Spin reorientation behaviour and dielectric properties of Fe-doped h-HoMnO3

We have studied the magnetic structure, spin reorientation behaviour and dielectric properties of polycrystalline HoMn1-xFexO3(0.0 ⩽x⩽ 0.25) compounds using magnetization, neutron diffraction and dielectric measurements. These compounds crystallize predominantly in the hexagonal phase (P63cm) with a small phase fraction of the orthorhombic phase (Pnma) which increases with increase in dopant concentration and a total suppression of the hexagonal phase is observed atx= 0.25. Doping Fe at the Mn site leads to an increase in the spin reorientation temperature (TSR) from 33 K (x= 0) to 55 K (x= 0.1) while theTNremains nearly constant at 72 K. The magnetic structure of the hexagonal phase was found to be Γ4(P63'c'm) belowTNand Γ3(P63'cm') belowTSR. The magnetic ordering temperature of Ho3+ions at 2(a) site appears to coincide with theTSRonly in the case ofx= 0 sample. The Ho ions at 4(b) site are found to magnetically order below 8 K. TheTNof the Ho ions at both 4(b) and 2(a) sites do not appear to be affected by doping at the Mn site. The temperature variation of the Mn and Ho moments follow the Brillioun function dependence albeit with differing values of the molecular field constantλ0andλ1. Short range magnetic order alone was found for the completely orthorhombic sample (x= 0.25). An anomalous suppression of the dielectric constant (ε) atTNis observed in the case of hexagonal samples. Further, a linear correlation between Δε(=ε(T) -ε(0)) and the square of the antiferromagnetic momentM, is observed in these compounds.