Interplay of magnetic and electric coupling across the spin density wave to conical magnetic ordering in a BaHoFeO4 spin-cluster chain compound

In this study, we performed a detailed analysis of the magnetoelectric properties of a polycrystalline BaHoFeO4 system. Rietveld refinement of the synchrotron x-ray powder diffraction pattern (SXRD) with space group Pnma confirmed that the orthorhombic crystal structure was preserved down to the lowest temperature (T) = 15 K. The DC magnetization indicated complex magnetic behavior with multiple magnetic transitions at TN1 = 49 K, TN2 = 36 K, and TN3 = 7 K. The complex interplay of 3d and 4f magnetic sublattices, and the competing interactions of two different Fe-sites can explain the field (H)-induced metamagnetic behavior in BaHoFeO4 at T < TN3 and TN3< T < TN2, respectively. A strong anomaly in the dielectric constant (ε′) was observed near TN2 and TN3, which exemplified the coupling between magnetism and dielectric properties. The magnetodielectric (MD) coupling measurements via ε′ (T, H) under different H confirmed the unprecedented magnetoelectric (ME) nature with MD sign changes at the onset of TN1, TN2, and TN3 magnetic transitions; subsequently, the ME H-T phase diagram was constructed. Furthermore, the thermal variation in the lattice parameters exhibited minute changes at TN2. Spin-spiral calculations demonstrated that the spin moments of the Fe atoms are modulated in the ab-plane, whereas the spin moments of the Ho atoms can point in any direction. Our results demonstrate that the interplay between the complex magnetic modulation of Ho and Fe magnetic sublattices may play a vital role in the ME properties of BaHoFeO4.