Alternating-current Magnetic Susceptibility Research Articles

Alkyl Chains Modulated Magnetization Dynamics of Mononuclear Trigonal Prismatic CoII Complexes.

Four benzeneboron-capped mononuclear CoII complexes with different alkyl substitutions on the fourth position of phenylboronic acid were obtained. The CoII ions are all wrapped by the pocket-like ligands and located in trigonal prismatic coordination geometries. Alternating-current magnetic susceptibility measurements reveal that they show different magnetization dynamics, such as distinct relaxation rates at the same temperature, the faster QTM rates for the ethyl and propyl substituted complexes, as well as different relaxation processes. Magneto-structural correlation study reveals that the various deviations of coordination geometry of CoII ion, diverse crystal packings and possible different vibration modes of substituents caused by modifying alkyl chains are the key factors affecting the magnetization dynamics. This work demonstrates that the alkyl chains even locating far away from the metal center can have a large impact on the magnetic behavior of the CoII complex with a very rigid coordination geometry, offering a new perspective towards transition metal based single-molecule magnets.

Complex magnetism of single-crystalline AlCoCrFeNi nanostructured high-entropy alloy

We have investigated magnetism of the Al28Co20Cr11Fe15Ni26 single-crystalline high-entropy alloy. The material is nanostructured, composed of a B2 matrix with dispersed spherical-like A2 nanoparticles of average diameter 64nm. The magnetism was studied from 2 to 400K via direct-current magnetization, hysteresis curves, alternating-current magnetic susceptibility, and thermoremanent magnetization time decay, to determine the magnetic state that develops in this highly structurally and chemically inhomogeneous material. The results reveal that the Cr-free B2 matrix of composition Al28Co25Fe15Ni32 forms a disordered ferromagnetic (FM) state that undergoes an FM transition at 390K. The Al- and Ni-free A2 nanoparticles of average composition Co19Cr56Fe25 adopt a core-shell structure, where the shells of about 2nm thickness are CoFe enriched. While the shells are FM, the nanoparticle cores are asperomagnetic, classifying into the broad class of spin glasses. Asperomagnetism develops below 15K and exhibits broken-ergodicity phenomena, typical of magnetically frustrated systems.

A spherical capped square antiprismatic DyIII complex encapsulated three acylhydrazone Schiff base ligands behaving field-induced single-ion magnet behaviour

One mononuclear DyIII based complex, [Dy(L)3]·0·25H2O (1) (HL= N'-(2-hydroxybenzoyl)pyridine-2-carbohydrazonamide) has been successfully synthesized and systematically characterized. Single-crystal X-ray diffraction reveals that 1 crystallizes in the orthorhombic system with space group P/21. The nine-coordinated DyIII ion in 1 adopts distorted spherical capped square antiprism configuration (C4v-CSAPR) with three tridentate coordination pockets. In addition, the alternating-current (ac) magnetic susceptibility investigations show that 1 exhibits slow magnetic relaxation behavior under an applied 1000 Oe field with effective energy barrier (Ueff) of 83.10 K. To understand the magnetic behaviour in depth, the magnetic axes and magneto-structural correlations are analyzed to reveal that the coordination of three ligands effectively enhances the axiality of the nine-coordinated mononuclear DyIII complexes, thereby exhibiting the slow magnetic relaxation behaviour. This work provides a strategy to effectively improve the performance of single-ion magnets (SIMs) by introducing more ligands around the DyIII ion, and regularizing the coordination configuration of the DyIII ion towards an axial-type structure.

