Tetragonal Axis Research Articles

Magnetic anisotropy of L1[formula omitted] FeNi (001), (010), and (111) ultrathin films: A first-principles study

In previous experiments, L10 FeNi thin films with different surfaces, including (001), (110), and (111), were produced and studied. Each surface defines a different alignment of the crystallographic tetragonal axis with respect to the film’s plane, resulting in different magnetic anisotropies. In this study, we use density functional theory calculations to examine three series of L10 FeNi films with surfaces (001), (010), and (111), and with thicknesses ranging from 0.5 to 3 nm (from 4 to 16 atomic monolayers). Our results show that films (001) have perpendicular magnetic anisotropy, while (010) favor in-plane magnetization, with a clear preference for the tetragonal axis [001]. We proposed calling this type of in-plane anisotropy fixed in-plane. A film with a surface (111) and a thickness of four atomic monolayers has a magnetization easy axis almost perpendicular to the plane of the film. As the thickness of the (111) film increases, the direction of magnetization rotates towards a tetragonal axis [001], positioned at an angle of about 45° to the plane of the film. Furthermore, the most significant changes in spin and orbital magnetic moments occur at a depth of about three near-surface atomic monolayers. Ultrathin L10 FeNi films with varying magnetic anisotropies may find applications in spintronic devices.

Tetrafluorosubstituted titanyl phthalocyanines: Structure of single crystals and phase transition in thin films

In this work, tetrafluorinated titanyl phthalocyanines with F-substituents in both peripheral (TiOPcF4-p) and non-peripheral (TiOPcF4-np) positions were synthesized and characterized by the methods of elemental analysis, IR and electronic absorption spectroscopies. The influence of the position of F-substituents on the structure of TiOPcF4-p and TiOPcF4-np single crystals and thin films grown by vacuum sublimation was studied. TiOPcF4-p crystallizes in the I4/m space group and its molecules form uniform stacks along the tetragonal axis. Introduction of F-substituents to non-peripheral positions leads to the change of the crystal structure: TiOPcF4-np crystallizes in the P-1 space group and its molecules are packed into 2D layers. Both phthalocyanines form oriented polycrystalline films when deposited by thermal sublimation in vacuum, but their phase composition is different from that of single crystals. The effect of post-deposition annealing of TiOPcF4-p and TiOPcF4-np films on their phase composition, morphology, optical absorption and Raman spectra, as well as conductivity was revealed. It was shown that a phase transition, which led to the appearance of an additional band in the near-IR region in the optical absorption spectrum, was observed in TiOPcF4-p films when heated, whereas no phase transition was observed in TiOPcF4-np films.

Epifluorescence microscopy study of a quadruple node of triple junctions of grain boundaries in a Eu2+-decorated highly textured composite of (Cl, Br)(K, Rb) and I(K, Rb) solid solutions.

The structural nature and geometry, as well as the lattice-relative orientation, of an arrangement of crystal defects in a highly textured Eu2+-doped composite of two alkali-halide solid solutions was studied by epifluorescence microscopy (EFM) using the doping ion as a fluorochrome. A three-dimensional reconstruction and a skeleton type model, as built from a sequence of EFM images of different optical cross-sections of this arrangement, are presented. Structurally, this arrangement is a quadruple node (QN) of triple junctions of grain boundaries. The QN core geometry is that of a tetragonal tristetrahedron (TTTH), centred at the QN site, whose tetrahedron vertices and edges are on the QN triple junctions and grain boundaries, respectively, whereas the tristetrahedron tetragonal axis is nearly parallel to the lattice [001]-axis. The measured values of the angles between triple junctions and between the grain boundaries forming them are reported. The distinct chemical compositions of the composite solid solutions are discussed to be responsible, in last instance, for the tristetrahedron departure from a cubic configuration. Collaterally, certain families of translationally periodic almost-parallel (TPAP)-wall-like regions which consist of TPAP-columns of TPAP-spindle-like singularities, as well as certain zigzag arrays of columns of this like, existing into the QN grains, are reported to be observed. Three-dimensional reconstructions of typical individuals of these families and arrays as well as of their constituent parts are presented and geometrically analysed. These families and arrays are discussed to be families of tilt subboundaries, whose constituent dislocations are decorated by cylindrical second-phase europium di-halide precipitates, and regularly faceted tilt subboundaries, respectively. Crystal growing and sample preparation, composite structural characterisation by powder and single-slab X-ray diffraction (PXRD and SSXRD, respectively), microscopy and fluorescence-cube unit optics, image processing, electronic three-dimensional reconstruction and measuring methodologies, are all described in detail.

