Journal of Physics: Condensed Matter最新文献

We report a detailed experimental study of the structural, magnetic and electrical properties of La and Ru doped (Sr_1-xLa_x)₂Ir_1-xRu_xO₄(x= 0.05, 0.15). X-ray diffraction analysis reveals that both samples crystallize in a tetragonal structure with a space groupI4₁/acdwithout impurities. Substitution with La and Ru leads to an increase in the lattice parameteraand a decrease inc. With increasing doping concentration, the Ir-O-Ir bond angle increases while the Ir-O bond length decreases. X-ray photoelectron spectroscopy (XPS) shows that Ir has Ir³⁺(5d⁶) and Ir⁴⁺(5d⁵) charge states, where the Ir⁴⁺charge state decreases with an increase in doping concentration. Thedcmagnetic susceptibilityχ(T) ofx= 0.05 reveals a transition from paramagnetic to weak ferromagnetic (wFM) atT_C∼ 229 K, arising from the canted antiferromagnetic (AFM) spin arrangement. The magnetic ordering temperatureT_Cremains unaltered for higher doping, whereas the magnetic moment is significantly reduced. The analysis of real and imaginary components ofacsusceptibility data, based on conventional critical slow model, frequency shift per decade and Vogel-Fulcher law, unanimously evidences the existence of reentrant spin-glass behavior (RSG), i.e. the coexistence of weak ferromagnetism and spin glass phases for the lowest doping ofx= 0.05. On the other hand, for higher doping (x= 0.15) of hole and electron, the RSG phase vanishes, leaving only the wFM phase at the same temperature as observed inx= 0.05. This suggests the higher doping of La and Ru does not affect the magnetic order, but removes the disorder between FM and AFM phases. The electrical resistivity (ρ) measurement analysis reveals that both the samples show semiconducting/insulating behavior across the temperature range. Theρof thex= 0.05 sample is lower than that of pure sample Sr₂IrO₄(Bhattiet al 2015 J. Phys.:Condens. Matter27016005), whileρofx= 0.15 shows two orders of magnitude larger than thex= 0.05 sample at low temperatures. The conduction mechanism of both samples is described by the 2D Mott's variable-range hopping model. Our results demonstrate that co-doping of two cation sites generates intriguing, competing hopping and magnetic processes.

We systematically investigate the magnetization and thermodynamic responses associated with the antiferromagnetic (AFM) transitions in magnetic semiconductor Eu₃InAs₃. The linear thermal expansion measurements reveal thataaxis expands whereasbandcaxes contract with the onset of the two AFM transitions atTN1andTN2. Using a simplified mean-field model incorporating AFM exchange interactions, easy-axis anisotropy, and Zeeman coupling, we analyze the potential magnetic structure change associated with the spin-flop and spin-flip transitions in field. The agreement between experimental and calculated magnetization data suggests that the1/3plateau alongbaxis results from a partial spin-flip transition in a multiple-easy-axis magnetic structure, where Eu₂-Eu₃and Eu₁sublattices order antiferromagnetically along thebandaaxes atTN1andTN2, respectively. Consistently, field dependence of magnetic entropy determined using low-Tadiabatic magnetocaloric effect indicates that the number of the ordered Eu²⁺moments atTN1is nearly twice that atTN2. Our results demonstrate that the magnetic structure in materials with strong spin-lattice coupling can be simply approached by a combined magnetization and thermodynamic study.

β-Mn-type chiral cubic Co_xZn_yMn_z(x+y+z= 20) alloys present a intriguing platform for exploring topological magnetic orderings with promising spintronic potential. This study examines the magnetotransport properties of Co_6.5Ru_1.5Zn₈Mn₄, a skyrmion-hostingβ-Mn-type chiral compound. The longitudinal resistivity (ρ_xx) exhibits field-insensitive low-temperature minima due to quantum interference effects, driven byT1/2-dependent electron-electron interactions. We observe a substantial intrinsic anomalous Hall conductivity, unaffected by quantum interference. Additionally, a pronounced topological Hall effect is observed at the metastable skyrmionic state, persisting up toTCand achieving notable magnitudes for stoichiometric compounds. These results position the Co_xZn_yMn_zfamily favourably to leverage the rich pallete of emergent magnetotransport properties for spintronic applications.

We report the detailed investigation of the magnetic, transport, and magnetocaloric effects (MCEs) of GdSbSe by magnetic susceptibilityχ(T), isothermal magnetizationM(H), resistivityρ(T,H), and heat capacityCp(T)measurements, crystallizing in the ZrSiS-type tetragonal crystal system with space group P4/nmm. Temperature-dependent magnetic susceptibility measurements revealed long-range antiferromagnetic ordering with two additional magnetic anomalies below Néel temperature (TN≈8.6K), corroborated through magnetocaloric and specific heat studies. Isothermal magnetization measurements unveil hidden metamagnetic signatures through a clear deviation from linearity. In addition, the enhanced value of the Sommerfeld coefficient (γ= 152(5) mJ mol^-1K²) suggests strong electronic correlations in GdSbSe. The entropy of magnetization derived from magnetic isotherms unfolds the field-induced transition from Inverse MCE to Conventional MCE. The detailed transport properties indicate a semimetallic behavior, strongly coupled with magnetic order. Furthermore, the linear field dependence of MR in the high-field region anticipate the possibility of Dirac-like dispersion. Deviations from Kohler's rule and non-linear Hall resistivity suggest the multiband nature of GdSbSe.

