Crystal Electric Field Research Articles

Faraday effect of bismuth iron garnet thin film prepared by mist CVD method

Metastable bismuth iron garnet (BIG, an abbreviation of Bi3Fe5O12), one kind of garnet-type ferrites, is known to manifest very large Faraday rotation as well as low optical absorption in the visible to infrared region. We report on successful synthesis of thin film composed of single-phase BIG epitaxially grown on single-crystalline gadolinium gallium garnet (Gd3Ga5O12, GGG) substrate by using mist chemical vapor deposition (CVD) method, which is an emerging technique for preparation of thin films. The crystal structure, surface morphology, and magnetic, optical and magneto-optical properties of the resultant thin films have been explored. The BIG thin film has a relatively flat surface free from roughness compared to those prepared by other vapor deposition methods. Saturation magnetization is about 1620 G at room temperature, which is close to that expected from the ideal magnetic structure of BIG. The maximum value of Faraday rotation angle reaches 54.3 deg/µm at a wavelength of 424 nm. This value is rather large when compared with those reported for BIG thin films prepared by other techniques. The wavelength dependence of Faraday rotation angle is analyzed well in terms of the crystal electric field (CEF) level schema. Our result suggests that the mist CVD method is a simple and effective technique to synthesize BIG thin film with excellent magneto-optical properties.

Anisotropy effect on the caloric properties of NdAl2 single crystal

In this paper we theoretically discuss the effect of anisotropy on the magnetocaloric properties of NdAl2 single crystal. To this end, we use a model Hamiltonian of interacting magnetic moments under the influence of the crystal electric field. The magnetocaloric quantity, ΔSiso, calculated for 7T magnetic field variation is in a reasonable agreement with the available experimental data. Moreover, we predict the existence of anomalies in the magnetocaloric effect when the magnetic field of constant intensity rotates from 〈100〉 to 〈110〉 direction.

Rotating magnetocaloric effect in HoAl2 single crystal

In this paper we theoretically discuss the rotating magnetocaloric effect in HoAl2 single crystal. In order to do that, we use a model Hamiltonian of interacting magnetic moments including a term to account for the crystal electric field. Our theoretical calculations of the entropy changes are in a reasonable agreement with the available experimental data. Moreover, we predict the existence of an anomalous rotating magnetocaloric effect for some directions of the magnetic field rotation.

Muon spin rotation and neutron scattering study of the noncentrosymmetric tetragonal compoundCeAuAl3

We have investigated the noncentrosymmetric tetragonal heavy fermion compound $\mathrm{CeAuA}{\mathrm{l}}_{3}$ using muon spin rotation $(\ensuremath{\mu}\mathrm{SR})$, neutron diffraction (ND), and inelastic neutron scattering (INS) measurements. We have also revisited the magnetic, transport, and thermal properties. The magnetic susceptibility reveals an antiferromagnetic transition at 1.1 K with, possibly, another magnetic transition near 0.18 K. The heat capacity shows a sharp $\ensuremath{\lambda}$-type anomaly at 1.1 K in zero field, which broadens and moves to a higher temperature in an applied magnetic field. Our zero-field $\ensuremath{\mu}\mathrm{SR}$ and ND measurements confirm the existence of a long-range magnetic ground state below 1.2 K. Further, the ND study reveals an incommensurate magnetic order with a magnetic propagation vector $\mathbf{k}=(0,0,0.52(1))$ and a spiral structure of Ce moments coupled ferromagnetically within the $ab$ plane. Our INS study reveals the presence of two well-defined crystal electric field (CEF) excitations at 5.1 and 24.6 meV in the paramagnetic phase of $\mathrm{CeAuA}{\mathrm{l}}_{3}$ that can be explained on the basis of the CEF theory and the Kramer's theorem for a Ce ion having a $4{f}^{1}$ electronic state. Furthermore, low energy quasielastic excitations show a Gaussian line shape below 30 K compared to a Lorentzian line shape above 30 K, indicating a slowdown of spin fluctuations below 30 K. We have estimated a Kondo temperature of ${T}_{\mathrm{K}}=3.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ from the quasielastic linewidth, which is in good agreement with that estimated from the heat capacity. This study also indicates the absence of any CEF-phonon coupling unlike that observed in isostructural $\mathrm{CeCuA}{\mathrm{l}}_{3}$ The CEF parameters, energy level scheme, and their wave functions obtained from the analysis of INS data explain satisfactorily the single crystal susceptibility in the presence of two-ion anisotropic exchange interaction in $\mathrm{CeAuA}{\mathrm{l}}_{3}$.

