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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Non-perturbative many-body treatment of molecular magnets

Molecular magnets have received significant attention because of their potential applications in quantum information and quantum computing. A delicate balance of electron correlation, spin–orbit coupling (SOC), ligand field splitting, and other effects produces a persistent magnetic moment within each molecular magnet unit. The discovery and design of molecular magnets with improved functionalities would be greatly aided by accurate computations. However, the competition among the different effects poses a challenge for theoretical treatments. Electron correlation plays a central role since d- or f-element ions, which provide the magnetic states in molecular magnets, often require explicit many-body treatments. SOC, which expands the dimensionality of the Hilbert space, can also lead to non-perturbative effects in the presence of strong interaction. Furthermore, molecular magnets are large, with tens of atoms in even the smallest systems. We show how an ab initio treatment of molecular magnets can be achieved with auxiliary-field quantum Monte Carlo, in which electron correlation, SOC, and material specificity are included accurately and on an equal footing. Furthermore, the approach is demonstrated by an application to compute the zero-field splitting of a locally linear Co 2+ complex.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Evidence for entanglement at high temperatures in an engineered molecular magnet

The molecular compound [Fe-2(mu(2)-oxo)(C3H4N2)(6)(C2O4)(2)] was designed and synthesized for the first time and its structure was determined using single-crystal X-ray diffraction. The magnetic susceptibility of this compound was measured from 2 to 300 K. The analysis of the susceptibility data using protocols developed for other spin singlet ground-state systems indicates that the quantum entanglement would remain at temperatures up to 732 K, significantly above the highest entanglement temperature reported to date. The large gap between the ground state and the first-excited state (282 K) suggests that the spin system may be somewhat immune to decohering mechanisms. Our measurements strongly suggest that molecular magnets are promising candidate platforms for quantum information processing.

Molecular Magnetism↗
DOE OSTI2023

Direct observation of electric field-induced magnetism in a molecular magnet

Abstract We report the direct observation of an electrically-induced magnetic susceptibility in the molecular nano- magnet [Fe 3 O(O 2 CPh) 6 (py) 3 ]ClO 4 · py, an Fe 3 trimer. This magnetoelectric effect results from the breaking of spatial inversion symmetry due to the spin configurations of the antiferromagnetic trimer. Both static and very low frequency electric fields were used. Fractional changes of the magnetic susceptibility of 11 ppb $$\pm 2$$ ± 2 per kVm -1 for the temperature range 8 . 5 < T < 13 . 5 K were observed for applied electric fields up to 62 kV m − 1 . The changes in susceptibility were measured using a tunnel diode oscillator operating at liquid helium temperatures while the sample is held at a higher regulated temperature.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2022

Magnetic order and spin liquid behavior in [Mo 3 ] 11+ molecular magnets

Molecular magnets based on [Mo 3 ] 11+ units with one unpaired electron per trimer have attracted recent interest due to the identification of quantum spin liquid candidacy in some family members. Here, we present comprehensive measurements on polycrystalline samples of ZnScMo 3 O 8 , MgScMo 3 O 8 , and Na 3 Sc 2 Mo 5 O 16 with the same Mo 3 O 13 magnetic building blocks. In this work, the crystal structures are characterized with x-ray or neutron powder diffraction and the magnetic ground states are determined by performing ac and dc susceptibility, specific heat, neutron powder diffraction, and muon spin relaxation measurements. Our work indicates that ZnScMo 3 O 8 and MgScMo 3 O 8 have ferromagnetic Curie-Weiss temperatures of 18.5 and 11.9 K, ordered ground states with net moments (low-moment ferromagnetism or canted antiferromagnetism), and zero field ordering temperatures of $T_c$ = 6 K and $T_c$ < 2 K, respectively. On the other hand, Na 3 Sc 2 Mo 5 O 16 hosts a dynamical magnetic ground state with no evidence for magnetic ordering or spin freezing down to 20 mK despite an antiferromagnetic Curie-Weiss temperature of –36.2 K, and therefore is a candidate for quantum spin liquid behavior. By comparing the present results to past work on the same family of materials, we construct a phase diagram which illustrates that the magnetic ground states of these Mo-based molecular magnets are very sensitive to small changes in the nearest-neighbor Mo-Mo distance.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Synthesis, Structure, Adsorption Space and Magnetic Properties of Ni-oxalate Porous Molecular Magnet

