This work addresses the effect of substituting Mn\(^{3+}\) by Fe\(^{3+}\) at the octahedral site of TbMnO\(_3\) on the magnetic phase sequence, ferroelectric and magnetoelectric properties, keeping ...the Fe\(^{3+}\) concentration below 5%. The temperature dependence of the specific heat, dielectric permittivity and electric polarization was studied as a function of Fe\(^{3+}\) concentration and applied magnetic field. From the experimental results a strong decrease of the electric polarization with increasing Fe\(^{3+}\) substitution is observed, vanishing above a concentration of 4%. However, within this range, a significant increase of the magnetic sensitivity of the electric polarization is obtained by increasing Fe\(^{3+}\) concentration. Above that value, a non-polar, weak ferromagnetic phase emerges, in good agreement with the predictions of the Dzyalowshinskii-Moriya model. This behavior reveals the crucial effect of Fe\(^{3+}\) substitution in octahedral sites on the magnetic phase sequence, polar and magnetoelectric behavior of the TbMn\(_{1-x}\)Fe\(_x\)O\(_3\) system. From the results obtained in this work, it is understood that this behavior is not associated with the eg electronic configuration, but instead to the competition between ferromagnetic and antiferromagnetic interactions, which is very sensitive to both local fields and distortions.
Eu1-xYxMnO3 exhibits, unlike other magnetoelectric systems, very distinctive features. Its magnetoelectric properties is driven by the magnetic spin of the Mn3+ ion, but they can be drastically ...changed by varying the content of Y3+, which it does not carry any magnetic moment. Though the x = 0.40 composition has been studied extensively, some basic questions still remain to be thoroughly understood. Thus, this work is aimed at studying some of its polar properties and their magnetic field dependence as well. The experimental results here reported have shown that this material is very easily polarisable under external electric fields, and so, whenever the polarization is obtained from time integration of the displacement currents, an induced polarization is superposed to the spontaneous one, eventually masking the occurrence of ferroelectricity. We have found clear evidence for the influence of a magnetic field in the polar properties of Eu0.6Y0.4MnO3. The study of electric polarization of Eu0.6Y0.4MnO3 under an external magnetic field yields a value with the same order of magnitude of the remanent polarization determined from polarization reversal experiments. The comparison of the magnetic induced changes on the polarization obtained in polycrystalline samples and single crystals confirms the threshold magnetic field value for the polarization rotation from the a- to the c-direction, and evidencing the importance of the granular nature of the samples in the polar response to magnetic field.
We present the magnetic phase diagram of TbMn1-xFexO3 substitutional solid solution in the whole concentration range 0 <= x <= 1 as determined from magnetization and specific heat measurements. We ...have found that the dominant magnetic ion in the concentration range 0 <= x < 0.3 is manganese, while iron ions do not create independent magnetic structure, but strongly affect magnetic properties of the parent compound by reducing transition to magnetically ordered state and transition into a cycloidal phase. The magnetism in the concentration range 0.3 < x <= 1 is driven by the Fe sublattice. The manganese ions again do not order in long range magnetic ordered state, but stabilize four different magnetic structures of Fe sublattice above 2 K. The magnetic ordering of Tb sublattice was observed only on parent compounds TbMnO3 and TbFeO3 and for doping level below 0.1, or over 0.9.
In this work we present a detailed study of the structural and lattice dynamic properties of Y-doped EuMnO3 ceramics (Eu1-xYxMnO3, with 0<x<0.55). A thorough analysis towards the correlation between ...both structural and Raman modes parameters has been undertaken. Our results provide evidence for two main structural distortions of MnO6 octahedra, arising from a cooperative Jahn-Teller and rotational distortions in these compounds. The temperature dependence of the B1g symmetric stretching mode of the MnO6 units has revealed either a positive or negative shift regarding the pure anharmonic temperature dependence of the phonon frequency, which strongly depends on the Y-concentration. This frequency renormalization is explained in terms of a competition between ferro and antiferromagnetic interactions. The pronounced frequency renormalization of the symmetric stretching mode for x=0.2 evidences the predominance of the ferromagnetic interactions against the antiferromagnetic ones, which is in good correlation with the spontaneous magnetization measured in this compound. The emerging of the shifts referred well above the Neel temperature is likely associated with the coupling between phonons and dynamical fluctuations of the magnetic system, which provides further grounds for the existence of strong spin-phonon coupling in this compound.
During a period of twelve years--January 1983 to December 1994, 371 children suspected of foreign body inhalation were admitted in Hospital Pediatric of Coimbra. The diagnosis was confirmed in 200 of ...them (54%), and this group was analysed. The incidence has increased until 1989 and stabilized in the last 5 years with a median of 18 cases/year. Two third of the children were boys and 84% were under three years old. A history of choking was obtained in 87% of the patients but only 39% of the cases had an early diagnosis (within 24 hours). The most frequent clinical findings were abnormal auscultation, sternal retraction, cough, wheezing and fever. Sixty percent of them were asymptomatic. The chest radiology findings were air trapping in 45%, consolidation in 21% and in 17% there were no abnormalities. Radiopaque foreign bodies were found in 9%. Organic bodies were the most frequent (74%) and among these, peanuts, lupines and beans. Food aspiration in one case took to cardiorespiratory arrest and in another with a late diagnosis bronchial stenosis needed a surgical treatment. Complications of foreign bodies extraction had no consequences.
Hemangioma of urinary tract are unusual, being about 2% of all hemangiomas. We present a case of a glans penis hemangioma. There is controversy concerning their treatment and outcome. Our patient was ...treated with a Neodymium: Yag laser irradiation, with complete morphological recuperation.
Within the context of an AUTC funded Project: Information and Communication Technologies and Their Role in Flexible Learning, this paper presents an analysis of learning designs using ICTs and how ...this grounded approach might be a more useful structure to design effective learning environments. The project has developed generic or reusable frameworks for technology-enhanced high quality learning experiences in higher education and this paper will present several examples, of the original design and how the key elements were selected and developed for use by others. As this project is currently developing these generic exemplars of learning designs, the final presentation will demonstrate how the designs might be reengineered to become useful templates for other instructors and other knowledge domains.
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