Anomalous Resonance Absorption in Cobalt Ferrite and Co-Zn Binary Ferrites

Microwave resonance absorption in Co-ferrite and Co-Zn binary ferrites at 3.22cm wave-length were observed at high temperature and from room temperature to -195℃, respectively. Resonance absorption in Co-ferrite could not be detected at the temperature below 40℃, because of a large anisotropic energy in Co-ferrite. Such phenomena had not been found in other ferrites, so the resonance experiment was undertaken at high temperatures ranging from 40° to Curie point. In Co-Zn binary ferrites, the absorption disappeared below the temperature of -90℃ and -140℃ in 4CoOZnO5Fe_2O_3 and 3CoO2ZnO5Fe_2O_3, respectively, but the absorption in CoO4ZnO5Fe_2O_3 could be observed down to -186℃. The resonance fields corresponding to the maximum absorption were observed as a function of the temperature. In the case of Co-ferrite, the resonance field corresponding to the maximum absorption gradually decreased with increasing temperature up to ca. 250℃ and then rapidly increased to the Curie point. On the other hand, the absorption amount at first increased linearly with increasing temperature, afterwards passed through a maximum and then decreased rapidly up to the Curie point. The half line widths and g-factor were also obtained as functions of temperature up to the Curie point ; the half line width monotonously decreased with increase of temperature up to the Curie temperature, at which the absorption disappeared. The g-factor increased with the rise of temperature, afterwards passed through broad maximum and then decreased rapidly to the Curie point ; the value of the reonance field just about at the Curie point was found to be within 3300±100 Oe, for which g-factor was determined to be 2.02±0.06 by using the paramagnetic resonance condition

Research on the Specific Heat and the Hall Effect of Magnetite

In the present paper, the specific heats and the Hall effects of the artificial and the natural magnetite have been measured at various low temperatures by means of Sykes\u27 method. The specific heats on various heat treated magnetites were measured and it has been confirmed experimentally that the peak appearing on the curves of specific heat versus temperature changes by the heat treatment, if the specimen is heated above 1000°. From the measurement of Hall effect, it has been found that the electric current in magnetite is contributed to only the conduction electron on impurity level ; furthermore, the curve of the Hall constant against temperature has knick points at the transformation temperature at which the intensity of magnetization abruptly decreases

Research on the Ferromagnetic Property and Electrical Conductivity of Magnetite

In succession with the former paper, magnetic moment, electric conductivity and magneto-resistance of natural and artificial magnetites have been measured before and after the transformation. It has been found that the amount of the change in magnetic moment of artificial magnetite at the transformation in the magnetic field strength of 828 orsted varies according to the heat treatments and that the activation energies of both magnetites have been determined

Ferromagnetic Resonance in Various Ferrites at Low and High Temperatures

Ferromagnetic resonances in manganese, copper, and magnesium ferrites and nickel-zinc binary ferrites were tried at low and high temperatures at the frequency of 9310 MC ; in the temperature range of magnetic transition for manganese ferrite, double peaks were observed ; with lowering of the temperature, a small peak at low field overlapped the ordinary large peak showing an asymmetrical resonance curve which tended to be symmetrical at the lowest temperature. g-factors and the half line widths were determined up to the Curie temperatures. In general, the line width of simple ferrites decreases monotonously to the Curie temperature, but those of binary ferrites containing zinc ferrite first decreases rapidly with rising temperature from the liquid nitrogen temperature and then increases near the Curie temperature ; especially, it is most interesting to notice that the curve of line width versus temperature for high zinc ferrite in Zinc-Nickel ferrites shows minimum and maximum, the behaviour seems to correspond to a type predicted by Neel, which appears in the diagram for saturation magnetization versus temperature. Moreover, we could determined g-factor of various Ni-Zn binary ferrites just at Curie point, by using paramagnetic resonance condition ; the value of g-factor monotonously decreases with increasing content of zinc ferrite. The fact is quite in contradistinction to the change of g-value with varying zinc content in Zn-Ni ferrites at room and low temperatures. The size effect reported by Beljers and Polder could not be observed for nickel ferrite and Ni-Zn binary ferrite at the frequency of 9310 Mc/sec., but recently it was observed at 23, 500 Mc/sec. at room and low temperature on several ferrites