23Na Nuclear Magnetic Resonance Study of the Structure and Dynamic of Natrolite

Abstract The temperature dependences of nuclear magnetic resonance (NMR) and magic angle spinning (MAS) NMR spectra of 23Na nuclei in natrolite (Na2Al2Si3O10·2H2O) have been studied. The temperature dependences of the spin-lattice relaxation times T1 in natrolite have also been studied. It has been shown that the spin-lattice relaxation of the 23Na is governed by the electric quadrupole interaction with the crystal electric field gradients modulated by translational motion of H2O molecules in the natrolite pores. The dipolar interactions with paramagnetic impurities become significant as a relaxation mechanism of the 23Na nuclei only at low temperature (<270 K).

Magnetic properties and specific heat of R2Ni2In (R=Gd-Tm) compounds

The R2Ni2In (R=Gd-Tm) compounds were investigated by means of X-ray diffraction, magnetic and specific heat measurements. The compounds crystallize in the orthorhombic Mn2AlB2-type crystal structure. A low temperature ground state is antiferromagnetic. Critical temperature of magnetic ordering does not fulfill the de Gennes scaling which points to the influence of crystal electric field on stabilization of magnetic order.

Elastic anomalies of YbIrGe in magnetic fields

The Yb-based heavy-fermion compound YbIrGe, which has the orthorhombic structure, shows the crystal electric field effect at high temperatures and antiferromagnetic orderings at TN = 2.4 K and Tm = 1.4 K. We previously found anomalous elastic softening in zero magnetic field originating from an indirect quadrupole interaction between the ground doublet and the excited doublets, and determined the crystal electric field level scheme: the ground doublet and an excited doublet at 138 K. To investigate the antiferromagnetic orderings at TN and Tm, we performed ultrasonic measurements under magnetic fields along the a-axis on YbIrGe single crystals. Temperature dependence of elastic modulus C11 exhibits elastic hardening below both TN and Tm at 0 T. As increasing the magnetic field along the a-axis, both TN and Tm decrease monotonically, suggesting that both transitions are antiferromagnetic ordering. TN closes around 2 T, and Tm disappears above 1 T. We clarified the magnetic field- temperature phase diagram along the a-axis.

Ytterbium ESR in a lattice with weak coupling: the case of YbPt2Sn

We observed a well-defined Yb3+ electron spin resonance (ESR) line in YbPt2Sn. The single crystal ESR data show strongly anisotropic g factors, being largest in the basal plane, in agreement with magnetization data. This proves the intrinsic nature of the ESR signal. Analysis of these results indicates the crystal electric field ground state to be the Γ7 doublet. Although the Kondo and intersite interactions are at least one order of magnitude weaker than in the Kondo lattices YbRh2Si2 and YbIr2Si2, the temperature dependence of linewidth and g factors show qualitative similarities.

Magnetic properties of the tetragonal RCuGa3 (R=Pr, Nd and Gd) single crystals

Single crystals of tetragonal RCuGa3 (R=La, Pr, Nd and Gd), with BaNiSn3 type structure (space group I4mm), have been grown by high temperature solution growth technique using Ga as flux. Their magnetic properties were determined by heat capacity and the measurement of magnetization and electrical resistivity along [100] and [001] directions. Except LaCuGa3, the compounds order magnetically. PrCuGa3 undergoes a ferromagnetic transition with Curie temperature of 4.6K. NdCuGa3 shows a bulk magnetic transition at 3.3K. The data on GdCuGa3 indicate combined characteristics of spin glass and antiferromagnetic behavior at low temperatures. From the Schottky heat capacity data the crystal electric field level energy spectra have been determined. Further we have performed temperature dependent measurements of electron spin resonance (ESR) on GdCuGa3 between 11K and room temperature. The ESR data indicate an enhancement of magnetic fluctuations associated with spin reorientation and both homogeneous and inhomogeneous thermal broadening of the linewidth.

