Dy Magnetic Moments Research Articles

Rare earth based Mg- chalcogenides MgDy2(S/Se)4 as an emerging aspirant for spintronic and thermoelectric applications

The magnesium based spinel chalcogenides are outstanding materials for spintronic technology and energy applications. Herein, the modified Becke Johnson potential (TB-mBJ) was employed to investigate the electrical, ferromagnetism, and thermoelectric properties of MgDy2(S/Se)4 spinels comprehensively. The energy emitted during optimization as well as formation energy has both been used to demonstrate the stability of the cubic phase. The density of states, Curie temperature, exchange coupling, and spin polarization are elaborated to address the nature of ferromagnetism. Further, half metallic ferromagnetism is studied in terms of hybridization, exchange energies, and exchange constants. In contrast to the clustering effect of the internal magnetic of Dy atoms in the structure, the lowering of Dy's magnetic moment and its transferring on Mg, and S/Se sites demonstrate that the ferromagnetism is caused by the exchange of electron spin. Furthermore, thermoelectric properties were studied and various thermoelectric parameters such as electrical and thermal conductivities, Seebeck coefficient (S), and power factor (PF) of the examined spinels have been determined.

Anisotropy of 4f states in 3d−4f single-molecule magnets

We have measured angular-dependent fluorescence-yield x-ray magnetic circular dichroism spectra on single crystals of the heterometallic $3d\ensuremath{-}4f$ 12-metallacrown-4 ${\mathrm{TbMn}}_{4}$ and ${\mathrm{DyMn}}_{4}$ complexes. Simulated spectra using crystal-field multiplet calculations reproduce the experimentally observed spectra. The orientation of the molecules causes linear dichroism spectra of the $4f$ absorption spectra. This natural linear dichroism shows the anisotropic charge distribution of the rare-earth $4f$ state in the tetragonal crystal field despite the small $4f$ crystal-field splitting. The magnetic moment of the molecule is dominated by the rare-earth moment revealing a considerably large contribution of orbital moment. From a sum-rule analysis of experimental and simulated x-ray magnetic circular dichroism, we determined corrected spin and orbital Dy moments at low temperature (14 K) within a magnetic field of 7 T. We find a significant angular dependence of the Dy magnetic moments, indicating the presence of fourth-order magnetic anisotropy.

Precise measurement of angles between two magnetic moments and their configurational stability in single-molecule magnets

A key parameter for the low-temperature magnetic coupling of in dinuclear lanthanide single-molecule magnets (SMMs) is the barrier $U_{FA}$ resulting from the exchange and dipole interactions between the two $4f$ moments. Here we extend the pseudospin model previously used to describe the ground state of dinuclear endofullerenes to account for variations in the orientation of the single-ion anisotropy axes and apply it to the two SMMs Dy$_2$ScN@C$_{80}$ and Dy$_2$TiC@C$_{80}$. While x-ray magnetic circular dichroism (XMCD) indicates the same $J_z=15/2$ Dy groundstate in both molecules, the Dy-Dy coupling strength and the stability of magnetization is distinct. We demonstrate that both the magnitude of the barrier $U_{FA}$ and the angle between the two $4f$ moments are determined directly from precise temperature-dependent magnetization data to an accuracy better than $1^{\circ}$. The experimentally found angles between the $4f$ moments are in excellent agreement with calculated angles between the quantisation axes of the two Dy ions. Theory indicates a larger deviation of the orientation of the Dy magnetic moments from the Dy bond axes to the central ion in Dy$_2$TiC@C$_{80}$. This may explain the lower stability of the magnetisation in Dy$_2$TiC@C$_{80}$, although it exhibits a $\sim 49\%$ stronger exchange coupling than in Dy$_2$ScN@C$_{80}$.

Indirect Spin-Readout of Rare-Earth-Based Single-Molecule Magnet with Scanning Tunneling Microscopy.

Rare-earth based single-molecule magnets are promising candidates for magnetic information storage including qubits as their large magnetic moments are carried by localized 4f electrons. This shielding from the environment in turn hampers a direct electronic access to the magnetic moment. Here, we present the indirect readout of the Dy moment in Bis(phthalocyaninato)dysprosium (DyPc_{2}) molecules on Au(111) using milli-Kelvin scanning tunneling microscopy. Because of an unpaired electron on the exposed Pc ligand, the molecules show a Kondo resonance that is, however, split by the ferromagnetic exchange interaction between the unpaired electron and the Dy angular momentum. Using spin-polarized scanning tunneling spectroscopy, we read out the Dy magnetic moment as a function of the applied magnetic field, exploiting the spin polarization of the exchange-split Kondo state.

