Increasing Ho Content Research Articles

High-field magnetic and magnetocaloric properties of pseudo-binary Er1−xHoxNi2 (x = 0.25–0.75) solid solutions

Hydrogen is quickly becoming a desired type of fuel, however, the energy and cost required for liquefaction using today’s cooling technology is excessively high. Magnetic cooling based on the magnetocaloric effect is an energy-efficient and environmentally friendly alternative to commonly used vapor compression, but improvements in refrigerants are crucial for this technology to succeed. Polycrystalline Er1−xHoxNi2 (x = 0.25, 0.5, 0.75) Laves-phase solid solutions obtained by the arc-melting method have been investigated due to their potential for low-temperature refrigerants. Er0.75Ho0.25Ni2 and Er0.5Ho0.5Ni2 crystallize in cubic Laves phase superstructure (space group F-43 m), while Er0.25Ho0.75Ni2, similarly to the initial ErNi2 and HoNi2 binary compounds, crystallizes with the formation of the regular cubic C15 structure (space group Fd-3 m). To evaluate how the structure affects magnetic and magnetocaloric properties, studies in a wide magnetic field range, up to 14 T, were conducted. Measurements show all samples obey the second-order magnetic phase transition from ferromagnetic to paramagnetic state, and their Curie temperatures increase with increasing Ho content from 8 K for Er0.75Ho0.25Ni2 to 12.3 K for Er0.25Ho0.75Ni2. At higher temperatures, all solid solutions are Curie-Weiss paramagnets. However, it has been observed that the formation of the superstructure with lower translational symmetry seems to affect magnetic moments and magnetic entropy values. Er0.25Ho0.75Ni2, with the regular cubic C15 structure, showed the highest entropy changes of 43.5 J/kgK around 12 K, while Er0.75Ho0.25Ni2 and Er0.5Ho0.5Ni2, with cubic superstructure, provided ∼30 % lower results of 30.3 and 35.1 J/kgK, around 8 and 10 K, respectively, for magnetic field change of 14 T. Nevertheless, relatively large and reversible values of magnetic entropy prove that these compounds can be promising candidates for magnetic cooling operating within the low-temperature range needed for hydrogen liquefaction.

Magnetocaloric prospects of mutual substitutions of rare-earth elements in pseudobinary Tb1−xHoxNi2 compositions (x = 0.25–0.75)

As the magnetocaloric characterization of polycrystalline Tb1−xHoxNi2 intermetallic compounds (with x = 0.25, 0.5, and 0.75), their relative cooling power (RCP) and refrigerant capacity (RC) are estimated based on comprehensive investigations of the magnetic and thermodynamic properties of the compositions, the structure of which was studied in detail by x-ray diffraction analysis and scanning electron microscopy. The taken x-ray diffraction patterns demonstrate the similarity between the Ho-depleted compound (x = 0.25) and the parent TbNi2 and HoNi2 compounds, i.e., the regular C15 cubic structure forms in them, whereas, in the case of x = 0.5 and 0.75, the C15-based superstructure is found.Both magnetic and heat capacity measurements showed that all of the studied compounds exhibit the transition from the ferromagnetic to paramagnetic state, which is confirmed to be the second order magnetic phase transition with the Curie temperature that decreases from 31.1 to 18.6 K in passing from the Tb-enriched Tb0.75Ho0.25Ni2 to the Ho-enriched Tb0.25Ho0.75Ni2 composition.The high values of RCP and RC are shown can be reached for the compositions and experimentally are demonstrated based on the performed measurements of magnetic and thermodynamic parameters. Under an external magnetic field change of 0–5 T, the maximum magnetic entropy change -ΔSmag for the Tb1−xHoxNi2 compounds increases from 13.9 to 19.5 J/kgK as x increases from 0.25 to 0.75. These experimental results are compared with and confirmed by available theoretical data. The maximum adiabatic temperature change ΔTad for Tb0.75Ho0.25Ni2 and Tb0.5Ho0.5Ni2 at the 2 T magnetic field change reaches 3.0 K, and substantially increases, namely, to 4.5 K in the case of the Tb0.25Ho0.75Ni2 composition near its Curie temperature TC. The effect of increasing Ho content in the Laves-phase compounds on their magnetic and magnetocaloric properties is discussed.

