NUM division - Publication Highlights

The magnetic field induced rearrangement of the cycloidal spin structure in ferroelectric monodomain single crystals of the room-temperature multiferroic BiFeO₃ is studied using small-angle neutron scattering. The cycloid propagation vectors are observed to rotate when magnetic fields applied perpendicular to the rhombohedral (polar) axis exceed a pinning threshold value of ∼5T.

Excitations in a spin ice behave as magnetic monopoles, and their population and mobility control the dynamics of a spin ice at low temperature. CdEr₂Se₄ is reported to have the Pauling entropy characteristic of a spin ice, but its dynamics are three orders of magnitude faster than the canonical spin ice Dy₂Ti₂O₇.

A quantum spin liquid state has long been predicted to arise in spin-1/2 Heisenberg square-lattice antiferromagnets at the boundary region between Néel (nearest-neighbor interaction dominates) and columnar (next-nearest-neighbor interaction dominates) antiferromagnetic order. However, there are no known compounds in this region. Here we use d¹⁰ – d⁰ cation mixing to tune the magnetic interactions on the square lattice while simultaneously introducing disorder.

We report the discovery of a field driven transition from a single-q to multi-q spin density wave (SDW) in the tetragonal heavy fermion compound CeAuSb₂. Polarized along c, the sinusoidal SDW amplitude is 1.8(2)μ_B/Ce for T<N=6.25(10)K with a wave vector q₁=(η,η,1/2) [η=0.136(2)]. For H || c, harmonics appearing at 2q₁ evidence a striped magnetic texture below μ₀H₁=2.78(1) T.

High carrier density quantum wells embedded within a Mott insulating matrix present a rich arena for exploring unconventional electronic phase behavior ranging from non-Fermi-liquid transport and signatures of quantum criticality to pseudogap formation. Probing the proposed connection between unconventional magnetotransport and incipient electronic order within these quantum wells has however remained an enduring challenge due to the ultra-thin layer thicknesses required.

Ultrasoft colloids typically do not spontaneously crystallize, but rather vitrify, at high concentrations. Combining in situ rheo–small-angle-neutron-scattering experiments and numerical simulations we show that shear facilitates crystallization of colloidal star polymers in the vicinity of their glass transition. With increasing shear rate well beyond rheological yielding, a transition is found from an initial bcc-dominated structure to an fcc-dominated one.

Through the use of Time-of-Flight Three Dimensional Polarimetric Neutron Tomography (ToF 3DPNT) we have for the first time successfully demonstrated a technique capable of measuring and reconstructing three dimensional magnetic field strengths and directions unobtrusively and non-destructively with the potential to probe the interior of bulk samples which is not amenable otherwise.

The real-space spin texture and the relevant magnetic parameters were investigated for an easy-axis non-centrosymmetric ferromagnet Cr₁₁Ge₁₉ with Nowotny chimney ladder structure. Using Lorentz transmission electron microscopy,we report the formation of bi-Skyrmions,i.e., pairs of spin vortices with opposite magnetic helicities.

The compound Sr_0.5Ce_0.5FBiS₂ belongs to the intensively studied family of layered BiS₂ superconductors. It attracts special attention because superconductivity at T_sc = 2.8 K was found to coexist with local-moment ferromagnetic order with a Curie temperature T_C = 7.5 K. Recently it was reported that upon replacing S by Se T_C drops and ferromagnetism becomes of an itinerant nature.