New heteroleptic l-argininato copper(II) complex with bromide and N, N’– heterocyclic ligands – synthesis, supramolecular, spectroscopic, magnetic and theoretical investigations

A new heteroleptic [CuBr(l−Arg)(bpy)]Br·2H2O (1) (l−Arg=l−Arginine, bpy=2,2’−bipyridine) complex has been synthesized and its molecular and supramolecular structure aspects have been discussed based on the X−ray single crystal structure and Hirshfeld analyses. In addition, the properties of complex 1 have been elucidated using different spectroscopic methods (FT−IR / FIR, Raman, NIR−Vis−UV, Q− / X− band EPR) and magnetic measurements. In this complex, the bromide anion occupies the apex of a slightly distorted square pyramid (τ = 0.12). The [CuBr(l−Arg)(bpy)]+ complex units exhibit a ribbon−like organization, with Cu(II) metal centers located at the corners of triangles where the shortest Cu∙∙∙Cu distance is 5.579 Å. The aromatic moieties of bpy are aligned nearly parallel leading to π···π interactions. Both, non−bonded and coordinated, Br− ions act as hydrogen−bond acceptors for guanidinium groups. Hirshfeld analysis indicated the importance of the Br∙∙∙H (17.9 − 18.4 %), O∙∙∙H (14.9−15.2 %), and H∙∙∙H (42.3−43.1 %) interactions in the molecular packing of the studied complex. Atoms in molecules (AIM) calculations indicated mainly the closed shell character for the Cu−N, Cu−O and Cu−Br coordination interactions. The G value calculated using the Q−band EPR spectra parameters g|| = 2.235 and g⊥= 2.05 is 4.7, what indicating negligible coupling and that local tetragonal axes are aligned parallel. A negative value of Weiss temperature θCW = -0.32 K indicates the presence of weak antiferromagnetic coupling between the neighboring Cu(II) ions mediated through hydrogen bonds and π-π stacking of aromatic moieties of bpy. The value of gav= 2.113 obtained from Q−band EPR spectra is consistent with that corresponding to the Curie constant (C = 0.4138 emu K mol−1), i.e.g = 2.101, and that obtained from the best fitting to the Brillouin function: g = 2.139.

Magnetic structures and properties of new 1:1 MoB-type RCo0.6Ni0.4 and RCo0.5Ni0.5 (R = Tb, Dy, Ho): Structural transition induced by magnetic ordering

The magnetic properties, the crystal and the magnetic structures of the new 1: 1 RCo1−xNix phase formed by R = Tb, Dy and Ho, have been studied for x = 0.4 and 0.5 by means of physical property measurements, neutron and X-ray (from both laboratory and synchrotron) diffraction methods. These compounds crystallize in the tetragonal MoB structure type (tI16, I41/amd) at room temperature, with no ordered arrangement of Co/Ni atoms on the 8e Wyckoff site available for the transition element. Both the lattice parameters a and c (and unit cell volume, Vobs) decrease from Tb to Ho, with a and c following a linear and a quadratic trend, respectively. A magnetic phase transition is detected by heat capacity and magnetization data for TbCo0.6Ni0.4 at about 85 K. Similar transitions appear in DyCo0.6Ni0.4 and HoCo0.6Ni0.4 at 49 K and 27 K, respectively. These TC well follow the de Gennes factor along the lanthanide series. Neutron diffraction shows for the Tb- and Ho-compounds that strongly ferromagnetic structures characterized by a k = 0 magnetic propagation vector are formed on two different rare earth sublattices which are canted to each other. Only in the Tb-containing phases the magnetic transition leads to a symmetry reduction from tetragonal I41/amd to at least monoclinic I2/a. Magnetic symmetry analysis is used to argue that the presence of a magnetic moment component along the original tetragonal axis should be at the origin of this magneto-structural transition in the Tb-compounds with a possible further symmetry lowering.

