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(2) N. MIyATA. 14. The time decrease of initial permeability after demagnetization, so called disaccomodation of this ferrite system is also interest. This phenomenon is explained by the stabilization of magnetic domain walls at each position and two mechanisms have been presented as an origin of disaccomodation of ferrites: the first mechanism assumes the presence of electron diffusion between cations (Fe2+, Fe3", Mn2", Mn3" etc.) and the second one assumes that of ionic diffusion. Previously ENz2) analysed hisexperimental results on disaccomodation for a single crystal of Mn-Fe ferrite from the former stand point. Re-. .. `. cently OHTA3) studied on disaccomodation for many kinds of ferrites and pointed out that the activation energy of disaccomodation was several times larger than that obtained from electric conduction or high frequency relaxation loss and the heat treatment of iron excess ferrites in N2 atmosphere suppressed disaccomodation. These facts support the second rnechanism with a role of cation vacancy for disaccomodation. He reported also in his paper that in the case of a Ni-Zn ferrite single crystal, although ceramics with the same composition showed fairly large disaccomodation, negligibly small disaccomodation was observed at room temperature and was attributable to negligible vacancy concentration. Disaccomodation spectrum in a wide temperature region was observed for sintered Mn-Fe ferrites and its dependence on oxygen concentration was discussed by KRuplcKA`) and BRAGINsKI et al.5) From these points of view it is interesting for us to reexamine the observation of disaccomodation of Mn-Fe ferrite crystals with negligible vacancy. In this paper, experimental results on magnetization curve and initial permeability of Mn.Fe3..04 ferrite system (x==O.4rvl.15) made from the melt is presented and discussed from the stand point mentioned above.. g2. Specimens and Experimental Methods Toroidal specimens with 3 and 10 mm in inner and outer diameter, respectively, and height of 4mm were cut from single or coarse-grained crystals grown in Pt-crucibles by BRIDGMAN method in the air atmosphere. Crystallographic investigations on them were reported in the previous paperi). Their compositions were Mn.Fe3-.04 with x=O.4, O.6, O.75, O,95, 1.05 and 1.15,. Magnetization curves and initial permeabilities were measured by ballistic. method and Maxwell-Bridge, respectively. Disaccomodation in a short time period was observed with a suitable recorder. These experiments were carried out at room temperature. Magnetic field (ltvlOO kc/s) used for measurements. of permeability was about5mOe or less which was low enough to obtain initial permeability.. g3. Experimental Results and Discussions (1) Disaccomodation Time dependence of pti just after demagnetization and that for a long period are given in Fig. 1 and Fig. 2, respectively. Dispersion of observed. -,. `.
(3) MagneticPropertiesofMn.Fe3-.04 ' !5 2.2. 2.0. L8. /. xtO.4. /. x:O.6. T/`i(t}/,u... L6 I.4 1.2. l.o. t(sec). l IO to2 lo5 lo4 11. Fig. 1. Timedependenceofyijust after demagnetization: (relative value of yi(t) to that just before demagnetization pto) vs. (time t in second). Speci-. mens with x=O.75nul.05 show the same character as x =O.6.. ' o.I. o. o. T. -O.3. o. o o. 1'{t(t)"'/"e(l5). -O.i. -O.2. o. ./LL,(l5). p. '. I. -. o:x=O.6. n:o.4. -O A. o. ?. t(min). o. D. io to2 to3 lo4 to5. r. 1. Fig. 2. Time dependence of pti for a long period: (rate of change pti(t)-th(15)/th(15)) vs. (time tin minute), where pti(15) means th taken 15 minutes after demagnetization. Specimens with x =O.75Nl.05 have the same character as x==O.6.. '. values in the latter figure may be attributed to the fluctuation of room temIt is clearly seen in figures thar negligible time dependence of pti is observed. for x==O.6rvl.05. This result is contrary to fairly large disaccomodation reported by ENz2) for a single crystal of the same ferrite system. The discrepancy is attributable to the difference of vacancy concentration, which comes. from excess oxygen, as OHTA pointed out for his Ni-Zn ferrite3): Excess oxygen compared with stoichiometry is contained in the specimen used by ENZ, Mno.s4Fe2.i404, although the method of crystal growth is not known for us. Contrary to this, specimens used bytheauthor are not excess in oxygen.
