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DOE OSTI2018

Large-amplitude Blazar Polarization Angle Swing as a Signature of Magnetic Reconnection

We report that relativistic magnetic reconnection events may exist in magnetized plasmas in astrophysical systems. During this process, oppositely directed magnetic field lines reconnect and release magnetic energy, efficiently accelerating nonthermal particles. However, so far there is little clear observational signatures of relativistic magnetic reconnection events in astrophysical systems. Blazars are relativistic magnetized plasma outflows from supermassive black holes. Their multi-wavelength flares may be powered by relativistic magnetic reconnection. The highly variable radiation and polarization signatures are well covered by multi-wavelength observation campaigns, making them ideal targets to examine the magnetic reconnection model. Recent observations have found that several blazar flares are accompanied by optical polarization angle swings that may have an amplitude as large as >180°, challenging existing theoretical models. In this Letter, we present integrated particle-in-cell and polarized radiation transfer simulations of magnetic reconnection events. We find that plasmoid coalescences in the reconnection layer can give rise to highly variable light curves, low and fluctuating polarization degree, and rotating polarization angle. Lastly, in particular, large-amplitude polarization angle swings, similar to those observed during blazar flares, can be a unique signature of relativistic magnetic reconnection events.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2019

Permanent Magnet Dipole-Quadrupole and Correcto-Tuner for Small Bore Accelerators

Electromagnets are used to bend electron beams and generate X-ray light. Permanent magnets have many advantages over electromagnets and are being studied as an alternative for small bore accelerators. This paper focuses on the mechanical design of two holders. First, a holder for the corrector and tuner permanent magnet assembly, which aims to correct the errors in the permanent magnetic field strength and orientation. Second, a holder for the dipole-quadrupole magnet assembly, which aims to provide the required magnetic strength to steer the electrons. Prototypes for the corrector, tuner and dipole-quadrupole holders were designed and tested to validate conceptual design. Results show that the corrector magnets can be oriented into a prescribed configuration, the tuner magnets can be oriented simultaneously regardless of the magnetic forces involved, and the dipole-quadrupole magnets can provide the magnetic strength required to steer electrons.

Huschke, Christopher↗

DOE OSTI2020

Methods and apparatus for making magnetic skyrmions

A system and a method for the deterministic generation of magnetic skyrmions includes a magnetic strip configured to store and transport skyrmions. The magnetic strip includes one or more spatial inhomogeneities configured to generate a skyrmion at known locations when excited by a current pulse. A current pulse generator is used to inject current pulses into the magnetic strip via contact pads electrically coupled to both the current pulse generator and the magnetic strip. The system also includes a magnetic field source to apply an out-of-plane magnetic field across the magnetic strip to facilitate generation of skyrmions. Skyrmions can be generated by applying an out-of-plane magnetic field to the magnetic strip and injecting a current pulse with sufficient current density towards the spatial inhomogeneities. Once a skyrmion is generated, another current pulse with sufficient current density can be injected to move the skyrmion.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

Understanding magnetic phase coexistence in Ru 2 Mn 1-x Fe x Sn Heusler alloys: A neutron scattering, thermodynamic, and phenomenological analysis

The random substitutional solid solution between the antiferromagnetic (AFM) full-Heusler alloy Ru 2 MnSn and the ferromagnetic (FM) full-Heusler alloy Ru 2 FeSn provides a rare opportunity to study FM-AFM phase competition in a near-lattice-matched, cubic system, with full solubility. At intermediate x in Ru 2 Mn 1-x Fe x Sn this system displays suppressed magnetic ordering temperatures, spatially coexisting FM and AFM order, and strong coercivity enhancement, despite rigorous chemical homogeneity. Here, we construct the most detailed temperature- and x-dependent understanding of the magnetic phase competition and coexistence in this system to date, combining wide-temperature-range neutron diffraction and small-angle neutron scattering with magnetometry and specific heat measurements on thoroughly characterized polycrystals. A complete magnetic phase diagram is generated, showing FM-AFM coexistence between x ≈ 0.30 and x ≈ 0.70. Furthermore, important insight is gained from the extracted length scales for magnetic phase coexistence (25–100 nm), the relative magnetic volume fractions and ordering temperatures, and remarkable x-dependent trends in magnetic and electronic contributions to specific heat. An unusual feature in the magnetic phase diagram (an intermediate FM phase) is also shown to arise from an extrinsic effect related to a minor Ru-rich secondary phase. The established magnetic phase diagram is then discussed with the aid of phenomenological modeling, clarifying the nature of the mesoscale phase coexistence with respect to the understanding of disordered Heisenberg models.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Remote temperature distribution sensing using permanent magnets

Remote temperature sensing is essential for applications in enclosed vessels where feedthroughs or optical access points are not possible. A unique sensing method for measuring the temperature of multiple closely-spaced points is proposed using permanent magnets and several three-axis magnetic field sensors. The magnetic field theory for multiple magnets is discussed and a solution technique is presented. Experimental calibration procedures, solution inversion considerations and methods for optimizing the magnet orientations are described in order to obtain low-noise temperature estimates. The experimental setup and the properties of permanent magnets are shown. Finally, experiments were conducted to determine the temperature of nine magnets in different configurations over a temperature range of 5 to 60 degrees Celsius and for a sensor-to-magnet distance of up to 35 mm. Furthermore, to show the possible applications of this sensing system for measuring temperatures through metal walls, additional experiments were conducted inside an opaque 304 stainless steel cylinder.