Investigation of ferroelectric Ba1−xCaxZryTi1−yO3 single crystal by in situ temperature-dependent x-ray diffraction and first-principles calculations

In situ temperature-dependent crystal structure of lead-free ferroelectric perovskite Ba0.798Ca0.202Zr0.006Ti0.994O3 single crystal was characterized using x-ray diffraction from 170 to 380 K. Three phases were identified at different temperatures of 170, 220, and 298 K, revealing rhombohedral (R3m), orthorhombic (Pmm2), and tetragonal (P4mm) crystal structures, respectively. The change in the bond length and its distortion are reported for both AO12 and BO6 polyhedrons, allowing for the estimation of the spontaneous polarization. The Debye–Waller factor is reported as a function of temperature for A and B-sites. Density-functional theory calculations on the tetragonal phase were performed to obtain information on the distribution of the Ca ions, the local atomic displacements, and the ideal value of the spontaneous polarization of a defect-free crystal at 0 K. We find that Ca prefers to arrange in columnar 2D plates oriented along the tetragonal axis. The Ca ions avoid being next neighbors of Zr; however, the specific arrangement of Ca has only a minor impact on the spontaneous polarization.

Dielectric effects, crystal field, and shape anisotropy tuning of the exciton fine structure of halide perovskite nanocrystals

We present a theoretical study of the excitonic band edge states applied to the more commonly studied inorganic perovskite nanocrystals: ${\mathrm{CsPbBr}}_{3}$. We highlight the key role played by the electron-hole exchange interaction, including long-range and short range terms, in the positioning and splitting of dark and bright exciton sublevels, and discuss the influence of dielectric confinement, crystal field and shape anisotropy effects on the excitonic fine structure. The electron-hole exchange interaction splits the four excitonic states into three bright excitonic states at higher energy and a singlet dark state at lower energy. We find that, whatever the crystal phase, the bright-dark splitting is weakly sensitive to shape anisotropy. However, a strong enhancement, of about 50%, is obtained at the maximum of the dielectric contrast. For two crystalline symmetries, we particularly analyze how the bright exciton triplet energies vary, taking into account the states polarizations and considering the directions along which shape elongation/contraction applies. The main effect of the dielectric contrast is to increase significantly the exciton energies, for all the configurations. For a cubic crystal---${\mathrm{O}}_{h}$ symmetry---the bright exciton triplet degeneracy can be partially or fully lifted with anisotropic shape along one or two directions, respectively. For a tetragonal crystal---${\mathrm{D}}_{4h}$ symmetry---the partial triplet degeneracy can be completely lifted by a single distortion from the cubic shape along a direction perpendicular to the tetragonal axis but a partial degeneracy is maintained for small distortions along the tetragonal axis. The amplitude of bright exciton splittings are basically driven by the shape anisotropy and is almost insensitive to the dielectric contrast. On the basis of this model, we discuss recent results on ${\mathrm{CsPbBr}}_{3}$ nanocrystals photoluminescence.

Vibrational properties of SrVO2H with large spin-phonon coupling

The antiferromagnetic transition metal oxyhydride ${\mathrm{SrVO}}_{2}\mathrm{H}$ is distinguished by its stoichiometric composition and an ordered arrangement of H atoms. The tetragonal structure is related to the cubic perovskite and consists of alternating layers of ${\mathrm{VO}}_{2}$ and SrH. ${d}^{2}$ V(III) attains a sixfold coordination by four O and two H atoms. The latter are arranged in a trans fashion, which produces H--V--H chains along the tetragonal axis. Here, we investigate the vibrational properties of ${\mathrm{SrVO}}_{2}\mathrm{H}$ by inelastic neutron scattering and infrared spectroscopy combined with phonon calculations based on density functional theory. The H-based vibrational modes divide into a degenerate bending motion perpendicular to the H--V--H chain direction and a highly dispersed stretching motion along the H--V--H chain direction. The bending motion, with a vibrational frequency of approximately 800 ${\mathrm{cm}}^{\ensuremath{-}1}$, is split into two components separated by about 50 ${\mathrm{cm}}^{\ensuremath{-}1}$, owing to the doubled unit cell from the antiferromagnetic structure. Interestingly, spin-phonon coupling stiffens the H-based modes by $50\ensuremath{-}100\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ although super-exchange coupling via H is very small. Frequency shifts of the same order of magnitude also occur for V--O modes. It is inferred that ${\mathrm{SrVO}}_{2}\mathrm{H}$ displays the hitherto largest recognized coupling between magnetism and phonons in a material.

