La-Co置換M形Srフェライト磁石の保磁力の温度係数に関する検討(ハード・ソフト磁性材料)

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The relationship between the temperature coefficient of coercivity {α(H_<cj>)} and the ratio S_v to H_<cj> was investigated for M-type Sr-ferrite substituted by La and Co (Sri_<-x>La_xFe_<12-x>Co_xO_<19>) in the temperature range from 173 to 423 K, where S_v and H_<cj> were the magnetic viscosity constant, which essentially determined the thermal stability, and the coercivity, respectively. The value of x was varied between O, 0.3, and 0.6. The value of α(H_<cj>) for x=0 with S_vHcj=0.038 was 0.35%/K, whereas that for x=0.3 with S_vH_<cj>=0.034 was 0.1%/K at 298 K. Furthermore, α(H_<cj>) for x=0.6 with S_v/H_<cj>=0.026 was almost zero at 298 K. The following relation of α(H_<cj>) to S_v/H_<cj> was also found to hold in these M-type Sr-ferrite magnets substituted by La and Co, as in the case of Nd-Dy-Fe-Al-B-Sn sintered magnets. α(H_<cj>) was expressed as {28.5k-(OE/δT)_H}/kT-(S_v/H_<cj>), where, k, E, T, and H were the Boltzmann constant, the activation energy, the absolute temperature, and the magnetic field, respectively. The equation shows that smaller S_vH_<cj> values are necessary for ensuring small α(H_<cj>) values, which are very important for permanent magnets.
社団法人日本磁気学会の論文
2007-03-01