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All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Nickel‐Based Single‐Molecule Catalysts with Synergistic Geometric Transition and Magnetic Field‐Assisted Spin Selection Outperform RuO 2 for Oxygen Evolution

Overcoming slow kinetics and high overpotential in electrocatalytic oxygen evolution reaction (OER) requires innovative catalysts and approaches that transcend the scaling relationship between binding energies for intermediates and catalyst surfaces. Inorganic complexes provide unique, customizable geometries, which can help enhance their efficiencies. However, they are unstable and susceptible to chemical reaction under extreme pH conditions. Immobilizing complexes on substrates creates single‐molecule catalysts (SMCs) with functional similarities to single‐atom catalysts (SACs). Here, in this work, an efficient SMC, composed of dichloro(1,3‐bis(diphenylphosphino)propane) nickel [NiCl 2 dppp] anchored to a graphene acid (GA), is presented. This SMC surpasses ruthenium‐based OER benchmarks, exhibiting an ultra‐low onset and overpotential at 10 mAcm −2 when exposed to a static magnetic field. Comprehensive experimental and theoretical analyses imply that an interfacial charge transfer from the Ni center in NiCl 2 dppp to GA enhances the OER activity. Spectroscopic investigations reveal an in situ geometrical transformation of the complex and the formation of a paramagnetic Ni center, which under a magnetic field, enables spin‐selective electron transfer, resulting in enhanced OER performance. The results highlight the significance of in situ geometric transformations in SMCs and underline the potential of an external magnetic field to enhance OER performance at a single‐molecule level.

in situ geometrical changes↗
DOE OSTI2015

ANALYSIS OF EPR AND FISH STUDIES OF RADIATION DOSES IN PERSONS WHO LIVED IN THE UPPER REACHES OF THE TECHA RIVER

Waterborne radioactive releases into the Techa River from the Mayak Production Association in Russia during 1949–1956 resulted in significant doses to about 30,000 persons who lived in downstream settlements. The residents were exposed to internal and external radiation. Two methods for reconstruction of the external dose are considered in this paper, electron paramagnetic resonance (EPR) measurements of teeth and fluorescence in situ hybridization (FISH) measurements of chromosome translocations in circulating lymphocytes. The main issue in the application of the EPR and FISH methods for reconstruction of the external dose for the Techa Riverside residents was strontium radioisotopes incorporated in teeth and bones that served as a source of confounding local exposures. In order to estimate and subtract doses from incorporated 89,90Sr, the EPR and FISH assays were supported by measurements of 90Sr-body burdens and estimates of 90Sr concentrations in dental tissues by the luminescence method. The resulting dose estimates derived from EPR and FISH measurements for residents of the upper Techa River were found to be consistent: the mean values vary from 510 – 550 mGy for the villages located close to the site of radioactive release to 130 – 160 mGy for the more distant villages. The upper bound of individual estimates for both methods is equal to 2.2 – 2.3 Gy. The EPR- and FISH-based dose estimates were compared with the doses calculated for the donors using the Techa River Dosimetry System (TRDS). The TRDS external dose assessments were based on the data on contamination of the Techa River floodplain, simulation of ai r kerma above the contaminated soil, age-dependent life-styles and individual residence histories. For correct comparison TRDS-based doses were calculated from two sources: external exposure from the contaminated environment and internal exposure from 137Cs incorporated in donors’ soft tissues. The TRDS-based absorbed doses in tooth enamel and muscle were in agreement with with EPR- and FISH-based estimates within uncertainty bounds. Basically, the agreement between the estimates has confirmed the validity of external doses calculated with the Techa River Dosimetry System.

dose reconstruction↗
DOE OSTI2018

Development of a New 4-Amino-1,8-Naphthalimide Derivative as a Fluorescent Probe for Monitoring the Divalent Copper Ion

