Spin-flip Transitions Research Articles

Weak ferromagnetic interactions of [formula omitted] induced by coupling of the crystal and related lattice vibrations

There is an increase in demand of the next-generation spintronic devices with stable structural and magnetic properties in varying temperatures. An orthoferrites structure of the Pnma space group has been successfully prepared using high temperature solid-state reaction. In the Sm2Fe2O5+δ (SFO) material, Fe3+ ions occupy edge-cantered and face-cantered positions forming the tilted FeO6 octahedrons with Glazer's notation tilt a−a−c+. The ordering of the rare-earth ions at compensation temperature (Tcomp=2.3K), spin-flip transition in the range of 9.4−45.6K, and a second-type spin-reorientation transition around the anisotropy barrier with lower and higher transitional temperatures, TL=465 and TH=480K respectively. The canting of spins along with disordered spins at the surface results in a non-zero Tcomp and unsaturated magnetization. It is inferred that thermal activation of particle's moment over the anisotropy barriers (known as Kneller's law) only occurs above room temperature.

Imaging nanomagnetism and magnetic phase transitions in atomically thin CrSBr

Since their first observation in 2017, atomically thin van der Waals (vdW) magnets have attracted significant fundamental, and application-driven attention. However, their low ordering temperatures, Tc, sensitivity to atmospheric conditions and difficulties in preparing clean large-area samples still present major limitations to further progress, especially amongst van der Waals magnetic semiconductors. The remarkably stable, high-Tc vdW magnet CrSBr has the potential to overcome these key shortcomings, but its nanoscale properties and rich magnetic phase diagram remain poorly understood. Here we use single spin magnetometry to quantitatively characterise saturation magnetization, magnetic anisotropy constants, and magnetic phase transitions in few-layer CrSBr by direct magnetic imaging. We show pristine magnetic phases, devoid of defects on micron length-scales, and demonstrate remarkable air-stability down the monolayer limit. We furthermore address the spin-flip transition in bilayer CrSBr by imaging the phase-coexistence of regions of antiferromagnetically (AFM) ordered and fully aligned spins. Our work will enable the engineering of exotic electronic and magnetic phases in CrSBr and the realization of novel nanomagnetic devices based on this highly promising vdW magnet.

Magnetic exchange interactions and non-Debye relaxation in spin-3/2 frustrated Kagomé magnet Co3V2O8

We report the experimental determination of the magnetic exchange parameter ( J/kB = 2.88 ± 0.02 K) for the Spin-3/2 ferromagnetic (FM) Kagomé lattice system: Co3V2O8 using the temperature dependence of dc-magnetic susceptibility χ(T) data by employing the fundamental Heisenberg linear chain model. Our results are quite consistent with the theoretically reported nearest neighbor dominant FM exchange coupling strength Jex−NN∼ 2.45 K. Five different magnetic phase transitions (6.2–11.2 K) and spin-flip transitions (9.6–7.7 kOe) have been probed using the ∂ ( χT )/ ∂T vs. T, heat capacity (CP -T) and differential isothermal magnetization curves. Among such sequence of transitions, the prominent ones being incommensurate antiferromagnetic (AFM) state at 11.2 K, commensurate AFM state at 8.8 K, and commensurate FM state across 6.2 K. All the successive magnetic phase transitions have been mapped onto a single H-T plane through which one can easily distinguish the above-mentioned different phases. The magnetic contribution of the CP -T near TN (11.2 K) has been analyzed using the power-law expression CM = A|T — TN|−α resulting in the critical exponent α = 0.18 ± 0.01 (0.15 ± 0.003) for T < TN (T > TN ), respectively for the Co3V2O8. It is interesting to note that non-Debye type dipole relaxation is quite prominent in Co3V2O8 and was evident from the Kohlrausch–Williams–Watts analysis of complex modulus and impedance spectra (0 ⩽β⩽ 1). Mott’s variable-range hopping of charge carriers process is evident through the resistivity analysis ( ρac -T −1/4 ) in the temperature range 275 ∘C–350 ∘C. Moreover, the frequency-dependent analysis of σac (ω) follows Jonscher’s power law yielding two distinct activation energies ( Ea∼ 0.37 and 2.29 eV) between the temperature range 39 ∘C–99 ∘C and 240 ∘C–321 ∘C.

