Low-field ac susceptibility was measured on bulk ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_3$ prepared by a partial melting technique. Discontinuous jumps with heights of $(1\mathrm{}–2)\times {10}^{-5}\mathrm{emu}$ at temperature intervals of 3–5 K were observed in the ac susceptibility. 28 jumps were observed in the temperature range between 4.2 K and the Curie temperature of 250 K, with an ac field amplitude of 1 Oe, a frequency of 117 Hz, and a dc bias field of 5 and 20 Oe. Upon increasing the frequency up to 5000 Hz, the jumps shifted to lower temperature. For a dc bias field of 50 Oe and an ac field with an amplitude of 0.1 Oe and a frequency between 117 and 5000 Hz, only three jumps with heights of about $3\times {10}^{-5}\mathrm{emu}$ at large temperature intervals of about 60 K were observed for $T<\mathrm{}{T}_c.$ With increasing frequencies, the three jumps shifted to lower temperatures without changing jump height. The discontinuous jumps in ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_3$ were interpreted in terms of thermally and ac-field-activated domain-wall jumps.

• Received 17 November 1997

DOI:https://doi.org/10.1103/PhysRevB.58.2434