We introduce a machine learning prediction workflow to study the impact of defects on the Raman response of 2D materials. By combining the use of machine-learned interatomic potentials, the Raman-active Γ-weighted density of states method and splitting configurations in independant patches, we are able to reach simulation sizes in the tens of thousands of atoms, with diagonalization now being the main bottleneck of the simulation. We apply the method to two systems, isotopic graphene and defective hexagonal boron nitride, and compare our predicted Raman response to experimental results, with good agreement. Our method opens up many possibilities for future studies of Raman response in solid-state physics.

Chirality induced spin selectivity (CISS) effect implies the relationship between chirality and magnetism, attracting extensive attention in the fields of physics, chemistry and biology. Since it was first discovered with photoemission method in 1999, the CISS effect has been investigated and measured by a variety of methods. Among different means of measurements, scanning probe microscopy (SPM) as a powerful tool to explore the CISS effect, can directly measure and present the spin filtering property of chiral molecules in electron transport. In this paper, we summarize the recent experiments on the CISS effect studied with scanning tunneling microscopy and atomic force microscopy, analyzing the experimental setups and results, and delving into the underlying mechanisms. The present review offers a concise introduction to several chiral molecules which are investigated by SPM for the CISS effect, and a detailed exploration of various experimental techniques tailored to the unique adsorption structures of these molecules. The impact of molecular structure on spin selectivity and the profound implications of CISS are also demonstrated together with a concise overview of CISS theory. A conclusive synopsis and forward-looking perspectives on the investigation of the CISS effect in electron transport utilizing SPM techniques are presented.

Monolayer atomic thin films of group-V elements have a high potential for application in spintronics and valleytronics because of their unique crystal structure and strong spin-orbit coupling. We fabricated Sb and Bi monolayers on a SiC(0001) substrate by the molecular-beam-epitaxy method and studied the electronic structure by angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. The fabricated Sb film shows the (√3×√3)R30º superstructure associated with the formation of ⍺-Sb, and exhibits a semiconducting nature with a band gap of more than 1.8 eV. Spin-resolved ARPES measurements of isostructural ⍺-Bi revealed the in-plane spin polarization for the topmost valence band, demonstrating its Rashbasplittingof nature due to the space-inversion-symmetry breaking. We discuss the originobserved characteristic band structure and its similarity and difference between Sband Bi. .

We study topological charge pumping (TCP) in the Rice-Mele (RM) model with irreciprocal hopping. The non-Hermiticity gives rise to interesting pumping physics, owing to the presence of skin effect and exceptional points. In the static one-dimensional (1D) RM model, we find two independent tuning knobs that can drive the topological transition, namely, non-Hermitian parameter $gamma$ and system size $N$. To elucidate the system-size dependency, we use a finite-size generalized Brillouin zone (GBZ) scheme to show that the edge modes can be distinguished from the non-hermiticity induced skin modes. Moreover, this scheme can capture the state pumping of topological edge modes as a function of $gamma$ in the static 1D RM model and it further provides insight into engineering novel gapless exceptional edge modes with the help of adiabatic drive. Furthermore, we show that the standard topological pumping due to the adiabatic and periodic variation of the model parameters survives even with finite $gamma$. However, we observe that it depends upon the driving protocols and strength of the non-Hermiticity ($gamma$). With increasing $gamma$, the adiabatic pumping for non-trivial protocols is destroyed first and then re-emerges as an anomalous pumping which does not have any Hermitian counterpart. Additionally, we observe that even a trivial adiabatic protocol can give rise to pumping as opposed to the Hermitian system. This is attributed to the inherent point gap physics of non-Hermitian system which we explain by reformulating a non-Bloch topological invariant for the 1+1D RM model. This invariant explains the number of pumped charges (in each period) for all the driving protocols.

Boron nitride (BN), renowned for its exceptional optoelectrical properties, mechanical robustness, and thermal stability, has emerged as a promising two-dimensional material. Reinforcing AZ80 magnesium alloy with BN can significantly enhance its mechanical properties. To investigate and predict this enhancement during hot deformation, we introduce two independent modeling approaches a modified Johnson-Cook constitutive model and an artificial neural network (ANN). These models aim to capture both linear and nonlinear deformation characteristics. Hot compression tests conducted across various temperatures and strain rates provided a comprehensive dataset for model validation. The MJCC model, accounting for strain rate and temperature effects, achieved a correlation coefficientRof 0.96 and an average absolute relative error (AARE) of 6.28%. In contrast, the ANN, trained on experimental data, improved the correlation coefficient toRof 0.99 and reduced the AARE to below 1.5%, significantly enhancing predictive accuracy. These results indicate that while the modified J-C model provides reliable predictions under moderate conditions, the ANN more effectively captures complex behaviors under extreme deformation conditions. By comparing these modeling approaches, our study offers valuable insights for accurately predicting the rheological behavior of BN-reinforced AZ80 magnesium composite, aiding process optimization in industrial applications.

Scandium (Sc) can orderly occupy interstitial sites within the Ω phase of aluminum alloys, forming a new phase that significantly enhances the thermal stability of the alloy. However, Sc is relatively expensive and rare. In this work, we employ first-principles calculations to delve into the physical essence interstitial ordering of Sc in enhancing thermal stability at the electronic level, thereby revealing the crucial factors responsible for this improvement. By computationally screening all potential metallic elements across the periodic table, we uncover that, in addition to Sc, a diverse range of elements including lithium (Li), calcium (Ca), strontium (Sr), and some of rare earth elements (Sm, Ce, Y), possess the potential to contribute to thermal stability enhancement through interstitial ordering mechanisms in aluminum alloys. This study deepens our understanding of microstructural thermal stability and offers novel strategies for designing improved thermally stable Al alloys.