Enhanced Microwave Absorption Property of Ho–Ce–Co Alloy

In this study, HoxCe2–xCo17 (x = 0, 0.2, 0.6, 1.0) powders were fabricated by melting and ball milling successfully. The influence of Ho content on phase structure, morphology, electromagnetic parameters and microwave absorbing property is examined by relevant equipment. The consequences revealed that the addition of Ho content has no effects on the main phase Ce2Co17 and there is a decrease in particle size. As a whole, the minimum absorption peak frequency shifts to a lower frequency with increasing Ho content. The minimum reflection loss (RL) value of Ho0.6Ce1.4Co17 can reach –42.99 dB at 6.48 GHz with the thickness of 2.0 mm and the bandwidth of RL < –10 dB achieve 1.6 GHz. With the different thicknesses of 1.5 to 3.5 mm, the minimum RL value of Ho0.6Ce1.4Co17 powder is less than –15 dB in the whole C-band (4–8 GHz), and the Ho0.6Ce1.4Co17 powder can achieve the minimum RL of –12.74 dB at 3.6 GHz with the thickness of 3.5 mm in the S-band (2–4 GHz). These results indicate that the Ho–Ce–Co alloy has better potential to be applied in broadband and low frequency with better absorbing properties.

Structural and magnetic properties of charge-ordered La0.5-xHoxCa0.5MnO3 (0≤x≤0.15)

We investigate the effect of holmium substitution on the structural and magnetic proprieties of La0.5-xHoxCa0.5MnO3 (0 ≤ x ≤ 0.15) manganites synthesized by sol-gel method. The structural analysis shows that all the holmium-based samples are single phase and crystallize in the orthorhombic structure with Pnma space group. The magnetic characterization have shown that increasing Ho content leads to the weakening of ferromagnetic interaction in favor of charge ordering which changes its magnetic nature from antiferromagnetic to paramagnetic. In addition, a suppression of the spin-glass like state is induced by the increase in Ho concentration. All the studied compounds are characterized by magnetic phase separation phenomenon.

Effects of Ho addition on thermal stability, thermoplastic deformation and magnetic properties of FeHoNbB bulk metallic glasses

The influences of Ho addition on the thermal stability of supercooled liquids, thermoplastic deformation as well as mechanical and soft-magnetic behaviors of Fe71-xHoxNb6B23 bulk metallic glasses (BMGs) were investigated. With increasing Ho content from 1 to 5 at. %, the supercooled liquid region (SCLR) increased from 48 to 90 K, and the thermal stability is largely enhanced through remained chemical short- or medium-ordering. Combined with the competitive formation process of the complex Fe23B6 and Ho2Fe14B phases, the glass-forming ability (GFA) of the alloy system was improved, allowing for the fabrication of glassy rods up to 3 mm in diameter. Due to the large SCLR and GFA, the Fe66Ho5Nb6B23 BMG with high fracture strength of 3.45 GPa shows outstanding thermoplastic forming ability accompanied with good soft magnetic performance.

Effects of Ho content on microstructures and mechanical properties of Mg-Ho-Zn alloys

In this work, the microstructures and mechanical properties of as-cast Mg-xHo-2Zn (x = 4, 6 and 8 wt%) alloys have been studied by using optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and tensile test at different temperatures. The Ho element exhibits an influence on the grain refinement of the alloys. Increasing Ho content promotes the formation of long period stacking ordered (LPSO) structure, which changes the mechanical properties of the alloys. As a consequence, the strength of the alloy rises with the increase of Ho addition at room temperature and elevated temperature. However, the elongation of the alloy increases at room temperature but slightly decreases at high temperature when the Ho addition increases. These results are explained from morphology evolution of W-phase and the presence of LPSO phase in different alloys.

Effect of holmium doping on structural, electrical and piezoelectric properties of lead-free (Ba,Ca)(Ti,Sn)O3 ceramics

Lead-free (Ba0.91Ca0.09Sn0.07Ti0.93)O3 (BCST) ceramics, doped with holmium (Ho) in the range 0–1.0 mol%, were synthesized using conventional solid-state sintering method. XRD analyses of these ceramic samples confirm single phase pure perovskite structure. Evidence of Ho3+ substituting Ba2+ via electronic charge compensation exists in the range 0–0.4 mol%, while ionic charge compensation mechanism dominates beyond 0.4 mol%. Crystallite size and lattice strain undergo systematic change, while the room temperature dielectric constant (ert) decreases with increasing Ho content. The Curie temperature Tc and maximum dielectric constant (em) at Tc remain almost unchanged. Remnant polarization (Pr), electromechanical coupling constant (kp) and piezoelectric charge coefficient (d33) exhibit increasing trend with increasing Ho content and reach their maximum values of 8.2 µC/cm2, 25% and 220 pC/N respectively at 1.0 mol% of Ho content. The study reveals that doping of BCST system with appropriate quantity of Ho can improve its ferroelectric and piezoelectric properties.