Element‐Specific Magnetization Damping in Ferrimagnetic DyCo5 Alloys Revealed by Ultrafast X‐ray Measurements

The dynamic response of magnetically ordered materials to an ultrashort external stimulus depends on microscopic parameters, such as magnetic moment, exchange, and spin–orbit interactions. Whereas it is well established that, in multicomponent magnetic alloys and compounds, the speed of demagnetization and spin switching processes has an element‐specific character, the magnetization damping was assumed to be a universal parameter for all constituent magnetic elements irrespective of their different spin–orbit couplings and electronic structure. Herein, experimental and theoretical evidence for an element‐specific magnetic damping parameter is provided by investigating the ultrafast magnetization response of a high‐anisotropy ferrimagnetic DyCo5 alloy to femtosecond laser excitation. Strikingly different demagnetization and remagnetization dynamics of Dy and Co magnetic moments is revealed by employing femtosecond laser pump–X‐ray magnetic circular dichroism probe measurements combined with atomistic spin dynamics (ASD) simulations using ab initio calculated parameters. These observations, fully corroborated by the ASD simulations, are linked to the element‐specific spin–orbit coupling strengths of Dy and Co, which are incorporated in the phenomenological magnetization damping parameters. These findings can be used as a recipe for tuning the speed and magnitude of laser‐driven magnetic processes and consequently allow control over various dynamic functionalities in multicomponent magnetic materials.

Observation of compact ferrimagnetic skyrmions in DyCo3 film.

Owing to the experimental discovery of magnetic skyrmions stabilized by the Dzyaloshinskii-Moriya and/or dipolar interactions in thin films, there is a recent upsurge of interest in magnetic skyrmions with antiferromagnetic spins in order to overcome the fundamental limitations inherent with skyrmions in ferromagnetic materials. Here, we report on the observation of compact ferrimagnetic skyrmions for the class of amorphous alloys consisting of 4f rare-earth and 3d transition-metal elements with perpendicular magnetic anisotropy, using a DyCo3 film, that are identified by combining X-ray magnetic scattering, scanning transmission X-ray microscopy, and Hall transport technique. These skyrmions, with antiparallel aligned Dy and Co magnetic moments and a characteristic core radius of about 40 nm, are formed during the nucleation and annihilation of the magnetic maze-like domain pattern exhibiting a topological Hall effect contribution. Our findings provide a promising route for fundamental research in the field of ferrimagnetic/antiferromagnetic spintronics towards practical applications.

Magnetic hysteresis and strong ferromagnetic coupling of sulfur-bridged Dy ions in clusterfullerene Dy2S@C82.

Two isomers of metallofullerene Dy2S@C82 with sulfur-bridged Dy ions exhibit broad magnetic hysteresis with sharp steps at sub-Kelvin temperature. Analysis of the level crossing events for different orientations of a magnetic field showed that even in powder samples, the hysteresis steps caused by quantum tunneling of magnetization can provide precise information on the strength of intramolecular Dy⋯Dy inter-actions. A comparison of different methods to determine the energy difference between ferromagnetic and antiferromagnetic states showed that sub-Kelvin hysteresis gives the most robust and reliable values. The ground state in Dy2S@C82 has ferromagnetic coupling of Dy magnetic moments, whereas the state with antiferromagnetic coupling in C s and C 3v cage isomers is 10.7 and 5.1 cm−1 higher, respectively. The value for the C s isomer is among the highest found in metallofullerenes and is considerably larger than that reported in non-fullerene dinuclear molecular magnets. Magnetization relaxation times measured in zero magnetic field at sub-Kelvin temperatures tend to level off near 900 and 3200 s in C s and C 3v isomers. These times correspond to the quantum tunneling relaxation mechanism, in which the whole magnetic moment of the Dy2S@C82 molecule flips at once as a single entity.

Neutron Diffraction Investigation of the DyFe11Ti Magnetic Structure and Its Spin Reorientations

Abstract In this article, we report on the magnetic structure of DyFe11Ti and its thermal evolution as probed by neutron powder diffraction. A thermodiffraction technique was used to follow the temperature dependence of the magnetic moments, as well as their orientation. The Dy and Fe moments were coupled to each other in an antiparallel manner to form a ferrimagnet, where the easy magnetization direction at 2 K was the [110] axis in the basal (a, b) plane. This magnetic structure underwent two successive spin reorientation phenomena with increasing temperature. A large Dy magnetic moment of 9.7 Bohr magneton (μB) was obtained at low temperatures, and the magnitude decreased rapidly to 7.5μB at 200 K. The largest Fe magnetic moment was observed on the Fe 8i position. A ThMn12-type crystal structure was preserved in the studied temperature range, despite the large changes of the magnetic structure. A sharp tilt was observed at the first-order spin reorientation, TSR1; the angle between the easy magnetization axis and the crystal c axis was reduced from 90° at 2 K to about 20° at 200 K (where c is the easy axis above 200 K); and the Dy and Fe magnetic moments maintained an antiparallel coupling.