47 OTHER INSTRUMENTATION↗

DOE OSTI2021

Magnetic‐Field‐Switchable Laser via Optical Pumping of Rubrene

Abstract Volumetric optical imaging of magnetic fields is challenging with existing magneto‐optical materials, motivating the search for dyes with strong magnetic field interactions, distinct emission spectra, and an ability to withstand high photon flux and incorporation within samples. Here, the magnetic field effect on singlet‐exciton fission is exploited to demonstrate spatial imaging of magnetic fields in a thin film of rubrene. Doping rubrene with the high‐quantum yield dye dibenzotetraphenylperiflanthene (DBP) is shown to enable optically pumped, slab waveguide lasing. This laser is magnetic‐field‐switchable: when operated just below the lasing threshold, application of a 0.4 T magnetic field switches the device between nonlasing and lasing modes, accompanied by an intensity modulation of +360%. This is thought to be the first demonstration of a magnetically switchable laser, as well as the largest magnetically induced change in emission brightness in a singlet‐fission material to date. These results demonstrate that singlet‐fission materials are promising materials for magnetic sensing applications and could inspire a new class of magneto‐optical modulators.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Quantum Disordered State of Magnetic Charges in Nanoengineered Honeycomb Lattice

Abstract A quantum magnetic state due to magnetic charges is never observed, even though they are treated as quantum mechanical variables in theoretical calculations. Here, the occurrence of a novel quantum disordered state of magnetic charges in a nanoengineered magnetic honeycomb lattice of ultra‐small connecting elements is demonstrated. The experimental research, performed using spin resolved neutron scattering, reveals a massively degenerate ground state, comprised of low integer and energetically forbidden high integer magnetic charges, that manifests cooperative paramagnetism at low temperature. The system tends to preserve the degenerate configuration even under large magnetic field application. It exemplifies the robustness of disordered correlation of magnetic charges in a 2D honeycomb lattice. The realization of quantum disordered ground state elucidates the dominance of exchange energy, which is enabled due to the nanoscopic magnetic element size in nanoengineered honeycomb. Consequently, an archetypal platform is envisaged to study quantum mechanical phenomena due to emergent magnetic charges.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2021

The Magneto-Transport Properties of Cr 1/3 TaS 2 with Chiral Magnetic Solitons

Cr 1/3 TaS 2 —a candidate of chiral magnet—has been reported as a trivial ferromagnetic material. In contrast, the Cr 1/3 TaS 2 single crystals exhibit a chiral helimagnetic (CHM) transition near 140 K. The magnetic moment versus magnetic field curves reveal a CHM—chiral soliton lattice (CSL)—forced ferromagnetic (FFM) transition in the magnetic ordered state. The conducting electrons interact with the CHM and CSL orders, giving rise to the nontrivial magnetoresistance (MR) in the Cr 1/3 TaS 2 single crystals. The normalized magnetic moment and normalized MR fit well with the analytical functions for chiral soliton density. The magnetic phase diagrams constructed from the magnetic moment data and MR data suggest a possible tri-critical point. Compared with the isostructural Cr 1/3 NbS 2 , the CHM transition temperature of Cr 1/3 TaS 2 is 13 K higher, the CSL—FFM transition field is about 10 times larger, and the Dzyaloshinskii-Moriya interaction strength is 3 times bigger. The latter two likely originate from the strong spin-orbit coupling (SOC) of Cr 1/3 TaS 2 . This work clarifies that high-quality Cr 1/3 TaS 2 single crystals are chiral magnets and Cr 1/3 (Nb,Ta)S 2 could serve as an intriguing platform for the flexible engineering of chiral magnetic solitons with tunable SOC.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Investigation of Magnetic Properties of Multilayer Thin Films with Spin-Wave Resonance

