Tuning the Room Temperature Ferromagnetism in Fe5GeTe2 by Arsenic Substitution

In order to tune the magnetic properties of the cleavable high-Curie temperature ferromagnet Fe5-xGeTe2, the effect of increasing the electron count through arsenic substitution has been investigated. Small additions of arsenic (2.5 and 5%) seemingly enhance ferromagnetic order in polycrystalline samples by quenching fluctuations on one of the three magnetic sublattices, whereas larger As concentrations decrease the ferromagnetic Curie temperature (TC) and saturation magnetization. This work also describes the growth and characterization of Fe4.8AsTe2 single crystals that are structurally analogous to Fe5-xGeTe2 but with some phase stability complications. Magnetization measurements reveal dominant antiferromagnetic behavior in Fe4.8AsTe2 with a Neel temperature of TN ≈42K. A field-induced spin-flop below TN results in a switch from negative to positive magnetoresistance, with significant hysteresis causing butterfly-shaped resistance loops. In addition to reporting the properties of Fe4.8GeTe2, this work shows the importance of manipulating the individual magnetic sublattices in Fe5-xGeTe2 and motivates further efforts to control the magnetic properties in related materials by fine tuning of the Fermi energy or crystal chemistry.

Anomalous and anisotropic nonlinear susceptibility in the proximate Kitaev magnet α-RuCl3

The leading order nonlinear (NL) susceptibility, χ3, in a paramagnet is negative and diverges as T → 0. This divergence is destroyed when spins correlate and the NL response provides unique insights into magnetic order. Dimensionality, exchange interaction, and preponderance of quantum effects all imprint their signatures in the NL magnetic response. Here, we study the NL susceptibilities in the proximate Kitaev magnet α-RuCl3, which differs from the expected antiferromagnetic behavior. For T < Tc = 7.5 K and field B in the ab-plane, we obtain contrasting NL responses in low (<2 T) and high field regions. For low fields, the NL behavior is dominated by a quadratic response (positive χ2), which shows a rapid rise below Tc. This large χ2 > 0 implies a broken sublattice symmetry of magnetic order at low temperatures. Classical Monte Carlo (CMC) simulations in the standard K − H − Γ model secure such a quadratic B dependence of M, only for T ≈ Tc with χ2 being zero as T → 0. It is also zero for all temperatures in exact diagonalization calculations. On the other hand, we find an exclusive cubic term (χ3) that describes the high field NL behavior well. χ3 is large and positive both below and above Tc crossing zero only for T > 50 K. In contrast, for B ∥ c-axis, no separate low/high field behaviors are measured and only a much smaller χ3 is apparent.

Four octamolybdate complexes constructed from a quinoline–imidazole–monoamide ligand: structures and electrochemical, photocatalytic and magnetic properties

Four octamolybdate-based complexes synthesized by employing N-(quinoline-5-yl)-1H-imidazole-4-carboxamide as a ligand exhibit excellent electrocatalytic activities, photocatalytic properties and antiferromagnetic behavior.

Multiferroicity in the YFeO3 crystal

In this paper, orthoferrite YFeO3 was synthesized by hydrothermal method. The space group of YFeO3 is Pnma and the spin state of [Formula: see text] ion is low spin (LS). The YFeO3 crystal exhibits a weak antiferromagnetic behavior by magnetic measurement. For the electrical polarization measurement, micron-scale Pt electrodes were deposited on the both sides of the YFeO3 crystal by FIB-induced deposition. The saturation polarization value is 0.1994[Formula: see text][Formula: see text]C/cm2 at room temperature. The crystal exhibits ferroelectric behavior through the Dzyaloshinskii–Moriya interaction induced by additional spin canting of the antiferromagnetic ordering. This work may be applied to further study of the multiferroicity in rare-earth orthoferrites RFeO3.

Synthesis of Carbon Showing Weak Antiferromagnetic Behavior at a Low Temperature

In this short communication, we report a new carbon material prepared from meta-linked polyaniline that exhibits weak antiferromagnetic interactions at low temperature. The synthesis of poly(meta-aniline), abbreviated as m-PANI, was conducted using the Ullmann reaction with the aid of Cu+ as a catalyst in the presence of K2CO3. After the generation of radical cations by vapor-phase doping with iodine, carbonization was performed to prepare carbon polyaniline (C-PANI), which comprises condensed benzene rings. Analysis with a superconducting quantum interference device revealed that the resultant carbon exhibits antiferromagnetism at low temperatures. The discovery of this weak antiferromagnetic carbon may contribute to the development of carbon magnets.

Metallic and antiferromagnetic fixed points from gravity

We consider [Formula: see text] gauge theory coupled to matter field in adjoints and study RG group flow. We constructed Callan–Symanzik equation and subsequent [Formula: see text] functions and study the fixed points. We find there are two fixed points, showing metallic and antiferromagnetic behavior. We have shown that metallic phase develops an instability if certain parametric conditions are satisfied.

Antiferromagnetism in two-dimensional polyradical nanosheets

2D polyradical nanosheets were prepared using interfacial polymerization and exhibited obvious antiferromagnetic behavior.