... Figure 4.21 shows the magnetic hysteresis loop of CoFe2-xZnxO4 powders at room temperature, with a maximum applied field of up to 8 kOe. The saturated magnetization, remanence and coercivity are summarized in Table 4.10. Also, Figure 4.22 presented variations of saturated magnetization and coercivities for CoFe2-xZnxO4 powders as a function of compositions calcined at 900 ºC for 48 h. The magnetization value of doped samples increased sharply with the external magnetic field strength at the low field region. The highest saturated magnetization can be obtained in x = 0.1 Zn doped cobalt ferrites. Increasing in saturated magnetization can be attributed to influence of the cationic stoichiometry and its occupancy in specific sites. The magnetic order in the cubic system of ferromagnetic spinels was due to occurrence of the super-exchange interaction mechanism between metal ions in the tetrahedral A-site and octahedral B-site [20]. When the nonmagnetic zinc ion was substituted by the cobalt ferrite lattice, due to the zinc ferrite being a normal spinel, it had a stronger preference for the tetrahedral site and thus reduced the amount of Fe3+ in the A site. The net result, due to antiferromagnetic coupling, was an increase in magnetic moment on the B lattice and an increase in saturated magnetization. However, at high levels of zinc substitution in x > 0.1, the A-site magnetic ion becomes so diluted that coupling between the two lattices was lost, and the saturated magnetization drops...
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...Nevertheless, the specific saturation magnetization is reduced due to a dead magnetic layer at the surface of the particles [3] if the temperature and the time of annealing are decreased. In the case of strontium ferrites, the influence of a strontium excess on the crystallografic structure is the same. The lattice occupation is not perturbed if an excess of strontium according to n = 5.25 is used. For a larger amount of strontium in the starting xerogel, the intermediate phase SrFe03., can be separated by etching with HC1. Nevertheless, in the range n = 5.25 6.0, the influence of the surplus on the static magnetic properties is typically different compared to intrinsic barium hexaferrites. Here, the specific saturation magnetization of the powders annealed at 950°C for 5h does not depend on the ratio n, whereas HCM decreases from 480 kA/m for n = 6.0 to 400 kA/m in the case of n = 5.25. This decrease of the coercive field strength for n < 6.0 can be avoided by reducing the annealing temperature to 850°C. According to the irreversible part of the FMR-spectra in figure 2 (right) showing no shift of the high field resonance peak with decreasing annealing temperature, the effective anisotropy field strength of the samples is not influenced, whereas the transition from incoherent to coherent magnetization reversal, indicated by the height of the low field resonance peak, by reducing the annealing temperature is obvious. If the annealing time is decreased, the coercive...
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...Contact lenses General Purpose: To demonstrate how to put in contact lenses safely. Specific Purpose: At the end of my speech, the audience should be able to safely put in contacts. Central Statement: Knowing how to put your own contacts in safely. Introduction I. Original opening: Many people have eye problems from children to adults, but most wear glasses because they are unsure how to use contact lenses. II. Qualifying statement: I myself have visual problems when I was in the 4th grade I was teased a lot for having to wear glasses; so when I became old enough to buy my first pair of contacts I was ecstatic and needed to learn how to put them in on my own. III. Statement relating topic to audience: (same as Qualifying statement) IV. Preview statement: I have been wearing contacts for a little over 20 years and now I see that contacts are coming more into styles. Body I. Things you need before you get started. a. Contact lenses b. Clean hands II. How to put in contact lenses. c. Wash your hands with soap. d. Remove one contact from its case. e. Place the contact on the index finger you’re most comfortable with using. f. Gently pull your skin away from your eye. g. Move the contact towards your eye calmly and steadily. h. Gently place the contact on your eye. i. Let go of the skin around your eye. j. Blink slowly so as to not dislodge the contact. k. Repeat the process with...
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