| Quantum paraelectric SrTiO3 has many strange electric and optical properties,and it is widely used in communication,digital storage and other fields.Recently,a few studies find that the stress and minor elements doping in the material can induce some new interesting phenomena and properties including ferroelectric,ferromagnetism and magnetoelastic,etc.It extends the application of SrTiO3 to other wider fields such as multiple-state storage and continues to be the research focus of the condensed matter physics and materials science.In this paper,we are going to systematically study the microstructures,magnetic properties,dielectric and ferroelectric properties of the dilute magnetic doping SrTi03 ceramics prepared by the traditional solid phase method.The physical mechanism of the ferroic induced by doping is discussed.The main contents are as follows:1.The different components of Fe-doped SrTiO3 ceramics were synthesized by solid state method.The experimental results show that a slight change of the relative molar ratio of Sr/Ti ratio can greatly affect the magnetic properties and dielectric properties of Fe-doped SrTiO3.Unlike the paramagnetic properties of SrTi0.9Fe0.1O3-?,the Sr0.98Ti0.9Fe0.1O3-? and Sr0.98Ti0.92Fe0.1O3-? have the characteristics of room-temperature ferromagnetism and low-temperature spin glass.It is confirmed by EPR and oxygen treatment that the ferromagnetism is derived from the occupying on the Sr-sites by more low-valence Fe ions,thereby enhancing the ferromagnetic double exchange between the mixed valence Fe ions and the ferromagnetic exchange of non-linear bonding Fe ions occupied on the Sr-sites and Ti-sites.At the same time,the dielectric relaxation peaks appearing in Sr0.98Ti0.9Fe0.1O3-? and Sr0.98Ti0.92Fe0.1O3-?indicate a dipole glass behavior exists at low-temperature.The results from the test of oxygen treatment,pyroelectric and specific heat indicate that the origin of dipole glass is a correlate defective dipole ciusters formed by off-center Fe2+ ions occupied on Sr-site and oxygen vacancies.2.A series of Mn-doped SrTiO3 ceramics with different components were prepared and the substitution site effect of Mn ions was studied.It was found that both A site and AB site co-doped samples can induce spin glass and dipole glass behavior at low temperature.The results from the test of TGA,EPR and oxygen treatment confirmed that the spin glass is originated from the exchange between non-equivalent Mn ions,and the dipole glass mainly comes from the motion of the local dipoles{Mn2+-O2--Mn3+}.The magnetic dielectric measurements show that the Sr0.96Mn0.04Ti0.94Mn0.06O3 has a low temperature magnetic dielectric effect of up to 12%,which may be from the coupling effect of spin glass and dipole glass.3.We prepared the(BaxMn1-x)0.4Sr0.6TiO3(x=0,0.05,0.075,0.1,BMST)ceramics by doping.With the increase of Mn content,the spin glass behavior is observed at low temperature,and the sample x=0.075 has the strongest magnetic properties.It is confirmed by the results of the test of TGA and EPR that the magnetism is derived from the ferromagnetic exchange interaction of non-equivalent Mn ions.The dielectric properties of BMST can be controlled by the substitutions of Mn.Besides,the Mn-doping can reduce the Curie temperature and dielectric relaxation activation energy of BST.The sample x=0.075 has a more obvious hysteresis loop at room temperature,which probably is derived from the dispersion of the ferroelectric phase transition peak.Only samples x=0.05 and x=0.1 have a weak magnetic dielectric effect,which may be related to the magnetoelectric interaction of the local dipoles. |
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