19171

2155 دكتري

دكتري

ماده چگال

اصفهان : دانشگاه صنعتي اصفهان

1402

چهارده، 153ص. مصور، جدول، نمودار

1402/10/30

كتابنامه

فيزيك

فيزيك

1402/11/04

23005224

ﻣﻮﺍﺩ ﻣﻐﻨﺎﻃﻴﺴﻲ ﺑﻪ ﺩﻟﻴﻞ ﻛﺎﺭﺑﺮﺩﻫﺎﻱ ﻣﺘﻨﻮﻉ ﺗﻮﺟﻪ ﻣﺤﻘﻘﺎﻥ ﺑﺴﻴﺎﺭﻱ ﺭﺍ ﺑﻪ ﺧﻮﺩ ﻣﻌﻄﻮﻑ ﻛﺮﺩﻩﺍﻧﺪ. ﺍﺯ ﻃﺮﻓﻲ ﺑﺮﺭﺳﻲ ﺍﻳﻦ ﻣﻮﺍﺩ ﺑﻪ ﺩﻟﻴﻞ ﭘﻴﭽﻴﺪﮔﻲﻫﺎﻳﻲ ﻛﻪ ﺩﺭ ﺳﺎﺧﺘﺎﺭ ﺍﻟﻜﺘﺮﻭﻧﻲ ﺁﻥﻫﺎ ﻭﺟﻮﺩ ﺩﺍﺭﺩ ﻫﻤﻮﺍﺭﻩ ﻳﻚ ﭼﺎﻟﺶ ﺟﺪﻱ ﺑﻮﺩﻩ ﺍﺳﺖ. ﺍﻳﻦ ﺭﺳﺎﻟﻪ ﺑﺮ ﻣﻮﺍﺩ ﭘﺎﺩﻓﺮﻭﻣﻐﻨﺎﻃﻴﺴﻲ ﻣﺘﻤﺮﻛﺰ ﺷﺪﻩ ﺍﺳﺖ ﻛﻪ ﻋﻨﺼﺮ ﻣﻐﻨﺎﻃﻴﺴﻲ ﺁﻥ ﻳﻜﻲ ﺍﺯ ﻋﻨﺎﺻﺮ ﻭﺍﺳﻄﻪ 3d ﺍﺳﺖ. ﺑﺮﺍﻱ ﺍﻳﻦ ﻣﻨﻈﻮﺭ 30 ﺗﺮﻛﻴﺐ ﻣﺘﻔﺎﻭﺕ ﺑﺎ ﺳﺎﺧﺘﺎﺭ ﻓﻀﺎﻳﻲ ﮔﻮﻧﺎﮔﻮﻥ ﺍﻧﺘﺨﺎﺏ ﺷﺪ. ﺑﻪ ﺩﻟﻴﻞ ﺍﻫﻤﻴﺖ ﭘﺎﺭﺍﻣﺘﺮ ﻫﺎﺑﺎﺭﺩ ﺩﺭ ﺗﻌﻴﻴﻦ ﺧﺼﻮﺻﻴﺎﺕ ﺍﻳﻦ ﻣﻮﺍﺩ ﺍﺑﺘﺪﺍ ﺑﺎ ﺍﺳﺘﻔﺎﺩﻩ ﺍﺯ ﻣﺤﺎﺳﺒﺎﺕ ﺍﺑﺘﺪﺍ ﺑﻪ ﺳﺎﻛﻦ ﺑﻪ ﺗﻌﻴﻴﻦ ﺩﻗﻴﻖ ﺍﻳﻦ ﭘﺎﺭﺍﻣﺘﺮ ﭘﺮﺩﺍﺧﺘﻴﻢ. ﻣﺤﺎﺳﺒﺎﺕ ﺑﺎ ﺍﺳﺘﻔﺎﺩﻩ ﺍﺯ ﻛﺪ ﻛﻮﺍﻧﺘﻮﻡ ﺍﺳﭙﺮﺳﻮ ﻭ ﺑﺎ ﺭﻭﺵﻫﺎﻱ ﻣﺨﺘﻠﻔﻲ ﺍﺯ ﺟﻤﻠﻪ ﺭﻭﺵ ﭘﺎﺳﺦ ﺧﻄﻲ ﻭ ﻧﻈﺮﻳﻪ ﺗﺎﺑﻌﻲ ﭼﮕﺎﻟﻲ ﺍﺧﺘﻼﻟﻲ ﺍﻧﺠﺎﻡ ﺷﺪ. ﺑﻪ ﻣﻨﻈﻮﺭ ﺩﺳﺘﻴﺎﺑﻲ ﺑﻪ ﻣﻘﺪﺍﺭ ﺩﻗﻴﻖﺗﺮ ﭘﺎﺭﺍﻣﺘﺮ ﻫﺎﺑﺎﺭﺩ ﻣﺤﺎﺳﺒﺎﺕ ﺑﻪ ﺻﻮﺭﺕ ﺧﻮﺩﺳﺎﺯﮔﺎﺭ ﺍﻧﺠﺎﻡ ﺷﺪ. ﺩﺭ ﺍﺩﺍﻣﻪ ﺭﻫﻴﺎﻓﺖ DFT+U+V ﻣﻮﺭﺩ ﺍﺳﺘﻔﺎﺩﻩ ﻗﺮﺍﺭ ﮔﺮﻓﺖ ﺗﺎ ﭘﺎﺭﺍﻣﺘﺮ ﻫﺎﺑﺎﺭﺩ ﺩﺭﻭﻥ ﺟﺎﻳﮕﺎﻫﻲ (U) ﻭ ﺑﺮﻭﻥ ﺟﺎﻳﮕﺎﻫﻲ (V) ﺑﻪ ﺩﺳﺖ ﺁﻳﺪ. ﻧﺘﺎﻳﺞ ﻣﺤﺎﺳﺒﻪ ﭘﺎﺭﺍﻣﺘﺮ ﻫﺎﺑﺎﺭﺩ ﺩﺭ ﺩﻭ ﺭﻭﺵ ﭘﺎﺳﺦ ﺧﻄﻲ ﻭ ﺭﻭﺵ ﺗﺎﺑﻌﻲ ﭼﮕﺎﻟﻲ ﺍﺧﺘﻼﻟﻲ ﻧﺸﺎﻥ ﺩﺍﺩ ﻛﻪ ﺣﺪﺍﻛﺜﺮ ﺍﺧﺘﻼﻑ ﻣﻴﺎﻥ ﻧﺘﺎﻳﺞ ﺣﺎﺻﻞ ﺍﺯ ﺳﻪ ﺭﻭﺵ ﻳﻚ ﺻﺪﻡ ﺍﻟﻜﺘﺮﻭﻥ ﻭﻟﺖ ﺍﺳﺖ. ﺍﺯ ﺍﻳﻦ ﺭﻭ ﺩﺭ ﺍﺩﺍﻣﻪ ﺑﻪ ﺩﻟﻴﻞ ﺁﻥﻛﻪ ﺭﻭﺵ ﺗﺎﺑﻌﻲ ﭼﮕﺎﻟﻲ ﺍﺧﺘﻼﻟﻲ ﻋﻠﻲﺭﻏﻢ ﺩﻗﺖ ﺑﺎﻻ ﻫﺰﻳﻨﻪ ﻣﺤﺎﺳﺒﺎﺗﻲ ﻛﻤﺘﺮﻱ ﺩﺍﺷﺖ ﺍﻳﻦ ﺭﻭﺵ ﺑﺮﺍﻱ ﺗﻌﻴﻴﻦ ﭘﺎﺭﺍﻣﺘﺮ ﻫﺎﺑﺎﺭﺩ ﻣﻮﺭﺩ ﺍﺳﺘﻔﺎﺩﻩ ﻗﺮﺍﺭ ﮔﺮﻓﺖ. ﺩﺭ ﺍﺩﺍﻣﻪ ﺑﺮﺍﻱ ﺗﻌﻴﻴﻦ ﺧﻮﺍﺹ ﻣﻐﻨﺎﻃﻴﺴﻲ ﺗﺮﻛﻴﺒﺎﺕ ﻣﻮﺭﺩ ﺑﺮﺭﺳﻲ ﺑﻪ ﻣﺤﺎﺳﺒﻪ ﺑﺮﻫﻢﻛﻨﺶ ﺗﺒﺎﺩﻟﻲ ﭘﺮﺩﺍﺧﺘﻴﻢ. ﺑﺮﺍﻱ ﺍﻳﻦ ﻣﻨﻈﻮﺭ ﺍﺯ ﺭﻭﺵ ﺍﺧﺘﻼﻑ ﺍﻧﺮﮊﻱ ﺍﺳﺘﻔﺎﺩﻩ ﻛﺮﺩﻳﻢ. ﺑﻪ ﻣﻨﻈﻮﺭ ﺗﻌﻴﻴﻦ ﺩﻗﻴﻖ ﺗﻌﺪﺍﺩ ﺿﺮﺍﻳﺐ ﺗﺒﺎﺩﻟﻲ ﻣﻮﺭﺩ ﻧﻴﺎﺯ ﺩﺭ ﺍﻧﺠﺎﻡ ﻣﺤﺎﺳﺒﺎﺕ ﺑﺮﺍﻱ ﻫﺮ ﺳﺎﺧﺘﺎﺭ، ﺍﺯ ﻣﻔﻬﻮﻡ ﻓﻀﺎﻱ ﭘﻮﭼﻲ ﺩﺭ ﻳﻚ ﻣﺎﺗﺮﻳﺲ ﺍﺳﺘﻔﺎﺩﻩ ﻛﺮﺩﻳﻢ. ﺿﺮﺍﻳﺐ ﺗﺒﺎﺩﻟﻲ ﻫﺎﻳﺰﻧﺒﺮﮒ ﺩﺭ ﺩﻭ ﺭﻫﻴﺎﻓﺖ DFT+U ﻭ DFT+U+V ﻣﺤﺎﺳﺒﻪ ﺷﺪﻧﺪ. ﺩﺭ ﻧﻬﺎﻳﺖ ﺑﺎ ﺩﺭ ﻧﻈﺮ ﮔﺮﻓﺘﻦ ﻫﺎﻣﻴﻠﺘﻮﻧﻲ ﺍﺳﭙﻴﻨﻲ ﺩﻣﺎﻱ ﺑﺤﺮﺍﻧﻲ ﺍﻳﻦ ﻣﻮﺍﺩ ﺑﺎ ﺍﺳﺘﻔﺎﺩﻩ ﺍﺯ ﺍﻟﮕﻮﺭﻳﺘﻢ ﻣﺒﺎﺩﻟﻪ ﭘﻴﻜﺮﺑﻨﺪﻱ ﺩﺭ ﭼﺎﺭﭼﻮﺏ ﺷﺒﻴﻪﺳﺎﺯﻱ ﻣﻮﻧﺖ ﻛﺎﺭﻟﻮ ﻣﺤﺎﺳﺒﻪ ﺷﺪ. ﺑﺮﺍﻱ ﺍﻳﻦ ﻣﻨﻈﻮﺭ ﺍﺯ ﻛﺪ ESpinS ﺍﺳﺘﻔﺎﺩﻩ ﺷﺪ. ﻣﺤﺎﺳﺒﺎﺕ ﺑﺮﺍﻱ ﺗﻌﻴﻴﻦ ﮔﺬﺍﺭ ﺩﺭ ﺳﻪ ﺭﻫﻴﺎﻓﺖ ﻣﺘﻔﺎﻭﺕ ﺍﻧﺠﺎﻡ ﺷﺪ. ﻧﺘﺎﻳﺞ ﻧﺸﺎﻥ ﺩﺍﺩ ﻛﻪ ﺭﻫﻴﺎﻓﺖ GGA ﺩﻣﺎﻱ ﮔﺬﺍﺭ ﺭﺍ ﺑﺴﻴﺎﺭ ﺑﻴﺸﺘﺮ ﺍﺯ ﻣﻘﺪﺍﺭ ﺗﺠﺮﺑﻲ ﻭ ﺑﺎ 113 ﺩﺭﺻﺪ ﺧﻄﺎ ﭘﻴﺶﺑﻴﻨﻲ ﻣﻲﻛﻨﺪ. ﺭﻫﻴﺎﻓﺖ GGA+U ﻣﻨﺠﺮ ﺑﻪ ﺩﻣﺎﻫﺎﻱ ﻧﺰﺩﻳﻚﺗﺮ ﺑﻪ ﻣﻘﺪﺍﺭ ﺗﺠﺮﺑﻲ ﺷﺪ. ﺑﻪ ﻃﻮﺭﻱ ﻛﻪ ﺧﻄﺎﻱ ﻣﻴﺎﻥ ﻣﻘﺎﺩﻳﺮ ﮔﺰﺍﺭﺵ ﺷﺪﻩ ﺑﺎ ﻣﻘﺎﺩﻳﺮ ﺗﺠﺮﺑﻲ ﺑﻪ 53 ﺩﺭﺻﺪ ﺭﺳﻴﺪ. ﺑﻪ ﻣﻨﻈﻮﺭ ﺑﻬﺒﻮﺩ ﻧﺘﺎﻳﺞ ﺣﺎﺻﻞ ﺍﺯ ﺍﻳﻦ ﺭﻫﻴﺎﻓﺖ ﻭ ﻧﻴﺰ ﺩﺭ ﻧﻈﺮ ﮔﺮﻓﺘﻦ ماهيت كوانتمي اسپين ضريب تصحيح (S+1)/S را بر دماهاي به دست آمده اعمال كرديم. ﺩﺭ ﻧﺘﻴﺠﻪ ﺍﻋﻤﺎﻝ ﺍﻳﻦ ﺗﺼﺤﻴﺢ ﺩﺭﺻﺪ ﺧﻄﺎ ﺑﻪ 44 ﺩﺭﺻﺪ ﻛﺎﻫﺶ ﻳﺎﻓﺖ. ﻋﻼﻭﻩ ﺑﺮ ﺍﻳﻦ ﺿﺮﻳﺐ ﻫﻤﺒﺴﺘﮕﻲ ﭘﻴﺮﺳﻮﻥ ﺑﺎﻻﻳﻲ )ﺗﻘﺮﻳﺒﺎ (0/92 ﺩﻣﺎﻱ ﻣﺤﺎﺳﺒﻪ ﺷﺪﻩ ﺑﺎ ﺩﻣﺎﻱ ﮔﺰﺍﺭﺵ ﺷﺪﻩ ﺗﺠﺮﺑﻲ ﺑﻪ ﺩﺳﺖ ﺁﻣﺪ. ﻧﺘﺎﻳﺞ ﻫﻤﭽﻨﻴﻦ ﻧﺸﺎﻥ ﺩﺍﺩ ﻛﻪ ﻭﺍﻫﻠﺶ ﺳﺎﺧﺘﺎﺭ ﺩﺭﺻﺪ ﺧﻄﺎﻱ ﺩﻣﺎﻱ ﺑﻪ ﺩﺳﺖ ﺁﻣﺪﻩ ﺭﺍ ﻛﺎﻫﺶ ﻣﻲﺩﻫﺪ.