This article presents the design and synthesis of a new variant of the 4-amino-1,8-naphthalimide fluorescent probe for monitoring the divalent copper ion, Cu{sup 2+}. The probe BRST, functionalized with two propionic carboxylic acid groups in its receptor moiety, demonstrated high selectivity and sensitivity for the detection of Cu{sup 2+} in competitive media of various metal ions in DMSO/HEPES buffer solution (1:1; pH 7.4), with a fluorescence quenching of 75.41%. Besides its good linearity with Cu{sup 2+}, the probe yielded commendable values of the association constant and the detection limit, 5.54 × 10{sup 5} M{sup –1} and 4.33 × 10{sup –9} M, respectively. The quenching of the fluorescence intensity of the sensor in the presence of Cu{sup 2+} ions is attributable to the strong paramagnetic nature of the Cu{sup 2+} ion. The fluorescence 'turn off' behavior of this simple and effective probe was successfully applied for the determination of Cu{sup 2+} levels in untreated water samples, with excellent recovery rates of 98–105.8%.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

A Dual-Target Fluorescent Probe with Response-Time Dependent Selectivity for Cd{sup 2+} and Cu{sup 2+}

A novel fluorescent probe (NT) was developed by merging 2-hydrazinylbenzothiazole with 2-hydroxy-1-naphthaldehyde for the detection of Cd{sup 2+} and Cu{sup 2+}. The probe alone is almost nonfluorescent due to the isomerization of C=N in the excited state. The addition of Cd{sup 2+} can cause an immediate strong green fluorescence owing to the suppression of C=N isomerization by Cd{sup 2+}-coordination. Furthermore, NT gives a delayed turn-on fluorescence response to Cu{sup 2+} although it is a vigorous fluorescence quencher, which was thanks to the inhibition of the electron transfer between excited fluorophore and paramagnetic Cu{sup 2+} by sulfur donor. Based on fluorescence spectra and ESI-MS analysis, the binding modes between NT and Cd{sup 2+}/Cu{sup 2+} were proposed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Comparative Magnetic and Structural Properties Study of Micro- and Nanopowders of Nd{sub 2}Fe{sub 14}B Doped with Ni

Micropowders of melted and heat-treated Nd{sub 16}(Fe{sub 76−x}Ni{sub x})B{sub 8} alloys system, with x = 0, 10, 20, and 25 (size distribution under 20 μm), were studied and compared with the study of nanopowders obtained, from the previous ones, by surfactant-assisted ball-milling process during 2 h. By XRD, a majority of Nd{sub 2}Fe{sub 14}B hard phase and a minority of α-Fe, Nd{sub 1.1}Fe{sub 4}B{sub 4} and NdNi{sub 2} phases were detected. The last one increases with Ni content. The crystallite size of the hard phase, in both types of samples, is not affected by the Ni content; however, the grains in micropowders are oblate, with a mean size of 37 nm, while those of the nanopowders are symmetric, with a mean size of 35 nm. Mössbauer spectra were fitted with seven sextets, which correspond to the six ferromagnetic sites of the hard phase and that of the α-Fe, and a doublet corresponding to the paramagnetic Nd{sub 1.1}Fe{sub 4}B{sub 4} phase. The mean hyperfine magnetic field, for both types of samples, decreases with Ni content. The hysteresis loops of both types of samples show a hard magnetic character, however, the coercive field and the M{sub r}/M{sub s} values for nanopowders are greater than those obtained for micropowders for all the Ni contents. Values of H{sub c} = 2 kOe and M{sub r}/ M{sub s} = 0.54 were obtained for nanopowders with 10 at.% Ni. From the hysteresis loops, which include the initial magnetization curve, Henkel plots for all the samples were obtained. These plots show that for micropowders, the predominant magnetic interaction is of dipolar type, while for nanopowders, the ferromagnetic exchange is the predominant one, which favored the magnetization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

First-principles Calculations of Structural, Magnetic Electronic and Optical Properties of Rare-earth Metals TbX (X=N, O, S, Se)

