Atomic Moments Research Articles

Emergence of Magnetic Transition in Cobalt Oxide Nanowires on Vicinal Pt Substrate

This letter is devoted to a theoretical study of the magnetic properties of supported pure and oxidized Co nanowires (NWs) on the vicinal surface of a Pt substrate. The main goal is to study the influence of oxygen on the magnetic properties of Co NWs. Transition metal atoms are magnetic, and oxygen effectively interacts with electromagnetic (EM) radiation in the optical range. Thus, by choosing the resonant frequency, it becomes possible to change the magnetic properties of oxide NW as a whole and switch the magnetic state of the wire by using an EM field. Our study has shown that Co oxide (CoO) NWs can exhibit magnetic properties in the ground state. Moreover, we observed the emergence of magnetic transition from a ferromagnetic to an antiferromagnetic state in a CoO NW under surface oxidation. We show that the magnetic properties of oxidized NWs depend strongly on the surface geometry. The study of the electronic structure of CoO NWs explains the reason for the formation of several magnetic states. The analysis of band structures of pure and oxidized Co NW shows that changes in magnetic states can be explained by the changes in band structure due to oxidation and that oxidation decreases the value of magnetic moments of the Co atoms in comparison to the pure NW. However, the values of these moments are still high.

A multiferroic iron arsenide monolayer.

Iron arsenide (FeAs) monolayers are known as a key component for building iron-based superconductors. Here, we predict by first-principles calculations that the FeAs monolayer is a highly stable and multiferroic material with coexisting ferroelasticity and antiferromagnetism. The ferroelasticity entails a reversible elastic strain of as large as 18% and an activation barrier of 20 meV per atom, attributed to a weak hybridization between Fe d and As p orbitals. The local moments of Fe atoms are oriented out-of-plane, so that the magnetic ordering is weakly coupled to the structural polarization. Interestingly, fluorination of the FeAs monolayer can align the local moments in parallel and reorient the easy axis along the in-plane direction. As such, the fluorinated FeAs monolayer is potentially a long-sought multiferroic material that enables a strong coupling between ferroelasticity and ferromagnetism.

Intriguing strain-governed magnetic phase transitions in 2D vanadium porphyrin sheets

The strain effect on the magnetic response of 2D materials as spintronic devices is always important in actual applications. Due to the intriguing electronic and magnetic properties of two-dimensional (2D) vanadium porphyrin (V-PP) sheets, we studied the strain-induced magnetic coupling changes in 2D V-PP sheets by using the density functional theory method and found intriguing magnetic variation characters. The calculated results indicate that biaxial strain can modulate the magnetic moments of the central transition metal vanadium atoms and more importantly can induce phase transitions among three magnetic modes with four magnetic states (ferromagnetic (FM), ferrimagnetic (FIM), and two antiferromagnetic (AFM: AFM1 featuring a parallel spin lattice versus AFM2 featuring a crossing spin lattice)) with unique conversion pathways due to their different responses to the strain. As the compressive strain increases, the magnetic characteristics of 2D-VPP transitions as FM → FIM → AFM1 with two critical points (-4.7% and -6%), while the tensile strain can induce the original FM coupling to transition to another AFM state (FM → AFM2) at 5.3%. Analyses of the density of states, spin densities, and Bader charges reveal that the rich magnetic response properties of the system originate from the electron transfer between the central V and the porphyrin ligand induced by strain. This work provides intriguing information regarding the strain-induced magnetic phase transition mechanism and also presents a viable development direction to design 2D porphyrin magnetic semiconductors and spintronic devices.

Mechanism of strain-induced magnetic properties changes for metal magnetic memory technology on atomic scale

Magnetic non-destructive testing technology is widely used to detect stresses and defects in ferromagnetic materials based on the magneto-mechanical coupling effect. In the existing studies, calculated are the magnetic moment variations of the <i>α</i>-Fe system under axial tension and compression by using first-principles study, and the magneto-mechanical coupling mechanism is preliminarily discussed at an atomic level for the magnetic testing technology. In this work, taking the more complex doping systems Fe-C and Fe-Mn for examples, under different loading conditions of tension, compression and shearing, the coupling mechanisms such as the magnetic moment changes in different types of atomic doping systems are discussed in detail. The results show that the <i>α</i>-Fe and doping systems follow different changing laws of magnetic moments and energy under different types of strains. The detailed analyses of the density of states, the band structure, and the atomic magnetic moment show that doping elements change the morphology of band structure and the peak value of density of states by affecting the magnetic moment of Fe atoms, which leads the changing laws of magnetic moment and energy to be different from each other. In this work, discussed are the magneto-mechanical effects on the atomic level for ferromagnetic materials with different loading types, different doping elements and different element content. The results can be used as an important part of the multi-field coupling mechanism for magnetic testing technology.

