Crystalline Electric Field Interaction Research Articles

Analysis of metamagnetic transitions in antiferromagnetic arrangements in the RRhIn5 (R[dbnd]Nd, Tb, Dy, and Ho) series using a four sublattice model

The RRhIn5 (RNd, Tb, Dy, and Ho) series of compounds crystallizes in the Ho2CoGa8 tetragonal type-structure, with P4/mmm space group. A Hamiltonian model of four magnetic sublattices is used to reproduce the metamagnetic transitions of these series, considering the crystalline electric field interaction and the exchange interaction in the molecular field approximation. The crystalline electric field parameters were extracted from literature sources, while the exchange parameters were adjusted to optimize the agreement between the proposed model and the experimental data. The four sublattice model presented here successfully describes the metamagnetic transitions that appeared, at the low magnetic fields, in the RRhIn5 (RNd, Tb, Dy, and Ho) series, in contrast to other molecular field model found in the literature that inadequately reproduces these transitions.

Theoretical investigation of magnetic and thermal properties in Dy1−x Sc x Ni2 series

We report on the thermal and magnetic properties of Dy1−xScxNi2 series compounds (x=0.1,0.3,0.5,and0.7), which were investigated through a model Hamiltonian including the exchange, Zeeman, and crystalline electric field interactions. We investigated the effect of Sc substitution on the Dy site on the magnetic and magnetocaloric properties of these compounds. Theoretical results were simulated for heat capacity, entropy, and the magnetocaloric effect quantities. Our model reproduced the decrease of the magnetic ordering temperature and of the isothermal entropy change peaks as Sc concentration increases. Our theoretical results were confronted with experimental data from the literature, showing good agreement.

Theoretical investigation of rotating magnetocaloric effect in PrRu2

The magnetic anisotropy in the cubic ferromagnetic PrRu2 compound (TC = 34 K) is due to the crystalline electrical field interaction. Using a model Hamiltonian which includes the crystalline electrical field, exchange and Zeeman interactions we calculated the rotating magnetocaloric effect, considering the magnetic field changes along the three main cubic crystallographic directions 〈001〉, 〈011〉 and 〈111〉. The influence of the spin reorientation, along the field directions, on the magnetocaloric potentials were quantitatively obtained and discussed.

New ternary aluminides Ce0.67Pd2Al5, Ce1.33Pd3Al8, and Ce1.74Pd5.29Al11.71

Polycrystalline samples of novel compounds Ce 0.67 Pd 2 Al 5 , Ce 1.33 Pd 3 Al 8 , and Ce 1.74 Pd 5.29 Al 11.71 were prepared by arc-melting. The crystal structure of the latter compound was determined from the single-crystal X-ray diffraction data to be a disordered variant of the hexagonal Th 2 Ni 17 type [ P 6 3 / mmc , a = 9.1961(5) Å, c = 8.8861(5) Å]. The crystal structures of the other aluminides were examined by powder X-ray diffraction and found to be isotypic with Sc 0.67 Fe 2 Si 5 [ P 6 3 / mmc , a = 4.3385(5) Å, c = 16.5255(15) Å] and Gd 1.33 Pt 3 Al 8 [ R 3 ¯ m , a = 4.37960(10) Å, c = 39.1683(9) Å], respectively. Based on the thermodynamic and electrical resistivity data measured down to 0.4 K in external magnetic fields up to 9 T, the new materials were characterized as metallic Curie-Weiss paramagnets due to fairly stable trivalent Ce ions. In Ce 1.33 Pd 3 Al 8 , an antiferromagnetic ordering was established below T N = 2.3 K, while no long-range magnetic order was found in the other compounds. All three phases exhibit electrical conductivity that is governed by the interplay of Kondo and crystalline electric field interactions, and significantly affected by structural disorder inherent to their crystal lattices. • Novel compounds Ce 0.67 Pd 2 Al 5 , Ce 1.33 Pd 3 Al 8 , and Ce 1.74 Pd 5.29 Al 11.71 were synthesized. • They form with Sc 0.67 Fe 2 Si 5 , Gd 1.33 Pt 3 Al 8 , and Th 2 Ni 17 structure types, respectively. • Electrical transport is strongly affected by structural disorder and Kondo effect.. • They are Curie-Weiss paramagnets; Ce 1.33 Pd 3 Al 8 orders antiferromagnetically at 2.3 K.

