Фізика спінової електроніки та магнетизму

🧲 GMR

Giant magnetoresistance

Fe/Cu/Fe multilayer: resistance change при applied field. ΔR/R ~ 50-100%. Parallel vs antiparallel alignment.

Mechanism

Spin-dependent scattering: minority spins scattered strongly. Majority weakly. Parallel low R.

Applications

HDD read heads: density ↑. Magnetic sensors. 2007 Nobel. Commercial: ~1997.

Amplitude

ΔR/R ~ 100% @ low T, ~10-20% room T. Clean interfaces, thin layers. Spacer thickness.

🔬 TMR

Tunnel magnetoresistance

MgO barriers: FeCoB/MgO/FeCoB. High ΔR/R ~ 500% room T. Tunneling matrix elements.

MTJ

Magnetic tunnel junction: two FM, insulator. Bias dependence. Symmetry filtering.

MRAM

Memory: non-volatile, fast. STT-MRAM: spin-transfer torque switching. Dense arrays.

Mechanisms

Julliere formula: TMR = 2P₁P₂/(1-P₁P₂). Barrier quality, matching. Δ₁ symmetry.

🌊 Спінові хвилі

Magnons

Quantized magnetic excitations. Dispersion: ω(k) ~ Dk² for FM. Spin wave stiffness D. GHz frequencies.

Propagation

Phase, amplitude modes. Damping α ~ 0.001-0.01. Long wavelengths: coherent transport.

Logic

Spin wave computing: interference, logic gates. Low power. Non-reciprocal devices.

Magnonics

Signal processing: filters, delay lines. YIG, Permalloy. GHz communication.

⚡ Спіновий Голл

Hall effect

Charge current → transverse spin current. σ_SH = θ_SH·σ. θ_SH: efficiency.

Materials

Pt: θ_SH ~ 0.1. W, Ta heavy metals. SHE for injection. Inverse SHE for detection.

Injection

Charge → spin: SHE. Detection: inverse SHE. Spin pumping. YIG|Pt.

Applications

Spin torque, switching. Spin-logic. Low power devices.

🔬 Spin transfer torque

Switching

Spin-polarized current → magnetization reversal. τ_STT ~ J × M. Current-induced.

MTJ switching

STT-MRAM: current → switching. Low J_c, fast ns. Write endurance.

Domain wall motion

Current-driven DW motion. Race tracks, racetrack memory. Velocity.

Spin-orbit torque

SOT: Rashba, SHE. Field-free switching. W, Pt, heavy metals.

🔬 Magneto-optics

Faraday rotation

Light → magnetization: θ_F = V·M·l. Verdet constant V. Bulk, thin films.

Kerr effect

Reflection: rotation, ellipticity. Polar, longitudinal, transverse. Surface sensitivity.

Detection

Optical spin detection: Kerr, MOKE. Spin dynamics. Domain imaging.

Applications

Magneto-optical storage. Magnon-phonon coupling. THz generation.

📊 Графіки та діаграми

GMR effect

R vs H:

High field: parallel, low R. Zero field: antiparallel, high R. Hysteresis.

Spin wave dispersion

ω(k):

GHz frequencies. Long wavelengths: coherent, low damping. YIG, Permalloy.

ΔR/R = (R_AP - R_P)/R_P R_P: parallel alignment R_AP: antiparallel ΔR/R ~ 100% @ 4.2 K ~10-20% @ room T

🧪 Практичні приклади

Приклад 1: HDD read heads

GMR: density ↑ 10×, ~1997-2007. TMR: continued ↑. Current: HAMR, MAMR.

Приклад 2: STT-MRAM

Memory: non-volatile, fast ns. Low power. Embedded, standalone. Everspin, Samsung.

Приклад 3: Spin wave logic

YIG waveguides: interference, gates. Non-reciprocal. Low power. GHz operation.

Приклад 4: SHE injectors

Pt: charge → spin. Detection: inverse SHE. Spin pumping YIG|Pt. Efficient.

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