Strong magnetic coupling in the hexagonal R5Pb3 compounds (R=Gd–Tm)

We have synthesized the R5Pb3 (R=Gd–Tm) compounds in polycrystalline form and performed neutron scattering and magnetization measurements. For all R5Pb3 reported here the Weiss temperatures θW are several times smaller than the ordering temperatures TORD, while the latter are remarkably high (TORD up to 275K for R=Gd) compared to other known R–M binaries (M=Si, Ge, Sn and Sb). The magnetic order changes from ferromagnetic (FM) in R=Gd, Tb to antiferromagnetic (AFM) in R=Dy–Tm. Below TORD, the magnetization measurements together with neutron powder diffraction show complex magnetic behaviors and reveal the existence of up to three additional phase transitions, believed to be a result of large anisotropic exchange and/or crystal electric field effects, induced high anisotropy. The R5Pb3 magnetic unit cells for R=Tb–Tm can be described with incommensurate magnetic wave vectors with spin modulation either along the c axis in R=Tb, Er and Tm, or within the ab plane in R=Dy and Ho.

Elastic Softening and Phase Transition Characteristics in YbPtGe

YbPtGe with the orthorhombic ɛ-TiNiSi-type structure is reported as a heavy-fermion ferromagnet with TC = 5.4K. Recent research suggested that its magnetic anisotropy can be ascribed to the crystal electric field (CEF) effect which acts on the eight-fold multiplet of Yb3+ ions. In order to clarify the CEF effect and to investigate the magnetic phase transition in this compound, ultrasonic measurements of YbPtGe and related theoretical calculation have been performed. The transverse elastic modulus C66 exhibits a softening characteristic with a peak at 180K while the longitudinal modulus C33 shows a continuous hardening in the whole temperature range. According to the theoretical strain-susceptibility fitting of the transverse elastic modulus C66 by using the CEF parameters reported by Katoh et al., we argue the softening at higher temperatures (>50K) to be a result of quadrupole interaction between the CEF ground and excited Kramers doublets. With further decreasing the temperature below TC, C66 mode exhibits a step-like softening which is quite different from that of the C33 mode and the possible mechanism is discussed.

Elastic Softening in HoFe2Al10

To investigate the 4f-electronic states under the crystal electric field (CEF) in HoFe2Al10, we carried out ultrasonic and specific heat measurements on single-crystalline samples. We found elastic softening of the transverse elastic modulus C55 below 20K and two Schottky peaks at 2 and 20K in the magnetic specific heat. By theoretical analyses of the modulus and the magnetic specific heat based on the CEF theory, we reproduced the elastic softening and the two Schottky peaks, and obtained the CEF parameters.

Elastic Softening in the Orthorhombic Compound YbPdGe

The Yb-based compound YbPdGe with the orthorhombic structure shows a ferromagnetic phase transition at 11.4K. YbPdGe has localized 4f-electrons of Yb3+ ions and the crystal electric field (CEF) effect at high temperatures. On the other hand, a heavy-fermion state is reported at low temperatures, indicating that YbPdGe is a heavy-fermion ferromagnet. To investigate the phase transition at 11.4K and the CEF effect, we carried out ultrasonic measurements on a single-crystalline sample. Characteristic elastic softening below 170K is observed at high temperatures in the transverse elastic modulus C66 in contrast to the longitudinal modulus C22 without the softening. In the orthorhombic compound YbIrGe, the transverse moduli exhibit a similar elastic softening originating from the CEF effect, suggesting that the softening of C66 in YbPdGe is also caused by the CEF effect. At the phase transition, C22 and C66 show abrupt elastic hardening and softening, respectively, due to the magnetostriction.

