Magnetic Losses in Soft Ferrites

We review the basic phenomenology of magnetic losses from DC to 1 GHz in commercial and laboratory-prepared soft ferrites considering recent concepts regarding their physical interpretation. This is based, on the one hand, on the identification of the contributions to the magnetization process provided by spin rotations and domain walls and, on the other hand, the concept of loss separation. It additionally contemplates a distinction between the involved microscopic dissipation mechanisms: spin damping and eddy currents. Selected experimental results on the broadband behavior of complex permeability and losses in Mn-Zn ferrites provide significant examples of their dependence on sintering methods, solute elements, and working temperature. We also highlight the peculiar frequency and temperature response of Ni-Zn ferrites, which can be heavily affected by magnetic aftereffects. The physical modeling of the losses brings to light the role of the magnetic anisotropy and the way its magnitude distribution, affected by the internal demagnetizing fields, acts upon the magnetization process and its dependence on temperature and frequency. It is shown that the effective anisotropy governs the interplay of domain wall and rotational processes and their distinctive dissipation mechanisms, whose contributions are recognized in terms of different loss components

Measuring and modeling broadband magnetic losses versus temperature and aging effects in CoO-doped Mn-Zn ferrites

We analyze the physical mechanisms associated with addition of CoO to sintered Mn-Zn ferrites and the ensuing stabilization versus temperature of their magnetic properties. We determine, in particular, the value and behavior of the magnetic anisotropy as a function of doping and temperature and we model in physical terms the evolution of the energy loss in the investigated frequency (DC - 1 GHz) and temperature (20 degrees C - +130 degrees C) ranges. We show that magnetic aging by long exposure of the CoO-doped ferrites at 200 degrees C is minimized by additional TiO2 doping. This is observed to restrain the increase of the extra-anisotropy induced by directional ordering of the Co2+ cations

Magnetic losses versus sintering treatment in Mn-Zn ferrites

partially_open5sìpartially_openBeatrice, Cinzia; Tsakaloudi, Vasiliki; Dobák, Samuel; Zaspalis, Vassilios; Fiorillo, FaustoBeatrice, Cinzia; Tsakaloudi, Vasiliki; Dobák, Samuel; Zaspalis, Vassilios; Fiorillo, Faust

The temperature dependence of magnetic losses in CoO-doped Mn-Zn ferrites

CoO-doping is known to stabilize the temperature dependence of initial permeability and magnetic losses in Mn-Zn ferrites, besides providing, with appropriate dopant contents, good soft magnetic response at and around room temperature. These effects, thought to derive from the mechanism of anisotropy compensation, are, however, poorly assessed from a quantitative viewpoint. In this work, we overcome such limitations by providing, besides extensive experimental investigation vs frequency (DC–1GHz), CoO content (0 ≤ CoO ≤ 6000 ppm), and temperature (−20 °C ≤ T ≤ 130 °C) of permeability and losses of sintered Mn-Zn ferrites, a comprehensive theoretical framework. This relies on the separate identification of domain wall motion and moment rotations and on a generalized approach to magnetic loss decomposition. The average effective anisotropy constant ⟨Keff⟩ is obtained and found to monotonically decrease with temperature, depending on the CoO content. The quasistatic energy loss Wh is then predicted to pass through a deep minimum for CoO = 3000–4000 ppm at and below the room temperature, while becoming weakly dependent on CoO under increas- ing T. The rotational loss Wrot(f) is calculated via the complex permeability, as obtained from the Landau-Lifshitz equation for distributed values of the local effective anisotropy field Hk,eff (i.e., ferromagnetic resonance frequency). Finally, the excess loss Wexc(f) is derived and found to comply with suitable analytical formulation. It is concluded that, by achieving, via the rotational permeability, value and behavior of the magnetic anisotropy constant, we can predict the ensuing properties of hysteresis, excess, and rotational losses

Magnetic loss, permeability, and anisotropy compensation in CoO-doped Mn-Zn ferrites

