ThepreliminarylearningofMumax3.92018.11.09目录•Thesoftwareofbeinglearned•Thefourexamples①theclassicmumagstandardproblem②PyRacetrack③Hysteresis④Geometry•ThefollowingworkThesoftwareofbeinglearned•Oringin9.1•OommfOOMMFisaprojectintheAppliedandComputationalMathematicsDivision(ACMD)ofITL/NIST,inclosecooperationwithµMAG,aimedatdevelopingportable,extensiblepublicdomainprogramsandtoolsformicromagnetics.Thiscodeformsacompletelyfunctionalmicromagneticspackage,withtheadditionalcapabilitytobeextendedbyotherprogrammerssothatpeopledevelopingnewcodecanbuildontheOOMMFfoundation.OOMMFiswritteninC++,awidely-available,object-orientedlanguagethatcanproduceprogramswithgoodperformanceaswellasextensibility.Forportableuserinterfaces,wemakeuseofTcl/TksothatOOMMFoperatesacrossawiderangeofUnix,Windows,andMacOSXplatforms.ThemaincontributorstoOOMMFareMikeDonahue,andDonPorter.•Mumax3.9mumax3isaGPU-acceleratedmicromagneticsimulationprogramdevelopedattheDyNaMatgroupofProf.VanWaeyenbergeatGhentUniversity.ThecodeiswrittenandmaintainedbyArneVansteenkiste.Aspeed-upoftheorderof100xcomparedtoCPU-basedsimulationscaneasilybereached,evenwithrelativelyinexpensivegamingGPUs.Additionally,thesoftwareisoptimizedforlowmemoryuseandcanhandleabout16millionFDcellswith2GBofGPURAM.Let‘sstartwiththeclassicµ-mag（Micromagnetic）standardproblem•SetGridsize(128,32,1)//SetsthenumberofcellsforX,Y,Z•SetCellsize(500e-9/128,125e-9/32,3e-9)//SetstheX,Y,Zcellsizeinmeters•Msat=800e3//saturationmagnetization•Aex=13e-12//Exchangestiffness(J/m)•alpha=0.02//Landau-Lifshitzdampingconstant•m=uniform(1,.1,0)//Uniformmagnetizationingivendirection•relax()•//Thisfunctionassumesallexcitationshavebeenturnedoff(temperature,electricalcurrent,time-dependentmagneticfields).•save(m)//relaxedstate•autosave(m,200e-12)//Autosavespace-dependentquantityeveryperiod(s).•tableautosave(10e-12)//Auto-savethedatatableeveryperiod(s).•B_ext=vector(-24.6E-3,4.3E-3,0)//Externallyappliedfield(T)•run(1e-9)//Run(time)runsthesimulationforagiventimeinsecondsxyzcell,基元500nm125nmm=uniform(1,0.1,0)m=uniform(1,1,0)m=uniform(0,0,1)relax()m000000m000001m000002m000003m000004m000005m000006Theconditionofevery200e-12sB_ext=vector(-24.6E-3,4.3E-3,0)//unit(T)m.svg0.00.20.40.60.81.0-1.0-0.50.00.51.0Magnetization(Norm.)t(ns)MxMyMzPyRacetracksetGridSize(256,64,1)//setGridSize(256,64,1)setCellSize(3e-9,3e-9,10e-9)//SetstheX,Y,ZcellsizeinmetersMsat=860e3//saturationmagnetizationAex=13e-12//Exchangestiffness(J/m)Xi=0.1//Non-adiabaticityofspin-transfer-torquealpha=0.02//Landau-Lifshitzdampingconstantm=twodomain(1,0,0,0,1,0,-1,0,0)//Twodomainmagnetizationwithwithgivenmagnetizationinleftdomain,wall,andrightdomainnotch:=rect(15e-9,15e-9).RotZ(45*pi/180).transl(0,32*3e-9,0).inverse()setGeom(notch.Repeat(200e-9,64*3e-9,0))//Setsthegeometrytoagivenshape//Removesurfacechargesfromleft(mx=1)andright(mx=-1)sidestomimicinfinitelylongwire.Wehavetospecifytheregion(0)attheboundaries.BoundaryRegion:=0MagLeft:=1MagRight:=-1ext_rmSurfaceCharge(BoundaryRegion,MagLeft,MagRight)//Compensatemagneticchargesontheleftandrightsidesofanin-planemagnetizedwire.Arguments:region,mxonleftandrightside,resp.relax()ext_centerWall(0)//keepm[0](m_x)closetozero//Scheduleoutputautosave(m,50e-12)tableadd(ext_dwpos)//domainwallpositiontableautosave(10e-12)//Runthesimulationwithcurrentthroughthesample...