Here, we synthesized about sixty metal organic materials. Only three were metal organic frameworks (MOFs). One of them was a porous molecular magnet (PMM). For the PMM synthesis Ni was the node, oxalic acid the organic linker and DMF the solvent and shaping molecule. This PMM was studied with DRIFTS, Raman spectrometry, TGA, XRD, adsorption and with a VSM. TGA and adsorption data indicated that a microporous material with a pore volume, W = 0.10 ± 0.01 cm 3 /g was obtained. Furthermore, the analysis of the XRD profile indicated that it is a layered compound. The DRIFTS, Raman and XRD data revealed that each layer is formed by nickel cations linked by bis-bidentate and bridging-bis-bidentate oxalate ligands and the DMF molecules are perpendicularly linked to the nickel cations to produce stacking. Additionally, the Raman data allowed us to propose that the nickel cations are located in octahedral and pentacoordinated sites as Ni 2+ and Ni 3+ . The Pawley fitting of the XRD profiles pointed out that the hydrated sample crystallizes in the P2/m space group. The cell parameters calculated are consistent with the proposed structure. Two different adsorption states showing different adsorption energies, in the physical adsorption range, were observed. The small amount estimated for the dispersive and quadrupole adsorption interaction energies was a confirmation of the proposed layered structure. The VSM study yielded an effective magnetic moment, μ eff = 4.9 μ B . Our figure is consistent with nickel located in octahedral and pentacoordinated sites as Ni 2+ and Ni 3+ . We had then obtained a new Ni-oxalic porous molecular magnet (Ni-Ox-PMM). The significance of this PMM is related to its porosity, that is, during degassing it release water turning into a porous stable structure, showing notable magnetic properties. In this case been porous, it means that the electronic structure of the nickel cations can be manipulated from outside with adsorbed molecules. Thereafter, the material could sense small molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Structural and magnetic properties of Prussian blue analogue molecular magnet Fe{sub 1.5}[Cr(CN){sub 6}]·mH{sub 2}O

Molecular magnets, based on Prussian blue analogues, Fe{sub 1.5}[Cr(CN){sub 6}]·mH{sub 2}O have been synthesized in the bulk as well as nanoparticle forms using a co-precipitation method, and their structural and magnetic properties have been investigated using x-ray diffraction (XRD) Mössbauer spectroscopy and dc magnetization. The XRD study confirms the single phase crystalline and nanoparticle nature of the compounds with a face centered cubic (fcc) structure of space group Fm3m. The values of lattice constant are found to be ~10.18(5) Å and ~9.98(9)Å, for the bulk and nanoparticle samples, respectively. The dc magnetization shows a Curie temperature (T{sub C}) of ~17 K and ~5 K for the bulk and nanopartcile samples, respectively. The Mossouber spectroscopy reveal that the compound shows spin flipping from the high spin (HS) Fe (Cr{sup III}–C≡N–Fe{sup II}) to low spin (LS) Fe{sup II} ions (Cr{sup III}–N≡C–Fe{sup II}). Moreover, the T{sub C} and the HS state of the Fe ions decreases (converts to its LS states) with time as well as in the nanoparticle form compared to bulk.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Alternating current magnetic susceptibility of a molecular magnet submonolayer directly patterned onto a micro superconducting quantum interference device

We report the controlled integration, via dip pen nanolithography, of monolayer dots of ferritin-based CoO nanoparticles (12 μ{sub B}) into the most sensitive areas of a microSQUID sensor. The nearly optimum flux coupling between these nanomagnets and the microSQUID improves the achievable sensitivity by a factor 10{sup 2}, enabling us to measure the linear susceptibility of the molecular array down to very low temperatures (13 mK). This method opens the possibility of applying ac susceptibility experiments to characterize two-dimensional arrays of single molecule magnets within a wide range of temperatures and frequencies.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Room temperature colossal superparamagnetic order in aminoferrocene–graphene molecular magnets

Intensive studies are published for graphene-based molecular magnets due to their remarkable electric, thermal, and mechanical properties. However, to date, most of all produced molecular magnets are ligand based and subject to challenges regarding the stability of the ligand(s). The lack of long-range coupling limits high operating temperature and leads to a short-range magnetic order. Herein, we introduce an aminoferrocene-based graphene system with room temperature superparamagnetic behavior in the long-range magnetic order that exhibits colossal magnetocrystalline anisotropy of 8 × 10 5 and 3 × 10 7 J/m 3 in aminoferrocene and graphene-based aminoferrocene, respectively. These values are comparable to and even two orders of magnitude larger than pure iron metal. Aminoferrocene [C 10 H 11 FeN] + is synthesized by an electrophilic substitution reaction. It was then reacted with graphene oxide that was prepared by the modified Hammers method. The phase structure and functionalization of surface groups were characterized and confirmed by XRD, FT-IR, and Raman spectroscopy. To model the behavior of the aminoferrocene between two sheets of hydroxylated graphene, we have used density functional theory by placing the aminoferrocene molecule between two highly ordered hydroxylated sheets and allowing the structure to relax. Here, the strong bowing of the isolated graphene sheets suggests that the charge transfer and resulting magnetization could be strongly influenced by pressure effects. In contrast to strategies based on ligands surface attachment, our present work that uses interlayer intercalated aminoferrocene opens routes for future molecular magnets as well as the design of qubit arrays and quantum systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Analysis of vibronic coupling in a 4f molecular magnet with FIRMS

