Magnetocrystalline anisotropy and dynamic spin reorientation of half-doped Nd_(0.5)Pr_(0.5)FeO_(3)single crystal

The single crystals of Nd_(0.5)Pr_(0.5)FeO_(3)were successfully grown by optical floating zone method.Room temperature x-ray diffraction and Laue photograph declared the homogeneity and high quality of the crystal.The significant magnetic anisotropy and multiple magnetic transitions illustrate the complex magnetic structure.At high temperatures(T>66 K),it shows the typical characteristics ofΓ_(4)(G_(x),A_(y),F_(z))state.With the decrease of the temperature,it undergoes a first-order spin reorientation transition fromΓ_(4)(G_(x),A_(y),F_(z))toΓ_(2)(F_(x),C_(y),G_(z))state in the temperature window of 45-66 K under an applied magnetic field of 0.01 T.As the temperature drops to~17 K,a new magnetic interaction mechanism works,which results in a further enhancement of magnetization.The T-H phase diagram of Nd_(0.5)Pr_(0.5)FeO_(3)single crystal was finally constructed.

Two-Dimensional Electron Gas in MoSi_(2)N_(4)/VSi_(2)N_(4)Heterojunction by First Principles Calculation

Van der Waals(vdW)layered two-dimensional(2D)materials,which may have high carrier mobility,valley polarization,excellent mechanical properties and air stability,have been widely investigated before.We explore the possibility of producing a spin-polarized two-dimensional electron gas(2DEG)in the heterojunction composed of insulators MoSi_(2)N_(4)and VSi_(2)N_(4)by using first-principles calculations.Due to the charge transfer effect,the 2DEG at the interface of the MoSi_(2)N_(4)/VSi_(2)N_(4)heterojunction is found.Further,for different kinds of stacking of heterojunctions,lattice strain and electric fields can effectively tune the electronic structures and lead to metal-to-semiconductor transition.Under compressive strain or electric field parallel to c axis,the 2DEG disappears and band gap opening occurs.On the contrary,interlayer electron transfer enforces the system to become metallic under the condition of tensile strain or electric field anti-parallel to c axis.These changes are mainly attributed to electronic redistribution and orbitals’reconstruction.In addition,we reveal that MoSi_(2)N_(4)/VSi_(2)N_(4)lateral heterojunctions of armchair and zigzag edges exhibit different electronic properties,such as a large band gap semiconductor and a metallic state.Our findings provide insights into electronic band engineering of MoSi_(2)N_(4)/VSi_(2)N_(4)heterojunctions and pave the way for future spintronics applications.

Magnetic phase transition and continuous spin switching in a high-entropy orthoferrite single crystal

Rare-earth orthoferrite REFeO_(3)(where RE is a rare-earth ion)is gaining interest.We created a high-entropy orthoferrite(Tm_(0.2)Nd_(0.2)Dy_(0.2)Y_(0.2)Yb_(0.2))FeO_(3)(HEOR)by doping five RE ions in equimolar ratios and grew the single crystal by optical floating zone method.It strongly tends to form a single-phase structure stabilized by high configurational entropy.In the low-temperature region(11.6‒14.4 K),the spin reorientation transition(SRT)ofΓ_(2)(F_(x),C_(y),G_(z))‒Γ_(24)‒Γ_(4)(G_(x),A_(y),F_(z))occurs.The weak ferromagnetic(FM)moment,which comes from the Fe sublattices distortion,rotates from the a-to c-axis.The two-step dynamic processes(Γ_(2)‒Γ_(24)‒Γ_(4))are identified by AC susceptibility measurements.SRT in HEOR can be tuned in the range of 50‒60000 Oe,which is an order of magnitude larger than that of orthoferrites in the peer system,making it a candidate for high-field spin sensing.Typical spin-switching(SSW)and continuous spin-switching(CSSW)effects occur under low magnetic fields due to the strong interactions between RE‒Fe sublattices.The CSSW effect is tunable between 20‒50 Oe,and hence,HEOR potentially can be applied to spin modulation devices.Furthermore,because of the strong anisotropy of magnetic entropy change()and refrigeration capacity(RC)based on its high configurational entropy,HEOR is expected to provide a novel approach for refrigeration by altering the orientations of the crystallographic axes(anisotropic configurational entropy).

