Lemma 28.26.2. Let $X$ be a scheme. Let $\mathcal{L}$ be an invertible $\mathcal{O}_ X$-module. Let $n \geq 1$. Then $\mathcal{L}$ is ample if and only if $\mathcal{L}^{\otimes n}$ is ample.
[II Proposition 4.5.6(i), EGA]
Proof.
This follows from the fact that $X_{s^ n} = X_ s$.
$\square$
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