A bit stored not as charge but as a direction of spin. This is a spin-transfer-torque MRAM cell: a spin-polarized current tips a tiny magnet's magnetization over an energy barrier from one stable pole to the other — governed by the Landau–Lifshitz–Gilbert equation. When the current stops, the direction stays. No refresh, no leakage: non-volatile memory written with spin.
The dynamics are real: the arrow precesses around the effective field (the fast spiral), damping α spirals it toward the nearest easy-axis pole (the two energy minima = the two bit states), and the spin-transfer torque from the polarized current pushes against that damping. Slonczewski and Berger showed (1996) a spin-polarized current transfers angular momentum to the free layer — enough of it, and the magnet flips. That flip, made a memory cell, is STT-MRAM: shipping silicon today (embedded MRAM at TSMC, Samsung, Everspin).
Ask what physically carries the information and you get a family: charge → electronic, light → photonic, lattice-vibration → phononic, spin → spintronic. This sphere is the fourth. (Push it exotic and the carrier becomes the graviton — the gravity outlier of the set.) The point of spin as a carrier: a magnetization direction is non-volatile — it holds its bit with the power off — where charge on a capacitor drains and must be refreshed.
Real, and correctly simulated: the Landau–Lifshitz–Gilbert equation (precession + Gilbert damping) with a Slonczewski spin-transfer-torque term is the standard macrospin model of a magnetic free layer; the current threshold Ic above which the cell switches (the spin-torque anti-damping must exceed the Gilbert damping) is a genuine feature, verified here to switch above 1× and fail below; STT-MRAM is real, shipping non-volatile memory. The canvas integrates the actual LLG dynamics.
A reduced model / disclosure: this is a single-macrospin cell (one coherent magnetization). Real devices add thermal fluctuations, sub-volume incoherent reversal, tunnel-magnetoresistance readout, and process variation; the numbers here are normalized (I in units of the threshold), not a datasheet. The "ROOT0 spintronic device" framing is a design/disclosure standing on established magnetism, not a fabricated part.
To disclose a design is real work; it is not a granted patent or a fabricated device. Built to complete David's carrier tensor {photonic, gravity, electronic, phononic} — the missing pillar is spin.