First-principles study of Fe atom adsorbed biphenylene monolayer

Biphenylene monolayer is composed of four-, six- and eight-membered carbon rings and has a monatomic layer structure similar to graphene. It was synthesized in experiment recently and reported in <i>Science</i> in May 2021, which has attracted considerable attention in the research field of two-dimensional materials. By the density functional method of the first principle, we study the adsorption configuration of Fe atoms on biphenylene monolayer and analyze its electronic structure. The calculation of structural optimization, adsorption energy and molecular dynamics show that the biphenylene monolayer is a good matrix of Fe atoms. For Fe atoms, the hollow site in the four-membered ring of the biphenylene monolayer is the most stable adsorption site, and the adsorption energy can reach 1.56 eV. The calculation of charge transfer and density of states show that a stable bond can be formed between biphenylene monolayer and Fe atoms, and 0.73 electron is transferred from Fe atom to the neighbored carbon atom. After Fe atom being absorbed, biphenylene monolayer is magnetic, and the magnetic moment of Fe atom is about 1.81 <inline-formula><tex-math id="M2">\begin{document}${\mu}_{\mathrm{B}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20211631_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20211631_M2.png"/></alternatives></inline-formula> and points out of the plane. Compared with graphene, biphenylene monolayer adsorbs Fe atoms more stably, which provides a new platform for studying the electromagnetic, transport and catalytic properties of two-dimensional materials with adatoms.

Charge and spin communication between dual metal single-atom sites on C2N sheets: regulating electronic spin moments of Fe atoms for N2activation and reduction

The charge and spin communication constructed between dual single-metal atom sites on C2N sheets significantly regulated the electronic spin moments of Fe atom active sites, and thus boosted electrochemical N2reduction to NH3.

QSAR MODELING AND DESIGN OF A NEW MODEL OF ANTIHIV DRUG 1-ARYL-TETRAHYDROISOQUINOLINE DERIVED USING THE PM3 SEMIEMPIRICAL METHOD

Quantitative Structure-Activities Relationship Analysis (QSAR) on the 1-aryl-tetrahydroisoquinoline derivative as a candidate for the anti-HIV drug (Human Immunodeficiency Virus) has been done. The analysis using an electronic descriptor of atomic net charge, dipole moment, polarization, HOMO-LUMO energy, and log P was calculated using the PM3 semiempirical method. The best equation model is determined using multilinear regression analysis. The QSAR analysis show that the best QSAR equation model of 1-aryl-tetrahydroisoquinoline derivatives: pEC50= -23.019-10.867(qC3)-162.911(qC4)-107.057(qC6) + 53.621(qC8) - 0.047 (µ) + 0.158 (α) + 0.175 (log P); (n = 36; r = 0.935; r2 = 0.875; SE= 0.135927366; Fcount/Ftable= 7.945277618; PRESS = 2.857943). The compound with the higher activity value is the best theoretically derivative compound for the anti-HIV drug candidate. The new model of the 1-aryl-tetrahydroisoquinoline derivative from the design is expected to have better activity than the 1-aryltetrahydroisoquinoline derivative compound that already exists is 1-(6-acetylpyridine-2-yl)-7,8-methoxy-quinoline.

First-principle calculations of the magnetic anisotropy of Fe and Co films separated by an interlayer of non-magnetic metals

This paper presents the results of numerical calculations of the magnetic characteristics of Co and Fe monolayer films on Cu and Pt surfaces using the VASP software package. The values of the difference between the total energies of the antiferromagnetic and ferromagnetic configurations are calculated depending on the convergence parameters and the thickness of the nonmagnetic material. The values of the magnetic anisotropy and magnetic moment of atoms in the structures of Co/Cu/Co, Fe/Pt/Fe, Co/Pt/Co, Pt/Co/Cu/Co/Pt are determined depending on the orientation of the surface face. For the (110) and (111) faces, the phenomenon of reorientation in the Co/Cu/Co structure is confirmed, when the anisotropy of the cobalt films parallel to the surface plane is replaced by the perpendicular anisotropy due to the introduction of an ultrathin platinum film into the structure. Keywords: Magnetic anisotropy, ultrathin magnetic films.