Magnetic profile of proximity-coupled (Dy,Bi)2Te3/(Cr,Sb)2Te3 topological insulator heterostructures

Magnetic topological insulators (TIs) are an ideal playground for the study of novel quantum phenomena building on time-reversal symmetry-broken topological surface states. By combining different magnetic TIs in a heterostructure, their magnetic and electronic properties can be precisely tuned. Recently, we have combined high-moment $\mathrm{Dy}:{\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ with high transition temperature $\mathrm{Cr}:{\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ in a superlattice, and we found, using x-ray magnetic circular dichroism (XMCD), that long-range magnetic order can be introduced in the $\mathrm{Dy}:{\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ layers. Accompanying first-principles calculations indicated that the origin of the long-range magnetic order is a strong antiferromagnetic coupling between Dy and Cr magnetic moments at the interface extending over several layers. However, based on XMCD alone, which is either averaging over the entire thin-film stack or is surface-sensitive, this coupling scenario could not be fully confirmed. Here we use polarized neutron reflectometry, which is ideally suited for the detailed study of superlattices, to retrieve the magnetization in a layer- and interface-resolved way. We find that the magnetization is, in contrast to similar recent studies, homogeneous throughout the individual layers, with no apparent interfacial effects. This finding demonstrates that heterostructure engineering is a powerful way of controlling the magnetic properties of entire layers, with the effects of coupling reaching beyond the interface region.

Spontaneous and field-induced magnetic phase transitions inDy2Co3Al9: Effects of exchange frustration

Due to the long-range oscillatory character of RKKY exchange interactions, for ${\mathrm{Dy}}_{2}{\mathrm{Co}}_{3}{\mathrm{Al}}_{9}$ there exist positive and negative couplings between the Dy magnetic moments that lead to magnetic frustration. As a result, the ground state can be easily perturbed, and the system displays a number of spontaneous and field-induced phase transitions. We performed magnetization, magnetic-susceptibility, specific-heat, and electrical-resistivity measurements as well as neutron-diffraction experiments on a single crystal. We find two transitions to distinct incommensurate antiferromagnetic phases at 6.2 and 5.2 K that evolve to a commensurate phase at 3.7 K. In applied magnetic field, new phases emerge. Field-dependent magnetization exhibits a multistep metamagnetic process with sharp transitions accompanied by pronounced magnetoresistance changes. The large number of phases and their complex magnetic structures suggest that the physical properties of ${\mathrm{Dy}}_{2}{\mathrm{Co}}_{3}{\mathrm{Al}}_{9}$ are ruled by exchange frustration in the presence of a large magnetocrystalline anisotropy.

LDA + DMFT and LDA + U study of the electronic and magnetic properties of DyFeSi

Considering the strong correlation between 4f electrons in the rare earths has major effect on the calculated electronic and magnetic properties of compounds including rare earths, as neglecting this strong correlation in density functional theory (DFT) leads to the failing DFT for a proper description of mentioned properties. In this study, to consider the strong correlation between 4f electrons in Dy atom of DyFeSi compound, local Coulomb repulsion between 4f electrons, U, are treated both statically as in the LDA + U approximation and dynamically as in the dynamical mean-field theory in the Hubbard-I approximation (LDA + DMFT[HI]). In this regards, we apply first principle density functional calculation by using full potential linear muffin-tin orbital (FP-LMTO) method to present a comparative study between the calculated electronic and magnetic properties of DyFeSi within LDA + U and LDA + DMFT[HI] approaches and show that the LDA + DMFT[HI] approach presents so much better results compared to the LDA + U approach. In the magnetic properties we find that the calculation within LDA + DMFT[HI] reproduces the Dy magnetic moments in accordance to the observations and standard model of rare earth with the best accuracy. In the electronic properties we show that LDA + U just produces narrow energy bands of 4f-electrons and it is not able to produce atomic multiples features of 4f valance bands, while LDA + DMFT[HI] approach shows peaks caused by the formation of atomic multiples of the Dy atoms in DyFeSi compound.

