Nonmagnetic Rare Earth Research Articles

Transition metal (dis)order in single crystal multicomponent rare earth perovskites

The utilization of configurational entropy in materials design has accelerated the tailoring of oxides for a variety of technological applications. So called “high entropy” oxides (HEO) have more recently been investigated for their use in magnetocaloric refrigeration due to tunability of the spin glass phase. To advance our understanding of these magnetic interactions, we have grown single crystals ( 5 mm diameter, 3 cm length) of the multicomponent perovskite SmCo1/4Cr1/4Fe1/4Mn1/4O3 using the laser diode floating zone technique. This material deviates from its parent SmMO3 (MCo, Cr, Fe, Mn) magnetic behaviors by having two broad transitions with a large bifurcation in the zero-field cooled vs field cooled measurements. Measurements of magnetization as a function of field show spin canting of the transition metal ions, with exchange bias emerging as a function of temperature. Heat capacity measurements are utilized alongside the non-magnetic rare earth analog LaCo1/4Cr1/4Fe1/4Mn1/4O3 to understand the low temperature superexchange interactions. Such comparison supports the two magnetic sublattices operating at different energy scales. Overall single crystal growth of such HEO should be utilized due to the ease of growth using the floating zone technique and insight it gives into the magnetic characterization.

On the electronic and magnetic properties of RVO3 (R = Er, Ho, Y, Lu) vanadates: first principles study

In this paper, we investigate the influence of the rare earth element (R) on the physical properties of RVO3 (R = Er, Ho, Y, Lu). For this purpose, a theoretical work is reported in this study using ab initio method with the intent of enhancing our knowledge of the electronic, and magnetic properties of RVO3 (R = Er, Ho, Y, Lu) compounds. The electronic properties of these materials show the presence of Jahn-Teller effect, with a band gap of approximately 0.58eV, 1.57eV, 1.12eV, 1.28eV, for ErVO3, HoVO3, YVO3, LuVO3, respectively. The magnetic contribution of Ho, Er, and V atoms in HoVO3, and ErVO3 compounds was disentangled using X-ray magnetic circular dichroism (XMCD). The magnetic anisotropies of RVO3 with (R = Er, Ho, Y, Lu) are studied and analyzed using spin orbit coupling. We noticed an easy axis of magnetization along the c-direction with strong magneto-crystalline anisotropy energies for the non-magnetic rare earth elements (R = Lu, Y)VO3. For the magnetic rare earth elements, the easy and hard magnetization direction were found to be along b-axis and c-axis, and a-axis and c-axis for HoVO3, and ErVO3, respectively. This means that instead of the standard magnetization demagnetization process, large thermal effects can be obtained by spinning their single crystals in constant magnetic fields. The exchange coupling between (Ho–V) is also found to be greater than the other exchange interactions in HoVO3. Accordingly, a large conventional magnetocaloric could be created in HoVO3, since the Ho Ising moments experience a metamagnetic transition. However, the magnetocaloric effect (MCE) is expected to be lower in ErVO3 due to the weak (Er–V) exchange coupling.

Direct evidence of electron-hole compensation for extreme magnetoresistance in topologically trivial YBi

The prediction of topological states in rare earth monopnictide compounds has attracted renewed interest. Extreme magnetoresistance (XMR) has also been observed in several nonmagnetic rare earth monopnictide compounds. The origin of XMR in these compounds could be attributed to several mechanisms, such as topologically nontrivial electronic structures and electron-hole carrier balance. YBi is a typical rare earth monopnictide exhibiting XMR, and expected to have a nontrivial electronic structure. In this work, we performed a direct investigation of the electronic structure of YBi by combining angle resolved photoemission spectroscopy and theoretical calculations. Our results show that YBi is topologically trivial without the expected band inversion, and they rule out the topological effect as the cause of XMR in YBi. Furthermore, we directly observed perfect electron-hole compensation in the electronic structure of YBi, which could be the primary mechanism accounting for the XMR.