The Investigation of Spectroscopic and Electronic Properties of 3-Ethyl-4-(4-cinnamoyloxybenzylidenamino)-4,5-dihydro-1H-1,2,4-triazol-5-one Compound Using Density Functional Theory and Hartree-Fock Basis Sets

In this study, we reported a combined experimental and theoretical study on 3-n-propyl-4-(3-cinnamoyloxybenzylidenamino)-4,5-dihydro-1H-1,2,4-triazol-5-one compound. The title compound was prepared and characterized by Uv-Vis, FT-IR spectra, 1H and 13C NMR. UV-visible absorption spectra and the stimulation contributions in UV-visible transitions were obtained with TD-DFT/B3LYP and TD-FF methods and 6-311G(d) polarizer set based on optimized structure. Calculated absorption wavelengths (λ), oscillator power (f) and excitation energies were compared with experimental values. The calculated IR data of compound were calculated in gas phase by using of 6-31G(d) basis set of B3LYP and HF methods and are multiplied with appropriate scala factors. Theoretical infrared spectrums are formed from the data obtained according to B3LYP method. In the identification of calculated IR data was used the veda4f program. The molecular geometry, gauge including atomic orbital (GIAO), Experimental and theoretical values were inserted into the graphic according to equitation of δexp=a+b. δ calc. The standard error values were found via SigmaPlot program with regression coefficient of a and b constants. Obtained results indicate that there is a good agreement between the experimental and theoretical data. Also, HOMO-LUMO analyses properties, Mulliken’s atomic charges, dipole moment and total energy of the title compound in the ground state were investigated by using Hartree-Fock (HF) and density functional theory (DFT/B3LYP) methods with 6-31G(d) basic set.

First-principles study on structural, electronic, and magnetic properties of 3d transition metal-substituted chiral (6, 3) carbon nanotube

The effect of doping the chiral (6, 3) single-wall carbon nanotube (SWCNT) with 3d-transition metals (TM) was examined by using the M06–2X Minnesota functional level. Physical, chemical, and electrical properties of the TM-doped SWCNT were investigated through calculating the parameters such as the dipole magnetic moments, Mulliken charges, the atomic dipole moment corrected Hirshfeld, the density of states, and formation energy. Results showed that bond lengths and angles of the pristine SWCNT decrease by doping it with the 3d-TM atoms from left to right in a row periodic table and the formation process of TM-doped SWCNT is endothermic. The values of natural bond orbital indicate that the charge transfer between carbon atoms and the Sc, Cu, Zn dopants on the CNT are more than the other 3d-TM dopants. The electron localization function results reveal the decrease in the type of covalence bond of C–Fe, C–Cu, and C–Zn compared with the other dopants. We find that doping the pure CNT with Sc, V, Co, Mn, Cu atoms can donate the magnetic properties to the pristine SWCNT.

Accurate measurement of atomic magnetic moments by minimizing the tip magnetic field in STM-based electron paramagnetic resonance

Electron paramagnetic resonance (EPR) performed with a scanning tunneling microscope (STM) allows for probing the spin excitation of single atomic species with MHz energy resolution. One of the basic applications of conventional EPR is the precise determination of magnetic moments. However, in an STM, the local magnetic fields of the spin-polarized tip can introduce systematic errors in the measurement of the magnetic moments by EPR. We propose to solve this issue by finding tip-sample distances at which the EPR resonance shift caused by the magnetic field of the tip is minimized. To this end, we measure the dependence of the resonance field on the tip-sample distance at different radiofrequencies and identify specific distances for which the true magnetic moment is found. Additionally, we show that the tip's influence can be averaged out by using magnetically bistable tips, which provides a complementary method to accurately measure the magnetic moment of surface atoms using EPR STM.

