Observation of temperature-dependent Dzyaloshinskii–Moriya interaction within the 50–300 K range

The Dzyaloshinskii–Moriya interaction (DMI) is essential for the formation of chiral objects in magnetic heterostructures. Herein, the temperature (T)-dependence of the DMI in Pt/Co/MgO is investigated over a wide range below 300 K. The T-dependent behavior of the DMI is stronger than that of the Heisenberg exchange interaction; thus, the anisotropic exchange is more T-sensitive than the isotropic exchange. Additionally, D∝M4.79 and A∝M2 for Pt/Co/MgO, and different ferromagnet (FM) layers can originate from different scaling factors between D and M. Therefore, the DMI T-dependence in a Pt-based multilayer system depends on the FM type, which implies that orbital hybridization at an interface may elucidate the relation between D and M.

Effects of interfacial Dzyaloshinskii–Moriya interaction on magnetic dynamics

In the “Beyond Moore” era, the information device is expected to exhibit advantages including small sizes, high processing speed, and low power and dissipation. The novel magnetic information device with these advantages is made of heavy metal(HM)/ferromagnet (FM) composite. Owing to the asymmetric structure, the anisotropic exchange coupling named the interfacial Dzyaloshinskii–Moriya interaction (iDMI) is generated at the HM/FM interface. This iDMI influences the magnetic dynamics including ferromagnetic resonance (FMR), spin wave, and the motion of chiral DWs. These magnetic dynamic behaviors are the bases of the functions of novel magnetic information devices. Therefore, the influence of iDMI on the magnetic dynamics has attracted wide attention in recent years. In this topical review, we give a detailed introduction and discussion about recent investigation on the iDMI-relevant magnetic dynamics of the HM/FM bilayer system. This review consists of five sections: (1). the introduction about the background, the basic theory of magnetic dynamics and DMI; (2). the review about the effect of iDMI on the propagation of spin wave. Owing to the iDMI, the dispersion relationship of spin wave is asymmetric. This not only offers a precise method for measuring the iDMI constant, but also gives rise to potential application for novel magnonic devices. (3). the review about the effect of iDMI on the FMR. Unique iDMI-relevant mode was observed in the FMR spectra owing to the nonparallel alignment of magnetic moments. (4). the review about the motion of DWs with chiral structure due to iDMI. The iDMI plays a fundamental role in the high velocity of the chiral DWs. Meanwhile, the iDMI results in the tilting of DW plane, and the mechanism has been widely investigated. The tilting of the DW plane may be depressed by the interlayer exchange coupling. (5). finally, we summarize the review and give an outlook.

Slow Magnetic Relaxation in {[CoCxAPy)] 2.15 H2O}n MOF Built from Ladder-Structured 2D Layers with Dimeric SMM Rungs

We present the magnetic properties of the metal-organic framework {[CoCxAPy]·2.15 H2O}n (Cx = bis(carboxypropyl)tetramethyldisiloxane; APy = 4,4`-azopyridine) (1) that builds up from the stacking of 2D coordination polymers. The 2D-coordination polymer in the bc plane is formed by the adjacent bonding of [CoCxAPy] 1D two-leg ladders with Co dimer rungs, running parallel to the c-axis. The crystal packing of 2D layers shows the presence of infinite channels running along the c crystallographic axis, which accommodate the disordered solvate molecules. The Co(II) is six-coordinated in a distorted octahedral geometry, where the equatorial plane is occupied by four carboxylate oxygen atoms. Two nitrogen atoms from APy ligands are coordinated in apical positions. The single-ion magnetic anisotropy has been determined by low temperature EPR and magnetization measurements on an isostructural compound {[Zn0.8Co0.2CxAPy]·1.5 CH3OH}n (2). The results show that the Co(II) ion has orthorhombic anisotropy with the hard-axis direction in the C2V main axis, lying the easy axis in the distorted octahedron equatorial plane, as predicted by the ab initio calculations of the g-tensor. Magnetic and heat capacity properties at very low temperatures are rationalized within a S* = 1/2 magnetic dimer model with anisotropic antiferromagnetic interaction. The magnetic dimer exhibits slow relaxation of the magnetization (SMM) below 6 K in applied field, with a tlf ≈ 2 s direct process at low frequencies, and an Orbach process at higher frequencies with U/kB = 6.7 ± 0.5 K. This compound represents a singular SMM MOF built-up of Co-dimers with an anisotropic exchange interaction.

Extended spin coherence of the zinc-vacancy centers in ZnSe with fast optical access

Qubits based on crystal defect centers have been shown to exhibit long spin coherence times, up to seconds at room temperature. However, they are typically characterized by a comparatively slow initialization timescale. Here, fluorine implantation into ZnSe epilayers is used to induce defect states that are identified as zinc vacancies. We study the carrier spin relaxation in these samples using various pump-probe measurement methods, assessing phenomena such as resonant spin amplification, polarization recovery, and spin inertia in transverse or longitudinal magnetic field. The spin dynamics in isotopically natural ZnSe show a significant influence of the nuclear spin bath. Removing this source of relaxation by using isotopic purification, we isolate the anisotropic exchange interaction as the main spin dephasing mechanism and find spin coherence times of 100 ns at room temperature, with the possibility of fast optical access on the picosecond time scales through excitonic transitions of ZnSe.

Site-Controlled Telecom Single-Photon Emitters in Atomically-thin MoTe2

Quantum emitters (QEs) in two-dimensional transition metal dichalcogenides (2D TMDCs) have advanced to the forefront of quantum communication and transduction research1. To date, QEs capable of operating in O-C telecommunication bands have not been demonstrated in TMDCs.2-5 Here we report a deterministic creation of such telecom QEs emitting over the 1080 to 1550 nm wavelength range via coupling of 2D molybdenum ditelluride (MoTe2) to strain inducing nano-pillar arrays.6, 7 Our Hanbury Brown and Twiss experiment conducted at 10 K reveals clear photon antibunching with 90% single photon purity. The photon antibuching can be observed up to liquid nitrogen temperature (77 K). Polarization analysis further reveals that while some QEs display cross-linearly polarized doublets with ~1 meV splitting resulting from the strain induced anisotropic exchange interaction, valley degeneracy is preserved in other QEs. Valley Zeeman splitting as well as restoring of valley symmetry in cross-polarized doublets are observed under 8T magnetic field.