Collapsing the spin driven electric polarization in CaBaCo4O7 by doping small amount of orbital singlet and non-Jahn-Teller active Fe3+ ions at Co3+ sites

Chigurupati Dhanasekhar^1,2*, Pin Tai¹, C.T Lai¹, Ajay Tiwari¹, A. Venimadhav³, J-Y Lin⁴, D. Chandrasekhar Kakarla¹, H. D. Yang^1,2

¹Department of Physics, National Sun Yat-sen University, Kaohsiung, 80424, Taiwan
²Center of Crystal Research, National Sun Yat-sen University,, Kaohsiung, 80424, Taiwan
³Cryogenic Engineering Center,, Indian Institute of Technology, Kharagpur, 721302, India
⁴Institute of Physics, National Yang Ming Chiao Tung University, Hsinchu,300093, Taiwan

* Presenter:Chigurupati Dhanasekhar, email:dsekhar21nsysu@gmail.com

The 1147 family is a series of compounds with general formula ABaM4O7 (A= Ca, Y and Rare earth, M = Fe, Co, Ni). In this family of the materials only the CaBaCo4O7 (CBCO) and CaBaFe4O7 (CBFO) compounds shows the giant spin driven electric polarization and magnetoelectric (ME) coupling. Initially, in CBCO it has been believed that the charge ordering (Co2+: Co3+; 1:1) along with spin- lattice coupling plays a major role to induce the spin driven electric polarization. However, the recent studies (Physical Review Letters 130, 036801 (2023)) showed that, the orbital degrees of freedom associated with the Jahn-Teller (JT) active ions, i.e., Co3+ and Fe2+ plays major role to drive the ME in the above materials. In this study, we further show that the complete vanishing of the giant spin driven electric polarization in CBCO by replacing the JT active Co3+ ions with the small amount ( CaBaCo4-xFexO7 ; x = 0.10 ) of non-JT active, orbital singlet Fe3+ ions. The crystal structure of the Fe doped CBCO preserves the same Orthorhombic Pbn21 like parent compound and the magnetization studies shows the paramagnetic to AFM at 95 K and AFM to FiM at 50 K. The dielectric studies show two frequency independent transitions close to 90 K and 50 K and the pyroelectric current (PC) measurements show broad and symmetric peaks close to 40 K and 85 K, which are sensitive to the temperature heating rates, poling electric fields and poling temperatures and these peaks are assigned to thermally stimulated depolarization currents which arises from the excess holes. This work provides the strong insights between the Co3+ orbital degree of freedom and the spin driven electric polarization properties in this family of materials.

Keywords: Cobaltites, Jahn-Teller effect, Frustrated magnetism, Magnetoelectric , Multiferroics