The structural, magnetic, electronic and optical properties of Terbium-based binaries (TbX) (X = N, O, S and Se) in two cubic structures NaCl and CsCl have been investigated. This study is carried out by Full-Potential linearized Muffin-Tin orbitals (FP-LMTO) method in the framework of the functional theory of density (DFT) implemented in the lmtart code. The presence of f-state electrons in these induced high-correlation materials led us to study these systems using local density approximation (LDA) for the paramagnetic state and spin local density approximation (LSDA) for the ferromagnetic state within two cubic structures. We have demonstrated that these binaries are stable in the ferromagnetic state in the cubic phase of NaCl, which allows us to deduce the magnetic moments of these components. From the electronic band structures and density states, we have concluded that TbX (X = N, O, S and Se) are metallic in the NaCl phase. The results obtained in this work show that the theoretical parameters of the ground state, structure of the bands, density of the states (DOS) and optical properties agree well with other available theoretical and experimental data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetization in Nanocrystalline PLD Zinc Ferrite Thin Films Deposited on Fused Quartz Substrate

The nanocrystalline zinc ferrite (ZnFe{sub 2}O{sub 4}) thin films were grown on the fused quartz substrate using pulsed laser deposition. The effects of atmospheric conditions on structural, magnetic, and morphological properties have been systematically studied using X-ray diffraction, vibrating sample magnetometry, and atomic force microscopy. The films showed textured growth of zinc ferrite for the substrate temperatures at ≥ 600 °C irrespective of the ambient environment. Interestingly, thin films of zinc ferrite showed a magnetic hysteresis loop in contrast to the paramagnetic nature of their bulk counterpart. The value of saturation magnetization (4πM{sub s}) increased from 130 to 360 G when the substrate temperature was increased from room temperature (RT) to 800 °C in the oxygen atmosphere. In the absence of oxygen pressure, the value of 4πM{sub s} is observed to be 330 G for the film deposited at RT and found to increase to a value of 670 G when the film is deposited at 400 °C and the maximum value of 2580 G is observed for the film deposited at 700 °C. However, the value of 4πM{sub s} of 800 °C dropped down to 2000 G.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Influence of Ag Substitution on Structural, Critical Behavior and Magnetocaloric Characteristics in La{sub 0.5}Ca{sub 0.5−x}Ag{sub x}MnO{sub 3} (0 ≤ x ≤ 0.1) Systems

Based on the modified Arrott plots and the critical isotherm analysis, the critical exponents of both La{sub 0.5}Ca{sub 0.5}MnO{sub 3} and La{sub 0.5}Ca{sub 0.4}Ag{sub 0.1}MnO{sub 3} systems have been comprehensively studied and investigated near the paramagnetic-ferromagnetic (PM-FM) phase transition. Critical exponents, β, γ, and δ, which are corresponding to the thermal variation of the spontaneous magnetization, initial susceptibility, and the isothermal magnetization, respectively, obeyed the Widom scaling law δ = 1 + γ/β. It indicates thus the validity the obtained results. We performed then another analysis of the critical behavior via the magnetocaloric effect presenting an accord with the analysis of magnetization measurements. Relative cooling power (RCP) follows the evolution of the magnetic field as RCP ∼ H{sup 1+1/δ}. The acquired critical exponents were in conformity with those gotten from the modified Arrott plots and Widom scaling law.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Half-Metallic Ferrimagnetic Characteristics of Co{sub 2}YZ (Z = P, As, Sb, and Bi) New Full-Heusler Alloys: a DFT Study

