A Modification Of Magnetoelectric Effect In Metal-organic Frameworks By Doping

Magnetoelectric materials as new multi-functional materials have been a research hot topic due to the great potential application in the information storage technology and materials.From the viewpoint of practical application,ideal magnetoelectric materials should possess great magnetoelectric response,low operating magnetic field and room-temperature(or higher)operating temperature simultaneously.However,such materials are extremely rare,owing to giant magnetodielectric response upon applied small magnetic fields often requiring strong coupling between spins and electric dipoles.Metal organic frameworks(MOF)attract reseachers’ interest due to its adjustability and abundant structure.Although a series of MOFs with coexistence of the magnetic and ferroelectric properties have been reported,only a few of them exhibit magnetoelectric coupling effect.What is worse,the megnetoelectric coupling effect in these MOFs is not only fairly weak.but also often occurs in low temperature range.Thus,it is still a challenge to explore MOFs with magnetoelectric coupling effect.In this thesis.three multivariate metal-organic frameworks of[NH2(CH3)2][FeⅢFeⅡ1-xMgⅡx(HCOO)6](x = 0.38-0.49)(1).[NH2(CH3)2][FeⅢFeⅡ1-x NiⅡx(HCOO)6](x = 0.63-0.69)(2)and[NH2(CH3)2][FeⅢNiⅡ(HCOO)6](3)were prepared respectively through dopirng MgⅡ and NiⅡ ions into the mix-valence metal-organic framework[NH2(CH3)2][FeⅢFeⅡ(HCOO)6].Study on the magnetic peroperties,electric peroperties and magnetoelectric coupling effect of compound 1,2 and 3 reveals that doping is an efficient method to modificate the properties of’MOFs,the main results are shown below:1.The non-magnetic divalent metal ion MgⅡ was selected as a dopant to prepare the multivariate MOF of 1.The chemical formula was determined through single crystal structure and ICP-OES.The result of magnetic measurment showed that the Neel temperature changed from 37 K to 28 K.The activation energy of electron hopping of 1 was 0.399 eV for E//c and 0.406 eV for E丄c,which was smaller than that in the undoped MOF.However,there was little influence on the magnetoelectric effect,the magnetodielectric coeffcient of compound 1 was similar to the undoped MOF.2.The magnetic divalent metal ion NiⅡ was slected as a dopant to prepare two different doping content of multivariate MOF of 2 and 3.The chemical formula of 2 and 3 were determined through single crystal structure and ICP-OES.The magnetodielectric(MD)coefficient of 2 remaining between-20%and-24%in the 300-400 K temperature range,even at 0.1 T.While the magnetodielectric(MD)coefficient of the 3 is around-4%in the temperature of 400 K and a external magnetic field of 9 T.