Synthesis PbFCl-Type Mixed Anion <i>A</i>P<i>X</i>(<i>A</i>=Hf, <i>X</i>=S, Se) Superconductors Related with Topological Materials by High-Pressure Technique

We performed a systematic study of the crystal structure, physical properties, and electronic structure of PbFCl-type intermetallic APX(A=Zr, Hf, X=S and Se) superconductor. We successfully synthesized single-phase polycrystalline samples for the Se substitution range of 0.4≤x≤0.8 in Zr(P2-xSex) using high pressure technique. On the other hand, S substitution range in Zr(P2-xSx) was narrow of 0.4≤x≤0.6, the S substitution range in Hf(P2-xSx) was narrow of x≈0.55, and the Se substitution range in Hf(P2-xSex) was also very narrow of x≈0.4. Zr(P2-xSex) exhibits a dome-like superconducting phase diagram for the substitution amount x. The superconducting transition temperature (Tc) is achieved at approximately x≈0.75 at which point the Tcis 6.3 K for Zr(P1.25Se0.75), 5.5 K for Hf(P1.30Se0.70), 5.0 K for Zr(P1.325S0.675), and 4.6 K for Hf(P1.50S0.50), respectively. Tcfor Zr(P1.25Se0.75) is increased from 6.3 K to 7.6 K by partially substituting a non-magnetic rare earth Sc atom for Zr. Single crystals of Zr(P1.25Se0.75) and partially substituted by Sc atom for Zr site of the ZrP2-xSexwere also grain grown using high pressure technique. Plate-like single crystal with approximate edge sizes of up to 500 × 300 × 20 μm3for (Zr0.50Sc0.50)PSe nominal composition was obtained. Tc= 8.36 K was reached and the Hc1//c-axis(0) and Hc1⊥c-axis(0) roughly determined are 0.0045 T and 0.0038 T, respectively. Assuming the type-II superconductivity in dirty limit, the Hc2//c-axis(0) value of 1.33 T was also obtained. In this presentation, the crystal growth and physical properties of this APX(A=Zr, Hf, X=S and Se) superconductor has reported.

Magnetocaloric Effect in a Frustrated Gd-Garnet with No Long-Range Magnetic Order.

In this paper, the hyperkagome lattice of Gd spins in a garnet compound, Gd3CrGa4O12, is studied using bulk measurements and density functional computations, and the observation of large magnetocaloric effect corresponding to an entropy change, ΔSm = 45 J kg-1K-1 (≈ 45 J mol-1K-1) at 2 K, 8 T is reported. Though the compound defies long-range magnetic order down to 0.4 K, a broad feature below 10 K is observed in the specific heat with two low temperature anomalies at T* ≈ 0.7 K and TS ≈ 2.45 K. The anomaly at T* is reminiscent of one in Gd3Ga5O12, where it is related to the development of a complex magnetic phase, whereas the TS-peak is accounted for by a multilevel Schottky-like model. The spin-lattice relaxation times studied by nuclear magnetic resonance experiments show that the relaxation is dominated by the magnetic fluctuations in Cr which has a longer relaxation time compared to that of the garnet, Lu3CrGa4O12 containing a nonmagnetic rare earth. Our first-principles density functional theory calculations agree well with the experimental results and support short-range magnetic order in the Gd-sublattice and antiferromagnetism in the Cr-sublattice. The importance of spin fluctuations and short-range order in the rare earth and transition metal lattices in garnets resulting in large magnetocaloric effect is brought out through this work.

A comparative study on magnetic order and field-induced magnetic transition in double perovskite iridates: RE2ZnIrO6 and RE2MgIrO6 (RE = Pr, Nd, Sm, Eu, Gd)

We perform a comparative magnetic study on two series of rare-earth (RE) based double perovskite iridates RE2BIrO6 (RE = Pr, Nd, Sm–Gd; B = Zn, Mg), which show Mott insulating state with tunable charge energy gap from ∼330 meV to ∼560 meV by changing RE cations. For nonmagnetic RE = Eu cations, Eu2MgIrO6 shows antiferromagnetic (AFM) order and field-induced spin-flop transitions below Néel temperature (TN) in comparison with the ferromagnetic (FM)-like behaviors of Eu2ZnIrO6 at low temperatures. For magnetic-moment-containing RE ions, Gd2BIrO6 show contrasting magnetic behaviors with FM-like transition (B = Zn) and AFM order (B = Mg), respectively. While, for RE = Pr, Nd and Sm ions, all members show AFM ground state and field-induced spin-flop transitions below TN irrespective of B = Zn or Mg cations. Moreover, two successive field-induced metamagnetic transitions are observed for RE2ZnIrO6 (RE = Pr, Nd) in high field up to 56 T, the resultant field temperature (H–T) phase diagrams are constructed. The diverse magnetic behaviors in RE2BIrO6 reveal that the 4f-Ir exchange interactions between the RE and Ir sublattices can mediate their magnetism.