Mn-Zn ferrite samples prepared by conventional solid state reaction method and sintering at 1325 °C were Co-enriched by addition of CoO up to 6000 ppm and characterized versus frequency (DC – 1GHz), peak polarization (2 mT – 200 mT), and temperature (23 °C – 120 °C). The magnetic losses at room temperature are observed to pass through a deep minimum value around 4000 ppm CoO at all polarizations values. This trend is smoothed out either by approaching the MHz range or by increasing the temperature. Conversely, the initial permeability attains its maximum value around the same CoO content, while showing moderate monotonical decrease with increasing CoO at the typical working temperatures of 80 – 100 °C. The energy losses, measured by a combination of fluxmetric and transmission line methods, are affected by the eddy currents, on the conventional 5 mm thick ring samples, only beyond a few MHz. Their assessment relies on the separation of rotational and domain wall processes, which can be done by analysis of the complex permeability and its frequency behavior. This permits one, in particular, to calculate the magnetic anisotropy and its dependence on CoO content and temperature and bring to light its decomposition into the host lattice and Co2+ temperature dependent contributions. The temperature and doping dependence of initial permeability and magnetic losses can in this way be qualitatively justified, without invoking the passage through zero value of the effective anisotropy constant upon doping

Effect of microwave sintering on microstructure and mechanical properties in Y-TZP materials used for dental applications

The aim of this work is to study the application of microwave sintering to consolidate yttria-stabilized zirconia polycrystalline (Y-TZP) ceramics commonly applied in dentistry, so as to obtain highly dense materials and fine microstructure with shorter sintering cycles. Three Y-TZP materials are considered: two commercially available for dental applications and one laboratory studied powder. Microwave sintering was carried out at 1200 and 1300 degrees C for 10 min and conventional sintering at 1300 and 1400 degrees C for 2 h. Relative density, Vickers hardness and fracture toughness values for sintered samples were determined. Microwave sintering results, generally, in improved mechanical properties of the materials in terms of hardness and fracture toughness compared to conventional sintering and, in some cases, at lower sintering temperatures. A finer grain microstructure (final grain size < 250 min) was obtained with microwave sintering for both commercial materials. Fracture toughness values differ significantly between sintering techniques and chosen parameters. These results suggest that microwave heating can be employed to sinter Y-TZP commercial ceramics for dental applications obtaining improving the mechanical properties of the materials with a very important time and energy consumption reduction. Crown Copyright (C) 2015 Published by Elsevier Ltd and Techna Group S.r.l. All rights reserved.The authors would like to thank the financial support received from Universidad Politecnica de Valencia under Project 5P20120677 and Ministerio de Economia y Competitividad (MINECO) and co-funded by ERDF (European Regional Development Funds) through the Project (IEC2012-37532-C02-01). A. Borrell acknowledges the Spanish Ministry of Science and Innovation for her Juan de la Cierva Contract (JCI-2011-10498) and the Generalitat Valenciana for the financial support under Project GV/2014/009. A. Presenda acknowledges the Generalitat Valenciana for his Santiago Grisolia program scholarship (GRISOLLV2013/035). The authors would also like to acknowledge Prof. Dr. M. F. Sold from the Faculty of Medicine and Odontology at the Universidad de Valencia for supplying the commercial materials.Presenda, Á.; Salvador Moya, MD.; Penaranda-Foix, FL.; Moreno, R.; Borrell Tomás, MA. (2015). Effect of microwave sintering on microstructure and mechanical properties in Y-TZP materials used for dental applications. Ceramics International. 41(5, Part B):7125-7132. https://doi.org/10.1016/j.ceramint.2015.02.025S71257132415, Part

Manganese-zinc ferrites and nickel-zinc ferrites: composition, process, microstructure, properties