The full-Heusler alloys Co{sub 2}YZ (Z = P, As, Sb, and Bi) were investigated by using the state-of-the-art full-potential linearized augmented plane wave plus local orbital (FP-LAPW + lo) method within the framework of density functional theory (DFT), to understand the structural, electronic, and magnetic properties of these new Heusler alloys. The generalized gradient approximation (GGA) was chosen to define the exchange-correlation potential for studying the structural properties, whereas electronic and magnetic properties were developed by using the GGA + U scheme, where U is the Hubbard term, which explains the Coulomb repulsion and was applied to describe the “d” electrons. The structural properties indicated that the ferromagnetic states of these compounds are energetically more favorable than the paramagnetic states. Through results on the electronic structures (band structures and densities of states), it is found that all these alloys exhibit a complete half-metallic nature, with half-metallic gaps (E{sub HM}) of 0.632, 0.605, 1.223, and 0.922 eV for Co{sub 2}YP, Co{sub 2}YAs, Co{sub 2}YSb, and Co{sub 2}YBi alloys, respectively. The magnetic properties indicated that the total spin magnetic moments of these Heusler alloys obey the Slater-Pauling rule around value 2 µ{sub B} approximately. The local magnetic moments of Co and Y transition elements have opposite signs with different intensities, thus revealing the ferromagnetic character. Our study of both electronic and magnetic properties demonstrates in detail that Co{sub 2}YZ (Z = P, As, Sb, and Bi) full-Heusler alloys are complete half-metallic ferrimagnetic materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Small Fe Content on the Structure, Magnetic and Magnetocaloric Properties of SmNi{sub 3−x}Fe{sub x} (x = 0; 0.3 and 0.8) Intermetallic Compounds

The SmNi{sub 3−x}Fe{sub x} (x = 0; 0.3 and 0.8) were synthesized by arc melting and annealed at 1073 K for 1 week. The Rietveld refinement showed that these compounds crystallize in the PuNi{sub 3}-type structure (R3̄m-Space group) and the substitution of nickel by iron leads to an increase of the unit cell volume. The Curie temperature (T{sub C}) of the SmNi{sub 3−x}Fe{sub x} (x = 0; 0.3 and 0.8) samples increases from 60 K for SmNi{sub 3} to 230 K for SmNi{sub 2.2}Fe{sub 0.8}, the enhancement of T{sub C} is ruled by electronic and magnetovolumic effects. All the samples exhibit a second-order magnetic phase transition at Curie temperature T{sub C}. The magnetic entropy change ΔS{sub M} was estimated from isothermal magnetization curves and it decreases with the increase of Fe content from 2.3 J/kg.K (x = 0) to 0.6 J/kg.K (x = 0.8) at 50 kOe. The critical properties of SmNi{sub 2.7}Fe{sub 0.3} (as an example) intermetallic compound at the ferromagnetic-paramagnetic (FM-PM) transition have been analyzed. The estimated critical exponents derived from the magnetic data using various methods such as modified Arrott plot, Kouvel-Fisher method and critical magnetization isotherms M(T{sub C}, H). The critical exponent values for the material are in a close agreement with those predicted for the mean-field theory. The reason for this behavior may be long-range interactions between spins in this system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Mn Doping on the Structural, Magnetic, and Magnetocaloric Effect of Fe{sub 17}Dy{sub 2} Compounds

Crystal structural and magnetic properties of polycrystalline (Fe{sub 1−x}Mn{sub x}){sub 17}Dy{sub 2} (x = 0.0, 0.1, 0.2, and 0.3) compounds were studied by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) measurements. The results show that (Fe{sub 1−x}Mn{sub x}){sub 17}Dy{sub 2} forms as a substitutional solid solution with the hexagonal Th{sub 2}Ni{sub 17} type. The unit cell volume increases with Mn content. The Curie temperature (T{sub C}) can be tuned from 364 K for x = 0.0 to 80 K for x = 0.3. The magnetic transition at T{sub C} is a typical second-order ferromagnetic-paramagnetic transition. For an applied field change from 0 to 5 T, the maximum magnetic entropy change (| − ΔS{sub M}|) for (Fe{sub 1−x}Mn{sub x}){sub 17}Dy{sub 2} (x = 0.0, 0.1, and 0.2) compounds are 3.9, 2.8, and 1.7 J kg{sup −1} k{sup −1}, respectively. The high ΔS{sub M}, appropriate T{sub C}, and a high performance-to-cost ratio make (Fe{sub 1−x}Mn{sub x}){sub 17}Dy{sub 2} compounds a candidate materials for room-temperature magnetic refrigeration applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Stability, Magnetism and Hardness of Iron Carbides from First-Principles Calculations