Theory of acoustic-phonon involved exciton spin flip in perovskite semiconductors

We present a theory of the acoustic phonon assisted spin-flip Raman scattering (SFRS), or resonant photoluminescence with the spin flip of a photoexcited exciton localized in a bulk cubic-phase perovskite semiconductor. We consider the spin-flip transitions between the ground-state exciton spin sublevels in external magnetic field B and discuss the variation of their probability rate and polarization selection rules with the increase of B. The transitions are treated as two-quantum processes with the virtual to and fro transfer of the electron in the electron-hole pair between the bottom and first excited conduction bands. The transfer occurs due to both the electron-hole exchange interaction and the electron-phonon interaction. The theoretical results allow one to distinguish the phonon assisted Raman scattering from (a) the resonant Raman scattering with the combined spin flip of the localized resident electron and hole and (b) the biexciton-mediated SFRS analyzed previously.

Coercivity enhancement in hematite/permalloy heterostructures across the Morin transition

Interfacial effects between antiferromagnetic (AFM) and ferromagnetic (FM) materials have long been a center of magnetism studies. Aside from the exchange bias occurring at the AFM/FM interface, controlling the coercivity is another significant topic in magnetic recordings. The coercivity of FM materials is often determined through varying grain size, alloy composition, density of defects, etc., which is set during material growth and offers limited room for modification after growth. Hematite (α-Fe2O3) is an AFM material that undergoes a temperature-controlled spin-flip transition, the so-called Morin transition. This transition gives an extra degree of freedom making hematite an intriguing component to study the exchange coupling when interfaced with an FM material. In this work, changes in the magnetic properties of soft magnetic permalloy (Ni81Fe19, or Py) thin films grown on hematite were studied across the Morin transition. Surprisingly, these samples showed a remarkable change in coercivity during the Morin transition. We attribute this effect to the magnetic domain mixture of hematite during the Morin transition. Our findings present a novel method of controlling the coercivity of plain ferromagnetic thin films.

Layer Control of Magneto-Optical Effects and Their Quantization in Spin-Valley Splitting Antiferromagnets.

Magneto-optical effects (MOE), interfacing the fundamental interplay between magnetism and light, have served as a powerful probe for magnetic order, band topology, and valley index. Here, based on multiferroic and topological bilayer antiferromagnets (AFMs), we propose a layer control of MOE (L-MOE), which is created and annihilated by layer-stacking or an electric field effect. The key character of L-MOE is the sign-reversible response controlled by ferroelectric polarization, the Néel vector, or the electric field direction. Moreover, the sign-reversible L-MOE can be quantized in topologically insulating AFMs. We reveal that the switchable L-MOE originates from the combined contributions of spin-conserving and spin-flip interband transitions in spin-valley splitting AFMs, a phenomenon not observed in conventional AFMs. Our findings bridge the ancient MOE to the emergent realms of layertronics, valleytronics, and multiferroics and may hold immense potential in these fields.

Application of the Heavy-Atom Effect for (Sub)microsecond Thermally Activated Delayed Fluorescence and an All-Organic Light-Emitting Device with Low-Efficiency Roll-off.