Correlation between ferromagnetic resonance and densification of RE substituted polycrystalline ferrites

We report the dopant- and size-dependent variations in high-frequency magnetic and electrical transport properties of Ho-substituted Li-Mn polycrystalline ferrites. Thermal stability and phase identification were confirmed by thermal gravimetric analysis and X-ray diffraction experiments. The overall average crystallite size decreased from 29.6 to 17.5 nm, whereas the bulk density increased from 3.47 to 4.29 g/cm3 with increasing Ho content. Ferromagnetic resonance (FMR) measurements at the X-band revealed significant shifts in FMR linewidths and resonance positions as a function of composition. Both, FMR linewidth and porosity, were found to decrease with the systematic addition of Ho from 2538 to 2359 Oe and from 26% to 15.4%, respectively. The substitution of Ho3+ for Fe3+ reduced the net magnetization of the spinel lattice from 53 to 41 emu/g. Electrical measurements revealed that the resistivity is higher in samples with smaller grains possessing a greater number of thin insulating grain boundaries. The activation energy ∆E required for hopping increases from 0.09 to 0.16 eV with Ho addition, which may be well explained by the increase in resistivity. The substitution of Ho3+ for Fe3+ causes a decrease in Curie temperature Tc due to the damping of A-B exchange interactions.

Origin of enhanced multiferroic properties in Bi0.85−xLa0.15HoxFeO3 nanopowders

We report an experimental study of single-phase Bi0.85−xLa0.15HoxFeO3 nanoparticles (BLHxFO-NPs) that synthesized by a sol–gel method. The Rietveld refinement of X-ray diffraction pattern of BLHxFO samples indicate a phase transition from rhombohedral (space group R3c) to orthorhombic (space group Pbnm) structure with increasing Ho content. The bond lengths and angles for all samples were determined which supports the magnetic and electrical results. The average particles size of BLHxFO-NPs has been estimated from field emission scanning electron microscopy (FESEM) images and using a standard log-normal distribution equation. The remnant magnetisation in BLHxFO-NPs increase from 0.09 emu/g for x = 0–0.35 emu/g for x = 0.25 sample at 5 K. In order to clarify origin of magnetisation behaviour in BLHxFO-NPs, a systematic investigation has been performed on the magnetisation of all samples. The frequency (f) and composition (x) dependence of relative dielectric constant (ε) and dielectric loss (tan δ) have been studied for BLHxFO nanoparticles at room temperature. The dielectric properties indicates a local maximum in sample with x = 0.25 while maximum magnetodielectric coefficient occurs in x = 0.35. Simultaneous enhancement in magnetic and dielectric properties can play an important role for the practical applications.

Large magnetocaloric effect in hexagonal Yb1−xHoxMnO3

Magnetocaloric properties of polycrystalline hexagonal Yb1−xHoxMnO3 (x = 0.1, 0.2, and 0.3) compounds are studied through magnetization measurements. Temperature dependence of Zero Field Cooled magnetic moment measurements shows Néel temperature (TN1) of ∼83 K, corresponding to the Mn3+ antiferromagnetic ordering. At low temperatures (TN2 ∼ 5 K), all compounds show ferromagnetic ordering due to alignment of the Yb moments and the field induced magnetic transition is observed in the isothermal magnetization measurements. The maximum entropy change |ΔSMmax| and the relative cooling power (RCP) of Yb1−xHoxMnO3 are 3.75 ± 0.78 J/(mol K) and 90.0 ± 27 J/mol for x = 0.3 at ΔH = 100 kOe. Values of both |ΔSMmax| and RCP found to increase with increasing Ho content.

Magnetic phase diagram of Tb3−xHoxCu4Sn4 system

Magnetic phase diagram of Tb3−xHoxCu4Sn4 was determined on the basis of magnetic and heat capacity data. X-ray diffraction data proved that these compounds crystallize in the orthorhombic Gd3Cu4Ge4-type structure. The compounds are antiferromagnets at low temperatures and the reciprocal magnetic susceptibility obeys the Curie–Weiss law. The paramagnetic Curie temperatures are negative and their absolute values decrease with increasing Ho content. An anomalous concentration dependence of the Néel temperature is observed.

