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Directed self-assembly (DSA) of block copolymers (BCPs) has long been included in the semiconductor roadmap as a lithographic pathway to enable continued device scaling. Tremendous progress has been made in generating two-dimensional (2D) BCP patterns with device-relevant features and low defect density and in transferring these patterns to functional materials. Extension of pattern generation into 3D could markedly enhance the utility of BCPs in nanoscale manufacturing, but methods to template and synthesize well-ordered, nontrivial 3D structures are less well developed. Here, we demonstrate a hierarchical DSA method to generate cross-point structures with connected in-plane and out-of-plane segments and controlled orientation angle between the horizontal layers. Various highly ordered, 3D interconnected networks, including ladder and cross-point structures, are produced by combinations of surface modification, BCP periodicity, and topographic templates, expanding the capabilities of BCP-derived nanofabrication. 

Abstract Exchange bias (EB), manifested as a hysteresis‐loop offset after field‐cooling, is demonstrated in perovskite‐structured ferromagnet/antiferromagnet (La_0.67Sr_0.33MnO₃/YFeO₃)_nheterostructures grown on (100) SrTiO₃substrates. Bilayer samples show an EB of 306 Oe at 50 K, whereas multilayers with five layers exhibit an exchange bias of up to 424 Oe at 50 K. A spin valve consisting of La_0.67Sr_0.33MnO₃/SrTiO₃/La_0.67Sr_0.33MnO₃/YFeO₃shows stable remanent configurations resulting from pinning of the upper La_0.67Sr_0.33MnO₃layer by the YFeO₃. In contrast, EB is not observed on (111)‐oriented SrTiO₃substrates due to interface roughening. These results demonstrate YFeO₃as an alternative orthoferrite antiferromagnet compared to BiFeO₃and LaFeO₃for incorporation into exchange‐biased heterostructures. 

Writing magnetic bits through spin-orbit torque (SOT) switching is promising for fast and efficient magnetic random-access memory devices. While SOT switching of out-of-plane (OOP) magnetized states requires lateral symmetry breaking, in-plane (IP) magnetized states suffer from low storage density. Here, we demonstrate a field-free switching scheme using a 5-nanometer europium iron garnet film grown with a (110) orientation that shows a spin reorientation transition from OOP to IP above room temperature. This scheme combines the benefits of high-density storage in the OOP states at room temperature and the efficient field-free SOT switching in the IP states at elevated temperatures. While conventional switching of OOP bits faces the dilemma that high OOP anisotropy is required to improve bit stability and low OOP anisotropy is required to lower switching current density, this scheme disentangles this interdependence, allowing for low switching currents to be possible without sacrificing the bit stability, offering opportunities for future memory devices.