Imposing long-range ferromagnetic order in rare-earth-doped magnetic topological-insulator heterostructures

The combination of topological properties and magnetic order can lead to new quantum states and exotic physical phenomena, such as the quantum anomalous Hall (QAH) effect. The size of the magnetic gap in the topological surface states, key for the robust observation of the QAH state, scales with the magnetic moment of the doped three-dimensional topological insulator (TI). The pioneering transition-metal doped $({\mathrm{Sb},\mathrm{Bi})}_{2}({\mathrm{Se},\mathrm{Te})}_{3}$ thin films only allow for the observation of the QAH effect up to some 100 mK, despite the much higher magnetic ordering temperatures. On the other hand, high magnetic moment materials, such as rare-earth-doped $({\mathrm{Sb},\mathrm{Bi})}_{2}({\mathrm{Se},\mathrm{Te})}_{3}$ thin films, show large moments but no long-range magnetic order. Proximity coupling and interfacial effects, multiplied in artificial heterostructures, allow for the engineering of the electronic and magnetic properties. Here, we show the successful growth of high-quality Dy:${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$/Cr:${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ thin film heterostructures. Using x-ray magnetic spectroscopy we demonstrate that high transition temperature Cr:${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ can introduce long-range magnetic order in high-moment Dy:${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$---up to a temperature of 17 K---in excellent agreement with first-principles calculations, which reveal the origin of the long-range magnetic order in a strong antiferromagnetic coupling between Dy and Cr magnetic moments at the interface extending over several layers. Engineered magnetic TI heterostructures may be an ideal materials platform for observing the QAH effect at liquid He temperatures and above.

Coexistence of charge density wave and incommensurate antiferromagnetism in the cubic phase of DyGe2.85 synthesised under high pressure

A novel metastable phase of DyGe2.85 synthesised in the AuCu3-structure under high pressure, has been studied by means of the magnetic susceptibility and electrical resistivity measurements (under the pressure P≤3.1 GPa), neutron powder diffraction and time-differential γ-γ perturbed angular correlations (TDPAC) using 111Cd nuclear probes. Two distinct phase transitions have been found in this compound as the temperature is lowered. We assign the first transition occurring at the temperature TCDW=80 K with charge density wave formation and the second transition at TN≈18 K with an antiferromagnetic spiral ordering of Dy magnetic moments, and discuss a close relationship between them.

Magnetic structure and spin reorientation of quaternary Dy2Fe2Si2C

We have investigated the low temperature magnetic properties of Dy2Fe2Si2C by using magnetisation, specific heat, x-ray diffraction, neutron powder diffraction and 57Fe Mössbauer spectroscopy measurements over the temperature range 1.5 K–300 K. Dy2Fe2Si2C exhibits two magnetic transitions at low temperatures: an antiferromagnetic transition at K and a spin-reorientation transition at K. The magnetic structure above Tt can be described with a propagation vector with the ordering of the Dy magnetic moments along the monoclinic b-axis whereas on cooling below Tt the Dy moment tips away from the b-axis towards the ac-plane. We find that the spin-reorientation in Dy2Fe2Si2C is mainly driven by the competition between the second-order crystal field term B20 and the higher-order terms, in particular B40 and B64.

X-ray magnetic circular dichroism study of Dy-doped Bi2Te3 topological insulator thin films

Magnetic doping of topological insulators (TIs) is crucial for unlocking novel quantum phenomena, paving the way for spintronics applications. Recently, we have shown that doping with rare earth ions introduces large magnetic moments and allows for high doping concentrations without the loss of crystal quality, however no long range magnetic order was observed. In Dy-doped Bi2Te3 we found a band gap opening above a critical doping concentration, despite the paramagnetic bulk behavior. Here, we present a surface-sensitive x-ray magnetic circular dichroism (XMCD) study of an in situ cleaved film in the cleanest possible environment. The Dy M4,5 absorption spectra measured with circularly polarized x-rays are fitted using multiplet calculations to obtain the effective magnetic moment. Arrott–Noakes plots, measured by the Dy M5 XMCD as a function of field at low temperatures, give a negative transition temperature. The evaporation of a ferromagnetic Co thin film did not introduce ferromagnetic ordering of the Dy dopants either; instead a lowering of the transition temperature was observed, pointing towards an antiferromagnetic ordering scenario. This result shows that there is a competition between the magnetic exchange interaction and the Zeeman interaction. The latter favors the Co and Dy magnetic moments to be both aligned along the direction of the applied magnetic field, while the exchange interaction is minimized if the Dy and Co atoms are antiferromagnetically coupled, as in zero applied field.

