Fig. 1
From: Magnetic field-temperature phase diagram of multiferroic (NH4)2FeCl5·H2O
Crystal structure, exchange interactions, and energy scales. a Crystal structure of (NH4)2FeCl5⋅H2O at 300 K with five different exchange interactions are represented with colored dash line. J1 pass between two water ligands (Fe-O-H⋯Cl-Fe). J2 and J3 pass between two Cl− ions (Fe-Cl⋯Cl-Fe). J4 and J5 pass between two \({\mathrm{NH}}_4^ +\) ions (Fe-Cl⋯O-Fe). The magnetic coupling is three dimensional: strong quasi-two-dimensional interactions with antiferromagnetically coupled planes. b Calculated J values against distance between Fe3+ ions. c Schematic depicting the sequence of temperature and magnetic field transitions that occur in (NH4)2FeCl5⋅H2O. d Ratio of J interactions with respect to J1 depicting how the collinear and non-collinear states are stabilized with respect to the nature of the counterion. The blue star in the non-collinear state corresponds to (NH4)2FeCl5⋅H2O. The red star in the collinear state corresponds to K2FeCl5⋅H2O whose exchange constants are taken from ref. 31