Theoretical investigation of crystalline electric field influence on the magnetocaloric effect in the cubic praseodymium system PrNi2

We report a theoretical investigation of the magnetocaloric effect in paramagnetic intermetallic $\mathrm{Pr}{\mathrm{Ni}}_{2}$. We choose this particular compound because it presents high cubic symmetry, and two sets of crystalline electrical field parameters were reported, allowing a systematic study. In one of these sets, the magnetic entropy increases upon applied magnetic field in the low temperature region $(T<10\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ for $H=5\phantom{\rule{0.16em}{0ex}}\mathrm{T}$. This anomaly was investigated through a model Hamiltonian which includes the magnetic, exchange, and crystalline electric field interactions. The simulated curves of the temperature dependence of isothermal entropy variation and adiabatic temperature change present the inverse magnetocaloric effect, which is not expected for a paramagnetic system.

Synthesis, crystal chemistry, and magnetic properties of Ce3-xRhGa10+3x (x = 0.36): A new member of the [BaAl4]m[CaF2]n[AlB2]p homologous series

Ce3-xRhGa10+3x (x = 0.36) is a new member of the linear intergrowth structure series built up from segments of the BaAl4, AlB2 and CaF2 structure types. The compound crystallizes with a disordered variant of the Pr3NiGa10 type structure. Unlike the prototype, Ce3-xRhGa10+3x exhibits notable deficiency in rare-earth content, accompanied with significant excess of Ga atoms, corresponding to additional Ga environment of one of the Ce atoms. The novel compound is a Curie-Weiss paramagnet and orders antiferromagnetically at low temperatures. The electrical transport in Ce3-xRhGa10+3x has a metallic character, and bears contributions due to crystalline electric field, Kondo and magnetic exchange interactions.

Evolution of the magnetic properties in the antiferromagnet Ce2RhIn8 simultaneously doped with Cd and Ir.

We report the evolution of the magnetic properties of single crystals. In particular, for () and (), we have solved the magnetic structure of these compounds using single-crystal neutron magnetic diffraction experiments. Taking the magnetic structure of the heavy-fermion antiferromagnet as a reference, we have identified no changes in the magnetic wave vector; however, the direction of the ordered Ce3+ moments rotates toward the plane, under the influence of both dopants. By constraining the analysis of the crystalline electric field (CEF) with the experimental ordered moment's direction and high-temperature magnetic-susceptibility data, we have used a mean-field model with tetragonal CEF and exchange interactions to gain insight into the CEF scheme and anisotropy of the CEF ground-state wave function when Cd and Ir are introduced into . Consistent with previous work, we find that Cd doping in tends to rotate the magnetic moment toward the plane and lower the energy of the CEF excited states' levels. Interestingly, the presence of Ir also rotates the magnetic moment towards the plane although its connection to the CEF overall splitting evolution for the y = 0 samples may not be straightforward. These findings may shed light on the origin of the disordered spin-glass phase on the Ir-rich side of the phase diagram and also indicate that the compounds may not follow exactly the same Rh-Ir CEF effects trend established for the compounds.

Effect of structural and magnetic disorder on the 3d−5d exchange interactions in La2−xCaxCoIrO6

The delicate balance between spin-orbit coupling, Coulomb repulsion and crystalline electric field interactions observed in Ir-based oxides is usually manifested as exotic magnetic behavior. Here we investigate the evolution of the exchange coupling between Co and Ir for partial La substitution by Ca in La$_{2}$CoIrO$_6$. A great advantage of the use of Ca$^{2+}$ as replacement for La$^{3+}$ is the similarity of its ionic radii. Thus, the observed magnetic changes can more easily be associated to electronic variations. A thorough investigation of the structural, electronic and magnetic properties of the La$_{2-x}$Ca$_{x}$CoIrO$_6$ system was carried out by means of synchrotron x-ray powder diffraction, muon spin rotation and relaxation ($\mu$SR), AC and DC magnetization, XAS, XMCD, Raman spectroscopy, electrical resistivity and dielectric permittivity. Our XAS results show that up to 25% of Ca substitution at the La site results in the emergence of Co$^{3+}$, possibly in high spin state, while the introduction of larger amount of Ca leads to the increase of Ir valence. The competing magnetic interactions resulting from the mixed valences lead to a coexistence of a magnetically ordered and an emerging spin glass (SG) state for the doped samples. Our $\mu$SR results indicate that for La$_{2}$CoIrO$_6$ a nearly constant fraction of a paramagnetic (PM) phase persists down to low temperature, possibly related to the presence of a small amount of Ir$^{3+}$ and to the anti-site disorder at Co/Ir sites. For the doped compounds the PM phase freezes below 30 K, but there is still some dynamics associated with the SG. The dielectric data obtained for the parent compound and the one with 25% of Ca-doping indicate a possible magnetodielectric effect, which is discussed in terms of the electron hopping between the TM ions, the anti-site disorder and the distorted crystalline structure.