The Zeeman Effect in Ammonia Microwave Spectra

The microwave Zeeman effect of N^H_3 inversion spectra was investigated at strong magnetic field to observe molecular g-factor in the decoupled state of spin-rotation interaction. The result on J, K = 1, 1 line shows the transition from Zeeman effect to Paschen-Back effect near 10, 000 oersteds. The obtained molecular g-factors for several different JK value give some information on g-factor of N^H_3 both parallel and perpendicular to the molecular axis

On the Formation of Semiconductor of Spinel Type

The property of the ferromagnetic semiconductor often varies according to the process of its formation. In the present paper, the outline of and some precaution for the preparation of NiO Fe_2O_3 and Fe_3O_4 are mentioned, their properties being observed by means of the magnetic measurement. Furthermore the best procedure for obtaining the synthetic magnetite by wet method is described, thereby stressing to avoid the employment of NH_4OH as OH^-

Ferromagnetic Resonance in the Single Crystals of some Ferrites. I

The ferromagnetic resonance absorptions in the single crystals of Mn-Zn ferrite were studied at the wavelength of 3.22 cm and Co-Zn ferrite at 3.22 and 1.27 cm at the temperatures from -195℃ to the Curie-point and the resonance phenomena in the polycrystalline specimens having the same composition were also studied. The magnetic transition through which the first-order magnetocrystalline anisotropy constant K_1 changes its sign were found respectively, at ca. -100℃ and +70℃ for both ferrites and near these temperature two resonance peaks appeared on the resonance curves of polycrystalline specimens. The half line widths were found to depend on the crystallographic directions ; its temperature dependence was also observed. g-factors and K_1 of Co-Zn ferrite were observed as functions of temperature. For Co-Zn ferrite, the temperature dependence of the line width showed a complicated behaviour at first by a rough measurement, but it was found to be monotonous by a further precise investigation. g-value and the order of K_1 of Mn-Zn single crystal at the room temperature agreed with the results of Galt and co-workers, but the large descrepancies between our results and those of Galts\u27 are found in the sign of K_1 and the value of the half line width at the room temperature, i. e., K_1 has a positive sign in our result, but negative in Galts\u27, and the value of the half line widths by us is several times as large as that reported by Galt ; the latter seems to be attributed to the "size effect"

Study on the Magnetic Property of Artificial Magnetite and its related Phenomena

The results of the present investigation may be summarised as follows : We have ascertained, that in the artificial magnetite, the existence of magnetic transformation and break point of conductivity occurring when log σ is plotted against 1/T are due to an excess of oxygen in the crystal Moreover, the intensity of magnetization and conductivity increase with the concentration of oxygen in the crystal, may have been shown. Having concern about the diffusion of oxygen in the crystal, crystal of FeO・Fe_2O_3 will have perhaps vacant lattice point, for the ionic radius of oxygen is so large that oxygen atom can very seldom settle down interstitially into the lattice of FeO・Fe_2O_3. Comparing the conductivity of FeO・Fe_2O_3 with that of other semiconductors, it is similar to Cu_2O that the various values of activation energy can be expected with the increasing of oxygen concentration. We know, Cu_2O is a defect semiconductor, the current being carried by positive holes. In the case of FeO・Fe_2O_3, owing to the oxygen rich lattice, (3d)^ band of Fe^ or Fe^ ion loses electrons and forms the positive holes if Fe^ and Fe^ ions have higher energy than oxygen ions. The variation of activation energy and the existence of magnetic transformation will be illustrated if we assume the impurity level