Co40Fe40Y20 Nanofilms’ Structural, Magnetic, Electrical, and Nanomechanical Characteristics as a Function of Annealing Temperature and Thickness

To investigate the correlations between different thicknesses and heat treatments, this study used a sputtering method to create CoFeY films. The results of X-ray diffraction (XRD) revealed the appearance of oxide peaks at 2θ = 47.7°, 54.5°, and 56.3° in agreement with YFeO3 (212), Co2O3 (422), and Co2O3 (511), respectively. The findings also demonstrated a relationship between the low-frequency alternative-current magnetic susceptibility (χac) values and the thickness of the CoFeY thin films. At a thickness of 50 nm and an annealing temperature of 300 °C, the ideal value of ac was 0.159. The presence of Y and the thickness impact were both evident in the χac value, which improved spin-exchange coupling as well as grain refining. With increasing thickness, the resistance decreased. At 300 °C and 40 nm in thickness, this film has a maximum surface energy of 31.2 mJ/mm2. The hardness of the 50-nm films reached a maximum of 16.67 GPa when annealed at 100 °C. Due to the high χac, strong adhesion, good nanomechanical properties, and low resistivity, the optimal conditions were determined to be 50 nm with annealing at 300 °C.

Peroxido-bridged chiral double-decker dysprosium macrocycles.

Lanthanide peroxides show high reactivity in oxidative coupling of methane (OCM). However, the number of isolated and structurally characterized molecular species remains relatively small. To the best of our knowledge, homochiral molecule-based lanthanide peroxides have not been reported. Herein, two pairs of side-on peroxido-bridged dinuclear hexaazamacrocyclic dysprosium enantiomers with formulas [Dy2(LES/R)2L2O2](BPh4)2·CH3OH·CH3CN (where LE is derived from the condensation reaction between (1S,2S)/(1R,2R)-1,2-diphenylethylenediamine and 2,6-diformylpyridine; HL = 2,6-diphenylphenol) (1/2) and [Dy2(LES/R)2Cl2O2](BPh4)2·2CH3CN (3/4) are specially designed and created with the help of hydrogen peroxide. The out-of-phase alternating-current magnetic susceptibility of 1/2 gives rise to frequency-dependent peaks between 6 and 32 K under a zero applied direct current (dc) field, while no peak at any temperature and frequency was observed for 3/4 implying the presence of a weak axial crystal field (CF).

The Influence of Oxidation on the Magnetic, Electrical, and Mechanical Properties of Co40Fe40Yb20 Films

A typical body-centered cubic (BCC) CoFe(110) peak was discovered at approximately 2θ = 44.7°. At 2θ = 46°, 46.3°, 47.7°, 55.4°, 54.6°, and 56.4°, the Yb2O3 and Co2O3 oxide peaks were visible in all samples. However, with a heat treatment temperature of 300 °C, there was no typical peak of CoFe(110). Electrical characteristics demonstrated that resistivity and sheet resistance reduced dramatically as film thickness and annealing temperatures increased. At various heat treatments, the maximum hardness was 10 nm. The average hardness decreased as the thickness increased, and the hardness trend decreased slightly as the annealing temperature was higher. The highest low-frequency alternative-current magnetic susceptibility (χac) value was discovered after being annealed at 200 °C with 50 nm, and the optimal resonance frequency (fres) was discovered to be within the low-frequency range, indicating that the Co40Fe40Yb20 film can be used in low-frequency applications. The maximum saturation magnetization (Ms) was annealed at 200 °C for 50 nm. Thermal disturbance caused the Ms to decrease as the temperature reached to 300 °C. The results show that when the oxidation influence of as-deposited and thinner films is stronger than annealing treatments and thicker thickness, the magnetic and electrical properties can be enhanced by the weakening peak of the oxide, which can also reduce interference.

Effect of Annealing and Thickness of Co40Fe40Yb20 Thin Films on Various Physical Properties on a Glass Substrate.

The aim of this work is to investigate the effect of annealing and thickness on various physical properties in Co40Fe40Yb20 thin films. X-ray diffraction (XRD) was used to determine the amorphous structure of Co40Fe40Yb20 films. The maximum surface energy of 40 nm thin films at 300 °C is 34.54 mJ/mm2. The transmittance and resistivity decreased significantly as annealing temperatures and thickness increased. At all conditions, the 10 nm film had the highest hardness. The average hardness decreased as thickness increased, as predicted by the Hall-Petch effect. The highest low-frequency alternative-current magnetic susceptibility (χac) value was discovered when the film was annealed at 200 °C with 50 nm, and the optimal resonance frequency (ƒres) was in the low frequency range, indicating that the film has good applicability in the low frequency range. At annealed 200 °C and 50 nm, the maximum saturation magnetization (Ms) was discovered. Thermal disturbance caused the Ms to decrease when the temperature was raised to 300 °C. The optimum process conditions determined in this study are 200 °C and 50 nm, with the highest Ms, χac, strong adhesion, and low resistivity, which are suitable for magnetic applications, based on magnetic properties and surface energy.

