Study On The Magnetism Of Double Perovskite La_1.5Sr_0.5Co_1-xA_xMnO₆（A=Ga、Ni,0≤x＜1）

Double perovskite materials are widely used in electronic storage and other fields due to their excellent physical properties（such as magnetic phase transition,spin glass and exchange bias（EB）effect,etc.）.Recently,the large zero-field-cooling EB effect observed in La_1.5Sr_0.5CoMnO₆has attracted researchers’the attention.For this effect,this thesis takes La_1.5Sr_0.5CoMnO₆as the research object,and focuses on the regulation of the EB effect by doping non-magnetic ions and magnetic ions in its Co-site,respectively.The microscopic mechanism of related magnetism is discussed by comparision.Non-magnetic Ga-doped La_1.5S_r0.5Co_1-xGa_xMnO₆（x=0、0.1、0.2、0.3、0.35、0.4 and 0.5）and magnetic ion Ni-doped La_1.5S_r0.5Co_1-xNi_xMnO₆（x=0、0.1、0.2、0.3、0.35 and 0.4）series of samples were prepared by sol-gel method and their magnetic properties were studied.X-ray diffraction analysis shows that the sample can maintain the single-phase perovskite structure when the doping content is lower than 0.4.Magnetic measurements show that the Co³⁺–O^2-–Mn⁴⁺ferromagnetic（FM）superexchange interaction can be diluted with the substitution of non-magnetic Ga ions,resulting in a decrease in the value of the paramagnetic to ferromagnetic transition temperature T_C.In contrast,the substitution of Ni ions promoted the Co²⁺/Ni²⁺–O^2-–Mn⁴⁺FM superexchange interaction,resulting in an increase in T_C.What they have in common is that they can both induce anti-site disorder（ASD）and spin-glass（SG）phases,and realize the regulation of the EB effect.For the Ga-doped samples,when the doping content is 0.1,the samples exhibit the maximum exchange bias field(zero-field-cooling exchange bias field H_SEB=0.47T,and conventional exchange bias field H_CEB=0.93T).For Ni-doped samples,the maximum conventional exchange bias field occurs at a doping content of 0.1(H_CEB=1.27T),while the maximum zero-field-cooling exchange bias field occurs at a doping content of 0.2(H_SEB=0.47T).The analysis shows that for Ga-doped samples,the unidirectional interface anisotropic coupling between FM/antiferromagnetic（AFM）and/or FM/SG is the reason for the change of EB effect;For Ni-doped samples,the inverse relationship between ASD and SG affects EB effect,and SG is the key factor of zero-field-cooling EB effect.In short,the EB effect can be regulated by different ion doping,which has potential application value and provides a new opportunity for the development of spin valve devices.