Vibronic coupling, the interaction between molecular vibrations and electronic states, is a fundamental effect that profoundly affects chemical processes. In the case of molecular magnetic materials, vibronic, or spin-phonon, coupling leads to magnetic relaxation, which equates to loss of magnetic memory and loss of phase coherence in molecular magnets and qubits, respectively. The study of vibronic coupling is challenging, and most experimental evidence is indirect. Here we employ far-infrared magnetospectroscopy to directly probe vibronic transitions in [Yb(trensal)] (where H 3 trensal = 2,2,2-tris(salicylideneimino)trimethylamine). We find intense signals near electronic states, which we show arise due to an “envelope effect” in the vibronic coupling Hamiltonian, which we calculate fully ab initio to simulate the spectra. We subsequently show that vibronic coupling is strongest for vibrational modes that simultaneously distort the first coordination sphere and break the C 3 symmetry of the molecule. With this knowledge, vibrational modes could be identified and engineered to shift their energy towards or away from particular electronic states to alter their impact. Hence, these findings provide new insights towards developing general guidelines for the control of vibronic coupling in molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Low-temperature magnetization relaxation in magnetic molecular solids

The low temperature relaxation of the magnetization in molecular magnetic solids such as Fe{sub 8} is studied using Monte Carlo simulations. A set of rate equations is then developed to understand the simulations, and the results are compared. The simulations show that the magnetization of an initially saturated sample deviates as a square-root in time at short times, as observed experimentally, and this law is derived from the rate equations analytically. -- Highlights: •A novel set of non-linear rate equations for the coupled evolution of the magnetization and dipole field distribution. •An analytic derivation of the short-time square root in time behavior of the magnetization relaxation. •Agreement between theory and simulations without further fitting parameters.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Strangely attractive: Collaboration and feedback in the field of molecular magnetism

The fluid synergy between experimentalists and theoreticians has, for decades, led to a deeper understanding of the processes that govern single-molecule magnets. This approach has allowed for the establishment of proven design criteria for the control of magnetic properties through molecular architecture and the development of new magnetic measurement techniques and innovative computational methodologies. Here, we give an account of the experimental and theoretical joint endeavor carried out as part of the synthesis group led by David Mills and the computational/theoretical team led by Nicholas Chilton, together with colleagues in synthetic f-element chemistry and magnetism at the University of Manchester. In addition, we provide a personal perspective on collaborative work in molecular magnetism and how such collaborations are essential for advancing the field further.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Investigation of a V{sub 15} magnetic molecular nanocluster by the Monte Carlo method

Exchange interactions in a V{sub 15} magnetic molecular nanocluster are considered, and the process of magnetization reversal for various values of the set of exchange constants is analyzed by the Monte Carlo method. It is shown that the best agreement between the field dependence of susceptibility and experimental results is observed for the following set of exchange interaction constants in a V{sub 15} magnetic molecular nanocluster: J = 500 K, J Prime = 150 K, J Double-Prime = 225 K, J{sub 1} = 50 K, and J{sub 2} = 50 K. It is observed for the first time that, in a strong magnetic field, for each of the three transitions from low-spin to high-spin states, the heat capacity exhibits two closely spaced maxima.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Molecular Magnetism in North America Conference

The report provides information on the Molecular Magnetism in North America (MAGNA) conference that the DOE funding supported. It was held 2/21/2020 - 2/24/2020 at the King and Prince Hotel on St. Simon’s Island in southern Georgia. It brought together workers from academic institutions and government laboratories working in the field of molecular magnetism, including synthetic chemistry of molecular and 1D-3D molecule-based materials, and the various physical and spectroscopic methods for their study. The oral program spanned 3½ days and comprised 32 talks (30 mins each) by faculty and government scientists, and 12 talks (15 mins each) by junior people (graduate students and postdoctorals). The poster session took place at 6 pm on Saturday, Feb 22nd, and comprised 21 posters. Total registrations for the meeting were 68.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Synthesis and characterization of montmorillonite clay intercalated with molecular magnetic compounds