Observation of field-induced single-molecule magnet behavior in an octahedrally coordinated binuclear Co2 compound

A binuclear cobalt compound, namely, [Co2(L)2Cl2(H2O)4]·2Cl·2H2O (1), was synthesized by acylhydrazone Schiff base ligand N3-(4-pyridyl)-4-hydroxybenzoylhydrazone (HL) and CoCl2·6H2O. The crystal structure study suggests that each CoII ion in 1 is surrounded by two nitrogen atoms and one oxygen atom from ligand, one chloride ion and two oxygen atoms from two water molecules, giving rise to six-coordinated geometry, where two N atoms from two ligands as bridges link two CoII ions. The direct-current (dc) magnetic susceptibility measurements reveal the existence of antiferromagnetic coupling interaction in 1. The alternating-current (ac) magnetic susceptibility measurements indicate that 1 exhibits field-induced slow magnetic relaxation behavior with energy barrier (Ueff) of 51.80 K, standing out among Co2-SMMs. This study demonstrates that the large magnetic anisotropy of each CoII ion and the weak antiferromagnetic coupling interaction between two CoII ions can improve Co2-SMMs performance effectively.

LnIII2 compounds constructing by polydentate Schiff base ligand and β-diketonate coligand: structures, magnetocaloric effect and SMMs behaviors

Four new LnIII2 compounds [Ln2(dbm)2(L)2(CH3OH)] (Ln(III) = Gd (1), Tb (2), Ho (3), and Tm (4)), where H2L is 2-hydroxyamino-propionic acid (3,5-di-tert-butyl-2-hydroxy-benzylidene)-hydrazide and Hdbm is dibenzoylmethane, were successfully synthesized via solvothermalmethod and characterized structurally and magnetically. Magnetic studies reveal the anti-ferromagnetic interaction was existed in compound 1. Moreover, magnetic refrigeration property study suggests that compound 1 exhibits magnetocaloric effect with − ΔSm = 21.07 J kg−1 K−1 for ΔH = 7.0 T at 2.0 K. Alternating-current (ac) magnetic susceptibility study of 2 and 3 suggests that single-molecule magnet (SMM) behavior occurs for 2 and 3 under Hdc = 0 Oe with the effective energy barrier ΔE/kB of 20.05 K and τ0 of 2.93 × 10−6 s for 2 and ΔE/kB = 0.85 K and τ0 = 3.47 × 10−5 s for 3.

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe 2 Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe ₂ Co} Coordination Polymers via Metal-to-Metal Charge Transfer

AC magnetic susceptibility and heat dissipation of Zn-doped Mg-ferrite nanoparticles

Mg1-xZnxFe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8) nanoparticles surrounded by amorphous SiO2 were synthesized using the wet chemical method to improve their biocompatibility and magnetization, and for application as a heating medium for hyperthermia therapy. Magnetization was at its maximum for a composition of x = 0.2; this composition was then fixed and the particle size varied between 4 and 25 nm to optimize the heating effect. Analysis by alternating-current (AC) magnetic-susceptibility measurement suggested that particles sized 18 nm generated the most heat, with the system following a Debye relaxation. In the temperature-increase measurement, the maximum amount of heat was dissipated at a particle size of 18 nm, indicating that the system generates enough heat to kill cancer cells under electromagnetic fields that are acceptable to the human body. In an in vitro experiment using human breast cancer cells, we confirmed that hyperthermia suppressed 25% of the cancer cells in 30 min using 18 nm particles.

