Effect Of Ni And Mn Ion Doping On Physical Properties Of Y-type Hexagonal Ferrite Ba_0.5Sr_1.5Zn₂Fe₁₂O₂₂

Multiferroic materials with magnetoelectric?ME?coupling effect have attracted considerable attention,in view of various applications in new generation of information devices.Traditional single-phase multiferroic materials always have weak magnetoelectric coupling,which can only be realized at low temperature.Therefore,it is difficult to apply single-phase multiferroic materials in related devices.In recent years,It is found that the special helical magnetic order in hexagonal ferrite can induce polarization in a small magnetic field and rather higher temperature.It is intrinsic magnetoelectric coupling characteristics and hexagonal ferrite partly overcomes the weakpionts of single-phase multiferroic materials.In the hexagonal ferrite family,although Z-type and U-type ferrites can achieve magnetoelectronic coupling at room temperature,their magnetoelectronic coupling is very weak.Y-type hexagonal ferrites have stronger magnetoelectric coupling effect than Z-type and U-type ferrites.However,because of low resistivity and low mangnetic order transition temperature,the ME coupling is difficult to achieve at room temperature.Therefore,how to broaden the temperature range of magnetoelectric coupling effect in Y-type hexagonal ferrite to achieve has become the most concerned issue.Doping is one of the effective means to control the magnetic configuration and the resistivity of hexagonal ferrites.The series of polycrystalline samples of Ba_0.5Sr_1.5Zn₂Fe_12-xNi_xO₂₂?x=0,0.05,0.1,0.2,0.35 and 0.5?and Ba_0.5Sr_1.5Zn₂Fe_12-xMn_xO₂₂?x=0.1,0.3,0.5 and 0.7?were prepared by solid-state method.The investigation imply that the lattice constants?a,c?of the samples decrease from 5.8520???and 43.3524???to 5.8322???and 43.2420???,and Ni doping can depress the impurities of Z-type and M-type hexagonal ferrites in Y-type hexagonal ferrites;Ni doping changes the bond angles of Fe-O-Fe in the boundaries of S and T blocks,which enhances the superexchange interactions at the boundary of blocks in hexagonal ferrites,and increases the temperature at which the material changes from helical to ferromagnetic order.The temperature range of the helical magnetic oders and the magnetic field range which can produce polarization are expanded after Ni doping.Mn³⁺doping has no effect on the above properties of Y-type hexagonal ferrite.The experimental results show that the enhancement of Fe-O-Fe superexchange interactions in Y-type hexagonal ferrite is mainly resulted from the change of Fe-O-Fe bond angle,which is caused by ion substitution with different radius.As for dielectric properties of Y-type hexagonal ferrites,from low temperature to high temperature,three dielectric relaxations occur,which can be ascribed to variable range hopping of samll polaron,electron hopping beteween Fe²⁺and Fe³⁺,and the reversal of defect complex(Vo⁺⁺-V_Sr),respectively.After the doping,the doping inhibits the variable range hopping of small polaron in Ba_0.5Sr_1.5Zn₂Fe₁₂O₂₂,and the dielectric relaxation peak caused by redirection reversal of defect complex(Vo⁺⁺-V_Sr)may also be inhibited by doping.