Magnetic materials find numerous applications, ranging from energy harvesting to computer memories. In this study, we choose 30 different antiferromagnetic crystals, from well­known transition monoxides such as MnO and NiO to complicated compounds such as LiMnPO . We try to have a variety of crystal symmetries in our choice. We restrict our selections among materials with 3d valence magnetic atoms to avoid spin­orbit effects. We restrict our selections among materials with 3d valence magnetic atoms to avoid spin­orbit effects. The total energy calculations are performed using density functional theory in two different codes: the plane­wave pseudopotential QUANTUM ESPRESSO (QE) package and the full­potential local­orbital (FPLO) code. We estimate the self­consistent Hubbard U parameter with a precision of about 0.01 eV using linear response theory through density functional perturbation theory (DFPT). We also investigate the extended Hubbard model, so­ called DFT+U +V containing both onsite (U ) and intersite electronic interactions (V). We derive Heisenberg exchanges based on DFT total energies of different magnetic configurations. To obtain exchange parameters within a supercell, we have devised an innovative method that utilizes null­space analysis to identify and address the limitations imposed by the supercell on these exchange parameters. With obtained exchanges, we construct Heisenberg Hamiltonian to compute transition temperatures using classical Monte Carlo simulations. To refine the calculations, we apply linear response theory to compute onsite (U) and intersite (V) corrections through a self­consistent process. Our findings reveal that GGA significantly overestimates the transition temperature (by 113%), while GGA+U underestimates it (by53%). To improve GGA+U results, we propose adjusting the DFT results with the (S+1)/S coefficient to compensate for quantum effects in Monte Carlo simulation, resulting in a reduced error of 41%. Additionally, we discover a high Pearson correlation coefficient of approximately 0.92 between the transition temperatures calculated using the GGA+U method and the experimentally determined transition temperatures. Furthermore, we explore the impact of geometry optimization on a subset of samples. Using consistent structures with GGA+U and DFT+U +V theories reduced the error.

مجتبي اعلائي

جواد هاشمي فر

فرهاد شهبازي دستجرده , زهرا نوربخش , امين الله واعظ