Preparation of Compensation Ions Codoped SrTiO3:Pr3+ Red Phosphor with the Sol-Gel Method and Study of Its Luminescence Enhancement Mechanism

SrTiO3:Pr3+ is the most representative titanate matrix red phosphor for field emission display (FED). The red luminous efficiency of SrTiO3:Pr3+ will be greatly improved after the compensation ions codoping, so SrTiO3:Pr3+ red phosphor has been a research focus at home and abroad. SrTiO3:Pr3+, SrTiO3:Pr3+, Mg2+, and SrTiO3:Pr3+, Al3+ phosphors are synthesized by a new sol-gel method. Crystal structure, spectral characteristics, and luminescence enhancement mechanism of the sample were studied by XRD and PL spectra. The results showed that after co-doped, SrTiO3:Pr3+ phosphor is single SrTiO3 cubic phase, the main emission front is located at 614 nm, corresponding to Pr3+ ions 1D2→3H4 transition emission. SrTiO3:Pr3+, Mg2+ and SrTiO3:Pr3+, Al3+ phosphor luminescence intensity is enhanced, but the main luminescence mechanism is not changed. Acceptor impurity x = Mg2+, Al3+ will replace Ti bit after being doped into the crystal lattice to form XTi- charge compensation corresponding defect centers PrSr+ to reduce the demand of Sr2+ or Ti3+ vacancy. While Sr-doped Pr will make lattice distortion and transition energy of 4f-5d is very sensitive to crystal electric field changes around Pr atom. Doping different impurities will make electric field distribution around the icon have a different change. It increases energy transfer of 4f-5d transition and improves the luminous intensity of SrTiO3:Pr3+ red phosphor.

Anisotropic magnetocaloric effect in TmAl2 single crystal

In this paper, we theoretically discuss the anisotropic magnetocaloric effect in TmAl2 single crystal. To this end, we use a model Hamiltonian of interacting magnetic moments including an extra term to account for the crystal electric field. Our theoretical calculations are in a reasonable agreement with the available experimental data. Moreover, we predict the existence of an anomalous anisotropic magnetocaloric effect for some values of the applied magnetic field.

Magnetic, thermal and transport behavior in single crystalline RCu2Ge2 (R=La, Ce, Pr and Sm) compounds

Magnetic behavior of single crystalline RCu 2 Ge 2 (R=La, Ce, Pr and Sm) compounds is reported. Single crystals were grown using Cu–Ge flux. The compounds crystallize in a tetragonal structure with space group I4/mmm. LaCu 2 Ge 2 shows a diamagnetic behavior. CeCu 2 Ge 2 , PrCu 2 Ge 2 and SmCu 2 Ge 2 orders antiferromagnetically at ≈ 4.2 , 15 and 14.5 K respectively with [001] as the easy axis of magnetization. CeCu 2 Ge 2 shows a Kondo behavior. The Kondo temperature T K , calculated using two different models is of order of 5 K. In PrCu 2 Ge 2 , an additional magnetic transition is observed below 4 K. The origin of the magnetic behavior is attributed to magnetoelastic effects. A possibility of change in easy axis of magnetization after field cycling (below 4 K) is discussed and such effect is rarely observed. The magnetic and specific heat behavior of CeCu 2 Ge 2 and PrCu 2 Ge 2 are analyzed on the basis of crystalline electric field (CEF) model. The CEF splited ground state of rare earth ions is calculated. The magnetic isotherm of SmCu 2 Ge 2 exhibits de Haas-van Alphen oscillations. It is inferred from the frequency spectrum analysis that, the Fermi surface cross-section along [001] is large compared to [100]. • RCu 2 Ge 2 single crystals are grown by self-flux • Anomalous magnetic behavior was observed in PrCu 2 Ge 2 , which was explained on the basis of possible change in the easy axis of magnetization after field cycling. • Crystal electric field calculations were done to explain the observed magnetic properties. • de Haas–van Alphen oscillations were observed in SmCu 2 Ge 2 .

Ising-Type Ferromagnetic Ground State Driven by Anisotropic c–f Hybridization in CeRu2Al2B

The magnetic correlations between Ce 4f electrons and conduction electrons in the new tetragonal compound CeRu2Al2B have been investigated by 27Al nuclear magnetic resonance (NMR). The 27Al NMR spin–lattice relaxation rate 1/T1 exhibits a large magnetic anisotropy for field directions. Within a localized moment picture, the Ce 4f spin-fluctuation rates Γ|| for the c-axis and Γ⊥ for the c-plane are evaluated by taking account of the magnetic anisotropy. The relation of \(\Gamma _{\parallel } \gg \Gamma _{ \bot }\), which holds in the entire temperature range, indicates that the c–f hybridization between the ligand conduction electrons and the Ce 4f electrons with the \(\Gamma _{7}^{(1)}\) crystal electric field ground state is anisotropic. From the temperature dependence of Γ, it is found that the Kondo effect dominates the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction at high temperatures, whereas below 60 K the RKKY interaction overcomes the Kondo effect and causes the magnetic order. These results in...