On the basis of todays demand for the design and development of new magnetic MnZn and NiZn ferrite materials that satisfy the requirements of modern electronic and telecommunication applications, the present PhD thesis deals with the correlation between the several process parameters, the development of the polycrystalline microstructure and the electromagnetic behaviour of some MnZn and NiZn ferrite materials. The purpose of this research was the determination and understanding of the numerous phenomena that take place during the manufacturing of the above ferrite types and the combination of the mechanisms that are responsible for the required electromagnetic performance of the final materials with the chemical composition, the process parameters and the development of the polycrystalline microstructure during sintering. Through the completion of the above tasks, the design and manufacturing of high magnetic performing MnZn and NiZn ferrite materials that precisely meet the strict specifications of modern electronic and telecommunication applications was achieved. The role of the chemical composition of the raw materials, as well as the effect of dopant additions were studied for each of the selected ferrite types (MnZn and NiZn ferrites), under the prism of interaction between the above parameters and the conditions of the several process steps that determine their contribution to the development of the microstructure and magnetic performance. Regarding the chemical purity of the raw materials in the case of MnZn ferrites, the mechanism of the effect of the SiO2 impurity inherent presence in the Fe2O3 raw material was investigated, in relation to the magnetic quality of the sintered ferrite. The understanding of the phenomena that take place during the sintering process based on the study of grain growth kinetics, as well as the examination of the diffusion characteristics of SiO2 led to the tracking of the mechanisms that rule the effect of SiO2. The exploitation of the above findings enables the utilization of a low cost Fe2O3 raw material with high inherent SiO2 concentration, as the suggested adjustment of the manufacturing process enables the synthesis of final sintered MnZn ferrite products that are characterized by homogenous polycrystalline microstructure and satisfying magnetic performance. Regarding the effect of dopants in MnZn ferrites, the investigation of the mechanism through which the addition of TiO2 determines the magnetic properties and polycrystalline microstructure of MnZn ferrites and the detection of the process parameters that favour the controlled development of the polycrystalline microstructure led to the design of a new MnZn ferrite magnetic material which is ideal for high data transmission speed telecommunication applications, as it combines the absence of any chemical, structural and morphological imperfections with the demand for BH-loop linearity and significantly low signal distortion. The investigation of the mechanisms involved in the effect of CaO and Nb2O5 grain boundary dopants and CoO bulk dopant on the incremental magnetic permeability of the final MnZn ferrite, as well as the understanding of the role of process parameters on the magnetic behaviour of MnZn ferrites made possible the design of an adequate synthesis process that leads to the manufacturing of novel MnZn ferrite materials of high magnetic permeability for filter applications, which are characterized by high incremental permeability over a broad temperature range.