On free resolutions of Iwasawa modules

Let $\mathrm{\Lambda }$ (isomorphic to ${\mathbb{Z}}_p[[T]]$) denote the usual Iwasawa algebra and $G$ denote the Galois group of a finite Galois extension $L\mathrm{/}K$ of totally real fields. When the non-primitive Iwasawa module over the cyclotomic ${\mathbb{Z}}_p$-extension has a free resolution of length one over the group ring $\mathrm{\Lambda }[G]$, we prove that the validity of the non-commutative Iwasawa main conjecture allows us to find a representative for the non-primitive $p$-adic $L$-function (which is an element of a $K_1$-group) in a maximal $\mathrm{\Lambda }$-order. This integrality result involves a careful study of the Dieudonn'e determinant. Using a cohomolgoical criterion of Greenberg, we also deduce the precise conditions under which the non-primitive Iwasawa module has a free resolution of length one. As one application of the last result, we consider an elliptic curve over $\mathbb{Q}$ with a cyclic isogeny of degree $p^2$. We relate the characteristic ideal in the ring $\mathrm{\Lambda }$ of the Pontryagin dual of its non-primitive Selmer group to two characteristic ideals, viewed as elements of group rings over $\mathrm{\Lambda }$, associated to two non-primitive classical Iwasawa~modules.