Ferrimagnetic–ferromagnetic phase transition in Mn4N films favored by non-magnetic In doping

The ferrimagnet Mn4N forms a family of compounds useful in spintronics. In a compound comprising non-magnetic and magnetic elements, one basically expects the compound to become ferromagnetic when the proportion of the magnetic element increases. Conversely, one does not expect ferromagnetism when the proportion of the non-magnetic element increases. Surprisingly, Mn4N becomes ferromagnetic at room temperature when the Mn content is decreased by the addition of In atoms, a non-magnetic element. X-ray magnetic circular dichroism measurement reveals that the magnetic moment of Mn atoms at face-centered sites, Mn(II), reverses between x= 0.15 and 0.27 and aligns parallel to that of Mn atoms at corner sites, Mn(I), at x = 0.27 and 0.41. The sign of the anomalous Hall resistivity also changes between x = 0.15 and 0.27 in accordance with the reversal of the magnetic moment of the Mn(II) atoms. These results can be interpreted using first-principles calculations, showing that the magnetic moment of Mn(II) sites which are the nearest neighbors to the In atom align to that of Mn(I) sites.

Hunting for CP -violating axionlike particle interactions

The impact of axionlike particles (ALPs) on the search of permanent electric dipole moments (EDMs) of molecules, atoms, nuclei and nucleons is systematically investigated. Assuming the most general ALP effective field theory containing operators up to dimension-five, we evaluate the leading short-distance effects to the EDMs at two-loop order. The high sensitivity of EDMs to $CP$-violating ALP interactions is emphasized exploiting both the current and projected experimental sensitivities.

Anapole due to a tangentially polarized dipole near a subwavelength sphere: Inhibition and enhancement of spontaneous emission

There exist oscillating current distributions that cannot generate radiation; these configurations are known as anapoles. Our goal is to theoretically demonstrate that an oscillating electric dipole, located in the vicinity of a subwavelength sphere and polarized tangentially, can yield an anapole. This paper complements our recent study [J. R. Zurita-S\'anchez, Phys. Rev. Research 1, 033064 (2019)], devoted to an anapole arising from an electric dipole with radial polarization. Our methodology relies on the multipolar expansion of the excitation and scattered electromagnetic fields with respect to the center of the spherical particle. We found that an anapole arises when the effective electric and magnetic dipoles, induced by the dipolar source, vanish. The aforementioned anapole condition considers that the lowest multipolar order contribution is responsible for the radiative response of the emitter. However, high-order multipoles yield an unavoidable residual radiated power which is much smaller still than the radiated power of the dipole in the absence of the scatterer. Particularly, for a nonabsorbing sphere, the geometrical and dielectromagnetic parameters that lead to an anapole state are determined. As a practical scenario, we exploit the anapole excitation for controlling the spontaneous emission decay rate of an excited atom (or a molecule). In comparison to the decay rate of an excited atom without the scatterer, the radiative decay in the presence of the particle can be inhibited by a factor of about three orders of magnitude; this factor is quite large for an open system like ours. Furthermore, we show that by varying the orientation of the atomic transition dipole moment from a tangential direction, where the anapole condition is satisfied, to a radial direction, the atom can change from a state in which the spontaneous emission rate is inhibited to one in which this rate is enhanced. Hence, the anapole setup enables the versatile control of the radiative properties of an atom, and it provides the possibility for implementing applications related to the sensing and localization of atoms.

Microwave-assisted synthesis, DFT theoretical study and biological activities evaluation of two phosphonylated m-toluidine derivatives

An easy and efficient microwave-assisted method has been developed for the synthesis of two phosphonylated molecules: α-aminophosphonic acid (MTA) and α-aminophosphonate ester (MTE). To achieve these, we have synthesized the products from m-toluidine, under microwave conditions. All of the obtained compounds were characterized by Microanalysis, UV–Vis, FT-IR, and 1H, 13C and 31P NMR spectroscopic methods. The spectral results are in good line with the proposed structures. Density Functional theory (DFT) calculations were carried out using Gaussian09 program package, using 6–31G++(d,p) basis set. The frontier orbital energies were presented and have been used to predict global reactivity indices. Results showed that MTE is more reactive and less stable than MTA. The Mulliken atomic charges, dipole moment and thermodynamic proprieties were also calculated and discussed. In addition, the target compounds were evaluated for their in vitro antioxidant, antimicrobial and antienzymatic activities. The biological assays indicated that these compounds displayed potent inhibitory activity toward acetylcholinesterase (MTE: 92.71±0.91%, MTA: 67.32±0.52%) and butyrylcholinesterase (MTE: 79.16±0.47% and MTA 34.80±0.76%). It was also found that they act as excellent antiradical agents (ABTS: MTA/226.077±0.29 μg/ml, MTE/ 535,993±0.30 μg/ml and DPPH: MTA/311.853 ± 0.14 μg/ml, MTE/621.627 ± 0.12 μg/ml). In addition, these compounds exhibited the highest antibacterial and antifungal properties.

