Abstract
An A-site-ordered quadruple perovskite NdMn7O12 was prepared at high pressure of about 6 GPa and high temperature of about 1570 K. Its crystal structure was refined from synchrotron X-ray powder diffraction, and it crystallizes in space group I2/m at room temperature. One structural phase transition was detected at 664 K by differential scanning calorimetry. Three magnetic phase transitions were found in NdMn7O12 at TN1 = 84 K, TN2 = 12 K, and TN3 = 9 K by specific heat and direct current magnetic measurements. Alternating current magnetic measurements revealed additional frequency-dependent features: anomalies near 82 K (at Hac = 5 Oe), anomalies spanning between TN2 and about 70 K with maxima near 17 K, and anomalies near 6 K. Small kinks were found on dielectric constant at TN1 and TN2, and much stronger frequency-dependent steps on dielectric constant were observed between 20 and 35 K accompanied by sharp dielectric loss peaks; peak shifts followed the activation law. Pyroelectric current measurements did not detect any intrinsic ferroelectric polarization. Magnetic behaviour of NdMn7O12 is more complex than that of other members of the RMn7O12 family (R is a rare-earth cation).
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