The feature of abundant and environmentally friendly heavy atoms (HAs) like bromine to accelerate spin-forbidden transitions in organic molecules has been known for years. In combination with the easiness of incorporation, bromine derivatives of organic emitters showing thermally activated delayed fluorescence (TADF) emerge as a cheap and efficient solution for the slow reverse intersystem crossing (rISC) problem in such emitters and strong efficiency roll-off of all-organic light-emitting diodes (OLEDs). Here, we present a comprehensive photophysical study of a tri-PXZ-TRZ emitter reported previously and its hexabromo derivative showing a remarkable enhancement of rISC of up to 9 times and a short lifetime of delayed fluorescence of 2 μs. Analysis of the key molecular vibrations and TADF mechanism indicates almost compete blockage of the spin-flip transition between the charge-transfer states of different multiplicity 3CT → 1CT. In such a case, rISC as well as its enhancement by the HA is realized via the 3LE → 1CT transition, where 3LE is the triplet state localized on the same brominated phenoxazine donor involved in the formation of the 1CT state. Interestingly, the spin-orbit coupling (SOC) with two other 3LE states is negligible because they are localized on different donors and not involved in 1CT. We consider this as an example of an additional "localization" criterion that completes the well-known El Sayed rule on the different nature of states for nonzero SOC. The applicative potential of such a hexabromo emitter is tested in a "hyperfluorescent" system containing a red fluorescent dopant (tetraphenyldibenzoperiflanthene, DBP) as an acceptor of Förster resonance energy transfer, affording a narrow-band red-emitting system, with most of the emission in the submicrosecond domain. In fact, the fabricated red OLED devices show remarkable improvement of efficiency roll-off from 2-4 times depending on the luminance, mostly because of the increase of the rISC constant rate and the decrease of the overall delayed fluorescence lifetime thanks to the HA effect.

Electronic states of the constituent magnetic elements, superior magnetic properties and spin-flip metamagnetic transition in Cu3Dy(SeO3)2O2Cl

Dy based cuprate francisite [Cu3Dy(SeO3)2O2Cl, in short DyCufr] is so far potentially the most fascinating magnetic compound in the class of francisite compounds. Synthesized DyCufr has been investigated via structural, X-ray absorption near edge structure (XANES), X-ray photoelectron spectroscopy (XPS) and magnetization measurements. XANES and XPS provide consistent and corroborative results regarding electronic states of the constituent elements. The most striking observation is that the slope of magnetization for the field induced metamagnetic transition (MMT) attains nearly infinity (perfect), hysteresis associated with MMT is substantially high, and the critical field for MMT is very low. The antiferromagnetic ordering temperature (TN), saturation magnetization (MS) are very high, and the remanent magnetization (MR) is appreciable in DyCufr in contrast to few other similar compounds. Unpaired 4f electrons of Dy3+ causing high value of effective magnetic moment and spin-flip type metamagnetism are pivotal for producing magnetically the most superior francisite. Actually, sharp MMT as evidenced in DyCufr, has the potential to be used in magneto-refrigeration and spin-electronic devices because it can produce an avalanche flip of spin structure from low-spin (antiferromagnetic) to high-spin (ferromagnetic) state.

Magnetic properties and magnetocaloric effect of DyCo9Si4

Polycrystalline samples of DyCo9Si4 with the tetragonal LaFe9Si4-type structure have been synthesized by arc melting and high-temperature annealing. Results of the magnetization M and specific heat Cp measurements show the existence of two magnetic anomalies at TC = 40 K and Tm = 20 K. The transition at TC = 40 K is attributed to the ferromagnetic transition of the Co sublattice. The magnetic moments of Dy3+ appear to align gradually below TC, and almost fixed below Tm, at which a broad maximum in Cp has been observed. Field-dependent M at T = 2 K up to H = 7 T suggested that the magnetic moment of Dy3+ is coupled antiferromagnetically with those of Co, forming a ferrimagnetic structure. Magnetization measurements up to 50 T at low temperatures using a pulse magnet demonstrated a spin-flip transition around H = 20 T, above which the magnetic moments of Co and Dy are in parallel. The spin-flip transition becomes broad with increasing temperature but still remains at TC = 40 K, indicating a strong antiparallel coupling between Co and Dy moments even in the paramagnetic state. The magnetocaloric effect was evaluated from Cp and M, and also from the sample-temperature variation in the quasi-adiabatic process with the pulsed magnetic field. The maximum entropy change for the field change from 5 to 0 T was observed at around T = Tm with the value ΔS = 5 J/kg K. The maximum temperature of ΔS shifts to higher temperatures in high magnetic fields, resulting in the large value of ΔS = 24 J/kg K at T ∼ TC by the field change from 50 to 0 T. The present results demonstrate that the pulsed-field measurement is a powerful method to evaluate the magnetocaloric effect of materials.

