Ultrasharp Magnetization Steps in Perovskite Manganites

We report a detailed study of steplike metamagnetic transitions in polycrystalline $\mathrm{P}{\mathrm{r}}_{\mathrm{0.5}}\mathrm{C}{\mathrm{a}}_{\mathrm{0.5}}\mathrm{M}{\mathrm{n}}_{\mathrm{0.95}}\mathrm{C}{\mathrm{o}}_{\mathrm{0.05}}{\mathrm{O}}_{\mathrm{3}}$. The steps have a sudden onset below a critical temperature, are extremely sharp (width $<2\times {10}^{-4}\mathrm{T}$), and occur at critical fields which are linearly dependent on the absolute value of the cooling field in which the sample is prepared. Similar transitions are also observed at low temperature in non-Co doped manganites, including single crystal samples. These data show that the steps are an intrinsic property, qualitatively different from either previously observed higher temperature metamagnetic transitions in the manganites or metamagnetic transitions observed in other materials.

Figure 1

Temperature dependence of the magnetization of $\mathrm{P}{\mathrm{r}}_{\mathrm{0.5}}\mathrm{C}{\mathrm{a}}_{\mathrm{0.5}}\mathrm{M}{\mathrm{n}}_{\mathrm{0.95}}\mathrm{C}{\mathrm{o}}_{\mathrm{0.05}}{\mathrm{O}}_{\mathrm{3}}$ while warming from 2 K after zero field cooling and field cooling. The inset shows $H/M\left(T\right)$ in the high temperature range at $H=1\mathrm{T}$, where a kink indicates $T_{\mathrm{C}\mathrm{O}}$, the charge-orbital ordering temperature.

Figure 2

Field dependence of the magnetization at different temperatures measured while stepping from $H=0\mathrm{T}\to H=7\mathrm{T}\to H=0\mathrm{T}$ in 0.2 T steps. (a) $T=5\mathrm{K}$, (b) $T=4.7$ and 4.6 K, (c) $T=4\mathrm{K}$, and (d) $T=3\mathrm{K}$. Note that the smooth metamagnetic transition at $T=4.7\mathrm{K}$ changes to include an abrupt jump at $T=4.6\mathrm{K}$. Data are taken either after zero-field cooling (ZFC) or after field cooling (FC) from 120 K ($>T_C$) in the indicated magnetic fields (the FC data are taken on increasing field, after the field is first reduced to zero at the measurement temperature). The inset in (d) shows data taken with a field interval of 0.2 mT, placing an upper limit on the width of the steps.

Figure 3

Comparison of $M\left(H\right)$ at $T=2\mathrm{K}$ after cooling in positive and negative fields. Positive field-cooled data were taken in the same manner as the data in Fig. 2.

Figure 4

(a) Field dependence of the resistivity at $T=3\mathrm{K}$ in ZFC and FC modes showing steps which correspond to those observed in the magnetization [Fig. 2d]. The inset shows the onset of a similar step transition in single crystal $\mathrm{P}{\mathrm{r}}_{\mathrm{0.7}}\mathrm{C}{\mathrm{a}}_{\mathrm{0.3}}\mathrm{M}\mathrm{n}{\mathrm{O}}_{\mathrm{3}}$ at $T=2\mathrm{K}$ (sample preparation details given in 12). (b) Field dependence of the resistivity for $2\mathrm{K}\le T\le 5\mathrm{K}$. The inset shows the cooling field dependence of $H_c$ at different temperatures where the color of the symbols corresponds to the different temperatures in the main figure.