(4) N MIyATA. 16. for Mn-rich side in Mn-Fe ferrite system, as considered from SHAFER's diagram6).. .. ENz suggested in his reporV that disaccomodation had its activation energy several times larger than that obtained from electric conduction and its mechan-. ism might be a transition of electrons incorporating Mn3" ions, though a. s. transition with the lowest energy (Fe2+eFe3+ on octahedral sites as suggested by VERwEy) would beresponsible fortheelectrical conductivity. But, as seen in figures, fairly large disaccomodation is observed for the specimen with. x=O.4, which has much less Mn3" than specimens with larger x as estimated from saturation magnetization of this ferrite system at OeK, so that it is not. explained by ENz's mechanism. Further, it is an evidence to show a role of cation vacancy for disaccomodation, because magnetite side of this ferrite system made from the melt in the air atmosphere is estimated to be more oxidized than stoichiometry6). Of course the mechanism due to electron diffusion between Fe2" and Fe3" is useless, because it is obvious that specimens which show no disaccomodation contain considerable amount of ferrous ions7). (2) ComPosition dePendence of initial Permeability 2400 AIUCu. A pti (initial permeability) vs.. 20OO. x (composition) curve has a clear. maximum at x==O.95 as seen in. 1600. Fig. 3. Frequency dependence of 1kcls. 1200 u. 8OO. pti for this composition is shown in Fig. 4. It is well known that. the magnetization process in a 1. 400. R. o Fe304 O ,2. Fig.. 3.. x-. IOOkcls. O.4 o.6 o.8MnFe204L2 yi (initial permeability) vs.. x (composition).. low magnetic field region such as initial permeability is due to do-. main wall displacement and/or. magnetization, small anisotropy and small magnetostriction contribute to high initial permeability at. 2500. low frequency. These three magne-. tic constants at room temperature. 2000. of the ferrite system used here. "/uu. are cited in Fig. 5 from previous. 'l 500 "f?ed.'(kc/s)-. lOOO. 10 100. 1. Fig. 4.. Frequency dependence of pti for x=O.95.. .. rotation of magnetization in each domain and that large spontaneous. papers.i) From the figure maximum pti seems to correspond to small Zm, magnetostriction constant along the easy axis for speci-. mens with negative Kl. But higher pti is expected for x==O.6. ,.
(5) Magnetic Properties of Mn.Fe3d.04 17 rvO.8, because specimens of these composition have smaller IK,I (almost zero for x==O.6) and nearly. K,･io'4. erg!cc. J>tTQQ,)L,.,,l･lo5Msgaus3!cc lo. tion constant along the easy axis,. 500. ,. /[. equal absolute value of magnetostric-. 400. Msl. 8642o-2-4-6. Zioo in this case. So, it is not clear. 500. from this experiment why maximum. IX."i/. initial permeability appears at x= O.95. It is noticed that, as specimens. used here have not been annealed after the crystal growth, internal stress in them may subject the magnetlzatlon process to magnetostrlc-. O,2O.4O,6. tion rather than to crystalline aniso-. x)LIoe. eKt. tropy.. x. MnFe204. Fes04. ue. L2. Q. (3) DijSferenceofmagneticProPerties between sPecimens macle by melt-. ing and sintering Fig･ 5･ Spontaneous magnetization, crystalline anisotropy constant and mag-. To compare the magnetic pro- netostriction constants of Mn-Fe ferrite pertiesofporelessferritemadefrom systematroomtemperature･ the melt (M-ferrite) with sintered one (S-ferrite), initial permeability (pti), coercive force (H}), magnetic flux density at maximum field of 15 or 25 Oe (B.) and remanent flux density (B.),. the latter three quantities of which are obtained from the magnetization '. '. Table 1. Comparison of magnetic properties between melted and sintered MnFe204･ a) Specimens made by melting in the air atmosphere. Br (in Gauss). va (at 1kc/s). Hb (in Oe). Mne.geFe2.os04. 2150. O. 10. 600. 3600. Mnl.osFel.gs04. 1750. O. 09. 675. 3730. Br (in Gauss). B. (at 250e). Composition. B. (at 150e). b) Specimens made by sintering.. (1) By EcoNoMos Atmosphere during Sintering ' Stagnant air. th (at lkc/s) 56. 9. Hb (in Oe) 1. 67. 3'. 10. 1380. Less reducing than equilibrium. 188. O. 82. 2940. 4085. Carbon dioxide. 226. O. 50. 3335. 4125. Helium. 224. O. 82. 3225. 3815. of magnetite.