Magnetic circularly polarized luminescence from spin-flip transitions in a molecular ruby.

Magnetic circularly polarized luminescence (MCPL), i.e. the possibility of generating circularly polarized luminescence in the presence of a magnetic field in achiral or racemic compounds, is a technique of rising interest. Here we show that the far-red spin-flip (SF) transitions of a molecular Cr(iii) complex give intense MCD (magnetic circular dichroism) and in particular MCPL (g MCPL up to 6.3 × 10-3 T-1) even at magnetic fields as low as 0.4 T. Cr(iii) doublet states and SF emission are nowadays the object of many investigations, as they may open the way to several applications. Due to their nature, such transitions can be conveniently addressed by MCPL, which strongly depends on the zero field splitting and Zeeman splitting of the involved states. Despite the complexity of the nature of such states and the related photophysics, the obtained MCPL data can be rationalized consistently with the information recovered with more established techniques, such as HFEPR (high-frequency and -field electron paramagnetic resonance). We anticipate that emissive molecular Cr(iii) species may be useful in magneto-optical devices, such as magnetic CP-OLEDs.

Two-dimensional half-metals MSi2N4 (M = Al, Ga, In, Tl) with intrinsic p-type ferromagnetism and ultrawide bandgaps.

Intrinsic half-metallic nanomaterials with 100% spin polarization are highly demanded for next-generation spintronic devices. Here, by using first-principles calculations, we have designed a class of new two-dimensional (2D) p-type half-metals, MSi2N4 (M = Al, Ga, In and Tl), which show high mechanical, thermal and dynamic stabilities. MSi2N4 not only have ultrawide electronic bandgaps for spin-up channels in the range of 4.05 to 6.82 eV but also have large half-metallic gaps in the range of 0.75 to 1.47 eV, which are large enough to prevent the spin-flip transition. The calculated magnetic moment is 1 μB per cell, resulting from polarized N1-px/py orbitals. Moreover, MSi2N4 possess robust long-range ferromagnetic orderings with Curie temperatures in the range of 35-140 K, originating from the interplay of N1-M-N1 superexchange interactions. Furthermore, spin dependent electronic transport calculations reveal 100% spin polarization. Our results highlight new promising 2D ferromagnetic half-metals toward future spintronic applications.

Reentrant canonical spin-glass dynamics and tunable field-induced transitions in (GeMn)Co2O4 Kagomé lattice

We report on the reentrant canonical semi spin-glass characteristics and controllable field-induced transitions in distorted Kagomé symmetry of (GeMn)Co2O4. This B-site spinel exhibits complicated, yet interesting magnetic behaviour in which the longitudinal ferrimagnetic (FiM) order sets in below the Néel temperature T FN ∼ 77 K due to uneven moments of divalent Co (↑ 5.33 μ B) and tetravalent Mn (↓ 3.87 μ B) which coexists with transverse spin-glass state below 72.85 K. Such complicated magnetic behaviour is suggested to result from the competing anisotropic superexchange interactions (J AB/k B ∼ 4.3 K, J AA/k B ∼ −6.2 K and J BB/k B ∼ −3.3 K) between the cations, which is extracted following the Néel’s expression for the two-sublattice model of FiM. Dynamical susceptibility (χ ac (f, T)) and relaxation of thermoremanent magnetization, M TRM (t) data have been analysed by means of the empirical scaling-laws such as Vogel–Fulcher law and Power law of critical slowing down. Both of which reveal the reentrant spin-glass like character which evolves through a number of intermediate metastable states. The magnitude of Mydosh parameter (Ω ∼ 0.002), critical exponent zυ = (6.7 ± 0.07), spin relaxation time τ 0 = (2.33 ± 0.1) × 10−18 s, activation energy E a/k B = (69.8 ± 0.95) K and interparticle interaction strength (T 0 = 71.6 K) provide the experimental evidences for canonical spin-glass state below the spin freezing temperature T F = 72.85 K. The field dependence of T F obtained from χ ac (T) follows the irreversibility in terms of de Almeida–Thouless mean-field instability in which the magnitude of crossover scaling exponent Φ turns out to be ∼2.9 for the (Ge0.8Mn0.2)Co2O4. Isothermal magnetization plots reveal two field-induced transitions across 9.52 kOe (H SF1) and 45.6 kOe (H SF2) associated with the FiM domains and spin-flip transition, respectively. Analysis of the inverse paramagnetic susceptibility after subtracting the temperature independent diamagnetic term (=−3 × 10−3 emu mol−1 Oe−1) results in the effective magnetic moment = 7.654 μ B/f.u. This agrees well with the theoretically obtained = 7.58 μ B/f.u. resulting the cation distribution in support of the Hund’s ground state spin configuration and of Mn4+ and Co2+, respectively. The H–T phase diagram has been established by analysing all the parameters (T F(H), T FN(H), H SF1(T) and H SF2(T)) extracted from various magnetization measurements. This diagram enables clear differentiation among the different phases of the (GeMn)Co2O4 and also illustrates the demarcation between short-range and long-range ordered regions.