In this work montmorillonite (MMT) clay, whose matrix was modified with an ammonium salt (hexadecyltrimethylammonium bromide – CTAB), was employed as an inorganic host for the intercalation of three different molecular magnetic compounds through ion exchange: a nitronyl nitroxide derivative 2-[4-(N-ethyl)-pyridinium]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (p-EtRad{sup +}) and two binuclear coordination compounds, [Ni(valpn)Ln]{sup 3+}, where H{sub 2}valpn stands for 1,3-propanediyl-bis(2-iminomethylene-6-methoxy-phenol), and Ln=Gd{sup III}; Dy{sup III}. The pristine MMT and the intercalated materials were characterized by X-ray powder diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and magnetic measurements. The X-ray diffraction data analysis showed an increase of the interlamellar space of the intercalated MMT, indicating the intercalation of the magnetic compounds. Furthermore, the magnetic properties of the hybrid compounds were investigated, showing similar behavior as the pure magnetic guest species. - Graphical abstract: Montmorillonite clay was employed as inorganic host for the intercalation of three different molecular magnetic compounds through ion exchange - Highlights: • Montmorillonite was employed as a host material. • Three molecular magnetic compounds were intercalated through ion exchange. • The compounds were successful intercalated maintaining the layered structure. • The hybrid materials exhibited similar magnetic behavior as the pure magnetic guest.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Modeling carrier mobility in graphene as a sensitive probe of molecular magnets

Carrier mobility in graphene on a GaAs substrate and its change due to the adsorption of molecular magnets, Mn 12 and [Mn 3 ] 2 , on the surface of graphene, is calculated from first principles. Phonon limited mobility is also calculated for comparison. For Mn 12 adsorption on graphene, the mobility is compared for different organic ligands of Mn 12 (-H, -CH 3 , and - CHCl 2 ), while for [Mn 3 ] 2 dimers, the mobility is calculated for different linkers that yield the ferromagnetic and anti-ferromagnetic configurations of [Mn 3 ] 2 , as well as for different orientations of the molecule. Significant changes in carrier mobility due to the adsorption of the molecules and due to differences in linkers suggest mobility measurement as a possible sensitive probe of magnetic molecules.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Review of NMR studies of nanoscale molecular magnets composed of geometrically frustrated antiferromagnetic triangles

This paper presents a comprehensive review of nuclear magnetic resonance (NMR) studies performed on three nanoscale molecular magnets with different novel configurations of geometrically frustrated antiferromagnetic (AFM) triangles: (1) the isolated single AFM triangle K 6 [V 15 As 6 O 42 (H 2 O)]·8H 2 O (in short V15), (2) the spin ball [Mo 72 Fe 30 O 252 (Mo 2 O 7 (H 2 O)) 2 (Mo 2 O 8 H 2 (H 2 O)) (CH 3 COO) 12 (H 2 O) 91 ]·150H 2 O (in short Fe30 spin ball), and (3) the twisted triangular spin tube [(CuCl 2 tachH) 3 Cl]Cl 2 (in short Cu3 spin tube). In V15t, from 51 V NMR spectra, the local spin configurations were directly determined in both the nonfrustrated total spin S T = 3/2 state at higher magnetic fields (H ge; 2.7 T) and the two nearly degenerate S T = 1/2 ground states at lower magnetic fields (H ≤ 2.7 T). The dynamical magnetic properties of V15 were investigated by proton spin-lattice relaxation rate (1/T 1 ) measurements. In the S T = 3/2 state, 1/T 1 shows thermally activated behaviour as a function of temperature. On the other hand, the temperature independent behaviour of 1/T 1 at very low temperatures is observed in the frustrated S T = 1/2 ground state. Possible origins for the peculiar behaviour of 1/T 1 will be discussed in terms of magnetic fluctuations due to spin frustrations. In Fe30, static and dynamical properties of Fe 3+ (s = 5/2) have been investigated by proton NMR spectra and 1/T 1 measurements. From the temperature dependence of 1/T 1 , the fluctuation frequency of the Fe 3+ spins is found to decrease with decreasing temperature, indicating spin freezing at low temperatures. The spin freezing is also evidenced by the observation of a sudden broadening of 1 H NMR spectra below 0.6 K. Finally, 1 H NMR data in Cu3 will be described. An observation of magnetic broadening of 1 H NMR spectra at low temperatures below 1 K directly revealed a gapless ground state. The 1/T 1 measurements revealed a usual slow spin dynamics in the Cu3 spin tube.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