Hexagonal peaks form in ferrofluid above critical magnetic field — normal-field instability
H = 40 | H_c = — | λ_c = — mm
The Rosensweig (normal-field) instability occurs when magnetic pressure μ₀M²/2 overcomes surface tension 2γk
and gravity ρg/k. The critical field is H_c = (2√(ρg·γ)/μ₀M) at critical wavenumber k_c = √(ρg/γ).
Above H_c, a hexagonal array of peaks spontaneously forms. The 2D view shows peak height using a
pseudo-3D height map; brighter peaks indicate higher field surplus above critical. Peak spacing ≈ λ_c = 2π/k_c.