LaTeX Forum

\documentclass{standalone} 
\usepackage{tikz} 
\usetikzlibrary{decorations.markings}
\begin{document} 
\begin{tikzpicture}
\draw[thick,postaction={decorate,
  decoration={markings,mark=between positions 0 and .75 step .25
              with{\fill(140:.15)--(0:.15)--(-140:.15)--cycle;}}}
] circle [radius=2];
\end{tikzpicture} 
\end{document}

\documentclass{article}
\usepackage{tikz}
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{5pt}%

\begin{document}
\begin{tikzpicture}
\def \n {4}
\def \radius {3cm}
\def \margin {8} % margin in angles, depends on the radius
\foreach \s in {1,...,\n}
{
  \draw[->, >=latex] ({360/\n * (\s-1)+\margin}:\radius) 
    arc ({360/\n * (\s - 1)+\margin}:{360/\n * (\s)+\margin}:\radius);
}
\end{tikzpicture}
\end{document}