Inelastic neutron scattering from superconducting (SC) Ba(Fe$_{0.926}$Co$_{0.074}$)$_2$As$_2$ reveals anisotropic and quasi-two-dimensional (2D) magnetic excitations close to textbf{Q}$_{texttt{AFM}}=({1}{2}/{1}{2})$ - the 2D antiferromagnetic (AFM) wave-vector of the parent BaFe$_2$As$_2$ compound. The correlation length anisotropy of these low energy fluctuations is consistent with spin nematic correlations in the $J_1$-$J_2$ model with $J_1/J_2 sim$ 1. The spin resonance at $sim$8.3 meV in the SC state displays the same anisotropy. The anisotropic fluctuations experimentally evolve into two distinct maxima only along the direction transverse to textbf{Q}$_{texttt{AFM}}$ above $sim$80 meV indicating unusual quasi-propagating excitations.
Using synchrotron X-rays and neutron diffraction we disentangle spin-lattice order in highly frustrated ZnCr$_2$O$_4$ where magnetic chromium ions occupy the vertices of regular tetrahedra. Upon cooling below 12.5 K the quandary of anti-aligning spins surrounding the triangular faces of tetrahedra is resolved by establishing weak interactions on each triangle through an intricate lattice distortion. The resulting spin order is however, not simply a N{e}el state on strong bonds. A complex co-planar spin structure indicates that antisymmetric and/or further neighbor exchange interactions also play a role as ZnCr$_2$O$_4$ resolves conflicting magnetic interactions.
Neutron scattering is used to probe antiferromagnetic spin fluctuations in the d-wave heavy fermion superconductor CeCoIn$_{5}$ (T$_{c}$=2.3 K). Superconductivity develops from a state with slow ($hbarGamma$=0.3 $pm$ 0.15 meV) commensurate (${bf{Q_0}}$=(1/2,1/2,1/2)) antiferromagnetic spin fluctuations and nearly isotropic spin correlations. The characteristic wavevector in CeCoIn$_{5}$ is the same as CeIn$_{3}$ but differs from the incommensurate wavevector measured in antiferromagnetically ordered CeRhIn$_{5}$. A sharp spin resonance ($hbarGamma<0.07$ meV) at $hbar omega$ = 0.60 $pm$ 0.03 meV develops in the superconducting state removing spectral weight from low-energy transfers. The presence of a resonance peak is indicative of strong coupling between f-electron magnetism and superconductivity and consistent with a d-wave gap order parameter satisfying $Delta({bf q+Q_0})=-Delta({bf q})$.
