Nanocrystalline NH4MnF3 with controlled grain size: Synthesis and antiferromagnetism

Abstract Nanocrystalline NH 4 MnF 3 was prepared by precipitation in the inverse micelles of w/o-microemulsions using mixtures of ammonium substituted AOT and n-heptane which are able to stabilize large contents of concentrated NH 4 F and Mn(OAc) 2 aqueous solutions. By appropriate variation of the synthesis parameters the volume averaged crystallite diameter, as measured by X-ray diffraction line shape analysis, can be tuned to values of 10 nm ≤ D Vol ≤60 nm . NH 4 MnF 3 is antiferromagnetic with a weak canted ferromagnetism below the Neel temperature. Magnetic measurements have been performed using a SQUID magnetometer. For nanocrystalline NH 4 MnF 3 we observe the following changes of the magnetic properties with decreasing crystallite size: -the strength of the antiferromagnetic exchange interaction decreases; -the ferromagnetic contribution decreases as can be concluded from the magnetic field dependence of the molar susceptibility below the Neel temperature.