Magnetocaloric effect in the Nd2TIn8 (T=Rh, Ir) intermetallics

The magnetocaloric effect of Nd2TIn8 (T = Rh, Ir) intermetallics was studied theoretically. Both compounds have an antiferromagnetic interaction at low temperatures and crystallize in the same tetragonal Ho2CoGa8 structure. We considered a Hamiltonian spin model for two coupled magnetic sublattices that takes into account the effects of crystalline electrical field and exchange interaction in the mean-field approximation. The estimated crystal field parameters explain the magnetocrystalline anisotropy in these compounds and a comparison of the theoretical value of the magnetocaloric effect with the experimental one in Nd2RhIn8, and Nd2IrIn8 shows good agreement.

Magnetic and magnetocaloric properties in Gd1−yPryNi2 compounds

In this work, we report the magnetic and magnetocaloric properties of the Gd1−yPryNi2 compounds from both experimental and theoretical points of view. It is worth noting that this series shows a variety of magnetic arrangements depending on the Pr concentration, including paramagnetism, ferrimagnetism and ferromagnetism. Our experimental work consists of the systematic analysis of the magnetic properties of the compounds with y = 0.0, 0.25, 0.5, 0.75 and 1.0, which includes temperature and magnetic field dependence of the magnetization, heat capacity and isothermal entropy change obtained by isothermal magnetization curves. Also, we developed a model Hamiltonian, which takes into account the exchange interactions among Gd-Gd, Gd-Pr and Pr-Pr ions, the Zeeman interaction for both ions and the crystalline electrical field interaction for the Pr ions. We systematically investigated the magnetic properties of the series and obtained a good agreement when compared with our experimental data.

High-resolution X-ray absorption spectroscopy as a probe of crystal-field and covalency effects in actinide compounds

Applying the high-energy resolution fluorescence-detection (HERFD) mode of X-ray absorption spectroscopy (XAS), we were able to probe, for the first time to our knowledge, the crystalline electric field (CEF) splittings of the [Formula: see text] shell directly in the HERFD-XAS spectra of actinides. Using ThO2 as an example, data measured at the Th 3d edge were interpreted within the framework of the Anderson impurity model. Because the charge-transfer satellites were also resolved in the HERFD-XAS spectra, the analysis of these satellites revealed that ThO2 is not an ionic compound as previously believed. The Th [Formula: see text] occupancy in the ground state was estimated to be twice that of the Th [Formula: see text] states. We demonstrate that HERFD-XAS allows for characterization of the CEF interaction and degree of covalency in the ground state of actinide compounds as it is extensively done for 3d transition metal systems.

Ferromagnetism in the Kondo-lattice compound CePd2P2

We report physical properties of CePd2P2 crystallizing in the tetragonal ThCr2Si2-type structure (space group I4/mmm). Dc-magnetic susceptibility, magnetization, specific heat, electrical resistivity and magnetoresistance measurements establish a ferromagnetic ordering below the Curie temperature TC = 28.4 ± 0.2 K. Critical analysis of isothermal and isofield magnetization yields critical exponents of β = 0.405 ± 0.005, γ = 1.11 ± 0.05 and δ = 3.74 ± 0.04. The ordered state is characterized by saturation moment Ms ∼ 0.98μB and magnon energy gap Δ/kB ∼ 25–35 K. The studied properties reflect a competing influence of the Kondo and crystalline electric field (CEF) interactions. The strength of the Kondo effect is assigned by a low-temperature Kondo scale TK ∼ 19 ± 10 K and a high-temperature Kondo scale 117 ± 10 K. A model of the inelastic scattering of the conduction electrons with an exchanged CEF energy ΔCEF was applied to the magnetic resistivity. An average value ΔCEF = 260 ± 30 K is consistent in the relationships with TK and . We argue that the CePd2P2 compound appears to be a new ferromagnetic Kondo-lattice among the Ce-based intermetallics.

