Anomalous low-field magnetization in La2/3Ca1/3MnO3 near the critical point: Stable clusters?

Abstract

The magnetic behavior of bulk La2/3Ca1/3MnO3 (TC=267 K) at low fields in the paramagnetic phase was studied. Near TC(T−TC<30 K) we find a sequence of steplike features in the effective Curie constant C(T)=M(T−TC)/H at well defined temperatures and intermediate plateaus, accompanied by temperature hysteresis. On approaching TC, the C values at each plateau follow a geometrical progression, with the effective spin S doubled at each step. The first plateau gives S=5.5, corresponding to a cluster of three Mn3+ ions sharing one extra hole. This suggests that close to TC short range magnetic order at low fields develops hierarchically through a series of most stable cluster states.

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“…Note that these abnormal reciprocal susceptibility features have also been observed in other compounds that present strong interplay between the lattice and spin degrees of freedom (R 5 [Si,Ge] 4 and La[Sr,Ca]MO); 19,[31][32][33] thus, a similar analysis may explain these observations.…”

Crystal growth, transport and magnetic properties of rare-earth manganite

“…This may be due to shortrange ferromagnetic correlation between Mn 3þ and Mn 4þ ions and ratio Mn 3þ =Mn 4þ increases with x. As the temperature is lowered, this interaction leads to the formation of ferromagnetic clusters, which causes a deviation from the Curie-Weiss law at around 250 K. Such cluster formation though rare in conventional manganites is reported in La 2=3 Ca 1=3 MnO 3 around 20 K above its T c [13]. Extending this argument we can say that in our system the cluster formation occurs around 50 K above T c .…”

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