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Exceptional magnetoelectric coupling behavior of spin-chain compounds, Tb2BaNiO5 and Tb2BaCoO5

E V Sampathkumaran

TIFR Mumbai

Recently, we have made significant contributions to the currently exciting topic of ‘Multiferroics’ in Condensed Matter Physics area by poineering multiferroicity in a number of compounds in the spin-chain family, R2BaXO5 (X= Ni, Co). Among these, the behavior of Tb compounds is exceptional, which will be brought out in my talk. This compound is characterized by two magnetic ordering regions (<25 K, 25-63 K). However, multiferroicity occurs below 25 K only. The Co analogue also exhibits mutiferroicity below 18.8 K. The most notable observation is that the observed change in the dielectric constant below TN brought out by externally applied magnetic fields, following spin-reorientation, is the largest ever observed for bulk form of polycrystals of any compound literature [1]. Besides, the temperature dependence of magnetic structure demands a new theoretical approach to understand the origin of magnetism-induced ferroelectricity in these Tb compounds [2].

1. S.K. Upadhyay et al Phys. Rev. B 96, 014418 (2017); App. Phys. Lett. 112, 262902 (2018).
2. Ram Kumar et al, Phys. Rev. B 99, 100406(R), 2019.