Phase-Driving Hole Spin Qubits.

The spin-orbit interaction in spin qubits enables spin-flip transitions, resulting in Rabi oscillations when an external microwave field is resonant with the qubit frequency. Here, we introduce an alternative driving mechanism mediated by the strong spin-orbit interactions in hole spin qubits, where a far-detuned oscillating field couples to the qubit phase. Phase-driving at radio frequencies, orders of magnitude slower than the microwave qubit frequency, induces highly nontrivial spin dynamics, violating the Rabi resonance condition. By using a qubit integrated in a silicon fin field-effect transistor, we demonstrate a controllable suppression of resonant Rabi oscillations and their revivals at tunable sidebands. These sidebands enable alternative qubit control schemes using global fields and local far-detuned pulses, facilitating the design of dense large-scale qubit architectures with local qubit addressability. Phase-driving also decouples Rabi oscillations from noise, an effect due to a gapped Floquet spectrum and can enable Floquet engineering high-fidelity gates in future quantum processors.

Molecular Network Approach to Anisotropic Ising Lattices: Parsing Magnetization Dynamics in Er3+ Systems with 0-3-Dimensional Spin Interactivity.

We present a wide-ranging interrogation of the border between single-molecule and solid-state magnetism through a study of erbium-based Ising-type magnetic compounds with a fixed magnetic unit, using three different charge-balancing cations as the means to modulate the crystal packing environment. Properties rooted in the isolated spin Hamiltonian remain fixed, yet careful observation of the dynamics reveals the breakdown of this approximation in a number of interesting ways. First, differences in crystal packing lead to a striking 3 orders of magnitude suppression in magnetic relaxation rates, indicating a rich interplay between intermolecular interactions governed by the anisotropic Ising lattice stabilization and localized slow magnetic relaxation driven by the spin-forbidden nature of quantum tunneling of the f-electron-based magnetization. By means of diverse and rigorous physical methods, including temperature-dependent X-ray crystallography, field, temperature, and time-dependent magnetometry, and the application of a new magnetization fitting technique to quantify the magnetic susceptibility peakshape, we are able to construct a more nuanced view of the role nonzero-dimensional interactions can play in what are predominantly considered zero-dimensional magnetic materials. Specifically, we use low field susceptibility and virgin-curve analysis to isolate metamagnetic spin-flip transitions in each system with a field strength corresponding to the expected strength of the internal dipole-dipole lattice. This behavior is vital to a complete interpretation of the dynamics and is likely common for systems with such high anisotropy. This collective interactivity opens a new realm of possibility for molecular magnetic materials, where their unprecedented localized anisotropy is the determining factor in building higher dimensionality.

