Evolution of magnetic order in multiferroic Pb(Fe_2/3W_1/3)O₃-BiFeO₃ solid solution

Multiferroic materials have attracted much interest in the last decade due to both the intriguing fundamental science and the potential applications in spintronics and magnetoelectric data storage devices. In this work, we have investigated and discussed the evolution of the magnetic properties of the multiferroic (1-x)Pb(Fe_2/3W_1/3)O₃-xBiFeO₃ solid solution ((1-x)PFW-xBFO, x = 0, 0.025, 0.05, 0.075, 0.1 and 0.15). The magnetic phase diagram is established based on the magnetic measurement results, which reveals six magnetically ordered states on the PFW-rich side of the solid solution. The origins of the complex evolution of magnetic order in the PFW-BFO solid solution are discussed from the point view of the variations in both the –Fe–O–Fe– and –Fe–O–W–O–Fe– superexchange routes, which are intimately related to the ratio of magnetic Fe³⁺ ion concentration on the B-site and the changes in the local structural order/disorder and chemical homogeneities. Combining the magnetic phase diagram with the relaxor characteristic phase diagram of the (1-x)PFW-xBFO system, a striking feature is found that the ergodic relaxor (ER) state and the weakly ferromagnetic phase coexist in the composition range of 0.025 ≤ x ≤ 0.1 between the freezing temperature T_f and the Burns temperature T_B.