Canting Angle Behavior of Magnetic Moments in Y‐Substituted Tb2BaNiO5 and Its Relevance for Magnetoelectric Coupling

The Haldane‐spin chain compound, Tb2BaNiO5, has been known to be an exotic multiferroic system, exhibiting antiferromagnetic anomalies at T N1 = 63 K and T N2 = 25 K, with ferroelectricity appearing below T N2 only. Previous reports in addition have established that, interestingly, Tb ions play a direct and decisive role to lead to multiferroic properties with a critical canting angle of magnetic moments, unlike other well‐known multiferroics. Herein, the results of temperature‐dependent neutron powder diffraction studies on Tb2–x Y x BaNiO5 are reported, to get an insight into the critical canting angle for multiferroic behavior. While multiferroic transition temperature decreases linearly with Y concentration, there is an abrupt drop of relative canting angle (of Tb and Ni magnetic moments) with respect to that in the parent compound for an initial substitution of x = 0.5 in the multiferroic region, without any notable change thereafter. Therefore, it is inferred that this critical canting angle is made up of two components—cooperative (long‐range) and local (short‐range) contributions. The magnetic structure of Tb0.5Y1.5BaNiO5 at 2 K is studied. The criticality of the canting angle between the moments of Tb and Ni is responsible for multiferrocity in this compound. The Tb and Ni moments highlighted in red dotted circles signify the direction of canting of the moments between c‐axis and ab‐plane.