$n \log_2 n$ approximation to $n^x$

Question

$n \log_2 n$ approximation to $n^x$

I know that $F(n)=n \log_2 n - n^{1.5}<0$ (from $F'(n)<0$). So $ \log_2 n < \sqrt n$

But if $ \log_2 n <n^x$ what could be x which is less than 0.5?