Effect of Time to Detection on the Measured Concentrations of Blood Proteins Associated with Alzheimer’s Disease

Background: For assays using immunomagnetic reduction, a reagent composed of antibody-functionalized magnetic nanoparticles is dispersed in phosphate-buffered saline solution. The real-time signals of alternating-current (ac) magnetic susceptibility, χ_ac, of the reagent are subsequently recorded after mixing the reagent with a biofluid sample. After mixing the reagent and sample, the reduction in χ_ac of the mixture is calculated and used to quantify the concentration of the target biomarker in the sample. The reduction does not occur immediately but rather occurs at some time after mixing. This observation implies that the time elapsed before recording the real-time signals of χ_ac of a reagent-sample mixture needs to be investigated to ensure that the signals are fully recorded. In this work, the effect of time to detection on the measured concentrations of proteins in human plasma after mixing the reagent and sample is examined. Methods: The proteins analyzed are related to Alzheimer’s disease: amyloid β 1–40, amyloid β 1–42, and Tau protein. The investigated times to detection after the mixing the reagent and sample are 0, 20, 30, 40, and 120 min. Results: The results show that the recording of real-time signals of χ_ac should be conducted within 20 min after mixing the reagent and sample.

A unique terbium-fluoride-oxalate metal–organic framework containing [Tb-F]n chains with bifunctions of luminescent detection of Cr(VI) and catalyzing CO2 conversion to cyclic carbonates

The low cost, including material cost and energy cost, in large-scale production is an important metric for a metal–organic framework (MOF) towards real-world applications. This requires that the MOF can be efficiently synthesized in a high yield under mild enough conditions, while the employed organic ligands should be simple in structure and cheap. Motivated by such consideration, we established our work on a Tb-fluoride-oxalate framework [TbF(C2O4)(H2O)2]n∙2nH2O (1), which meets the requirements stated above. The synthesis of its single-crystal sample and its crystal structure are first reported here. X-ray diffraction test shows 1 has a 3D microporous framework structure constructed by 1D [Tb-F]n chains and C2O42− bridges. In fact, 1 is the unique complex that comprises [Tb-F]n chains. Though [Tb-F]n chain is of great interest in the field of molecular nanomagnets, direct-current and alternating-current magnetic susceptibilities reveal no slow magnetic relaxation behavior in 1. Luminescence investigation reveals that 1 exhibits strong green photoluminescence emission and can be used as a “turn-off” luminescent sensor for toxic Cr2O72− and CrO42− ions in aqueous solution with high selectivity and sensitivity. Besides, the strong Lewis acidity of Tb3+ also makes 1 a good heterogeneous catalyst for the cycloaddition reaction of CO2 with epoxides to cyclic carbonates.

Manipulating Selective Metal-to-Metal Electron Transfer to Achieve Multi-Phase Transitions in an Asymmetric [Fe2 Co]-Assembled Mixed-Valence Chain.

Manipulation of multi-functions in molecular materials is promising for future switching and memory devices, although it is currently difficult. Herein, we assembled the asymmetric {Fe2 Co} unit into a cyanide-bridged mixed-valence chain {[(Tp)Fe(CN)3 ]2 Co(BIT)} ⋅ 2CH3 OH (1) (Tp=hydrotris(pyrazolyl)borate and BIT=3,4-bis-(1H-imidazol-1-yl)thiophene), which showed reversible multi-phase transitions accompanied by photo-switchable single-chain magnet properties and a dielectric anomaly. Variable-temperature X-ray structural studies revealed thermo- and photo-induced selective electron transfer (ET) between the Co and one of the Fe ions. Alternating-current magnetic susceptibility studies revealed that 1 displayed on and off single-chain magnet behavior by alternating 946-nm and 532-nm light irradiation. A substantial anomaly in the dielectric constant was discovered during the electron transfer process, which is uncommon in similar ET complexes. These findings illustrate that 1 provided a new platform for multi-phase transitions and multi-switches adjusted by selective metal-to-metal ET.