Effect of non-magnetic rare earth substitution for A site in mixed anion APX superconductors

We report the improvement of superconducting transition temperature (T c) by nonmagnetic rare earth atom substitution for A site in APX-based Zr(P, S)2, Hf(P, Se)2 and Hf(P, S)2 superconductors. The partial non-magnetic rare earth Lu atom substitution at Zr site of ZrPS, as opposed to the case of Zr(P, Se)2, shows that lattice constants a and c decrease monotonically with increasing nominal substitution y. It is shown that the maximum T c for ZrPS was increased from 3.70 K to 6.36 K. In HfP1.55Se0.45, when Hf site is partially substituted with Lu atoms (or Y atoms), lattice constant a shrinks and c expands monotonically with increasing nominal rare earth substitution y. T c was also increased from 4.88 K to 5.89 K. In HfP1.45S0.55, when Hf site is partially substituted with Lu atoms (or Y atoms), lattice constant a shrinks slightly and c expands monotonically with increasing y. T c was also increased from 3.16 K to 5.86 K. In this paper, the doping behaviour by partial substitution and the increase of T c is discussed.

Effect of non-magnetic rare earth substitution for Zr on mixed anion Zr(P, Se)2 superconductors II

In ZrP1.25Se0.75, the superconducting transition temperature Tc is increased from 5.8 K to 7.6 K when Sc atoms are partially substituted for Zr atoms having almost the same atomic radius as Sc atoms. Transport measurements show that holes are doped with substituting Sc atoms. The density of states in (Zr, Sc)P1.25Se0.75 is derived from band structure calculations and its implication in the doping behaviour and the increase of Tc is discussed.

Effect of non-magnetic rare earth substitution for Zr on mixed anion Zr(P, Se)2 superconductors

It is shown that the maximum superconducting transition temperature, Tc for ZrP1.25Se0.75 is increased from 5.8 K to 7.2 K by partially substituting a non-magnetic rare earth atom Lu for Zr and on the other hand is decreased by substituting other non-magnetic rare earth atoms Y and La. Obviously, Tc is raised when lattice constants in the a-axis and the c-axis increase with replacing Zr. Its implications for further increasing Tc are discussed.

Single Crystal growth of mixed anion Zr(P, Se)2 superconductor and related materials

A new method to grow single crystals of PbFCl-type mixed anion AP2-xXx (A = Zr, Hf, X = S, Se) superconductor is examined. Using a wedge-type, cubic-anvil, high-pressure apparatus, single crystals of ZrP1.25Se0.75 (A = Zr, X = Se) were grain grown from nominal composition melts under a pressure of 2.0 GPa. Obtained Plate-like single crystal with approximate edge sizes of 160 × 160 × 20 μ m3 was measured on electron probe microanalysis and X-ray diffraction indicate that the as-grown boules are a single phase ZrP1.25Se0.75. Superconducting transition temperature (Tc) is 6.31 K for ZrP1.25Se0.75 single crystal. It also succeeded in single crystal growth of substitution of nonmagnetic rare earth atoms for A (A = Zr) site, Tc = 6.91 K was reached in the (Zr0.50Lu0.50)PSe nominal composition. In this paper, the crystal growth of these compound are also reported.

The relationship between magnetism and magneto-optical effects in rare earth doped aluminophosphate glasses

Aluminophosphate glasses from the Li2O-BaO-Al2O3-P2O5 system with the addition of nonmagnetic and paramagnetic rare earth ions, were prepared using a wet nonconventional method to process the raw materials, followed by a melting–quenching procedure. The glasses obtained were characterized with respect to their magnetic and magneto-optical properties using superconducting quantum interference device magnetometry and spectroscopic ellipsometry. The assumption of a linear dependence of the Verdet constant on the magnetic susceptibility, with a proportionality constant dependent on the type of vitreous matrix and doping ion, is critically discussed. The diamagnetic and paramagnetic contributions to the Faraday rotation were separately analyzed and specific designs for optimal active and passive elements are proposed.

