Hard and soft ferrites pdf
File Name: hard and soft ferrites .zip
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E-mail: ccannas unica. E-mail: jana mag. Bi-magnetic core—shell spinel ferrite-based nanoparticles with different CoFe 2 O 4 core size, chemical nature of the shell MnFe 2 O 4 and spinel iron oxide , and shell thickness were prepared using an efficient solvothermal approach to exploit the magnetic coupling between a hard and a soft ferrimagnetic phase for magnetic heat induction.
The magnetic behavior, together with morphology, stoichiometry, cation distribution, and spin canting, were investigated to identify the key parameters affecting the heat release. General trends in the heating abilities, as a function of the core size, the nature and the thickness of the shell, were hypothesized based on this systematic fundamental study and confirmed by experiments conducted on the water-based ferrofluids.
The evaluation of magnetic parameters provides hypotheses of general trends in the heating abilities as a function of the core size, the nature and the thickness of the shell, that have been then compared with experimental heat abilities obtained from aqueous ferrofluids.
The particle size distribution was obtained by measuring in the automatic mode over particles through the software Pebbles and adopting a spherical shape. The dried samples were digested using HNO 3. The analyses were performed twice on different portions of the samples. The chemical formulas were calculated by assuming the absence of anion vacancies.
The temperature dependencies of magnetization in the zero field cooled ZFC and field cooled FC regimes were measured as follows: first, the sample was cooled down to 10 K in the zero external magnetic field.
Next, the field of 10 mT was applied, and the temperature dependence of magnetization was measured on heating. Afterward, the sample was cooled down in the applied field of 10 mT, and the temperature dependence of magnetization was measured again.
The magnetization isotherms were recorded up to 7 T at selected temperatures in both polarities of the applied magnetic field. All data were corrected according to the organic content. AC susceptibility measurements were recorded with the amplitude of 0. The sample holder was surrounded by polystyrene and hosted in a glass Dewar, equipped by an ethylene glycol thermostat, to ensure the proper thermal insulation. The SAR, i. The core—shell samples showed larger crystalline size with respect to the core and different cell parameter a , higher for Cox Mn and lower for Cox Fe Table 1.
The TEM bright-field images Fig. Concerning the cores, almost stoichiometric cobalt ferrite with a degree of inversion of approximately 0.
In particular, this ratio should theoretically be 1. These findings allowed the shell to be described as primarily composed of maghemite, even though magnetite is also present, especially for the larger core—shell samples CoB Fe and CoC Fe.
In light of these results, the magnetic properties can be discussed beyond any stoichiometric or structural variability. The samples were characterized by DC and AC magnetometry measurements. The rigid coupling between the two FiM phases in the core—shell systems was highlighted by i the presence of a single-stage hysteresis loop at 10 K Fig. Due to the low thickness of the soft shell, the two phases are expected to be rigidly coupled and reverse at the same nucleation field, H n which, as a first approximation is assumed to correspond to the anisotropy field H K , listed in Table 2 , 61 which depends on the anisotropy constant, saturation magnetization, and volume fraction of the soft and hard phases.
At 10 K Fig. Anisotropy field H K is around 4 T for cobalt ferrite samples and in the range of 1. On the contrary, magnetization isotherms at K Fig. This is apparently in contrast with the results reported in the literature for similar systems prepared thought a different synthesis strategy, 33 where higher saturation magnetization values were found for manganese ferrite shells than iron-oxide ones.
Such a discrepancy could be related to differences in the formation mechanism of the nanoparticles, strictly dependent on the synthesis method, which may influence stoichiometry of the constituents, oxidation state of the metal s , degree of inversion, spin canting phenomena, and as a consequence the magnetic properties.
The experimental hyperthermic data collected on these three different core—shell series revealed some general aspects:. These results are totally consistent with the previous hypothesis based on the size and magnetic parameters of powdered samples. Nevertheless, to get close to the experimental conditions in which the heating abilities were evaluated, a set of AC magnetic measurements was carried out on the hydrophilic ferrofluids of the CoB series Fig.
Indeed, when the solution melts, Brownian motions may occur and also the interparticle interactions may change. Moreover, the T AC max values of the ferrofluids result to be shifted towards higher temperatures with respect to those of the powdered samples. Both the T max shift and the enhancement in the flatness of the FC curve are hints of stronger interparticle interactions, which are independent of the ferrofluid's concentration Fig.