Mapping domain-wall topology in the magnetic Weyl semimetal CeAlSi

We report full vector mapping of local magnetization in CeAlSi, a Weyl semimetal in which both inversion and time-reversal symmetries are broken. The vector maps reveal unanticipated features both within domains and at their boundaries. Boundaries between domains form two kinds of walls with distinct topology and therefore different interactions with Weyl fermions. Domain walls aligned along the tetragonal axes, e.g. (100), exhibit emergent chirality forbidden by the bulk space group, while diagonal walls are non-chiral. Within the domains, we observe that the previously reported set of four easy axes aligned along the in-plane diagonals of the tetragonal structure actually split to form an octet with decreasing temperature below the magnetic transition. All the above phenomena are ultimately traced to the noncollinear magnetic structure of CeAlSi.

Importance of Long‐Range Channel Sr Displacements for the Narrow Emission in Sr[Li2Al2O2N2]:Eu2+Phosphor

AbstractThe recently discovered Sr[Li2Al2O2N2]:Eu2+red phosphor, candidate for the next generation of eco‐efficient white light‐emitting diodes, exhibits excellent emission spectral position and exceptionally small linewidth. It belongs to the UCr4C4‐structure family of phosphors containing many potential candidates for commercial phosphors, whose small linewidth, tentatively ascribed to the high‐symmetry cuboid environment of the doping site, has drawn the attention of researchers in the last five years. Density functional theory, ΔSCF method, and configuration coordinate models (CCM) are used to provide a complete characterization of this material. Using a multi‐dimensional CCM, an accurate description of the coupling of the vibronic structure with the electronic 5d→4f transition is obtained, including the partial Huang–Rhys factors and frequency of the dominant modes. It is shown that, in addition to the first‐coordination shell cuboid deformation mode, low‐frequency phonon modes involving chains of strontium atoms along the tetragonal axis shape the emission linewidth in Sr[Li2Al2O2N2]:Eu2+. This finding sheds new light on the emission properties of UCr4C4‐structure phosphors, possessing similar Ca/Sr/Ba channel. The approach provides a robust theoretical framework to systematically study the emission spectra of such Eu‐doped phosphors, and predict candidates with expected similar or even sharper linewidth.

Shock-induced twinning in polycrystalline vanadium: II. Surface layer

In the course of study of shock-induced twinning in commercially pure (99.8 wt%) polycrystalline vanadium, some unexpected metallurgical features were found. In all vanadium samples softly recovered after planar impact loading by copper impactors with velocities ranging from 262 to 610 m/s, the domain of twinned grains (located at the distance 100–900 μm from an impacted sample surface) preceded by a relatively narrow strip, 60–100 μm, densely filled by martensite lenticles of micron size. The distribution of shock-induced twins and the stress, required for their nucleation, were considered in the Part I of the present paper series. Part II of this series is focused on the Transmission Electron Microscopy study of the lenticles, formed in immediate proximity to the impacted surface. It was found that these lenticular particles are oblate ellipsoids of micron size filled with the stacks of 10–30 nm thick planar slabs, which possess tetragonal crystal structure. The slabs have alternating orientation of tetragonal axes c while the parameters of their unit cell are derivatives of cubic lattice parameter of vanadium, aV, namely a = b = 2aV and c = aV. Possible model, based on a sequence of glides, capable to generate such microstructure, and the cause for the disappearance of the lenticles beyond 100 μm apart from the impacted surface are discussed.

Nature of the magnetic stripes in fully oxygenated La2CuO4+y

We present triple-axis neutron scattering studies of static and dynamic magnetic stripes in an optimally oxygen-doped cuprate superconductor, La$_{2}$CuO$_{4+y}$, which exhibits a clean superconducting transition at $T_{\rm c}=42$ K. Polarization analysis reveals that the magnetic stripe structure is equally represented along both of the tetragonal crystal axes and that the fluctuating stripes display significant weight for in-plane as well as out-of-plane spin components. Both static magnetic order as well as low-energy fluctuations are fully developed in zero applied magnetic field and the low-energy spin fluctuations at $\hbar \omega = 0.3-10$ meV intensify upon cooling. We interpret this as an indication that superconductivity and low-energy spin fluctuations co-exist microscopically in spatial regions which are separated from domains with static magnetic order.

Magnetization Density Distribution of Sr_{2}IrO_{4}: Deviation from a Local j_{eff}=1/2 Picture.