Magnetic and thermal property studies of RCrTeO6 (R=trivalent lanthanides) with layered honeycomb sublattices

We have investigated the magnetic ordering of the RCrTeO6 (R=Y, La, Tb and Er) samples comprising Cr3+ (S=3/2). The X-ray diffraction structure analysis revealed that all samples are a hexagonal structure with the space group P 3¯. The magnetic susceptibility χ(T) and heat capacity CP(T) measurement results reveal that both short range and long range antiferromagnetic (AFM) orderings exist in non-magnetic rare earth R=Y and La compounds. For isostructural compounds of R=Tb and Er, CP(T) curves show long range ordering at the same temperature as non-magnetic R=Y, which indicates that the super-super exchange of Cr spins dominates. For R elements of Tb and Er with large spins sitting between honeycomb sublattices composed of CrO6–TeO6 octahedra, the two sublattices of R and Cr appear to be independently magnetic.

Non-linear behavior of coercivity to the maximum applied magnetic field in La substituted nanocrystalline cobalt ferrite

The magnetic properties of nanocrystalline cobalt ferrite could be tuned with substituting small amount of non-magnetic rare earth cation at Fe site in cobalt ferrite. The variation in magnetic parameter of samples could also be obtained by measuring its anhysteretic magnetization curve without tailoring its chemical composition. The magnetic parameters such as coercivity, remanent magnetization and saturation magnetization critically depend upon different values of external magnetic fields. In the present study, the anhysteretic magnetization curve of the samples CoFe2−xLaxO4 (x=0.025, 0.05, 0.075 and 0.1) has been recorded and response of coercivity to different maximum values of applied field has been investigated. It has been observed that the response of coercivity to different maximum values of applied field shows non-linear behavior. The analysis of the response of coercivity to different values of applied field in low field regime has been carried out with the help of Rayleigh laws. The analysis of the plot yields significant information about magnetic anisotropy.

Dilution effect of Ce ion in CeRu2Al10

CeRu2Al10 causes a mysterious phase transition at T0∼27 K In order to examine the feature of this transition, we have measured the magnetic susceptibility and electrical resistivity of Ce1-xRxRu2Al10 (R=La, La0.63Y0.37, Y) system in which Ce ions in CeRu2Al10 are replaced by non-magnetic rare earth ions with different ionic radii, where the relationship among the ionic radii is La3+ > (***La0.63Y0.37)3+ ∼ Ce3+ > Y3+.*** The magnitude of the magnetic susceptibility becomes smaller with decreasing ionic radii, indicating Kondo temperature increases due to the chemical pressure effect. In the La- and La0.63Y0.37-substituted system, T0 decreases monotonically and disappears smoothly at x∼0.7, while in the Y-substituted system, T0 decreases more slowly and disappears suddenly between x=0.4 and 0.5. These behaviors cannot be understood by a simple magnetic phase transition, suggesting that the change in valence of Ce ion plays an important role in the mysterious phase transition.

Probing the precursor Cooper pairs in superconductors with magnetic impurities

The magnetization induced by superconducting fluctuations, Δ M, has been measured as a function of temperature above T C in La and in La alloyed with magnetic (Pr) and nonmagnetic (Lu) rare earths. It is found that while for pure La and La–Lu alloys Δ M( T) agrees, as expected, with the predictions based on the conventional Gaussian–Ginzburg–Landau approach, it is much larger for La–Pr alloys (about 500% for impurity concentrations 2 at.%). These results suggest that the presence of the superconducting Cooper pairs could modify the interaction between the magnetic ions, leading to an indirect contribution to Δ M.

Electronic band structure of the borocarbide superconductor LuNi2B2C

We present de Haas–van Alphen (dHvA) measurements of the nonmagnetic rareearth borocarbide superconductor LuNi2B2C which have been performed by using a torque cantilever for temperatures down to 0.45K and in magnetic fields up to 32.5T. We mapped the dHvA oscillations of a high-quality single crystal by rotating between all three principal crystallographic axes [100], [001], and [110]. This set of data gives a complete overview of the electronic band structure of LuNi2B2C. A comparison with band-structure calculations allowed us to assign the dHvA frequencies to individual bands. Overall positions and band dispersions resemble those observed in the isostructural compound YNi2B2C, which is another nonmagnetic member in the family of the borocarbide superconductors.

