<p>Nonreciprocity is a powerful tool in quantum technologies. It allows signals to be sent in one direction but not the other. In this article, we propose a method for achieving nonreciprocal entanglement and Gaussian interferometric power (GIP) via the Barnett effect. The yttrium iron garnet (YIG) is coupled to a microwave cavity that interacts with an optical parametric amplifier (OPA). Due to the Barnett effect, nonreciprocal entanglement can emerge. By fine-tuning the cavity detuning, the GIP can exhibit nonreciprocal behavior. The nonreciprocal entanglement can reach its ideal values within accessible parameter regimes by tuning the photon frequency detuning, selecting the cavity–magnon coupling regime, adjusting the nonlinear gain, and setting the phase shift of the OPA. Notably, both the degree of entanglement nonreciprocity and its robustness against thermal noise are significantly enhanced by increasing the OPA gain. This nonreciprocity can be significantly enhanced even at relatively high temperatures. Our work paves the way for developing nonreciprocal single-phonon devices, which could play a significant role in advancing quantum information processing and quantum communication technologies. This proposed scheme could pave the way for the development of novel nonreciprocal devices that remain robust under thermal fluctuations.</p>