Endomorphim Ring of Abelian Groups In the paper 
"Über die Abelschen Gruppen mit nullteilerfreiem Endomorphismenring." 
Szele considers the problem of describing all abelian groups with endomorphism ring contaning no zero-divisors. He proved that there is no such group among the mixed groups. While $C(p)$ and $C(p^\infty)$ are the only torsion groups of this property.
I do not have access to this paper. Moreover, I do not speak German, someone can give me a reference, in English or French, for this result or Sketch the Proof?   

Kulikov proved that an indecomposable abelian group is either torsion-free or $C(p^k)$ for some $k=0,1,\dots,\infty$. A direct summand creates a zero divisor in the endomorphism ring: Let $G = A \oplus B$ and define $e(a,b) = (a,0)$. Then $e^2=e$ and $e(1-e) = 0$. However $1-e$ is the endomorphism that takes $(a,b)$ to $(0,b)$ so it is not zero either.
