HfO 2 , a simple binary oxide, holds ultra-scalable ferroelectricity integrable into silicon technology. Polar orthorhombic (Pbc2 1 ) form in ultra-thin-films ascribes as the plausible rootcause of the astonishing ferroelectricity, which has thought not attainable in bulk crystals.Though, perplexities remain primarily due to the polymorphic nature and the characterization challenges at small-length scales. Herein, utilizing a state-of-the-art Laser-Diode-heated Floating Zone technique, we report ferroelectricity in bulk singlecrystalline HfO 2 :Y as well as the presence of anti-polar Pbca phase at different Y concentrations. Neutron diffraction and atomic imaging demonstrate (anti-)polar crystallographic signatures and abundant 90 o /180 o ferroelectric domains in addition to the switchable polarization with little wake-up effects. Density-functional theory calculations suggest that the Yttrium doping and rapid cooling are the key factors for the desired phase. Our observations provide new insights into the polymorphic nature and phase controlling of HfO 2 , remove the upper size limit for ferroelectricity, and also pave a new road toward the next-generation ferroelectric devices.

The control of domain walls or spin textures is crucial for spintronic applications of antiferromagnets. Despite many efforts, it has been challenging to directly visualize antiferromagnetic domains or domain walls with nanoscale resolution, especially in magnetic field. Here, we report magnetic imaging of domain walls in several uniaxial antiferromagnets, the topological insulator MnBi2Te4 family, using cryogenic magnetic force microscopy (MFM). Our MFM results reveal higher magnetic susceptibility inside the domain walls than in domains. Domain walls in these antiferromagnets form randomly with strong thermal and magnetic field dependence. The direct visualization of these domain walls and domain structures in the magnetic field will not only facilitate the exploration of intrinsic topological phenomena in antiferromagnetic topological insulators but will also open a new path toward control and manipulation of domain walls or spin textures in functional antiferromagnets.

Compared with the domain wall motion in a ferromagnetic nanowire, the chiral soliton motion could reach a much larger velocity at a much smaller current density. [9,11] The metallic chiral magnets that can host CSL are very rare. As far as we know, the formation of CSL in metallic chiral magnets has been only observed in Cr 1/3 NbS 2 and YbNi 3 Al 9 . [2,3,12,13] As the stability of chiral magnetic solitons is determined by the Dzyaloshinskii-Moriya (DM) interaction and the velocity of soliton motion is controlled by the non-adiabatic torque, searching for new chiral magnets associate with strong DM interaction and large non-adiabatic torque is of great importance in the emerging field of solitonics. [2,3,8,9] Among the various candidates, the magnetic ion (M = Cr, Mn, Fe, Co, and Ni) intercalated M 1/3 TaS 2 stands out because the parent compound TaS 2 has large spin-orbit coupling (SOC) and hosts a rich collection of exotic states including the Mott state, charge density wave, and quantum spin liquid. [14][15][16] As the magnetic ions insert into TaS 2 , the ordering of magnetic ions in M 1/3 TaS 2 results in a (1/3, 1/3, 0) superstructure with a chiral space group of P6 3 22. [17] The strong SOC and the chiral lattice structure of M 1/3 TaS 2 could induce strong DM interaction and large non-adiabatic torque, since the strength of DM interaction and non-adiabatic torque both are proportional to the SOC constant. [18,19] In the family of M 1/3 TaS 2 , only Fe 1/3 TaS 2 has been confirmed as a chiral magnet. [17,20] Nevertheless, the extremely large orbital magnetic moment of Fe 2+ ions yields the gigantic easy-axis magnetocrystalline anisotropy and brings on the Ising-type ferromagnetic structure in Fe 1/3 TaS 2 . [17,21] The crystal growth and characterization of several other M 1/3 TaS 2 have been studied as early as the 1980s, yet whether the crystals possess chiral lattice structure and chiral magnetism are in question. [22][23][24] For example, the Cr 1/3 TaS 2 has been reported to exhibit a trivial ferromagnetic (FM) transition near 115 K without any hints of chiral features. [22][23][24][25] In this work, we report the magneto-transport properties and magnetic phase diagrams of Cr 1/3 TaS 2 single crystals. In contrast with the reported trivial FM transition, our Cr 1/3 TaS 2 single crystals exhibit a chiral helimagnetic (CHM) transition near 140 K. The conducting electrons interact with the CHM and CSL orders, giving rise to the nontrivial magnetoresistance (MR) in Cr 1/3 TaS 2 . The normalized magnetic moment and Cr 1/3 TaS 2 -a candidate of chiral magnet-has been reported as a trivial ferromagnetic material. In contrast, the Cr 1/3 TaS 2 single crystals exhibit a chiral helimagnetic (CHM) transition near 140 K. The magnetic moment versus magnetic field curves reveal a CHM-chiral soliton lattice (CSL)-forced ferromagnetic (FFM) transition in the magnetic ordered state. The conducting electrons interact with the CHM and CSL orders, giving rise to the nontrivial magnetoresistance (MR) in the Cr 1/3 TaS 2 ...

We combined Raman scattering and magnetic susceptibility to explore the properties of [(CH 3 ) 2 NH 2 ]Mn-(HCOO) 3 under compression. Analysis of the formate bending mode reveals a broad two-phase region surrounding the 4.2 GPa critical pressure that becomes increasingly sluggish below the order−disorder transition due to the extensive hydrogen-bonding network. Although the paraelectric and ferroelectric phases have different space groups at ambient-pressure conditions, they both drive toward P1 symmetry under compression. This is a direct consequence of how the order−disorder transition changes under pressure. We bring these findings together with prior magnetization work to create a pressure−temperature−magnetic field phase diagram, unveiling entanglement, competition, and a progression of symmetry-breaking effects that underlie functionality in this molecule-based multiferroic. That the high-pressure P1 phase is a subgroup of the ferroelectric Cc suggests the possibility of enhanced electric polarization as well as opportunity for strain control.