Dipolar interactions most likely occur and cause the formation of secondary entities, whose size number of primary NPs and shape random or controlled clustering such as chain-like alignment affect the resulting magnetic behaviour and heating ability under an applied static or dynamic magnetic field. In the literature, specific studies on the effect on the heating abilities of the interparticle interactions for spinel ferrite-based core—shell nanoparticles are not available, probably due to the complexity of the systems in which many parameters may affect the magnetic and hyperthermic properties.
Concerning single-phase systems, some experimental studies reported the enhancement or reduction of SAR as a function of the dipolar interactions, 66—72 but other authors 73 provided a general theoretical model able to explain the heating release behaviour of NPs in the blocked-state, based on their intrinsic magnetic properties anisotropy, magnetization and experimental conditions concentration and magnetic field amplitude.
In our case, no changes occur in the strength of dipolar interactions, in the dispersions, in the concentration range 0. Moreover, also SAR values are independent of interparticle interactions, as reported in Fig. Unfortunately, besides this concentration and capping agent independences, it is not possible to speculate on the differences of magnetic properties between powder and colloidal dispersion, the mechanism of formation of secondary entities, and their role in the magnetic properties and in the heating efficiency.
Indeed, it has to be taken into account that ferrofluids are dynamic hybrid organic—inorganic systems in which the capping agents might be involved in different processes occurring in liquid phase and feature different physical properties e.
On the one hand, all the above findings seem to depict a more complex scenario behind the heating abilities of bi-magnetic core—shell systems than simple relationships with single magnetic or microstructural parameter s. The heating abilities of the aqueous colloidal dispersions of all samples were tested under mild experimental conditions. For all sets of samples, spinel iron oxide shells featured higher heat release than those of manganese ferrite ones.
Moreover, for the first time for hard core-based core—shell NPs, it was observed that the thicker the soft shell, the better the performances.
The study thus demonstrated the importance of a sophisticated approach based on the synergy of chemical, structural, and magnetic probes down to a single-particle level. Finally, considering the biocompatibility of the iron oxides, this systematic fundamental study proved that a proper design of cobalt ferrite cores coated with a homogenous crystalline shell of spinel iron oxide in principle should lead to biocompatible heat mediators with a net improvement in the heating abilities in comparison with the corresponding cores.
Received 18th February , Accepted 5th May CoA 8. Cobalt is represented in blue, manganese in green, iron in red. See DOI:
Applications of Hard and Soft Ferrites
Yogoro Kato and Dr. Takeshi Takei. Toroid information for the types between TC6. After reporting this twice I got NO reaction at all. Finally the download is offline now! Above link is to my own backup copy. As one extracted page it can also be found here.
Ferrite , a ceramic-like material with magnetic properties that are useful in many types of electronic devices. Ferrites are hard, brittle, iron-containing, and generally gray or black and are polycrystalline— i. They are composed of iron oxide and one or more other metals in chemical combination. A ferrite is formed by the reaction of ferric oxide iron oxide or rust with any of a number of other metals, including magnesium, aluminum, barium, manganese , copper, nickel , cobalt, or even iron itself. A ferrite is usually described by the formula M Fe x O y , where M represents any metal that forms divalent bonds, such as any of the elements mentioned earlier.
E-mail: ccannas unica. E-mail: jana mag. Bi-magnetic core—shell spinel ferrite-based nanoparticles with different CoFe 2 O 4 core size, chemical nature of the shell MnFe 2 O 4 and spinel iron oxide , and shell thickness were prepared using an efficient solvothermal approach to exploit the magnetic coupling between a hard and a soft ferrimagnetic phase for magnetic heat induction. The magnetic behavior, together with morphology, stoichiometry, cation distribution, and spin canting, were investigated to identify the key parameters affecting the heat release. General trends in the heating abilities, as a function of the core size, the nature and the thickness of the shell, were hypothesized based on this systematic fundamental study and confirmed by experiments conducted on the water-based ferrofluids. The evaluation of magnetic parameters provides hypotheses of general trends in the heating abilities as a function of the core size, the nature and the thickness of the shell, that have been then compared with experimental heat abilities obtained from aqueous ferrofluids.
Associate Editor: S. Claridge Beilstein J. Recent advances in the field of magnetic materials emphasize that the development of new and useful magnetic nanoparticles NPs requires an accurate and fundamental understanding of their collective magnetic behavior. Studies show that the magnetic properties are strongly affected by the magnetic anisotropy of NPs and by interparticle interactions that are the result of the collective magnetic behavior of NPs. Here we study these effects in more detail.
The ferromagnetic materials can be categorized into two; one is soft magnetic materials and the other is hard magnetic materials.
Types of Magnetic Material
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