Electron paramagnetic resonance of Mn²⁺ in (NH₄)₂SO₄ single crystal

Abstract

Electron paramagnetic resonance investigation of Mn²⁺ in (NH₄)₂SO₄ single crystal is discussed both in paraelectric and ferroelectric phases of the crystal. Mn²⁺ is found to substitute one of the two possible types (α andβ ) of NH₄⁺ ions and get associated with the second type of NH₄⁺ vacancy, the vacancy being the second distant neighbour in thebc-plane. As The line joining Mn²⁺ substituted NH₄⁺ site and NH₄⁺ vacancy lies at an angle of 18° from the crystallographicb-axis in the bc-plane. As the temperature is lowered to −56° C the crystal becomes ferroelectric and the spectrum in the paraelectric phase splits into two from which it appears that two sets of Mn²⁺ sites which are magnetically equivalent in the paraelectric phase become inequivalent in the ferroelectric phase. The spin Hamiltonian analysis is presented for the spectrum in the paraelectric phase.