Superexchange-induced valley splitting in two-dimensional transition metal dichalcogenides: A first-principles study for rational design

Monolayer transition metal dichalcogenides (TMDs) with spin-valley coupling are a well-studied class of two-dimensional materials with potential for novel optoelectronics applications. Breaking time-reversal symmetry via an external magnetic field or supporting magnetic substrate can lift the degeneracy of the band gaps at the inequivalent $K$ and ${K}^{\ensuremath{'}}$ high symmetry points, or valleys, in the monolayer TMD Brillouin zone, a phenomenon known as valley splitting. However, reported valley splittings thus far are modest, and a detailed structural and chemical understanding of valley splitting via magnetic substrates is lacking. Here we probe the underlying physical mechanism with a series of density functional theory (DFT) calculations of magnetic atoms with varying coverage on the surface of prototypical monolayer ${\mathrm{WSe}}_{2}$ and ${\mathrm{MoS}}_{2}$ TMDs. Near-valence band edge energies for variable magnetic atom height, lateral registry, and magnetic moment are calculated with DFT, and trends are rationalized with a model Hamiltonian with second-order spin-dependent exchange coupling. From our analysis, we demonstrate how large valley splittings may be achieved and that the valley splitting can be understood with a superexchange mechanism, which strongly depends on overlaps of TMD Bloch states at the valley extrema with the localized $d$ states of the magnetic atom, as well as the out-of-plane component of the magnetic moment of the magnetic atom. Our calculations provide a basis for understanding prior measurements of valley splitting and suggest routes for enhancing valley splitting in future systems of interest.

Combined Role of Biaxial Strain and Nonstoichiometry for the Electronic, Magnetic, and Redox Properties of Lithiated Metal-Oxide Films: The LiMn2O4 Case.

Understanding the interplay between strain and nonstoichiometry for the electronic, magnetic, and redox properties of LiMn2O4 films is essential for their development as Li-ion battery (LIB) cathodes, photoelectrodes, and systems for sustainable spintronics applications as well as for emerging applications that combine these technologies. Here, density functional theory (DFT) simulations suggest that compressive strain increases the reduction drive of (111) LiMn2O4 films by inducing >1 eV upshift of the valence band edge. The DFT results indicate that, regardless of the crystallographic orientation for the LiMn2O4 film, biaxial expansion increases the magnetic moments of the Mn atoms. Conversely, biaxial compression reduces them. For ferromagnetic films, these changes can be substantial and as large as over 4 Bohr magnetons per unit cell over the simulated range of strain (from -6 to +3%). The DFT simulations also uncover a compensation mechanism whereby strain induces opposite changes in the magnetic moment of the Mn and O atoms, leading to an overall constant magnetic moment for the ferromagnetic films. The calculated strain-induced changes in atomic magnetic moments reflect modifications in the local electronic hybridization of both the Mn and O atoms, which in turn suggests strain-tunable, local chemical, and electrochemical reactivity. Several energy-favored (110) and (111) ferromagnetic surfaces turn out to be half-metallic with minority-spin band gaps as large as 3.2 eV and compatible with spin-dependent electron-transport and possible spin-dependent electrochemical and electrocatalytic properties. The resilience of the ferromagnetic, half-metallic states to surface nonstoichiometry and compositional changes invites exploration of the potential of LiMn2O4 thin films for sustainable spintronic applications beyond state-of-the-art, rare-earth metal-based, ferromagnetic half-metallic oxides.

