Resonance Effect of Ionic Valences on the Structural and Magnetic Properties of Dy 2 NiMnO 6 Induced by Nonmagnetic Al Ion Doping

Magnetic and structural properties of nonmagnetic Al 3+ doping in Dy 2 NiMnO 6 compounds have been investigated systematically. The X‐ray diffraction shows that all the samples are crystallized in double perovskite. The UV–vis absorption spectra present a non‐monotonous dependence of optical band gap on the Al 3+ doping content, which is attributed to the local structural distortion induced by Al 3+ doping. Magnetization curves show three magnetic transitions corresponding to the temperatures T C1 , T C2 , and T N , which are attributed to ferromagnetic interactions of Mn 4+ –O–Ni 2+ , Mn 3+ –O–Ni 3+ , and antiferromagnetic interactions of the Dy 3+ with the Ni(Al)/Mn moments, respectively, changing with the Al 3+ doping content. A resonance effect of ionic valences has been observed while Al 3+ doping at Ni site (B site), i.e., not only the Mn valence decreasing, but also the Ni valence increasing, without destroying the long‐range Ni–O–Mn orders. The Al 3+ doping causes the weakening of the super‐exchange interaction between Mn 4+ and Ni 2+ ions and the Ni/Mn ordered degrees. Meanwhile, the amount of Mn 3+ and Ni 3+ ions and the strengthening of the Mn 3+ –O–Ni 3+ ferromagnetic interactions increase with trivalent Al ion doping. As a result, T C1 decreases, T C2 and T N increase first and then decrease, showing a non‐linear change, with the Al 3+ doping content increase. The resonance effect of ionic valences provides a new way to understand and adjust the magnetic properties for the application.