Καθώς οι σύγχρονες εφαρμογές ηλεκτρονικής και τηλεπικοινωνιών καθιστούν αναγκαίο τον εξειδικευμένο σχεδιασμό και την ανάπτυξη νέων μαγνητικών υλικών φερριτών MnZn και NiZn, η παρούσα διδακτορική διατριβή περιλαμβάνει τη μελέτη των μηχανισμών που διέπουν τις σχέσεις αλληλεπίδρασης μεταξύ της χημικής σύστασης, των διεργασιακών παραμέτρων, της πολυκρυσταλλικής μικροδομής και της μαγνητικής συμπεριφοράς ορισμένων υλικών φερρίτη MnZn και NiZn. Σκοπός της μελέτης αυτής ήταν ο προσδιορισμός και η κατανόηση των φαινομένων που λαμβάνουν χώρα κατά την παρασκευή των παραπάνω τύπων φερρίτη, και τελικά ο εντοπισμός των μηχανισμών που είναι υπεύθυνοι για τη διαμόρφωση της επιθυμητής μαγνητικής απόδοσης των τελικών υλικών. Η επίτευξη των παραπάνω στόχων κατέστησε δυνατό το σχεδιασμό εναλλακτικών διεργασιών και την παρασκευή νέων μαγνητικών υλικών φερρίτη MnZn και NiZn υψηλής μαγνητικής απόδοσης που συναντούν τις αυστηρές προδιαγραφές των σύγχρονων ηλεκτρονικών και τηλεπικοινωνιακών εφαρμογών. Ο ρόλος της χημικής σύστασης των πρώτων υλών, καθώς επίσης και η επίδραση των προσμίξεων μελετήθηκαν για καθέναν από τους παραπάνω τύπους φερρίτη (φερρίτες MnZn και NiZn) υπό το πρίσμα της αλληλεπίδρασης των παραπάνω παραμέτρων με τις συνθήκες διεργασίας που καθορίζουν τη συνεισφορά των πρώτων στη διαμόρφωση της πολυκρυσταλλικής μικροδομής και της μαγνητικής συμπεριφοράς των τελικών υλικών. Αναφορικά με τη χημική σύσταση των πρώτων υλών στην περίπτωση των φερριτών MnZn, μελετήθηκε ο μηχανισμός της επίδρασης της εγγενούς παρουσίας του SiO2 στην πρώτη ύλη Fe2O3 με τη μορφή πρόσμιξης στη μαγνητική ποιότητα των τελικών υλικών. Η κατανόηση των φαινομένων που λαμβάνουν χώρα κατά την πυροσυσσωμάτωση διαμέσου της κινητικής μελέτης της ανάπτυξης των κόκκων και η διερεύνηση των χαρακτηριστικών διάχυσης του SiO2 στην πρώτη ύλη οδήγησαν στον εντοπισμό των μηχανισμών που είναι υπεύθυνοι για τη δράση του SiO2. Η αξιοποίηση των παραπάνω ευρημάτων δίνει τη δυνατότητα για τη χρήση χαμηλού κόστους πρώτων υλών Fe2O3 με υψηλή εγγενή περιεκτικότητα σε SiO2, καθώς η προτεινόμενη προσαρμογή της διεργασίας παρασκευής επιτρέπει την παρασκευή τελικών υλικών φερρίτη MnZn που χαρακτηρίζονται από ομοιόμορφη πολυκρυσταλλική μικροδομή και ικανοποιητική μαγνητική απόδοση. Σχετικά με την επίδραση των προσμίξεων στους φερρίτες MnZn, η μελέτη του μηχανισμού επίδρασης του TiO2 στη μαγνητική ποιότητα φερριτών MnZn και ο εντοπισμός των διεργασιακών παραμέτρων που ευνοούν την ελεγχόμενη ανάπτυξη της πολυκρυσταλλικής μικροδομής οδήγησαν στην ανάπτυξη νέου μαγνητικού υλικού φερρίτη MnZn για εφαρμογές ταχείας μεταφοράς δεδομένων σε δίκτυα τηλεπικοινωνιών, το οποίο χαρακτηρίζεται από ελάχιστες χημικές, δομικές και μορφολογικές ατέλειες και ικανοποιεί τις ανάγκες γραμμικότητας του βρόχου υστέρησης και τελικά ελάχιστης παραμόρφωσης σήματος στο μετασχηματιστή

MnZn-ferrites: Targeted Material Design for New Emerging Application Products

In this article the main characteristics for emerging MnZn-ferrite applications are described on the basis of the new demands they possess on the ferrite material development. A number of recently developed MnZn-ferrite materials is presented together with the main scientific principles lying behind their development. These include: (i) high saturation flux density MnZn-ferrites (i.e. Bsat=550 mT at 10 kHz, 1200 A/m, 100°C), (ii) low power losses MnZn-ferrites (i.e. Pv~210 mW cm-3 at 100 kHz, 200mT, 100°C), (iii) MnZn-ferrites with broad temperature stability (i.e. PV<375 mW cm-3 for 25°C<T<140°C at 100 kHz, 200 mT), and (iv) MnZn-ferrites with high and frequency stable permeability (i.e. μi~12600 at 10 kHz, 0.1 mT, 25°C and tan(δ)/μi=20.5×10-6 at 100 kHz). In a final discussion the importance of defect chemistry for the time stability and stress sensitivity of the magnetic properties is discussed and some important issues are addressed, encountered during the transfer of a laboratory developed material to a large scale industrial production process