JUDD–OFELT THEORY ANALYSIS AND SPECTROSCOPIC PROPERTIES OF Ho:LiNbO3

A series of Ho : LiNbO 3 crystals with various concentration of Ho 2 O 3 were grown by Czochralski technique. Transmittance spectrum, absorption spectrum and modified Judd–Ofelt approach have been used to investigate its spectroscopic properties. Ho concentrations in crystals were analyzed by an inductively-coupled plasma optical emission spectrometry (ICP-OE/MS). The results of the spectroscopic analysis of transition strengths for Ho ion in a series of Ho : LiNbO 3 crystals with various Ho content are reported. It is concluded that all the Ωλ values of the Ho ion decrease with increasing Ho content. For Ho (4 mol%): LiNbO 3, the obtained intensity parameters and radiative lifetime of the 5 I 5 level are: Ω2=5.75×10-20 cm2, Ω4=22.69×10-20 cm2, Ω6=14.10×10-20 cm2, and τ=4.08 ms respectively. The results showed that the Ho 2 O 3-codoped LiNbO 3 crystal increases the Ho ion radiative lifetimes, but has less influence on the fluorescence branching ratio.

Effect of Ho additions on the microstructure and mechanical properties of Nb-22Ti-16Si-7Cr-3Al-3Ta-2Hf alloys

Abstract The effect of Ho additions on the microstructure and compressive properties of the alloy Nb-22Ti-16Si-7Cr-3Al-3Ta-2Hf (at.%) was investigated by using scanning electron microscopy, X-ray diffraction, transmission electron microscopy and by performing compression tests. The results show that Ho additions cause remarkable microstructural refinement. The addition of 0.1 at.% Ho to the alloy increases its strength and ductility. When the amount of Ho is increased to 0.2 at.%, the strength and ductility decreases. Ho addition inhibits the formation of the (Ti, Nb)5Si3 phase and the amount of the (Ti, Nb)5Si3 phase decreases, even disappears, with increasing Ho content. In addition, the fracture surfaces of Ho-free alloys deformed at room temperature in compression tests exhibit cleavage for both the (Nb, Ti) solid solution and the (Nb, Ti)5Si3 intermetallic compound, while limited local plastic strain of the (Nb, Ti) solid solution is observed in Ho-doped alloys. The effect and mechanism of strengthening and plastic deformation of Ho additions to the alloy was discussed in view of the microstructure.

Structure and magnetic properties of (Nd1−xHox)3Fe23−yCo6Vy compounds

The Ho-substituted (Nd1−xHox)3Fe23−yCo6Vy compounds with x=0–0.9 have been synthesized and their structure and intrinsic magnetic properties have been investigated by x-ray diffraction and magnetic measurements. It is found that all the investigated compounds crystallize in the Nd3(Fe,Ti)29-type structure with monoclinic symmetry and A2/m space group. The unit-cell volume V shows a decreasing tendency with increasing Ho content, reflecting the lanthanum contraction. All the compounds show easy-plan type anisotropy at room temperature. The Curie temperatures Tc are almost independent of the Ho content and the spin reorientation temperature, Tsr, decreases with increasing Ho content from 266 K for x=0 to 127 K for x=0.7. No spin reorientation occurs for x=0.9. The saturation magnetization Ms decreases linearly with increasing Ho content due to the antiferromagnetic coupling between Ho and Nd moments. The anisotropy field Ba increases first, going through a maximum at x=0.5, y=2.0, and then decreases with increasing Ho content.

Magnetic structure and superconductivity in (HoxY1−x)Ni2B2C

The superconducting transition and the magnetic structure of polycrystalline (HoxY1−x)Ni2B2C have been investigated for x⩾0.75 by resistivity measurements and neutron diffraction, respectively. For HoNi2B2C, the well known antiferromagnetic structure with c- and a-axis components existing between 4.5 and 6 K has been confirmed. Whereas for all investigated samples the component having the a-axis modulated structure exists in a narrow temperature range only, the intensity connected to the spiral magnetic state along the c-axis increases for x=0.85 and x=0.75 monotonically as the temperature decreases to the lowest measuring temperature of 1.6 K. Our results strongly suggest that the incommensurate modulated structure along the a-axis is responsible for pair breaking in the investigated (HoxY1−x)Ni2B2C samples. On the other hand, the magnetic spiral structure with c-axis wave vector was found to coexist with superconductivity. A linear suppression of the superconducting transition temperature with increasing Ho content was observed which is in agreement with the Abrikosov–Gor’kov theory. We found a linear scaling with the effective de Gennes factors (x DG) (Ho) for both the superconducting transition and the magnetic ordering temperatures.

