Magnetodielectric Properties In Mn-site Doped Ca₃CoMnO₆ Spin Frustrated System

The intricate spin configurations of low-dimensional spin frustrated systems result in diverse competitive interactions,containing rich physical phenomena,such as spin ice,spin glass,and spin liquid.These phenomena hold immense potential for applications in the materials science field.Due to its special ferroelectric polarization and the competition of various magnetic orders,the multiferroic material Ca₃CoMnO₆ with quasi-one-dimensional spin chains have become a typical representative.The magnetic and electrical properties of the material are highly sensitive to the Co/Mn ratio,and the experimental value of the ferroelectric polarization is greatly different from the theoretical prediction value,which has attracted extensive attention of researchers.In this study,Ca₃CoMnO₆ was selected as the research object.The influence of the microstructure and Co/Mn ratio on the magnetic and dielectric properties were systematically studied by Mn-site ion doping.In particular,some meaningful results were obtained,establishing a crucial experimental basis for comprehending the the mechanism of magnetoelectric coupling in the spin-frustrated system,regulating its magnetodielectric coupling effect,and designing and developing relevant functional devices.The main content of this paper is as follows:The microstructure,magnetic,and dielectric properties of Ca₃CoMnO₆ polycrystalline samples were studied.Due to the"order by disorder"effect,some long-range antiferromagnetic Co-Mn-Co-Mn spin chains were broken,and short-range magnetic correlations appeared.At the same time,Ca₃CoMnO₆ has polar nanoregions.The activation energy is E_a=6.31×10^-3 e V and the static freezing temperature is T_f=1.5 K,respectively.Both of them are lower about two orders of magnitude than the conventional relaxor ferroelectrics.Thus,the destruction of long-range ferroelectric order and the formed polar nanoregions should be responsible for the suppressed macroscopic ferroelectric polarization.The influence of Mn-site doping with non-magnetic Al³⁺ions on the microstructure,magnetic,and dielectric properties of Ca₃CoMnO₆ was studied.Due to the dilution effect of nonmagnetic Al³⁺ions to the spin chains,the magnetic frustration in Ca₃CoMnO₆ was released,and the spin freezing peak gradually disappeared,indicating that the competing short-range antiferromagnetic/ferromagnetic order caused by the“order by disorder”phenomenon was suppressed.At the same time,the doped samples presented a faster dynamic behavior and a nonmonotonic relaxation,indicating a more robust long-range antiferromagnetic order and the possible existence of quantum tunneling of magnetization.With the increase of Al³⁺doping amount,the relaxor ferroelectricity weakened and the activation energy E_a increased,inhibiting the formation of polar nanoregions.Thus,Al³⁺doping significantly enhanced the magnetodielectric effect of Ca₃CoMnO₆.The influence of Mn-doped magnetic Cr³⁺ions on the microstructure,magnetic,and dielectric properties of Ca₃CoMnO₆ was investigated.To keep the balance of the valence,partial Co²⁺ions change to Co³⁺ions with Cr³⁺substitution,leading to a decreased lattice volume.Correspondingly,the length of the short-range magnetic correlation is inhibited and a faster dynamic behavior is found.At the benefit of the magnetic structural changes with the introduction of Cr³⁺ions,the relaxor degree of the ferroelectric transition becomes lower,while the activation energy E_a increases and the static freezing temperature T_f decreases.Therefore,Cr³⁺doping is an effective method to enhance the magnetodielectric effect and optimize the ferroelectric properties of materials.