Here is slightly automated solution using tikz
. I measure the height and width of the text and place an arc whose size is based on the maximum of that. Am sure this can be improved, but this should get you started:

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz}
\usepackage{calc}
\makeatletter
\newlength\@SizeOfCirc%
\newcommand{\CricArrowRight}[1]{%
\setlength{\@SizeOfCirc}{\maxof{\widthof{#1}}{\heightof{#1}}}%
\tikz [x=1.0ex,y=1.0ex,line width=.15ex, draw=blue]%
\draw [->,anchor=center]%
node (0,0) {#1}%
(0,1.2\@SizeOfCirc) arc (85:-240:1.2\@SizeOfCirc);%
}%
\makeatother
\begin{document}
\CricArrowRight{$i$}
\CricArrowRight{$i_3$}
\CricArrowRight{$\frac{a}{b}$}
\CricArrowRight{$\dfrac{a}{b}$}
\end{document}
I created a temporary length \@SizeOfCirc
so as to minimize potential name conflicts, and need to use \maktatother
. See What do \makeatletter and \makeatother do? for more info if you are not familiar with that.