5d iridium oxides are of huge interest due to the potential for new quantum states driven by strong spin-orbit coupling. The strontium iridate Sr_{2}IrO_{4} is particularly in the spotlight because of the so-called j_{eff}=1/2 state consisting of a quantum superposition of the three local t_{2g} orbitals with, in its simplest version, nearly equal populations, which stabilizes an unconventional Mott insulating state. Here, we report an anisotropic and aspherical magnetization density distribution measured by polarized neutron diffraction in a magnetic field up to 5T at 4K, which strongly deviates from a local j_{eff}=1/2 picture even when distortion-induced deviations from the equal weights of the orbital populations are taken into account. Once reconstructed by the maximum entropy method and multipole expansion model refinement, the magnetization density shows four cross-shaped positive lobes along the crystallographic tetragonal axes with a large spatial extent, showing that the xy orbital contribution is dominant. The analogy to the superconducting copper oxide systems might then be weaker than commonly thought.

On Prediction of a Novel Chiral Material Y2H3O(OH): A Hydroxyhydride Holding Hydridic and Protonic Hydrogens.

Examination of possible pathways of how oxygen atoms can be added to a yttrium oxyhydride system allowed us to predict new derivatives such as hydroxyhydrides possessing the composition M2H3O(OH) (M = Y, Sc, La, and Gd) in which three different anions (H-, O2−, and OH-) share the common chemical space. The crystal data of the solid hydroxyhydrides obtained on the base of DFT modeling correspond to the tetragonal structure that is characterized by the chiral space group . The analysis of bonding situation in M2H3O(OH) showed that the microscopic mechanism governing chemical transformations is caused by the displacements of protons which are induced by interaction with oxygen atoms incorporated into the crystal lattice of the bulk oxyhydride. The oxygen-mediated transformation causes a change in the charge state of some adjacent hydridic sites, thus forming protonic sites associated with hydroxyl groups. The predicted materials demonstrate a specific charge ordering that is associated with the chiral structural organization of the metal cations and the anions because their lattice positions form helical curves spreading along the tetragonal axis. Moreover, the effect of spatial twisting of the H- and H+ sites provides additional linking via strong dihydrogen bonds. The structure–property relationships have been investigated in terms of structural, mechanical, electron, and optical features. It was shown that good polar properties of the materials make them possible prototypes for the design of nonlinear optical systems.

Strain-Engineered Tetragonal Phase and Ferroelectricity in GdMnO3 Thin Films Grown on SrTiO3 (001)

A previously unreported tetragonal phase has been discovered in a epitaxially strained GdMnO3 thin films deposited on (001)-oriented SrTiO3 substrates by radio frequency (RF) magnetron sputtering. The tetragonal axis of the films grown up to a 35 nm thickness is perpendicular to the film surface and the basal lattice parameters are imposed by the cubic structure of the substrate. Furthermore, the emergence of a spontaneous electric polarization below ~32 K points to the stabilization of an improper ferroelectric phase at low temperatures, which is not observed in bulk GdMnO3. This work shows how strain engineering can be used to tailor the structure and properties of strongly correlated oxides.

Atomic-scale mechanisms for magnetostriction in CoFe2O4 and La0.5Sr0.5CoO3 oxides determined by differential x-ray absorption spectroscopy

The atomic environments involved in the magnetostriction effect in CoFe$_2$O$_4$ and La$_{0.5}$Sr$_{0.5}$CoO$_3$ polycrystalline samples have been identified by differential extended x-ray absorption fine structure (DiffEXAFS) spectroscopy. We demonstrate that cobalt atoms at octahedral sites are responsible for their magnetostriction. The analysis of DiffEXAFS data indicates that the local-site magnetostrictive strains of Co atoms are reversed in these two oxides, in agreement with the macroscopic magnetostriction. For the CoFe$_2$O$_4$ spinel, a large negative strain along the (100) direction has been determined for the CoO$_6$ octahedron causing a tetragonal contraction in contrast with the La$_{0.5}$Sr$_{0.5}$CoO$_3$ perovskite, where a positive moderate strain along the (100) direction was found resulting in a tetragonal expansion. The different local-site magnetostriction is understood in terms of the different valence and spin state of the Co atoms for the two oxides. The macroscopicmagnetostriction would be explained then by the relative change in volume, either contraction in CoFe$_2$O$_4$ or expansion in La$_{0.5}$Sr$_{0.5}$CoO$_3$, when the tetragonal axis of the Co site is reoriented under an externally applied magnetic field.

