Magnetic and dielectric properties of hexagonal InMnO3

High quality ceramics of hexagonal InMnO3 were prepared using a high-pressure and high-temperature technique (at 6 GPa and 1373 K). Magnetic properties of InMnO3 were investigated using dc and ac magnetizations and specific heat. High-temperature behavior was studied with differential scanning calorimetry, differential thermal analysis, time-domain terahertz (THz) transmission, and infrared reflectivity spectroscopies. Antiferromagnetic long-range magnetic order takes place below T-N = 118 K with very weak anomalies on magnetic susceptibilities and a strong anomaly on specific heat. No change in specific heat was found at a magnetic field of 7 T. Very weak ferromagnetic properties were detected below T-N. High-temperature (above 250 K) low-frequency permittivity is strongly enhanced by the Maxwell-Wagner polarization but intrinsic permittivity measured in a THz range shows only small linear increase with temperature up to 900 K. Ferroelectric hysteresis loop measurements (below 250 K) revealed no spontaneous polarization; therefore, InMnO3 is nonferroelectric. Absence of a structural phase transition is also supported by infrared reflectivity studies (taken up to 850 K). However, low-frequency permittivity exhibits an anomaly near T-N giving evidence about a magnetoelectric coupling.