The stability, electronic structure, magnetism and hardness of iron carbides in eight different space groups were investigated by the first-principles calculations. The electron-ion interactions were modelled using the Vanderbilt ultra-soft pseudopotentials (USPP) and norm-conserving pseudopotentials (NCPP). Generalized gradient approximation (GGA) in the Perdew-Burke-Ernzerhof (PBE) formulation was used to describe the exchange-correlation energy. The calculated lattice parameters for USPP were in good agreement with experimental results. The formation enthalpy, cohesive energy and elastic constants revealed that with the exception of hex-Fe{sub 2}C, all Fe-C compounds were both thermodynamically and mechanically stable. Meanwhile, the iron carbides’ bulk and shear moduli were also calculated and compared. Furthermore, magnetic properties were studied and it was found that the average magnetic moment of Fe{sub 23}C{sub 6} (2.123 μ{sub B}) was the largest among these compounds, with a value close to that of pure α-Fe (2.24 μ{sub B}μ. As expected, hex-Fe{sub 2}C is a paramagnetic metal based on the obtained densities of states and partial densities of states. Furthermore, the magnetic behaviour of iron carbides with polymorphic transformation was almost identical. Finally, several semi-empirical methods were used for estimating the hardness of the iron carbides.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Sodium Doping on Magnetic and Magnetocaloric Properties of La{sub 0.65}Sr{sub 0.35}MnO{sub 3} Manganites

A series of Na-doped manganites La{sub 0.65}Sr{sub 0.35−x} Na{sub x}MnO{sub 3} (x = 0.20, 0.25, 0.30, and 0.35) were synthesized via sol-gel method. The structural, magnetic, and magnetocaloric properties of the samples were investigated by XRD, TEM, Raman spectroscopy, and magnetization measurement. Rietveld refinements of XRD patterns shown that samples were single phase with a space group R-3c. The variation of magnetization versus temperature in a magnetic applied field demonstrated a phase transition from ferromagnetic to paramagnetic. The value of T{sub C} decreased from 345 to 330 K when x increases from 0.20 to 0.35. Arrott plots shown that all samples exhibit a second-order magnetic phase transition. The maximum absolute values of the magnetic entropy change were found to be 0.91, 0.93, 1.12, and 1.10 J/kg for x = 0.2, 0.25, 0.3, and 0.35, respectively. Moreover, relative cooling power has been discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Mixed Spin (1, 5/2) Ising Ferromagnetic Blume-Capel Model Under Time-Dependent Sinusoidal Magnetic Field: an Effective-Field Theory Analysis

Non-equilibrium magnetic properties are studied in a two-dimensional mixed spin (1, 5/2) Blume-Capel Ising system under the influence sinusoidal magnetic fields using the effective-field theory based on a decoupling approximation. A dynamic equation of motion has been solved for a square lattice by utilizing a Glauber-type stochastic process. Dynamic phase diagrams are presented in the reduced magnetic field amplitude and reduced temperature plane (h,T) and reduced crystal-field and reduced temperature plane (Δ,T). We observe that the system exhibits dynamic tricritical behaviors. Phase diagrams contain the paramagnetic (p), ferrimagnetic (i), and coexistence or mixed-phase regions, namely the i,p, and i + p, which strongly depend on the crystal-field interaction parameter and oscillating magnetic field frequency. We have found that the system only exhibits a second-order transition line in the higher-frequency region. We have also compared our result with the mean-field prediction in order to indicate the effects of correlations and found that some of the dynamic first-order phase lines disappeared.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Investigation of Superparamagnetism in Microwave and Conventional Processed Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} Nanoparticles

