Calorimetric Study of Critical Phenomena in the Diluted Random Ferromagnet,Eu_xSr_<1-x>S

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The critical phenomena of a randomly diluted ferromagnet Eu.Sr. .S(1.0g,v>0.8) are studied through the measurement of specific heat. The transitiontemperature observed in EuS becomes low and the peak in the specific heat is loweredand rounded systematically with decreasing x. Except for a narrow temperatureregion containing T. and a range far apart from it, 1.he specific heat can be expressedby C,= (A / cc) l t l '-F- B -I-El for T >T. and by the same equaticcn with A' for T< T.,where t is (T - T.) / T.. The inner boundary of the scaling regiorx, where the above expression is valid, moves farther apart from T. with decreasing x, corresponding to therounding of the peak. The relation Ql=C5', predicted by the scaling law, is confirmed.The critical exponent (Y and ratio of the amplitude A / A' are determined for each con-centration. (Y is negative and its absolute value increases with decreasing x, reflectingthe lowering of the peak at T.. This is consistent with the results of magnetic measure-ments (J. Phys. Soc. Jpn. 51 (1982) 2746) as well as those of high-temperature expan-sion calculation by Kawasaki (private communication), though only qualitatively.
社団法人日本物理学会の論文
1988-10-15