Probing Dy3+ magnetic moments in multiferroic perovskite DyMnO3 by optical spectroscopy

We present a detailed temperature‐dependent (4–300 K) spectroscopic study of DyMnO3 single crystals with distorted perovskite structure. Energies of 36 crystal‐field levels of Dy3+ in paramagnetic DyMnO3 were determined. The Dy3+ ground Kramers doublet does not split at and splits below Tlock = 18 K. The splitting grows fast at temperatures near and reaches Δ0 ≈ 11 ± 2 cm–1 at 4 K. Using the experimental temperature dependence Δ0(T), we calculate the dysprosium magnetic moment mDy(T) and the dysprosium contribution into specific heat and magnetic susceptibility. Analysing all the experimental data, we conclude that the Dy–Mn interaction is of the Dzyaloshinskii–Moriya type. Intensity map in the temperature–wave number coordinates for a spectral line corresponding to the f–f transition of Dy3+ in DyMnO3 and a scheme of the splitting of the Dy ground Kramers doublet. Arrows represent Dy magnetic moments.magnified imageIntensity map in the temperature–wave number coordinates for a spectral line corresponding to the f–f transition of Dy3+ in DyMnO3 and a scheme of the splitting of the Dy ground Kramers doublet. Arrows represent Dy magnetic moments.

Spin-reorientation in DyGa

We have used neutron powder diffraction to determine the magnetic structure of DyGa. This compound crystallises in the orthorhombic CrB-type structure with the Cmcm space group (#63) and the magnetic structure comprises ferromagnetic order of the Dy sublattice along the c-axis below TC=115K. Upon cooling below 25K, the Dy magnetic moments cant away from the c-axis towards the a-axis. At 3K, the Dy moment is 9.8(2) μB and the Dy magnetic moments point in the direction θ=22(2)°, ϕ=0° relative to the c-axis.

Crystal structure and Mössbauer studies of the isotypic Fe6-cluster compounds RE15[Fe8C25], RE=Dy, Ho

The carboferrates RE15[Fe8C25] (RE=Dy, Ho) were prepared from mixtures of the elements by arc-melting followed with subsequent annealing at 1373K. The crystal structures were determined from single crystal X-ray diffraction data and revealed an isotypic relationship to Er15[Fe8C25] (hP48, P321). The main feature of the crystal structure is given by Fe6 cluster units characterized by covalent Fe–Fe bonding interactions. 57Fe Mössbauer spectra of Dy15[Fe8C25] were fitted by three subspectra with relative spectral weights of about 3:3:2 which is in general agreement with the crystal structure. Below 50K, an onset of magnetic hyperfine fields at the three iron sites is observed which is supposed to be caused by dipolar fields arising from neighboring, slowly relaxing Dy magnetic moments.

Temperature-dependent magnetic properties of ferrimagneticDyCo3alloy films

Synchrotron soft x-ray magnetic circular and linear dichroism (XMCD and XMLD) spectroscopies at the Dy ${M}_{4,5}$ and Co ${L}_{2,3}$ edges are reported to investigate the temperature-dependent magnetic properties of rare earth--transition metal ${\mathrm{DyCo}}_{3}$ alloy films. In a temperature region between 4.4 K and 300 K, the two sites of Co and Dy are ferrimagnetic alloy coupled, with the Dy magnetization aligned to the applied field as the dominant site. The combined method of XMCD and XMLD and the application of the sum rules allows one to monitor the detailed changes in the magnetic contribution from both sites separately. It reveals that Dy possesses a very large moment of $8.2\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$/atom at low temperatures. At higher temperatures, the reduction of the total magnetic moment is dominated by the behavior of the Dy magnetic moments which exhibit a steeper decrease, especially in the temperature regime between 150 K and 200 K. The reoccupation of the Zeeman split levels of the $4f$ sites of Dy indicates that thermal fluctuations are the driving force.

Study of 57Fe Mössbauer Effect on DyFe2Zn20 and YFe2Zn20

The 57Fe Mossbauer effect of DyFe2Zn20 and YFe2Zn20 was studied at temperatures between 8 and 301 K, and at room temperature in the presence of an external magnetic field. The spectra of the two compounds appeared almost the same at temperatures above 77 K. Each spectrum exhibited a double peak, which is attributed to the electric field gradient (EFG) present at the Fe nuclei. However, the spectrum of DyFe2Zn20 at 8 K exhibited a complicated shape, resulting from a magnetic hyperfine field and the EFG at the Fe nuclei. From the detailed analyses of the spectra, we concluded that Fe magnetic moments interact antiferromagnetically with Dy magnetic moments and that the Fe magnetic moments in DyFe2Zn20 at 8 K are approximately 0.2 µB/Fe.