Both FeO and γ-Fe2O3 have a similar cubic close packed array of oxide ions and this accounts for the ready interchangeability between the three compounds on oxidation and reduction as these reactions entail a relatively small change to the overall structure. Fe3O4 samples can be non-stoichiometric.The ferrimagnetism of Fe3O4 arises because the electron spins of the FeII and FeIII ions in the octahedral sites are coupled and the spins of the FeIII ions in the tetrahedral sites are coupled but anti-parallel to the former. The net effect is that the magnetic contributions of both sets are not balanced and there is a permanent magnetism.In the molten state, experimentally constrained models show that the iron ions are coordinated to 5 oxygen ions on average. There is a distribution of coordination sites in the liquid state, with the majority of both FeII and FeIII being 5-coordinated to oxygen and minority populations of both 4- and 6-fold coordinated iron. Properties
Fe3O4 is ferrimagnetic with a Curie temperature of 858 K (585 °C). There is a phase transition at 120 K (−153 °C), called Verwey transition where there is a discontinuity in the structure, conductivity and magnetic properties. This effect has been extensively investigated and whilst various explanations have been proposed, it does not appear to be fully understood.While it has much higher electrical resistivity than iron metal (96.1 nΩ m), Fe3O4s electrical resistivity (0.3 mΩ m ) is significantly lower than that of Fe2O3 (approx kΩ m).
This process is described by the Schikorr reaction:

  
    
      
        
          
            
              
                3
                
                Fe
                
                  
                    (
                    OH
                    )
                  
                  
                    2
                  
                  
                    
                  
                
              
              
                ferrous
                 
                hydroxide
              
            
          
          ⟶
          
            
              
                
                  Fe
                  
                    3
                  
                  
                    
                  
                
                
                  O
                  
                    4
                  
                  
                    
                  
                
              
              magnetite
            
          
          +
          
            
              
                H
                
                  2
                
                
                  
                
              
              hydrogen
            
          
          +
          
            
              
                2
                
                
                  H
                  
                    2
                  
                  
                    
                  
                
                O
              
              water
            
          
        
      
    
    {\displaystyle {\ce {{\underset {ferrous\ hydroxide}{3Fe(OH)2}}->{\underset {magnetite}{Fe3O4}}+{\underset {hydrogen}{H2}}+{\underset {water}{2H2O}}}}}
  This works because crystalline magnetite (Fe3O4) is thermodynamically more stable than amorphous ferrous hydroxide (Fe(OH)2 ).The Massart method of preparation of magnetite as a ferrofluid, is convenient in the laboratory: mix iron(II) chloride and iron(III) chloride in the presence of sodium hydroxide.A more efficient method of preparing magnetite without troublesome residues of sodium, is to use ammonia to promote chemical co-precipitation from the iron chlorides: first mix solutions of 0.1 M FeCl3·6H2O and FeCl2·4H2O with vigorous stirring at about 2000 rpm.