Phase stabilization of double perovskite Sm2FeMnO6 and the study on its Structural, magnetic and dielectric properties

Sm2FeMnO6 offers combined physical properties of two single perovskite compounds SmFeO3 and SmMnO3, making it a technologically feasible functional material. Sm2FeMnO6 crystallizes in a distorted orthorhombic Pbnm symmetry with lattice parameters a = 5.3805(2) Å, b = 5.6182(2) Å and c = 7.6434(3) Å. The Fe/Mn cation arrangement is found to be random in this symmetry. The phonon modes concurrent to the existence of (Fe/Mn)O6 octahedra and Jahn-Teller distortion due to Mn ions are found. Both Fe and Mn ions present at the B-octahedral sites have trivalent state. Temperature and field dependent magnetization measurements on Sm2FeMnO6 illustrate multiple transitions. A distinctive switching associated with a spontaneous spin-flip transition of Sm and Mn/Fe sublattices are observed at 201 K and 206 K in ZFC and FC curves respectively. The antiferromagnetic to paramagnetic transition occurred at a Neel temperature of 491 K. The transition temperatures are lowered compared to the reported single perovskite SmFeO3 indicating the influence of Mn ions on the magnetic exchange integral chains. Thermally activated dielectric relaxation processes are observed in the temperature range 300 K to 500 K and near 700 K. The anomaly is found to exist in the magnetic transition region, evidencing the coupling of magnetic order with electric order parameter. Thus, the collective effect of Fe and Mn ions at the B-site on various physical properties of Sm2FeMnO6 opens up new avenues in the field of magnetoelectric applications.

A theory for colors of strongly correlated electronic systems

Many strongly correlated transition metal insulators are colored, even though they have band gaps much larger than the highest energy photons from the visible light. An adequate explanation for the color requires a theoretical approach able to compute subgap excitons in periodic crystals, reliably and without free parameters—a formidable challenge. The literature often fails to disentangle two important factors: what makes excitons form and what makes them optically bright. We pick two archetypal cases as examples: NiO with green color and MnF2 with pink color, and employ two kinds of ab initio many body Green’s function theories; the first, a perturbative theory based on low-order extensions of the GW approximation, is able to explain the color in NiO, while the same theory is unable to explain why MnF2 is pink. We show its color originates from higher order spin-flip transitions that modify the optical response, which is contained in dynamical mean-field theory (DMFT). We show that symmetry lowering mechanisms may determine how ‘bright’ these excitons are, but they are not fundamental to their existence.

Spectroscopy of Spin-Split Andreev Levels in a Quantum Dot with Superconducting Leads.

We use a hybrid superconductor-semiconductor transmon device to perform spectroscopy of a quantum dot Josephson junction tuned to be in a spin-1/2 ground state with an unpaired quasiparticle. Because of spin-orbit coupling, we resolve two flux-sensitive branches in the transmon spectrum, depending on the spin of the quasiparticle. A finite magnetic field shifts the two branches in energy, favoring one spin state and resulting in the anomalous Josephson effect. We demonstrate the excitation of the direct spin-flip transition using all-electrical control. Manipulation and control of the spin-flip transition enable the future implementation of charging energy protected Andreev spin qubits.

On the general nature of 21-cm-Lyman α emitter cross-correlations during reionization

