A remarkable high entropy effect on the magnetic behaviour of quadruple perovskites

Abstract

Here, for the first time, we report the stabilization of high entropy quadruple perovskites of general formula with a typical structural feature of 1 : 3 ordering of A-site cations. The stabilized A-site high entropy phases (A_0.2)₅Cu_3−xMn_xTi_4−yMn_yO₁₂ (x = 0 and 0.5; 0 ≤ y ≤ 2.5) provide the scope to explore the role of the high entropy effect through manipulation of their magnetic properties over a wide range. The spin polarized ferromagnetic like cluster appears at the cost of the antiferromagnetic state in a low Mn containing sample, which is in huge contrast to conventional systems. The onset of magnetic ordering is largely suppressed in high entropy phases for more Mn doped samples. Although it is expected that the T_C value will increase with the increase in Mn content at the B-site, the T_C values of LaCu₃Ti₃MnO₁₂ and high entropy (La_0.2Pr_0.2Nd_0.2Sm_0.2Y_0.2)Cu₃Ti₂Mn₂O₁₂ are similar. The increase in Mn content with T_C is compensated by high entropy induced disordering. In addition, the magnetic ground states of high entropy phases are remarkably modified. The ferrimagnetic states of the conventional counterparts are most likely transformed into the ferromagnetic like canted antiferromagnetic states in high entropy phases. The observed magnetic behaviour can be understood by considering the local lattice distortion in the structural framework of multiple A-site cations, which has a profound impact on magnetic exchange interactions. The large distortion of M–O–M bond angles and fluctuating M–O bond lengths due to the different sized A-cations largely hamper the superexchange pathways. Our study provides an excellent opportunity to tailor the functionalities of quadruple perovskites through the high entropy based design approach.