Merge branch 'master' into local

src/lecture_8.md

@@ -71,7 +71,7 @@ $S=\frac{3}{2}$, $L=3$, $J=\frac{3}{2}$ $\Rightarrow$ $^{2S+1}L_J =\ ^4{\rm F}_{
 
 ![](figures/hund.svg)
 
-### Paramagnetism: free spin $\frac{1}{2}$
+### Paramagnetism: free spin ½
 If single electron spin ${\bf \sigma}$ is situated in a magnetic field ${\bf B}$, it can be described by the Zeeman Hamiltonian (note convention minus sign):
 
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