Nanoparticles of spinel cubic Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} are first prepared by the coprecipitation method and then subjected to conventional solid-state sintering and microwave processing techniques. Particle sizes are estimated by field emission scanning electron microscopy (FESEM) to be in the nanometer (5–13 nm) range. Transmission electron microscopy (TEM) also supports the FESEM data. The magnetization measurement by vibration sample magnetometry of the conventionally sintered sample shows a paramagnetic nature at room temperature, a superparamagnetic behaviour at low temperature, and a ferromagnetic nature at even lower temperature. The blocking temperature is estimated to be nearly 110 K. Microwave-processed samples show a superparamagnetic nature even at room temperature. The Fe{sup 3+} cations are found at both the sites confirmed by X-ray photoelectron spectroscopy (XPS), are prepared by microwave processing, and have better magnetic properties as compared to the conventionally sintered particles.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The Mean-Field Theory for the Study of the Magnetocaloric Effect of Nd{sub 0.67}Ba{sub 0.33}Mn{sub 0.98}Fe{sub 0.02}O{sub 3} Manganite

In this paper, we exploit the mean-field theory and the Bean-Rodbell model to justify the magnetocaloric effect (MCE) on Nd{sub 0.67}Ba{sub 0.33}Mn{sub 0.98}Fe{sub 0.02}O{sub 3} manganite. The modeling of magnetic properties was investigated. The Bean-Rodbell equation of state leads the system to second-order ferromagnetic (FM)-paramagnetic (PM) phase transition. The expressions describing the magnetic entropy change under the influence of magnetic field have been derived. A large magnetic entropy has been observed in our sample with a peak centered on the Curie temperature. The theoretical calculations are compared with experimental behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Hydrogen Annealing Effect on the Magnetic Properties of ZnCoO/MoS{sub 2} Hybrid

The ZnCoO/MoS{sub 2} hybrid is successfully synthesized through a general and facile process. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectra reveal that the hybrid consists of wurtzite ZnCoO and few layers of MoS{sub 2}, which shows a paramagnetic property. In contrast, the hybrid presents clear magnetic hysteresis at room temperature with a H{sub 2} post-annealing process. No Co metal nanoclusters can be identified by XRD and HRTEM. The red shift of E{sub 2g}{sup 1} and A{sub 1g} peak indicates the strain effect induced by H{sub 2} annealing. On the other hand, the disappeared peak at 477 cm{sup −1} can be ascribed to the modification of the interface and surface state of the ZnCoO. Temperature-dependent Raman spectroscopies demonstrate the significant H{sub 2} annealing effect on the structural properties of ZnCoO/MoS{sub 2} hybrid. The interplay between the electron interaction at the interface and oxygen vacancies of ZnCoO can be responsible for the magnetic properties of the ZnCoO/MoS{sub 2} hybrid. The tunable magnetic properties have a promising application in multifunctional MoS{sub 2}-based semiconductor and spintronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Lattice Location Effect of Ni{sub 50}Mn{sub 36}Sn{sub 14} Heusler Alloy

The magnetic properties of Ni{sub 50}Mn{sub 36}Sn{sub 14} Heusler alloy with L{sub 21} structure (L{sub 21}-NiMnSn HA) are investigated by using the Kaneyoshi approach (KA) within the effective field theory. Mn atoms have two different magnetic properties, and Sn atoms also have two different magnetic properties, according to the lattice location. The L{sub 21}-NiMnSn HA and its components (Mn1, Mn2, Sn1, Sn2, and Ni) exhibit a second-order phase transition from the ferromagnetic phase to the paramagnetic phase at T{sub C} = 2.824. The magnetizations of the HA are obtained as Sn2 > Ni > Mn2 > L{sub 21}-NiMnSn HA > Sn1 > Mn1 at T < T{sub C}. We suggest that the magnetizations of the HA decrease from that of its core atom to its corner atoms. We refer to the different magnetization behavior of the Mn atoms and the Sn atoms of the HA as “lattice location effect (LLE)” because the magnetic difference of the Mn atoms and the Sn atoms of the HA results from their lattice location on the L{sub 21} structure. While the coercive fields are the same with each other, their remanence magnetizations are different. Our theoretical results of M(T) and M(H) of L{sub 21}-NiMnSn HA are in quantitatively good agreement with some experimental results of NiMnSn alloys. Furthermore, the magnetization critical exponent is obtained. Its value is in good agreement with some experimental results and the mean field theory. This case indicates that the model exhibits a universal critical behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