Consider the Galois cyclotomic extension $\mathbb{Q}(\zeta_{7})/\mathbb{Q}$.
I've found via Galois theorem the following intermediate field of degree 2 \begin{equation} \mathbb{Q}(\zeta_{7}+\zeta_{7}^{2}+\zeta_{7}^{4}). \end{equation}
Some people told me that I can find a "nice" generator for this field, like $\sqrt{d}$, for some free-square integer $d$.
How can I do such a thing? Are there any references for this type of thing?