Role of 4f-Orbitals on the Magnetodielectric Properties and Spin-Phonon Coupling in Orthorhombic Sm_0.50M_0.50MnO₃ (M = Ho and Eu)

The polycrystalline samples of SmMnO3 (SMO), Sm0.50Ho0.50MnO3 (SHMO), and Sm0.50Eu0.50MnO3 (SEMO) have been synthesized to understand the effect of Ho and Eu substitution on the structural and physical properties. Detailed crystal structure, magnetic, dielectric, magnetodielectric (MD), and Raman spectroscopy measurements have been performed to investigate the role of 4f-orbital on the magnetic, MD, and spin-phonon coupling in these materials. The pristine SMO exhibits an antiferromagnetic (AFM) transition around 58 K due to the canted A-type AFM ordering of Mn3+ moments. The Mn–O–Mn bond angle, unit cell volume, and the AFM transition temperature decrease with the partial substitution of Ho and Eu. All the studied samples exhibit anomalies in the dielectric measurement corresponding to the magnetic ordering. The temperature-dependent dielectric results of SHMO illustrate a sharp peak at 22 K, which shifted toward the lower temperature side with increasing magnetic field. These results are similar to orthorhombic RMnO3. The temperature-dependent Raman measurements of all the studied samples reveal an anomaly at the magnetic ordering temperature, which suggests the spin-phonon coupling. The sign of MD is different for SEMO and SHMO samples. Our results demonstrated the enhancement of the MD value in SHMO and SEMO as compared to SMO. The SHMO exhibits both positive and negative MD in the magnetically ordered state. These findings highlight the strong magnetoelectric coupling in SHMO and SEMO as compared to pristine SMO.