Spin reorientation behaviour and dielectric properties of Fe-dopedh-HoMnO₃

We have studied the magnetic structure, spin reorientation behaviour and dielectric properties of polycrystalline HoMn_1-FeO₃(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 (T_SR) from 33 K (x= 0) to 55 K (x= 0.1) while theT_Nremains nearly constant at 72 K. The magnetic structure of the hexagonal phase was found to be Γ₄(P6₃'c'm) belowT_Nand Γ₃(P6₃'cm') belowT_SR. The magnetic ordering temperature of Ho³⁺ions at 2(a) site appears to coincide with theT_SRonly in the case ofx= 0 sample. The Ho ions at 4(b) site are found to magnetically order below 8 K. TheT_Nof 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) atT_Nis 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.