Magnetic susceptibility of La$_{0.7}$Ca$_{0.3}$MnO$_3$ at very low magnetic fields in the vicinity of the ferromagnetic transition*

Magnetic susceptibility ($\chi$) measured at magnetic fields $H$ as low as 0.2 Oe is reported for La$_{0.7}$Ca$_{0.3}$MnO$_ {3}$. A pronounced enhancement in $\chi$ is observed in the region above the critical temperature $T_c$ at very low $H$. As the magnetic field is increased, this feature is shifted toward $T_c$, eventually vanishing near $H$ = 400 Oe. Electrical resistivity measurements show a positive magnetoresistance effect between 0 and 500 Oe in a temperature range slightly above $T_c$. The results are discussed in a scenario of frustrated magnetism and the possibility of a Griffiths singularity is addressed.$^1$ $^1$ Chan, Goldenfield, and Salamon, Phys. Rev. Lett. 97 (2006) 137201.