Annealing-induced long-range charge density wave order in magnetic kagome FeGe:Fluctuations and disordered structure

Charge density wave(CDW) in kagome materials with the geometric frustration is able to carry unconventional characteristics.Recently, a CDW has been observed below the antiferromagnetic order in kagome FeGe, in which magnetism and CDW are intertwined to form an emergent quantum ground state. However, the CDW is only short-ranged and the structural modulation originating from it has yet to be determined experimentally. Here we realize a long-range CDW order by post-annealing process,and resolve the structure model through single crystal X-ray diffraction. Occupational disorder of Ge resulting from short-range CDW correlations above T_(CDW) is identified from structure refinements. The partial dimerization of Ge along the c axis is unveiled to be the dominant distortion for the CDW. Occupational disorder of Ge is also proved to exist in the CDW phase due to the random selection of partially dimerized Ge sites. Our work provides useful insights for understanding the unconventional nature of the CDW in FeGe.

Selected multiferroic perovskite oxides containing rare earth and transition metal elements

Multiferroic materials are currently the subject of intensive research worldwide, because of both their fundamental scientific problems and also possible technological applications. Among a number of candidates in the laboratories, compounds consisting of rare earth and transition metal perovskite oxides have very unusual structural and physical properties. In contrast to the so-called type I multiferroics, ferroelectricity may be induced by magnetic ordering or by applying external fields. In this review, the recent progress on the experimental and theoretical studies of some selected type II multiferroics is presented, with a focus on the perovskite oxides containing rare earth and transition metal elements. The rare earth orthoferrite crystals, rare earth titanate strained film, and rare earthbased superlattices are systematically reviewed to provide a broad overview on their promising electric, magnetic, and structural properties. The recent experimental advances in single-crystal growth by optical floating zone method are also presented. First-principles investigations, either supported by experimental results or awaiting for experimental verifications, are shown to offer useful guidance for the future applications of unconventional multiferroics.

Thermal control magnetic switching dominated by spin reorientation transition in Mn-doped PrFeO_(3) single crystals

Spin reorientation transition (SRT) has attracted substantial attention due to its important role in the ultrafast control of spins. However, the transition temperature is usually too low for its practical applications. Here, we demonstrate the ability to modulate the SRT temperature in PrFe_(1−x)Mn_(x)O_(3) single crystals from 196 K to 317 K across the room temperature by varying the Mn concentration. Interestingly, the Γ_(4) to Γ_(1) spin reorientation of the Mn-doped PrFeO_(3) is distinct from the Γ_(4) to Γ_(2) spin reorientation transition as in the parent material. Because of the coupling between rare-earth ions and transition-metal ions in determining the SRT temperature, the demonstrated control scheme of spin reorientation transition temperature by Mn-doping is expected to be used in temperature control magnetic switching devices and applicable to many other rare-earth orthoferrites.

Spin quantum well-like behavior in single-crystal Gd0.75La0.25FeO3

Rare earth orthoferrites(RFeO3,R=Y,Gd,Sm,Nd)have recently attracted much attention due to their novel magnetic and electrical properties such as magneto-electrics,magneto-dielectrics.and magneto-optics[1-3].The complex interactions between the two sublattices of R^3+and Fe^3+in RFeO3 provide the feasibility of control-ling spins in these solids,which makes them promising candidates for the spintronics[4].

Experimental evidence for type-1.5 superconductivity in ZrB_(12)single crystal

Recent studies proposed the two-band effect and the related type-1.5 superconductivity in Zr B12single crystal.Here,by combining both macroscopic and microscopic measurements,the superconducting properties and the intricate vortex matter of Zr B12are studied in detail.The vortex phase diagram is constructed,where the temperature dependence of the upper critical field can be well reproduced using a two-band Werthamer-Helfand-Hohenberg(WHH)model.A pronounced surface superconductivity is also found in the same temperature range,where the semi-Meissner state is observed.Both phenomena are attributed to the weakly coupled two-band effect.The direct visualization of the semi-Meissner state exhibits an inhomogeneous distribution of vortex clusters,vortex chains and large Meissner areas.With the increase of magnetic field,a transition from the semi-Meissner state to the mixed state is revealed and further supported by statistical analysis of the vortex pattern.Our results provide direct experimental evidence for the type-1.5 superconductivity in ZrB_(12).

A comprehensive first-principle study of borophene-based nano gas sensor with gold electrodes

Using density functional theory combined with nonequilibrium Green’s function method,the transport properties of borophene-based nano gas sensors with gold electrodes are calculated,and comprehensive understandings regarding the effects of gas molecules,MoS2 substrate and gold electrodes to the transport properties of borophene are made.Results show that borophene-based sensors can be used to detect and distinguish CO,NO,NO2 and NH3 gas molecules,MoS2 substrate leads to a nonlinear behavior on the current-voltage characteristic,and gold electrodes provide charges to borophene and form a potential barrier,which reduced the current values compared to the current of the systems without gold electrodes.Our studies not only provide useful information on the computationally design of borophene-based gas sensors,but also help understand the transport behaviors and underlying physics of 2D metallic materials with metal electrodes.