Powder neutron diffraction investigation of the crystal and magnetic structures of NH₄Fe(HPO₄)₂and its deuterated form

Abstract

Abstract. The NH 4 Fe(HPO 4 ) 2 and its deuterated form, ND 4 Fe(DPO 4 ) 2 , were investigated in detail from powder neutron diffraction data allowing a precise determination of the hydrogen positions and low temperature magnetic structures. Below TC = 17.82 K they order with a ferrimagnetic structure and the magnetic moments lying in the crystallographic plane ac. As the temperature is lowered to Tt = 3.52 K the system undergoes a magnetic phase transition to an equal moment antiphase structure characterized by the propagation vector close to k AF ≈ (1/16, 0, 1/16) and a magnetic moment for the Fe 3+ ions of 4.8 µ B at 1.89 K. The low symmetry of this crystal structure and the complex pattern of competing superexchange pathways are responsible for the existence of this double magnetic phase transition.

Neutron powder diffraction investigation in ammonium iron(III) bis (hydrogenphosphate)

“…Recently we have focused our interest on ND 4 Fe(DPO 4 ) 2 because it appears to behave magnetically in a complex manner. In previous works of ND 4 Fe(DPO 4 ) 2 we have investigated the crystal and magnetic structures from neutron powder diffraction [7,8] together with the physical properties [9]. The magnetic and specific heat measurements revealed the existence of two magnetic phases at low temperatures.…”