ABSTRACT We explore how the characteristics of the cross-correlation functions between the 21-cm emission from the spin-flip transition of neutral hydrogen (H $\scriptstyle \rm I $) and early Lyman α (Ly α) radiation emitting galaxies (Ly α emitters, LAEs) depend on the reionization history and topology and the simulated volume. For this purpose, we develop an analytic expression for the 21-cm-LAE cross-correlation function and compare it to results derived from different astraeus and 21cmfast reionization simulations covering a physically plausible range of scenarios where either low-mass (≲ 109.5 M⊙) or massive (≳ 109.5 M⊙) galaxies drive reionization. Our key findings are: (i) the negative small-scale (≲ 2 cMpc) cross-correlation amplitude scales with the intergalactic medium’s (IGM) average H $\scriptstyle \rm I $ fraction (〈χH i〉) and spin-temperature weighted overdensity in neutral regions (〈1 + δ〉H i); (ii) the inversion point of the cross-correlation function traces the peak of the size distribution of ionized regions around LAEs; (iii) the cross-correlation amplitude at small scales is sensitive to the reionization topology, with its anticorrelation or correlation decreasing the stronger the ionizing emissivity of the underlying galaxy population is correlated to the cosmic web gas distribution (i.e. the more low-mass galaxies drive reionization); (iv) the required simulation volume to not underpredict the 21-cm-LAE anticorrelation amplitude when the cross-correlation is derived via the cross-power spectrum rises as the size of ionized regions and their variance increases. Our analytic expression can serve two purposes: to test whether simulation volumes are sufficiently large, and to act as a fitting function when cross-correlating future 21-cm signal Square Kilometre Array and LAE galaxy observations.

Unraveling the magnetic structure of YbNiSn single crystal via crystal growth and neutron diffraction

Neutron and X-ray diffraction experiments were performed on the ternary intermetallic compound YbNiSn, formerly categorized as a ferromagnetic Kondo compound. At zero field, an increase in scattering intensity was observed on top of allowed and forbidden nuclear reflections below Tc, breaking the reflection condition of the crystal symmetry Pnma. This indicates that the magnetic structure of YbNiSn is antiferromagnetic-type, rather than the previously proposed simple collinear ferromagnetic structure. Temperature dependence of the scattering intensity of the 011 reflection confirmed the magnetic ordering at 5.77(2) K. No incommensurate satellite reflection was observed at 2.5 K. By applying external magnetic field of 1 T along the a axis, the magnetic intensity at the nuclear-forbidden 001 position was suppressed, while a slight enhancement at the nuclear-allowed 002 position was observed. This suggests a spin-flip transition under the external magnetic field along the a axis in YbNiSn. The proposed magnetic structures at zero field and 1 T correspond to the magnetic space groups of Pn'm'a and Pnm'a', respectively. The piezomagnetic effect and the switch between the two magnetic space groups by the external stress, which could be detected by the anomalous Hall effect, are proposed.

Biaxial ([110]) strain influence on the n-type half-metallicity and Curie temperature of Tc-doped Janus MoSSe monolayer

2D materials having stable half-metallic (HM) ferromagnetism are pivotal for multifunctional spintronic devices such as non-volatile random access magnetic memories and magnetic sensors. Using ab-initio calculations, we theoretically demonstrate that the electron-doped (Tc-doping at Mo site) Janus MoSSe monolayer (ML) is an n-type HM ferromagnetic (FM) with a charge carrier density of 2.9 × 1012 cm−2, which is thermally, mechanically, and dynamically stable. In addition, the large HM energy band gap of 1.63 eV is high enough to establish the long spin mean free path, high spin-filtering performance, and to avoid thermally excited spin-flip transition. Simultaneously, the calculated Curie temperature (TC) using a classical 2D Heisenberg model is 175 K, which indicates that Tc-doped MoSSe ML could be a stable FM structure. Interestingly, it is revealed that TC approaches to room temperature value for Fe 3d transition metals doping at Mo site, which makes the Fe-doped MoSSe ML highly desired for device application. Moreover, a direct-to-indirect band gap transition occurs in the pristine MoSSe ML for a biaxial ([110]) compressive/tensile (comp./tens.) strain of ≥−/+2%. It is also predicted that the n-type HM nature of the Tc-doped ML is very sensitive against applied strains and can be preserved under the -3% comp. to +2% tens. strain range. Along with this, the system undergoes a transition from FM to a non-magnetic state at a critical tensile strain of ＋ 5%, while the FM state remains robust under applied comp. strains. Correspondingly, it is also proposes that TC can be enhanced when a moderate compr. strain is adjusted. Hence, the present work are supposed to trigger further experimental studies to probe HM FM behavior in various Janus MLs by the combined effect of electron doping and strain engineering.