Unit-cell response of tetragonal hen egg white lysozyme upon controlled relative humidity variation

Variation of relative humidity (rH) greatly affects the internal order of solvent-based protein crystals, and the rearrangement of molecules can be efficiently recorded in distinct diffraction patterns. This study focuses on this topic, reporting the effect of rH variation experiments on hen egg white lysozyme (HEWL) polycrystalline precipitates of tetragonal symmetry using X-ray powder diffraction (XRPD).In situXRPD data were collected on HEWL specimens during dehydration and rehydration processes using laboratory instrumentation. A known polymorph [space groupP43212,a= 79.07181 (1),c= 38.0776 (1) Å] was identified during gradual dehydration from 95 to 63% rH and vice versa. Pawley analysis of collected data sets and accurate extraction of unit-cell parameters indicated a characteristic evolution of the tetragonal axes with rH. In addition, there is a low humidity level below which samples do not retain their crystallinity. This work illustrates the accuracy of laboratory XRPD as a probe for time-resolved studies of proteins andin situinvestigations of gradual structural modifications upon rH variation. These experiments provide essential information for improving production and post-production practices of microcrystalline protein-based pharmaceuticals.

Tetragonal Mn3Sn Heusler films with large perpendicular magnetic anisotropy deposited on metallic MnN underlayers using amorphous substrates

Tetragonal Heusler compounds that exhibit large perpendicular magnetic anisotropy are promising materials for advanced spintronic devices. A prerequisite are thin films whose tetragonal axis is oriented perpendicular to the plane of the films. Here we show that highly textured, (001) oriented, tetragonal Mn3Sn layers can be prepared using metallic zinc-blende (ZB) MnN as underlayers. Moreover, we show that these layers can be deposited on amorphous substrates using reactive magnetron sputtering. The ferrimagnetic Mn3Sn layers exhibit perpendicularly magnetized hysteresis loops with coercive fields of ∼2 T. Stoichiometric ZB-MnN underlayers share an “equivalent” Mn-Mn layer at the interface with Mn3Sn, thus promoting their oriented growth. Other nitride underlayers are not effective due to their rock-salt (RS) crystal structure and the absence of Mn. Density functional theory calculations confirm that tetragonal Mn3Sn Heusler films are energetically stable when interfaced with ZB-MnN underlayers and not with any of the other RS nitride underlayers considered here. Such Heusler compounds have much promise as electrodes for magnetic tunnel junction memory elements for deeply scaled magnetic random access memories.

Interplay Between Relaxation and Resonance in Ultrasound Attenuation by the Cubic Crystal ZnSe:Cr

Resonance ultrasound attenuation, albeit broadened, is observed in doped cubic crystal ZnSe with a part of the Zn2+ ions substituted by magnetic anisotropic Cr2+ ions. In the tetrahedral selenium environment the latter form a T term Jahn–Teller (JT) center with a T⊗e JT problem and three equivalent distortions along the three tetragonal axes. In sufficiently strong magnetic fields (B > 4 T) applied along the [001] direction the degeneracy of the ground state is removed, and the ultrasound wave propagating along [110] and polarized along (at T = 1.3 K) does not interact with the center, its impurity attenuation being reduced to zero. By comparison, this allows to estimate the contribution of the Cr centers to the attenuation of ultrasound in the ZnSe:Cr crystal in zero magnetic field. The experimental data revealed a strong dependence of the attenuation on the ultrasound frequency, evidencing for the resonance nature of the attenuation: there is no frequency dependence in relaxational attenuation with the relaxation time much larger than the period of the ultrasonic wave. The resonance attenuation is attributed to transitions between the ground state energy levels, split by spin‐orbital interaction. The high sensitivity of the resonance absorption on the ultrasound power is also discussed.

Direct observation of hyperfine level anticrossings in the optical spectra of a LiYF47:Ho3+ single crystal

We have investigated the hyperfine structure in high-resolution broadband optical absorption spectra of a strongly diluted paramagnet $^{7}\mathrm{LiYF}_{4}:{\mathrm{Ho}}^{3+}$ (0.1 at. %) in external magnetic fields parallel to the tetragonal symmetry axis of the crystal. Anticrossings in the hyperfine spectral pattern were observed. It is the first direct observation of the hyperfine level anticrossings in optical spectra. Analysis of the spectral envelopes corresponding to transitions between the electron-nuclear sublevels of crystal-field non-Kramers doublets and singlets of the ${\mathrm{Ho}}^{3+}$ ions, based on the microscopic model of the electronic $4{f}^{10}$ configuration, allowed us to retrieve information on the hyperfine structure of electronic singlets, nuclear quadroupole interactions, and random lattice strains.