Ferromagnetism, superconductivity and secondary phases in the dilute magnetic semiconductor Pt{sub 1-x}RE{sub x}Sb{sub 2} (RE = La, Ce, Gd, Yb)

We have measured the electrical transport, heat capacity, and magnetic properties of single crystals of semiconducting PtSb{sub 2}, doped with rare earth ions. Carrier concentrations in the doped crystals range from 10{sup 17} to 10{sup 20} cm{sup -3}, and in most cases, metallic resistivity was observed. Moment densities of 10{sup 20}-10{sup 23}{mu}{sub B}/cm{sup 3} were found for crystals doped with magnetic rare earths, and diamagnetic behavior for those doped with non-magnetic rare earths. Weak superconductivity and ferromagnetic order were observed separately in many of the doped crystals, and electron microscopy studies reveal that they likely originate with secondary surface phases. Accordingly, surface etching suppressed both the ferromagnetic and superconducting behaviors. Nonetheless, electrical transport and heat capacity measurements of the doped crystals suggest that the bulk electronic properties are modified relative to stoichiometric PtSb{sub 2}, making this a potentially interesting system for studying magnetism in a low carrier density environment.

Ferromagnetism, superconductivity and secondary phases in the dilute magnetic semiconductor Pt 1−xRE xSb 2 (RE = La, Ce, Gd, Yb)

We have measured the electrical transport, heat capacity, and magnetic properties of single crystals of semiconducting PtSb 2, doped with rare earth ions. Carrier concentrations in the doped crystals range from 10 17 to 10 20 cm −3, and in most cases, metallic resistivity was observed. Moment densities of 10 20–10 23 μ B /cm 3 were found for crystals doped with magnetic rare earths, and diamagnetic behavior for those doped with non-magnetic rare earths. Weak superconductivity and ferromagnetic order were observed separately in many of the doped crystals, and electron microscopy studies reveal that they likely originate with secondary surface phases. Accordingly, surface etching suppressed both the ferromagnetic and superconducting behaviors. Nonetheless, electrical transport and heat capacity measurements of the doped crystals suggest that the bulk electronic properties are modified relative to stoichiometric PtSb 2, making this a potentially interesting system for studying magnetism in a low carrier density environment.

Electrical conductivity of ThMn12- and Th2Zn17-type ternary intermetallic compounds in R–T–Al systems (R=Y, La, Ce, Gd, Tb; T=Mn, Fe)

Electrical resistivity measurements in the temperature range 1.5–300K were performed for ThMn12 and Th2Zn17 structure type RMnxAl12−x and R2MnxAl17−x (R=Y, La, Ce, Gd, Tb; T=Mn, Fe) ternary intermetallic compounds. There is a correlation between the ordering of the crystal structure and the type of the electrical conductivity in R–Mn–Al ternaries. Hopping conductivity in terms of variable range hopping (VRH) occurs in RMnxAl12−x (structure type ThMn12) and R2MnxAl17−x (structure type Th2Zn17) aluminides with disordered or partially ordered crystal structure, both for magnetic and nonmagnetic rare earths. Only for the RMn4Al8 stoichiometry with an ordered distribution of atoms, the resistivity exhibits metallic-type behavior. The presence of magnetic Fe atoms suppresses hopping conductivity in R–Fe–Al ternaries, evidencing that the 3d-element has a predominant influence on electronic transport in R–T–Al intermetallics.

The effect of thermal treatment on superconductivity in HoNi 2B 2C

We present detailed studies of the dependence of the low-temperature properties of HoNi 2B 2C on the annealing temperature. We could shift the superconducting transition temperature T c reversibly and continuously by changing the thermodynamic state of a sample via thermal treatment. The magnitude of this shift is as large as about 10% of T c. The superconducting transition temperature is correlated with the occurrence and strength of re-entrant behaviour. Upper critical field measurements of two samples annealed at 800°C and 1100°C indicate that the magnetic ordering temperatures are not affected by the thermal treatment. A reversible shift of T c with annealing temperature has also been observed for YNi 2B 2C and LuNi 2B 2C with non-magnetic rare earth ions.