Abstract
고상 반응법을 써서 전이금속(Cr, Ti)을 치환한 란탄칼슘망간산화물, <TEX>$La_{0.5}Ca_{0.5}(Mn_{0.98}TM_{0.02})O_3$</TEX>의 자성특성을 연구하였다. 자성 특성은 VSM을 써서 측정하였고, 50 Oe에서 zero field cooling과 field cooling을 하면서, 자화-온도측정을 Cr과 Ti 치환한 경우에 측정하였다. <TEX>$La_{0.5}Ca_{0.5}(Mn_{0.98}Cr_{0.02})O_3$</TEX>는 클러스터 또는 스핀유리와 유사한 거동을 보였으며, <TEX>$La_{0.5}Ca_{0.5}(Mn_{0.98}Ti_{0.02})O_3$</TEX>에서는 관찰되지 않았다. 큐리온도는 전이금속이 치환된 시편의 경우 란탄칼슘망간산화물 <TEX>$La_{0.5}Ca_{0.5}MnO_3$</TEX>의 큐리온도 245.5K에서 감소한, 235.5 K [<TEX>$La_{0.5}Ca_{0.5}(Mn_{0.98}Cr_{0.02})O_3$</TEX>], 232.7 K [<TEX>$La_{0.5}Ca_{0.5}(Mn_{0.98}Ti_{0.02})O_3$</TEX>]로 모두 감소하였다. 자벽 고정(domain wall pinning)을 알아보기 위해 온도에 따른 보자력 측정을 하였고, 이 결과를 defect와 자벽 간의 상호작용의 관점으로 해석하였다. Magnetic properties of transition metal doped <TEX>$La_{0.5}Ca_{0.5}(Mn_{0.98}TM_{0.02})O_3$</TEX>(TM=Cr and Ti) are studied. The samples are synthesized by the conventional solid-state method. Using vibrating sample magnetometer magnetization-temperature measurement were carried out with zero field cooling and field cooling at 50 Oe. Cr-doped sample shows cluster or spin glass like behavior while Ti doped does not. Curie temperature obtained were decreased from that of LCMO(245.5 K). Curie temperatures of Cr-doped and Ti-doped samples are 235.5 K and 232.7 K, respectively. The temperature-dependent coercivity <TEX>$H_c(T)$</TEX> was also measured. The coercive force continuously decreases with the substitution of Cr and Ti, The result can be understood in terms of the interaction between defect and domain wall.
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