Recently, the dc shot noise (DSN) of photocurrents has been proposed as its complementary probe to quantify the nonmagnetic gapped quantum materials. In this Letter, we have discovered two novel DSN terms that are crucial for understanding the properties of magnetically insulating quantum materials: linear magnetic shift DSN and circular magnetic injection DSN. Both magnetic shift and injection DSNs inherit quantum geometric information of Bloch states. Interestingly, these terms can appear only when the system breaks parity-time ($\mathcal{P}\mathcal{T}$) symmetry. Leveraging this unique symmetry sensitivity, we propose DSN as a noninvasive, symmetry-resolved diagnostic capable of distinguishing magnetic properties. We demonstrate the viability of this approach through both minimal altermagnet models and first-principles calculations of realistic monolayer and bilayer ${\mathrm{CrI}}_3$ in various magnetic configurations. We show that magnetic DSN not only captures the spin-split band structure of altermagnets, but also differentiates magnetic phases and parity of the number of layers in two-dimensional ${\mathrm{CrI}}_3$. This establishes DSN as a powerful tool for probing symmetry, quantum geometry, and spin textures in magnetic quantum materials.

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• Geometric & topological phases
• Photocurrent
• Shot noise
• 2-dimensional systems
• Magnetic systems
• First-principles calculations
• Linear response theory