the P.I. proposes to (1) extend the variable frequency FMR measurements to low temperature, where extremely large interface anisotropies are known to obtain in Ni/Mo and Ni/V and are proposed to exist in Ni/W; (2) obtain accurate dc anisotropies via a novel, variable temperature torque magnetometer currently under construction; (3) expand upon his initial findings in Fe/Cu multilayer investigations; (4) begin anisotropy investigations on Co/Ag and CoCr/Ag multilayers where the easy magnetization direction depends upon the Cr concentration; (4) make and characterize Bi based superconductors according to resistivity, thermal conductivity and thermoelectric power and construct YBaCuO based superconducting loop-gap'' resonators for use in his magnetic resonance work. 2 figs

Magnetic multilayer interface anisotropy

Učenje i poučavanje programiranja je teško. Poteškoće se pojavljuju kod svih uzrasta, a na fakultetima se odražavaju u obliku slabe prolaznosti. Studenti u kratkom vremenu moraju usvojiti apstraktne koncepte iz objektno orijentiranog programiranja (OOP) uz složenu sintaksu programskog jezika i okruženje. Zabrinjava činjenica da i nakon položenih početnih predmeta studenti i dalje imaju poteškoće. Obzirom na vremensko ograničenje potrebno je smanjiti irelevantno kognitivno opterećenje studenata. Jedan od načina je odabir početnog jezika s jednostavnijom sintaksom. Tijekom trogodišnjeg pilot istraživanja kod uvođenja vizualnih programskih jezika u visoko obrazovanje utvrđeno je da nema značajnog utjecaja na uspjeh u predmetima s tekstualnim jezicima, ali su određeni zahtjevi prema okviru za poučavanje objektno orijentiranog programiranja. Okvir OTTER temeljen na metodi didaktičkog skrivanja implementiran je u nastavi te su prikupljeni studentski projekti izrađeni pomoću OTTER-a tijekom pet godina. Postavljen je cilj istraživanja: utvrditi utjecaj primjene metode didaktičkog skrivanja pomoću okvira OTTER na usvajanje koncepata OOP-a. Razvijen je poseban alat za analizu projekata i izdvajanje objektno orijentiranih koncepata definiranih u radu. Faktorskom analizom izdvojeni su koncepti koji su vezani za grafičko korisničko sučelje i koncepti koji su isključivo vezani za OOP. Rezultati su pokazali da su studenti tijekom izrade projekata pomoću OTTER-a primjenjivali više koncepata OOP-a u odnosi na one koji nisu koristili okvir. Analiza podataka pomoću strukturalnog modeliranja je potvrdila rezultate te omogućila dodatno pojašnjenje odnosa među varijablama. Dokazana je opravdanost poučavanja OOP-a kod početnika u visokom obrazovanju primjenom metode didaktičkog skrivanja. Okvir omogućuje brži prijelaz iz početne faze usvajanja sintakse do izrade projekata.Learning and teaching programming is difficult. Difficulties are present with students of different ages, and evident at the universities through poor pass rate. Students have to acquire abstract concepts of object-oriented programming with complex syntax and environment. We are concerned with the fact that students seem to have the same problems even after they pass introductory programming courses. Based on time constraints, it is important to reduce irrelevant cognitive load. One way to tackle it is through the use of simple introductory languages. During a three-year pilot study in introducing visual programming languages in higher education, we found there was no significant influence on students' achievement in textual programming language courses. However, we have determined the requirements for the framework used in teaching object-oriented programming. OTTER framework is based on didactic reduction and implemented in teaching. We have collected students' projects for five years. The main goal of the research was set: determine the influence of didactic reduction using OTTER on acquiring OOP concepts. An analysis tool used to detect object-oriented concepts defined in this paper was developed for the research. Factor analysis separated concepts based on the graphical user interface and OOP. Results showed that students who used OTTER also applied more OOP concepts than students who didn't use the framework. Structured equation modeling confirmed results and enabled a better understanding of relationships among variables. Appropriateness of teaching OOP to higher education novice programmers using didactic reduction was proved. The framework enables faster transfer from the initial syntax learning stage to project development

Regulação da embriogênese semática in vitro com ênfase do papel de hormonios endógenos

Different aspects of the in vitro somatic embryogenesis regulation are reviewed in this paper.work. A description of g General aspects, such as terminology, uses, stages of development and factors associated with the somatic embryogenesis, are described. is carried out. Although a brief description ofn the effects of the addition of different plant growth regulators to the culture medium wasis given, the article is centereds itself on the effect that the endogenous hormone concentrations in the initial explants and in the tissue cultures derived from them could play oin the induction and expression of somatic embryogenesis. It is significant that few to emphasize the low amount of systematic studies have been conducted, in this subject, in which different species and hormone groups were compared in cultures with and without embryogenic capacity. Moreover, the lack of correlation between the results presented in different studies the distinct works indicates that the hormone content of the cultures is not the only factor involved.Neste trabalho se faz uma revisão de diversos aspectos da regulação da embriogêneses somático in vitro. Vários aspectos gerais a este fenômeno tem sido discutidos, tais como a definição de terminologia, descrição de eventuais aplicações, seus estados de desenvolvimento e outros fatores associados com sua indução e expressão. Embora se faça uma breve descrição do efeito da adição de diferentes reguladores de crescimento ao meio de cultivo, o artigo está centrado no efeito que as concentrações hormonais endogênas nos explantes iniciais e nos cultivos in vitro derivados deles podem ter na indução e expressão da embriogênese somática. Tem de se fazer ênfase na pouca quantidade de estudos sistemáticos realizados neste tema que comparem em várias espécies e diferentes grupos hormonais em cultivos com e sem competência embriogênica. Finalmente, indica-se que a falta de correlação entre os resultados destes poucos trabalhos parece indicar que os conteúdos hormonais endôgenos não são os únicos fatores envolvidos neste fenômeno.Grman Academic Exchange Service//DAAD/AlemaniaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Agroalimentarias::Centro para Investigaciones en Granos y Semillas (CIGRAS