<p>Unconventional antiferromagnets (AFMs) with non-relativistic spin-splitting, such as the recently discovered altermagnet, have recently gained significant interest due to their potential for novel quantum phenomena and spintronic applications. The compensated magnetization in unconventional AFMs is protected by spin-space symmetries. In this work, we explore the symmetry-breaking effects and identify three distinct mechanisms for inducing net spin magnetizations in unconventional AFMs with collinear or non-collinear spins: (1) finite size effect, (2) extrinsic spin canting effect, and (3) irradiation with circularly polarized light. We show that the induced spin magnetizations are controllable and manifest as diverse intriguing phenomena. For the finite size system, the confined direction of a two-dimensional AM creates quantum-well-like subbands that determine the spin magnetization. This effect can be experimentally probed by measuring the spin density of states and the spin-polarization of Andreev-bound states within planar Josephson junctions. In the case of spin canting effect, it leads to peculiar anisotropic and non-monotonic behaviors in the superconducting proximity effect. Lastly, with circularly polarized light, spin magnetization is driven by the polarized light and the chirality of non-collinear magnetic order, thus offering a direct means of detecting the chirality of magnetic order in real materials. Our findings provide valuable insight into understanding and probing the spin magnetization in unconventional AFM materials.</p>