Lub sijhawm sib nqus ntawm lub atom yog lub cev lub cev vector ntau uas ua rau cov khoom sib nqus ntawm cov khoom siv. Lub hauv paus ntawm kev tsim cov hlau nplaum, raws li kev tshawb xav classical electromagnetic, yog microcurrents tshwm sim los ntawm kev txav ntawm ib qho hluav taws xob hauv lub orbit. Lub sijhawm sib nqus yog ib qho khoom tseem ceeb ntawm tag nrho cov ntsiab lus, nuclei, atomic electron shells thiab molecules yam tsis muaj kev zam.
Magnetism, uas yog muaj nyob rau hauv tag nrho cov hauv paus ntsiab lus, raws li quantum mechanics, yog vim muaj ib tug neeg kho tshuab lub sij hawm nyob rau hauv lawv, hu ua spin (nws tus kheej mechanical momentum ntawm quantum xwm). Cov khoom sib nqus ntawm cov atomic nucleus yog tsim los ntawm lub sijhawm tig ntawm lub hauv paus ntawm cov nucleus - protons thiab neutrons. Lub plhaub hluav taws xob (intraatomic orbits) kuj muaj lub sijhawm sib nqus, uas yog qhov sib npaug ntawm lub sijhawm sib nqus ntawm cov electrons nyob ntawm nws.
Hauv lwm lo lus, lub sijhawm sib nqus ntawm theem pibhais thiab atomic orbitals yog vim muaj intra-atomic quantum mechanical effect hu ua spin momentum. Cov nyhuv no zoo ib yam li lub angular momentum ntawm kev sib hloov nyob ib ncig ntawm nws lub hauv paus axis. Spin momentum yog ntsuas nyob rau hauv Planck qhov tas li, qhov tseem ceeb ntawm quantum theory.
Txhua cov neutrons, electrons thiab protons, ntawm qhov tseeb, lub atom muaj, raws li Planck, muaj qhov sib npaug ntawm ½. Nyob rau hauv cov qauv ntawm ib tug atom, electrons, rotating ib ncig ntawm lub nucleus, ntxiv rau lub spin momentum, kuj muaj ib tug orbital angular momentum. Lub nucleus, txawm hais tias nws nyob hauv txoj hauj lwm zoo li qub, kuj muaj lub zog angular, uas yog tsim los ntawm cov nyhuv nuclear.
Lub teb chaws magnetic uas ua rau lub sij hawm atomic magnetic yog txiav txim los ntawm ntau hom ntawm lub angular momentum. Qhov kev pom zoo tshaj plaws rau kev tsim cov magnetic teb yog tsim los ntawm cov nyhuv spin. Raws li lub hauv paus ntsiab lus Pauli, raws li qhov uas ob zoo tib yam electrons tsis tuaj yeem nyob rau hauv tib lub xeev quantum, khi electrons sib koom ua ke, thaum lawv lub sijhawm tig tau txais diametrically opposite projections. Nyob rau hauv cov ntaub ntawv no, lub sij hawm sib nqus ntawm lub electron yog txo, uas txo cov magnetic zog ntawm tag nrho cov qauv. Hauv qee lub ntsiab lus uas muaj tus lej ntawm cov hluav taws xob, lub sijhawm no txo qis mus rau xoom, thiab cov khoom tsis muaj cov khoom sib nqus. Yog li, lub sij hawm sib nqus ntawm ib tus neeg theem pib muaj qhov cuam tshuam ncaj qha rau cov khoom sib nqus ntawm tag nrho cov nuclear-atomic system.
Ferromagnetic cov ntsiab lus nrog cov lej khib ntawm cov hluav taws xob yuav ib txwm muaj cov hlau nplaum tsis muaj xoom vim yog cov hluav taws xob tsis sib xws. Nyob rau hauv xws li cov ntsiab lus, nyob sib ze orbitals sib tshooj, thiab tag nrho cov spin lub sij hawm ntawm unpaired electrons coj tib txoj kev taw qhia nyob rau hauv qhov chaw, uas ua rau kom ua tau zoo ntawm lub zog qis tshaj lub xeev. Cov txheej txheem no hu ua kev sib pauv pauv.
Nrog rau qhov kev sib tw ntawm lub sijhawm sib nqus ntawm ferromagnetic atoms, ib qho chaw sib nqus tshwm sim. Thiab cov ntsiab lus paramagnetic, uas muaj cov atoms nrog lub sijhawm sib nqus tsis sib xws, tsis muaj lawv tus kheej magnetic teb. Tab sis yog tias koj ua rau lawv nrog lwm qhov chaw ntawm cov hlau nplaum, ces lub sijhawm sib nqus ntawm cov atoms yuav txawm tawm, thiab cov ntsiab lus no tseem yuav tau txais cov khoom sib nqus.