Magnetocaloric effect in [formula omitted] ([formula omitted] and Ho)

In this paper we theoretically discuss the magnetocaloric effect in (TbcR1-c)Co2 (R=Er and Ho). To this end, we use a model Hamiltonian in which are included the 4f electrons from rare earth ions and the 3d electrons from Co ions. In the model is also included an extra term to account for the crystal electric field, which plays an important role in the magnetic and caloric properties of these compounds.

Substitution effect on the magnetic and transport properties of CeNi0.8−xMnxBi2

We report the results of Mn substitution for Ni in CeNi0.8Bi2 (i.e., CeNi0.8−xMnxBi2). All the samples have an antiferromagnetic ordered state below TN = 5.0 K due to localized 4f-magnetic moment on the Ce ions. Besides this antiferromagnetic ordering caused by Ce, the magnetic and transport properties are abruptly changed with increasing Mn contents at the boundary composition of x = 0.4. The magnetic state is changed into a ferromagnetic state around 200 K for x > 0.4, where the electrical resistivity is strongly suppressed to become simple metallic. These results of ferromagnetism and metallicity can be explained by the double exchange mechanism, rather than the simple picture of Doniach phase diagram. The mixed valence states of Ni and Mn ions are confirmed by X-ray photoelectron spectroscopy. For x ≤ 0.4, the initial Ni3+ state gradually changes to the Ni2+ state with increasing x up to 0.4. On further increase of x > 0.4, the Ni2+ state is replaced by the Mn2+ state, which gradually changes to the final Mn3+ state. We also present an inelastic neutron scattering (INS) measurements on CeNi0.8Bi2 (i.e., x = 0) between 1.2 and 12 K. The high energy INS study reveals the presence of two well-defined crystal electric field (CEF) excitations near 9 meV and 19 meV at 1.2 K and 6 K, while the low energy INS study reveals the presence of quasielastic scattering above 4 K. We will discuss our INS results of CeNi0.8Bi2 based on the CEF model.

Electronic structure and low-temperature study of theCe1−xLaxRh4Sn13

Recently, it was reported that the skutterudite-related ${\mathrm{Ce}}_{3}{\mathrm{Rh}}_{4}{\mathrm{Sn}}_{13}$ heavy fermion compound has a large electronic specific heat coefficient $C(T)/T$ and short-range magnetic correlations, both suggest a possible quantum critical point (QCP). We present the low-temperature specific heat, resistivity, and susceptibility of ${\mathrm{Ce}}_{1\text{\ensuremath{-}}x}{\mathrm{La}}_{x}{\mathrm{Rh}}_{4}{\mathrm{Sn}}_{13}$, which do not confirm the presence of QCP. X-ray photoelectron spectroscopy revealed a stable configuration of Ce atoms consistent with magnetic susceptibility data. Magnetic susceptibility shows that the sixfold-degenerate multiplet of ${\mathrm{Ce}}^{3+}$ ion splits into three doublets due to the lower local symmetry of ${\mathrm{CeSn}}_{12}$ cage in the cubic ${\mathrm{Ce}}_{1\text{\ensuremath{-}}x}{\mathrm{La}}_{x}{\mathrm{Rh}}_{4}{\mathrm{Sn}}_{13}$ compounds. The resistivity, specific heat, and susceptibility data are consistent with our band-structure calculations. The chemical bondings in the unit cell of ${\mathrm{Ce}}_{1\text{\ensuremath{-}}x}{\mathrm{La}}_{x}{\mathrm{Rh}}_{4}{\mathrm{Sn}}_{13}$, analyzed based on the difference charge density maps from band-structure calculations within the virtual crystal approximation explain the deformation of the cages and the crystal electric field properties of the system.