Evolution of the 4f electron localization from YbRh2Si2 to YbRh2Pb studied by electron spin resonance

We report on electron spin resonance (ESR) experiments on the Heusler alloy YbRh2Pb and compare its spin dynamics with that of several other Yb-based intermetallics. A detailed analysis of the derived ESR parameters indicates the extremely weak hybridization, more localized distribution of the 4f states, and a smaller RKKY interaction in YbRh2Pb. These findings reveal the important interplay between hybridization effects, chemical substitution, and crystalline electric field interactions that determines the ground state properties of strongly correlated electron systems.

Theoretical investigations on the magnetocaloric and barocaloric effects in TbyGd(1−y)Al2 series

We report the calculations on the magnetocaloric and barocaloric effects in ferromagnetic series TbyGd(1−y)Al2. Our model includes the crystalline electrical field interaction, exchange interactions among Tb–Tb, Gd–Gd and Tb–Gd magnetic ions and the Zeeman effect for an anisotropic system. The lattice and electronic entropies were included in adiabatic processes. The magnetocaloric effect calculated for magnetic field changes along the easy magnetic direction 〈111〉 is in good agreement with the experimental data. Calculation along the hard magnetization direction 〈001〉 predicts anomalous magnetocaloric effect, which was ascribed to the spin reorientation processes. From the available experimental data of Curie temperature dependence on pressure, the exchange model parameters were scaled and the barocaloric effect was calculated.

Magnetovolume and magnetocaloric effects in Er2Fe17

Combining different experimental techniques, investigations in hexagonal $P{6}_{3}/mmc$ Er${}_{2}$Fe${}_{17}$ show remarkable magnetovolume anomalies below the Curie temperature, ${T}_{C}$. The spontaneous magnetostriction reaches $1.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ at 5 K and falls to zero well above ${T}_{C}$, owing to short-range magnetic correlations. Moreover, Er${}_{2}$Fe${}_{17}$ exhibits direct and inverse magnetocaloric effects (MCE) with moderate isothermal magnetic entropy $\ensuremath{\Delta}{S}_{M}$, and adiabatic temperature $\ensuremath{\Delta}{T}_{\mathrm{ad}}$ changes [$\ensuremath{\Delta}{S}_{M}\ensuremath{\sim}\ensuremath{-}4.7$ J(kgK)${}^{\ensuremath{-}1}$ and $\ensuremath{\Delta}{T}_{\mathrm{ad}}\ensuremath{\sim}2.5$ K near the ${T}_{C}$, and $\ensuremath{\Delta}{S}_{M}\ensuremath{\sim}1.3$ J(kgK)${}^{\ensuremath{-}1}$ and $\ensuremath{\Delta}{T}_{\mathrm{ad}}\ensuremath{\sim}\ensuremath{-}0.6$ K at 40 K for $\ensuremath{\Delta}H=80$ kOe, respectively, determined from magnetization measurements]. The existence of an inverse MCE seems to be related to a crystalline electric field-level crossover in the Er sublattice and the ferrimagnetic arrangement between the magnetic moments of the Er and Fe sublattice. The main trends found experimentally for the temperature dependence of $\ensuremath{\Delta}{S}_{M}$ and $\ensuremath{\Delta}{T}_{\mathrm{ad}}$ as well as for the atomic magnetic moments are qualitatively well described considering a mean-field Hamiltonian that incorporates both crystalline electric field and exchange interactions. $\ensuremath{\Delta}{S}_{M}(T)$ and $\ensuremath{\Delta}{T}_{\mathrm{ad}}(T)$ curves are essentially zero at $\ensuremath{\sim}$150 K, the temperature where the transition from direct to inverse MCE occurs. A possible interplay between the MCE and the magnetovolume anomalies is also discussed.