A centrosymmetric Dy2 compound derived from acylhydrazone Schiff base ligand exhibiting zero-field single-molecule magnet behavior

Based on acylhydrazone Schiff base ligand (2,3′-Hpcad, N3-(2-pyridoyl)-3-pyridinecarboxamidrazone), a binuclear DyIII compound, [Dy2(2,3′-pcad)2(C6H5COO)4(H2O)2] (1), has been successfully prepared by the hydrothermal synthesis method, and fully characterized by single-crystal X-ray diffraction, elemental analysis, Raman spectra, diffuse reflectance spectroscopy and magnetic property measurement system. Compond 1 exhibits a centrosymmetric binuclear structure bridged by benzoate groups and each eight-coordinated DyIII ion is located in a slightly distorted biaugmented trigonal prism configuration (C2v-BTPR). In addition, alternating-current magnetic susceptibility measurements illustrate that 1 exhibits zero-field single-molecule magnet behavior with the higher effective energy barrier (Ueff) value of 114.0 K compared to other Dy2 compounds with C2v-BTPR configuration. In addition, this study reveals configuration of each DyIII ion and intra-molecular magnetic coupling of two DyIII ions may synergistically effect Dy2-SMMs properties. Furthermore, the band gap energy of 1 is found to be 2.65 eV, which proves 1 could be used as the wide-gap semiconductor.

Crystal structure, magnetic properties and luminescent behavior of four mononuclear lanthanide-radical complexes

Four mononuclear lanthanide complexes based on a long nitronly nitroxide radical NIT-PhOPyrim, [Ln(hfac)3(NIT-PhOPyrim)(H2O)] (Ln(Ⅲ) = Gd 1, Tb 2, Dy 3, Er4; hfac = hexafluoroacetylacetonate; NIT-PhOPyrim = 2-[4-(pyrimidin-2-yloxy)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been synthesized and characterized. Single crystal X-ray diffraction analyses revealed that these four complexes are isomorphic in which each Ln(Ⅲ) ion is eight-coordinated by six oxygen atoms from three hfac ligands, one oxygen atom from one water molecule and one oxygen atom from the NO group of NIT-PhOPyrim ligand. Particularly, the coordinated water molecules were connected other mononuclear units through their hydrogen bonds into tetra-nuclear complexes and/or dimers. Variable temperature magnetization of complex 1 was shown the ferromagnetic interaction between Gd(III) ion and nitroxide radical, while weak intermolecular antiferromagnetic interactions through hydrogen bonds. Alternating-current (ac) magnetic susceptibility of complexes 2–4 revealed no magnetic relaxation behavior. Furthermore, Tb complex can detect Fe3+anion with a high sensitivity and selectivity through the fluorescence quenching effect.

Annealing Effect on the Characteristics of Co40Fe40W10B10 Thin Films on Si(100) Substrate.

This research explores the behavior of Co40Fe40W10B10 when it is sputtered onto Si(100) substrates with a thickness (tf) ranging from 10 nm to 100 nm, and then altered by an annealing process at temperatures of 200 °C, 250 °C, 300 °C, and 350 °C, respectively. The crystal structure and grain size of Co40Fe40W10B10 films with different thicknesses and annealing temperatures are observed and estimated by an X-ray diffractometer pattern (XRD) and full-width at half maximum (FWHM). The XRD of annealing Co40Fe40W10B10 films at 200 °C exhibited an amorphous status due to insufficient heating drive force. Moreover, the thicknesses and annealing temperatures of body-centered cubic (BCC) CoFe (110) peaks were detected when annealing at 250 °C with thicknesses ranging from 80 nm to 100 nm, annealing at 300 °C with thicknesses ranging from 50 nm to 100 nm, and annealing at 350 °C with thicknesses ranging from 10 nm to 100 nm. The FWHM of CoFe (110) decreased and the grain size increased when the thickness and annealing temperature increased. The CoFe (110) peak revealed magnetocrystalline anisotropy, which was related to strong low-frequency alternative-current magnetic susceptibility (χac) and induced an increasing trend in saturation magnetization (Ms) as the thickness and annealing temperature increased. The contact angles of all Co40Fe40W10B10 films were less than 90°, indicating the hydrophilic nature of Co40Fe40W10B10 films. Furthermore, the surface energy of Co40Fe40W10B10 presented an increased trend as the thickness and annealing temperature increased. According to the results, the optimal conditions are a thickness of 100 nm and an annealing temperature of 350 °C, owing to high χac, large Ms, and strong adhesion; this indicates that annealing Co40Fe40W10B10 at 350 °C and with a thickness of 100 nm exhibits good thermal stability and can become a free or pinned layer in a magnetic tunneling junction (MTJ) application.