(6) N MIyATA. 18. (2) By SHicHiJo et al.. Sintering temperature (OC). th (at lkc/s). H6 (in Oe). I. B. (in G4uss) B. (at 250e). 1200. 100. 2, 95. 1600. 2500. 1300. 160. O. 89. 2200. 3200. 1400. 210. O. 88. 2500. 3400. 1450. 260. O. 63. 2800. E. .. .. 3500. curve measurement, are given in Table 1 for both M- and S-ferrite whose compositions are near to MnFe204, where the properties of the latter are cited. from EcoNoMos8) and SmcmJo's9) reports. It is obviously seen that pti of M-ferrite is about ten times and Hb and B, are about one fifth or less of those. of S-ferrite with nearly the same B.. These results show a large effect of pores as obstacles to a motion of domain walls. g4. Conclus･ions Initial permeability, pti, with its time dependence and magnetization curve were measured at room temperature for Mn.Fe,-.O, (x =O.4, O.6, O.75, O.95, 1.05. and 1.15) made from the melt in the air atmosphere. Results are summarized as follows:. 1) No disaccomodation is observed for x==O.6tvl.05, contrary to ENz's results for Mno.s4Fe2.i404, while a fairly large disaccomodation is obtained for x=O.4. It is not explained by an electron diffusion mechanism but by an ion diffusion one with a role of cation vacancy. 2) Composition dependence of pti has a maximum for x =O.95 and its value is about ten times larger at 1 kc/s than that of sintered ferrite with nearly the. same composition. This composition does not correspond to small Ki but to small Riii. Coercive force and remanent magnetization are about one order of magnitude small compa'red with those of sintered ferrite. These results show a restrictive effect of pores to domain wall motion.. Acknowledgment The author wishes to express his thanks to Prof. Z. FuNAToGAwA for his. encouragement. He also thanks to Dr. T.KARAsAwA of Tokyo Denkikagaku Kogyo Co. Ltd. and Mr. S. IcHiKAwA in our laboratory*' for the measurement. This work is partly supported by the Scientific Research Expenditure of the Ministry of Education.. " PreSent at Nihon Ferrite Co. Ltd.. ,. ..
(7) 19. Magnetic Properties of MnxFe3.x04. References 1) N. N. 2) U. 3) K. 4) S. 5) A.. MiyATA: J. Phys. Soc. Japan 16 (1961) 1291. MiyATA et al: J. Phys. Soc. Japan 17 Suppl. B-I (1962) ENz: Physica 24 (1958) 609. OHTA: J. Phys. Soc. Japan 16 (1961) 250. KRupicKA: J. Phys. Soc. Japan 17 Suppl. B-I (1962) 304. BRAGiNsKi et al.: J. Phys. Soc. Japan 17 (1962) 1611.. 6) M.W. SHAFER: IMB Jour. July (1958) 193. 7) N. MiyATA: J. Phys. Soc. Japan 16 (1961) 206. 8) G. EcoNoMs: J. Amed Ceramic Soc. 38 (1955) 296. 9) Y. SHicHiJo et'al.: Ferrite (in Japanese) (1959) 78.. 279..
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