8851

8212

كارشناسي ارشد

ماده چگال

اصفهان: دانشگاه صنعتي اصفهان، دانشكده فيزيك

1392

دوازده،118ص.: مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

مجتبي اعلايي

فرهاد شهبازي

20/2/93

جواد هاشمي فر، اسماعيل عبدالحسيني سارسري

فيزيك

ID8212

AbstractIn this thesis we investigated the electronic and magnetic properties of T b2 T i2 O7 which is a frustrated cubic pyrochlore oxide with spin liqude phase We usedDensity Functional Theory DFT to explore the electronic and magnetic proper ties of this system All DFT calculations have been done with FP LAPW methodby use of Fleur code We approched exchange correlation energy of electronswith GGA and GGA U functionals The GGA calculations predict a magneticmetalic state for T b2 T i2 O7 which is in con ict with the experiment UsingGGA U we could correct coulomb interactions between f electrons thereforeT b2 T i2 O7 is converted to a magnetic insulator The analysis of electronic densityof state DOS shows 4f electrons of Tb atoms as the source of magnetism Thisanalysis also indicates a weak hybridization between Tb f orbitals and O porbitals Because of existance of strong spin orbit coupling SOC in f electronswe repeated the calculations with GGA U SOC for noncollinear con gurationsin addition to the collinear ones The magnetic moment of Tb obtained 7 3 Band 7 1 B from collinear and noncollinear calculations respectively But in theexperiment the magnetic moment of Tb was mesured about 5 B In fact theDFT calculations are traped in the local minima and in order to improve themagnetic moment of Tb we need a more sophisticated methods to nd the globalminimum in our electronic structure calculations To investigate the ground stateof T b2 T i2 O7 we compared total energies in two con gurations all in long rangeorder and two in two out spin ice order we found that the all in is more stablethan two in two out Keywords pyrochlore frustration density functional theory collinear mag netism noncollinear magnetism

مجتبي اعلايي

فرهاد شهبازي

جواد هاشمي فر، اسماعيل عبدالحسيني سارسري