We report observations of spontaneous formation of magnetic flux lines during a rapid quench of YBa(2)Cu(3)O(7-delta) films through T(c). This effect is predicted according to the Kibble-Zurek mechanism of creation of topological defects of the order parameter during a symmetry-breaking phase transition. Our previous experiment, at a quench rate of 20 K/s, gave null results. In the present experiment, the quench rate was increased to >10(8) K/s. The amount of spontaneous flux increases weakly with the cooling rate.

Exchange bias is a property of widespread technological utility, but whose underlying mechanism remains elusive, in part because it is rooted in the interaction of coexisting order parameters in the presence of complex magnetic disorder. Here, we show that a giant exchange bias housed within a spin-glass phase arises in a disordered antiferromagnet. The magnitude and robustness of the exchange bias emerges from a convolution of two energetic landscapes-the highly degenerate landscape of the spin-glass biased by the sublattice spin-configuration of the antiferromagnet. The former provides a source of uncompensated moment, while the latter provides a mechanism for its pinning, leading to the exchange bias. Tuning the relative strength of the spin-glass and antiferromagnet order parameters reveals a principle for tailoring the exchange bias, with potential applications to spintronic technologies.

The theory behind the electrical switching of antiferromagnets is premised on the existence of a well-defined broken symmetry state that can be rotated to encode information. A spin glass is, in many ways, the antithesis of this state, characterized by an ergodic landscape of nearly degenerate magnetic configurations, choosing to freeze into a distribution of these in a manner that is seemingly bereft of information. Here, we show that the coexistence of spin glass and antiferromagnetic order allows a novel mechanism to facilitate the switching of the antiferromagnet Fe1/3 + δNbS2, rooted in the electrically stimulated collective winding of the spin glass. The local texture of the spin glass opens an anisotropic channel of interaction that can be used to rotate the equilibrium orientation of the antiferromagnetic state. Manipulating antiferromagnetic spin textures using a spin glass’ collective dynamics opens the field of antiferromagnetic spintronics to new material platforms with complex magnetic textures.

We perform high-field magnetization measurements on the triangular lattice antiferromagnet Fe 1/3 NbS 2. We observe a plateau in the magnetization centered at approximately half the saturation magnetization over a wide range of temperature and magnetic field. From density functional theory calculations, we determine a likely set of magnetic exchange constants. Incorporating these constants into a minimal Hamiltonian model of our material, we find that the plateau and the Z 3 symmetry-breaking ground state both arise from the competition of interplane and intraplane exchange interactions. These findings are pertinent to the magnetoelectric properties of Fe 1/3 NbS 2 , which allow electrical switching of antiferromagnetic textures at relatively low current densities.