A low-energy perspective on the minimal left-right symmetric model

We perform a global analysis of the low-energy phenomenology of the minimal left-right symmetric model (mLRSM) with parity symmetry. We match the mLRSM to the Standard Model Effective Field Theory Lagrangian at the left-right-symmetry breaking scale and perform a comprehensive fit to low-energy data including mesonic, neutron, and nuclear β-decay processes, ∆F = 1 and ∆F = 2 CP-even and -odd processes in the bottom and strange sectors, and electric dipole moments (EDMs) of nucleons, nuclei, and atoms. We fit the Cabibbo-Kobayashi-Maskawa and mLRSM parameters simultaneously and determine a lower bound on the mass of the right-handed WR boson. In models where a Peccei-Quinn mechanism provides a solution to the strong CP problem, we obtain {M}_{W_R} ≳ 5.5 TeV at 95% C.L. which can be significantly improved with next-generation EDM experiments. In the P-symmetric mLRSM without a Peccei-Quinn mechanism we obtain a more stringent constraint {M}_{W_R} ≳ 17 TeV at 95% C.L., which is difficult to improve with low-energy measurements alone. In all cases, the additional scalar fields of the mLRSM are required to be a few times heavier than the right-handed gauge bosons. We consider a recent discrepancy in tests of first-row unitarity of the CKM matrix. We find that, while TeV-scale WR bosons can alleviate some of the tension found in the Vud,us determinations, a solution to the discrepancy is disfavored when taking into account other low-energy observables within the mLRSM.

Half-metallicity and Curie temperature enhancement of CrI3 through boron atoms adsorption

Monolayer chromium iodide (CrI 3 ) as a two-dimensional material with intrinsic ferromagnetism has been successfully prepared experimentally, expanding the applications of two-dimensional materials in the field of spintronics . In this paper, we have investigated the effect of boron atoms adsorption on the electronic structure, magnetic properties of monolayer CrI 3 through first-principles calculation based on density functional theory . Our results show that each boron atom adsorption enhance the magnetic moment of CrI 3 by 0.25 μ B . When the adsorption concentration increases from 1B@CrI 3 to 2B@CrI 3 , a semiconductor to half-metallicity transition occurs; when the concentration increases up to 4B@CrI 3 , CrI 3 tunes to semiconductor. The Monte Carlo simulation based on the Ising model predicts the Curie temperature are 81.5 K, 117.7 K, 129.4 K and 143.9 K for 1B@CrI 3 , 2B@CrI 3 , 3B@CrI 3 and 4B@CrI 3 , much higher than that of pristine CrI 3 . Our calculation results are theoretically instructive for the application of CrI 3 in spintronic devices. • The electronic structures and magnetic properties of boron adsorption CrI 3 have been investigated. • The semiconductor-half metallicity-semiconductor transition of adsorption systems depended on boron concentration. • The Curie temperature of CrI 3 can be largely enhanced through boron atoms adsorption. Firstly, we calculated the band structure of the 2 × 2 × 1 supercell CrI 3 (shown in Fig. 1(c)), and the results show that the monolayer CrI 3 is an indirect bandgap semiconductor with a bandgap of 1.16 eV. The intrinsic magnetic moment is 24 μ B for CrI 3 supercell, it means that the magnetic moment is 6 μ B for CrI 3 unit cell. The magnetic moments mainly come from the contribution of Cr atoms, and the magnetic moment of each Cr atom is 3 μ B , which is consistent with the results of previous studies [26,35]. The properties of CrI 3 with different concentrations of boron atoms adsorption are shown in Table 1, each adsorbed B atom increases the magnetic moment average to each CrI 3 primitive cell by about 0.25 μ B . This indicates that the magnetic properties of CrI 3 can be effectively tuned by boron atoms adsorption. The Bader charge analysis shows that each B atom transfers about 0.13 electrons to CrI 3 . The magnetic moments of top position Cr ( M ІCr ) do not much change, while the magnetic moments for other Cr atoms ( M ⅡCr ) increased with adsorption concentration. Since the B atoms are adsorbed on the surface of the CrI 3 layer, the nearly equal electrons per B atom transfer from the B atoms to CrI 3 increased almost equal magnetic moment of Cr atoms, which may be the reason for the increased total magnetic moments of 0.25 μ B of the monolayer CrI 3 .

Suppression of relaxation of higher polarization moments of alkali atoms in superfrequent spin-exchange collisions

Consideration of nonlinear spin-exchange equations showed that, in addition to the well-known suppression of the relaxation of the transverse orientation of atoms in a low magnetic field, relaxation of higher polarization moments (alignment, octupole, hexadecapole, etc) are also suppressed. Such suppression of relaxation is caused by the conservation of the transverse angular momentum of atoms in collisions.