Ternary aluminides R0.67Ni2Al6 (R=Sc, Y, Gd–Lu) with partly disordered structures

Ten rare-earth nickel aluminides R0.67Ni2Al6 (R=Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were synthesized by arc melting and their crystal structures studied by X-ray powder diffraction. They crystallize in the hexagonal structure type Yb0.67Ni2Al6: Pearson symbol hP11-2.33, space group P-6m2, a=4.18904(2), c=9.09816(6)Å, which can be decomposed into three kinds of layer. The sequence of layers along [001] is Yb0.67Al–NiAl2–Al–NiAl2, but stacking faults appear due to relative shifts of consecutive Yb0.67Al layers containing two rare-earth metal atoms for one Al-atom triangle. An ordered superstructure is the type ErNi3Al9 (Pearson symbol hR78, space group R32, a=3a0, c=3c0), refined on single crystals.The physical properties of the R0.67Ni2Al6 (R=Tb, Er, Tm, Yb, and Lu) compounds were determined by means of magnetic and electrical transport measurements. All these materials but Lu0.67Ni2Al6 exhibit Curie–Weiss paramagnetic behavior due to the trivalent R ions, and order magnetically at low temperatures. They show good metallic conductivity. The Yb-containing compound is a dense Kondo system with distinct features in the paramagnetic state of the interplay between Kondo and crystalline electric field interactions.

Magnetic properties and large inverse magnetocaloric effect in single crystal antiferromagnetic TbNiAl 4

The magnetic properties and magnetocaloric effect (MCE) in single crystal antiferromagnetic TbNiAl 4 were systematically studied by examining the temperature and field dependence of magnetization and heat capacity. These magnetic properties and the MCE show strong magnetocrystalline anisotropy. A field-induced step-like magnetization transition and large inverse MCE were observed at low temperatures with the magnetic field parallel to the a axis but not for the b or c axes. Such strong anisotropy originates from the crystalline electric field interaction of the Tb 3+ ions. The large inverse MCE is related to the field-induced step-like magnetic behaviour which is probably due to a transition from a commensurate antiferromagnetic phase to an incommensurate magnetic phase. The values of maximum magnetic entropy change ( Δ S M max ) reach 5.0 and 7.9 J Kg −1 K −1 for field changes of 2 and 6 T ( H // a axis), respectively; the corresponding maximum adiabatic temperature changes ( Δ T a d max ) are evaluated to be 1.4 and 3.4 K for single crystal TbNiAl 4.

Magnetocaloric effect in the Laves phase pseudobinaries [formula omitted] ( [formula omitted] and Ho)

In this work we calculate the magnetocaloric effect in the Laves phase pseudobinaries ( Dy 1 - c Er c ) Al 2 and ( Dy 1 - c Ho c ) Al 2 . We use a model Hamiltonian of interacting 4f-spins, including the crystalline electrical field interaction. The 4f spin–spin interaction is treated in an extended mean field approximation, in which the magnitude of the exchange interaction between 4f-spins depends on the type of rare earth ion is occupying the neighboring sites. The calculated isothermal entropy change and the adiabatic temperature change upon variations of the magnetic field are in good agreement with the available experimental data.

Separation of energy scales in the kagome antiferromagnet TmAgGe: A magnetic-field-orientation study up to55T

TmAgGe is an antiferromagnet in which the spins are confined to distorted kagome-like planes at low temperatures. We report angle-dependent measurements of the magnetization $M$ in fields of up to 55 T that show that there are two distinct and separate energy scales present in TmAgGe, each responsible for a set of step-like metamagnetic transitions; weak exchange interactions and strong crystalline electric field (CEF) interactions. Simulations of $M$ using a three-dimensional, free-energy minimization technique allow us to specify for the first time the physical origin of the metamagnetic transitions in low, in-plane fields. We also show that the transitions observed with the field perpendicular to the kagome planes are associated with the CEF-split multiplet of Tm.

Magnetic-field-orientation dependence of the metamagnetic transitions in TmAgGe up to 55 T

TmAgGe is an antiferromagnet based on the ZrNiAl structure. At low temperatures the spins are confined to distorted kagome-like planes, wherein the magnetisation is strongly anisotropic. A previous study has shown that a series of stepped magnetic transitions are apparent in low, in-plane magnetic fields and can be explained using a three-fold Ising-like model. Here we present high-magnetic-field magnetisation experiments showing that further stepped transitions are observed when the field is directed out of the kagome planes. Angledependent measurements in fields of up to 55 T show that there are at least two distinct and separate energy scales present in this system; the weak exchange interactions and the strong crystalline electric field interactions. Simulations of the magnetisation using a three-dimensional, free-energy minimisation technique allow us to suggest the nature and hierarchy of the forces acting on the Tm3+moments.