Polymeric Terbium(III) Squarate Hydrate as a Luminescent Magnet

Polymeric terbium(III) squarate hydrate [{Tb2(C4O4)3(H2O)8}n] was prepared from TbCl3 or Tb2O3 and squaric acid. The crystal structure was determined in a monoclinic Pc space group, and the whole molecular arrangement gives a sandwiched two-dimensional structure. The coordination polyhedra are described as a square antiprism. The solid complex emits green light under UV irradiation at room temperature with the quantum yield of 25%. Although Tb3+ is a non-Kramers ion, the alternating-current magnetic susceptibility showed frequency dependence in a 2000-Oe DC field, and the effective energy barrier for magnetization reorientation was 33(2) K. Thus, [{Tb2(C4O4)3(H2O)8}n] displayed functions of a potential luminescent magnet.

Larger magnetocaloric effect and single molecule magnet behavior in dinuclear Ln(III)-based compounds constructed from Schiff base ligand

A series of Ln(III)-based compounds with the formula [Ln2(HL)2(acac)2(CH3OH)2] (Ln (III) = Gd (1), Tb (2), Dy (3), Ho (4) and Er (5), Hacac = acetylacetone, H3L = 3-hydroxy-N’-[(1E)-(2-hydroxy-3-methoxyphenyl)methylidene]pyridine-2-carbohydrazide) based on a flexible Schiff base ligand H3L have been successfully synthesized, and the structures and magnetic properties of 1–5 have been systematacially studied. The crystal structures study indicates that compounds 1–5 are isostructural and possess a parallelogram Ln2O2 core. Magnetic properties measurements reveal that an antiferromagnetic interaction is exsisted in 1 and ferromagnetic interactions are exsisted in compounds 3 and 4. Remarkably, compound 1 displays well cryogenic magnetic refrigeration property with a larger magnetic entropy (−ΔSm = 28.79 J K−1 kg−1, T = 2.0 K and ΔH = 70 kOe). Moreover, alternating-current (ac) magnetic susceptibility research reveals that compound 3 shows slow magnetic relaxation behavior under zero dc field. Furthermore, under an external dc field of 1500 Oe, compound 3 displays remarkable SMM behavior with the effective barrier (ΔE/kB) of 14.9 K.

Impact of Annealing on Magnetic Properties and Structure of Co40Fe40W20 Thin Films on Si(100) Substrate.

Co40Fe40W20 monolayers of different thicknesses were deposited on Si(100) substrates by DC magnetron sputtering, with Co40Fe40W20 thicknesses from 10 to 50 nm. Co40Fe40W20 thin films were annealed at three conditions (as-deposited, 250 °C, and 350 °C) for 1 h. The structural and magnetic properties were then examined by X-ray diffraction (XRD), low-frequency alternative-current magnetic susceptibility (χac), and an alternating-gradient magnetometer (AGM). The XRD results showed that the CoFe (110) peak was located at 2θ = 44.6°, but the metal oxide peaks appeared at 2θ = 38.3, 47.6, 54.5, and 56.3°, corresponding to Fe2O3 (320), WO3 (002), Co2O3 (422), and Co2O3 (511), respectively. The saturation magnetization (Ms) was calculated from the slope of the magnetization (M) versus the CoFeW thickness. The Ms values calculated in this manner were 648, 876, 874, and 801 emu/cm3 at the as-deposited condition and post-annealing conditions at 250, 350, and 400 °C, respectively. The maximum MS was about 874 emu/cm3 at a thickness of 50 nm following annealing at 350 °C. It indicated that the MS and the χac values rose as the CoFeW thin films’ thickness increased. Owing to the thermal disturbance, the MS and χac values of CoFeW thin films after annealing at 350 °C were comparatively higher than at other annealing temperatures. More importantly, the Co40Fe40W20 films exhibited a good thermal stability. Therefore, replacing the magnetic layer with a CoFeW film improves thermal stability and is beneficial for electrode and strain gauge applications.