Magnetism and superconductivity in (HoxY1−x)Ni2B2C

The pseudoquarternary system (HoxY1−x)Ni2B2C, has been investigated by resistance and magnetization measurements. A linear depression of the superconducting transition temperature Tc found with increasing Ho content is interpreted in the framework of the Abrikosov-Gor'kov theory which predicts also a linear scaling of Tc with the de Gennes factor of the rare earth elementsR of theRNi2B2C family. We found that both cases follow a common linear scaling behaviour including the superconducting transition and the magnetic ordering temperature. A reentrant behaviour observed for Ho contents x≥0.5 results in maxima in the temperature dependence of the upper critical field Hc2(T), which are compared with Hc2(T) data of TmNi2B2C. In the paramagnetic range of field and temperature the sample magnetization can be described by a Brillouin function with a Ho-moment of 10.5μ B.

Magnetic and magnetostrictive properties of Sm 1 − xHo xFe 2

A series of pseudobinary compounds of Sm 1 − x Ho x Fe 2 ( x = 0.0, 0.25, 0.35, 0.45, 0.60, 0.80) have been prepared and investigated. Measurements of X-ray diffraction, magnetization and magnetostriction were carried out on these samples. It is shown that the system retains the cubic MgCu 2 structure over the whole range and the lattice constant a decreases linearly from 7.421 Å for x = 0.0 to 7.307 Å for x = 0.8. The concentration dependence of the saturation magnetization exhibits a minimum at x = 0.35 for 1.5 K and at x = 0.42 for room temperature, reflecting the occurrence of a compensation of the magnetic moment at various Sm:Ho ratios. A compensation of the anisotropy was also observed, while its minimum occurs for x = 0.25 at 1.5 K and for x = 0.35 at room temperature. The Curie temperature T C decreases linearly from 677 K for x = 0.0 to 617 K for x = 0.8, and the magnetostriction declines with increasing Ho content as a result of the compensation of λ 111 of the SmFe 2 and HoFe 2 sublattices in the Sm 1 − x Ho x Fe 2 system.

Normal state and superconducting properties of Bi 2Sr 2Ca 1−xHo xCu 2O y compounds

A series of compounds of the type Bi 2Sr 2Ca 1−xHo xCu 2O y (0≤ x≤1) were prepared by solid state reaction technique. The x-ray diffraction data showed single phase nature of all the samples. The c-lattice parameter and the volume of the unit cell decrease with x. The transition temperature as found from electrical resistivity and magnetic susceptibility measurements increases from 74K for x=0. to 80K for x=0.2 and decreases thereafter. The samples show a semiconducting behaviour for x>0.5. The critical current density as found from magnetisation measurements is seen to decrease with increasing Ho content. The thermopower is negative for x=0 at 250K but becomes positive for x=0.2.

Competing anisotropies and magnetization processes in the pseudoternary (HoxEr1−x)Fe10V2 tetragonal system

A study of temperature and composition dependence of the magnetic anisotropy in the tetragonal (HoxEr1−x)Fe10V2 polycrystalline compounds was made by means of the singular point detection technique. At 293 K the easy magnetization direction lies along the tetragonal c axis [001] in all the samples and the anisotropy field increases linearly with increasing Ho content. However, with decreasing temperature the competition among the anisotropy of the different magnetic sublattices gives rise to a spin reorientation transition axis to cone in Er containing samples. The TSR value increases with increasing Er content. A significant in-plane anisotropy was found in all the compounds. This planar anisotropy is larger in HoFe10V2, where it favors the [100] direction of the basal plane, while in ErFe10V2 the [110] is the preferred direction. The difference between the anisotropy field along [100] and [110] directions was found to decrease with increasing Er content. A first-order magnetization process of type 1 was observed below 120 K in all the compounds when the magnetic field is applied along the [100] direction.