We consider a local non-Frobenius ring \(R_p={\mathbb {F}}_p[u,v]/\langle u^2, v^2, uv,vu \rangle \) defined for each prime number p and study the ideal representation of the ring \(R_p[x]/\langle x^n+1\rangle \) , which is well-known to be related to negacyclic codes over \(R_p\) of length \(n=p^s\) with \(s \ge 1\) . We assume that n is a power of p, and under this setting, we show that a specific class of ideals can be represented uniquely in terms of degrees related to its generators. We also give a lower bound of the minimum Hamming distances of negacyclic codes over \(R_p\) , and show that the lower bound is sharp for several codes whose corresponding ideals of \(R_p[x]/\langle x^n+1\rangle \) belong to the aforementioned class.