14500

13085

كارشناسي ارشد

ماده چگال

اصفهان : دانشگاه صنعتي اصفهان

1397

سيزده، 87ص.: مصور، جدول،نمودار

مجتبي اعلائي، هادي اكبرزاده

نفيسه رضايي

ممتحن مدعو: فرهاد شهبازي; ممتحن داخلي: اسماعيل عبدالحسيني سارسري

1398/01/21

كتابنامه

فيزيك

فيزيك

1398/01/27

ID13085

Monte Carlo and Parallel Tempering simulations of Bi3Mn4O12 NO3 inter layer spin correlation for Homa Karimi homa karimi@ph iut ac ir Jan 16 2019 Department of Physics Isfahan University of Technology Isfahan 84156 83111 Iran University Code IUT 77142 Degree M S c Language Farsi supervisor Dr M Alaei Dr H Akbarzadeh m alaei@cc iut ac ir akbarzad@cc iut ac ir Abstract Bi3 Mn4 O12 NO3 is a honeycomb bilayers antiferromagnet each consists of Mn 4 3d3 S 3 2 ions The Curie Weiss temperature has a large value of CW 257K this indicates strong AF interactions and the presence of LRO in this compound however there is no sign of LRO down to very low temperature This compound is the first honey comb lattice system that shows no long range ordering The absence of magnetic LRO has been considered by theoretical and experimental scientists and is confirmed by different experiments such as Neutron Scattering experiments Ab initio methods based on DFT have also suggested an effective spin Hamiltonian for this substance This Hamiltonian involves the Heisenberg antiferromagnetic spin interactions The presence of frustration effects on this system is appropriate to compare different Monte Carlo methods In this thesis by considering a Heisenberg antiferromagnetic spin model we compare the results of implementing two Monte Carlo methods the metropolis algo rithm MC and the parallel tempering algorithm PT in the calculation of spin correlation function and neutron structure factor By this aim we use MCARLO code to simulate the behavior of this system In order to discover the bahavior of BMNO we calculated the inter layer spin spin correlation function and also to investigate the nature of its phase neutron structure factor has been calculated as a function of T in hl0 plane the computational cost of the calculation and also seed dependence of the magnitute of spin correlation function by using the metropolis algorithm lead to substitude a better algorithm For this purpose we used the PT algorithm In this step we recalculate the thermodynamic quantities and compare them with the results of the metropolis algorithm and ensure that our assumptions are correct we also calculate inter layer spin spin correlation function and neutron structure factor by use of PT algorithm and showed that without using different conditions the correct results of BMNO behavior can be obtained Keywords frustrated magnets bilayer honeycomb lattice Heisenberg spin model hamiltonian Monte Carlomethods metropolis algorithm parallel tempering correlation function neutron structure factor

مجتبي اعلائي، هادي اكبرزاده

نفيسه رضايي

ممتحن مدعو: فرهاد شهبازي; ممتحن داخلي: اسماعيل عبدالحسيني سارسري