Preparation And Magnetic Properties Of Tb(Gd)/Cr Bilayers And Multilayers

Controling the direction of the magnetic moment of electron spin has become a scientific issue that focuses on spintronics.The discovery of the giant magnetoresistance effect has led to great interest in the regulation of spin magnetic moments based on the exchange bias of ferromagnetic/antiferromagnetic(FM/AFM)systems.In recent decades,most researchers have studied the FM/AFM film system with a Curie temperature higher than that Neel temperature of the antiferromagnetic materials.And researches study little about higher temperature than the Curie temperature.So the study of the exchange bias of the FM/AFM film system with a Neel temperature higher than the Curie temperature will help to understand the exchange bias mechanism,and it will provide useful guidance to design spintronic device which are based on electron spin regulation.In this paper,we studied the exchange bias of double-layer film and multilayer film with T_C<T_N.The effects of annealing temperature,interface roughness and cooling field on exchange bias are studied.Ferromagnetic metal ruthenium(block T_C=220K),ferromagnetic metal ruthenium(block T_C=293K)and antiferromagnetic metal chrome(block T_N=311K)are selected and magnetron sputtering method is used in monocrystalline silicon.A two-layer film Tb/Cr,a multilayer film Tb/Cr,and a multilayer film Gd/Cr of different annealing temperatures were prepared on the sheet.The microstructure,hte thickness of films and magnetic properties of the film samples were characterized by X-ray diffractometer XRD,VSM and scanning electron microscopy.Experimental results show:(1)The Tb/Cr double-layer exhibits anomalous magnetic properties:When the temperature T<TC,the hysteresis behavior of the ferromagnetic layer indicates that the magnetic moments in the ferromagnetic layer are arranged in an orderly manner due to the interfacial coupling of the FM/AFM in the temperature region.When T>TN,the coercivity and the exchange bias field still exist.This behavior indicates that the exchange coupling effect exist in the FM/AFM interface,and there is a net spin in the ferromagnetic layer,which means that the Curie temperature of the ferromagnetic layer has become higher.(2)When the direction of the applied magnetic field coincides with the direction of the cooling field in the Tb/Cr double-layer,the sign of the exchange bias field is positive;when the direction of the applied magnetic field is opposite to the direction of the cooling field,the sign of the exchange bias field is negative;the coercivty HC as the cooling field increases,it gradually increases to near-stable,and the exchange bias field HE increases first and then decreases as the cooling field increases.We suspect that the anomalies in the films are caused by the competition between the Zeeman energy and the exchange coupling energy between the interfaces.(3)About the multilayersTb/Cr,its coercivity and temperature show a non-monotonic relvationship,the specific performance is that the coercivity decreases first and then increases with the increasing of temperature.When there is a range of fluctuations,a"double hysteresis"phenomenon occurs.This anomaly is closely related to the magnetic domain structure of the antiferromagnetic metal Cr and the FM/AFM interface coupling.We believe that the volume ratio of I-SDW and C-SDW magnetic structures in metallic chromium changes with temperature,resulting in a non-monotonic relationship between coercivity and temperature.(4)About the multilayers Gd/Cr,the exchange bias field and coercivity are related to the annealing temperature of the sample,the measured temperature,and the applied cooling field.As the annealing temperature increases,the roughness of the sample surface becomes larger;the exchange bias field of the sample with different annealing temperatures varies with the increasing of temperature,and when the temperature rises to the Nell temperature,the coercivity still exists;as the applied cooling field increases,the two samples with higher annealing temperatures show a change in the exchange bias from negative to positive.We hypothesize that as the cooling field changes,the competition between the exchange coupling energy and the magnetostatic energy in the film sample leads to a non-monotonic change between the exchange bias field,the coercivity and the cooling field.In summary,the exchange bias of T_C<T_N of FM/AFM film is different from that T_C>T_N of FM/AFM film system,especially at T_C<T<T_N and T>T_N,abnormal behavior has occurred.We believed that the results of this paper will provide a reference for the regulation of the spin magnetic moment of the T>T_C region and a deep understanding of the mechanism of the exchange bias effect.