A theory has been developed to simulate spin-wave resonance (SWR) modes in the multilayer systems consisting of alternate magnetic and nonmagnetic layers. An equation of motion of magnetization with Gilbert-type damping parameter for simulating SWR modes was used. It has been realized that the theory developed for the magnetic multilayer films is suitable to study the spin dynamics and extract various magnetic parameters. It has been shown that SWR modes strongly depend on an effective magnetic anisotropy constant (K{sub eff}), interlayer exchange coupling constant (A{sub 12}) and effective magnetization (M{sub eff}). The nature of the effective magnetic anisotropy and interlayer exchange coupling constants has been investigated by using the developed SWR theory in detail. The separation between optic and acoustic modes strongly depends on the magnitude of the interlayer exchange coupling constant, whereas the relative position of the acoustic and optic modes depends on the sign of A{sub 12}. With increasing the interlayer exchange coupling constant, the resonance field of the optic mode decreases (increases) for ferromagnetic (antiferromagnetic) coupling. When the effective magnetic anisotropy constant increases, the resonance field of the acoustic and optic modes increases for both the ferromagnetic and antiferromagnetic couplings. The increasing of the effective magnetization results in decreasing of the resonance field of SWR mode at parallel geometry, whereas that of SWR mode increases at the perpendicular geometry. The results are compatible to the other theories and experimental results.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Impact of Isotropic Strain on Magnetic Properties of Monolayer MoSe{sub 2}-Doped with Nonmagnetic Metal and Nonmetal Atoms

Electronic and magnetic properties of MoSe{sub 2} monolayer doped with different nonmagnetic metal (Ag, Al, Li, Mg, and Na) and nonmetal (B, C, F, N, and O) elements have been studied by using the density functional theory calculations. Magnetism has been induced by Ag, Al, and Mg doping. Then, we further have studied the effect of strain on the magnetism in Al-doped MoSe{sub 2} monolayer. We have applied an isotropic strain on the system. On the one hand, the magnetism disappeared while the compressive strain was applied. On the other hand, the magnetism kept stable under the tensile strain. Moreover, we investigated the magnetic coupling in two-Al-doped MoSe{sub 2} structures under the tensile strain. Interestingly, a tunable magnetic coupling was observed. As the tensile strain increased, the magnetic coupling between two Al atoms switched from nonmagnetic (NM) to ferromagnetic (FM). The analysis of the PDOS showed that the p-p hybridization between the Al atom and its neighboring Se atoms resulted in such magnetic behavior. Our results showed some potential applications in MoSe{sub 2}-based nanoscale devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

Antioxidative effects of magnetized extender containing bovine serum albumin on sperm oxidative stress during long-term liquid preservation of boar semen

Magnetized water is defined as water that has passed through a magnet and shows increased permeability into cells and electron-donating characteristics. These attributes can protect against membrane damage and remove reactive oxygen species (ROS) in mammalian cells. We explored the effects of improved magnetized semen extenders containing bovine serum albumin (BSA) as antioxidants on apoptosis in boar sperm. Ejaculated semen was diluted in magnetized extender (0G and 6000G) with or without BSA (0G + BSA and 6000G + BSA), and sperm were analyzed based on viability, acrosome reaction, and H{sub 2}O{sub 2} level of live sperm using flow cytometry. Sperm were then preserved for 11 days at 18 °C. We found that viability was significantly higher in 6000G + BSA than under the other treatments (P < 0.05). The acrosome reaction was significantly lower in the 6000G + BSA group compared with the other treatments (P < 0.05). Live sperm with high intracellular H{sub 2}O{sub 2} level were significantly lower in the 6000G + BSA group than under other treatments (P < 0.05). Based on our results, magnetized extenders have antioxidative effects on the liquid preservation of boar sperm. - Highlights: • Magnetized water is water that has been passed through a magnetic field. • Magnetized extender improve viability and decrease oxidative stress of boar sperm for preservation. • Ejaculated semen diluted with magnetized extender can improve liquid preservation period.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2020

Development of rare-earth-free bulk magnets with energy product up to 12 MGOe in field annealed Mn–Bi–Mg–In–Sb alloys

A treatment consisting of annealing in a moderately strong, ≤30 kOe, magnetic field was applied to arc-melted ingots and compacted melt-spun alloys with composition Mn 50 Bi 50-x-y-z Mg x In y Sb z . The high degree of texture of the magnetic α phase induced with annealing of the ingot samples (except the Mn–Bi–Sb one) allowed for accurate determination of the phase anisotropy field. Alloying was found to increase the anisotropy field from 45 kOe in the Mn 50 Bi 50 alloy to 65 kOe in the Mn 50 Bi 45 Mg 3 In 0.5 Sb 1.5 alloy. In the compacted melt-spun alloys subjected to field annealing, a higher degree of texture could be achieved after compaction which had involved less heating, when a smaller fraction of the metastable β' phase had been converted into the α phase; compaction at room temperature allowed for the highest degree of texture in the Mn 50 Bi 45 Mg 3 In 0.5 Sb 1.5 magnet. The addition of indium was found to decrease the solidus temperatures of the alloys, facilitating the development of the α phase during the field annealing and modifying the properties of the resulting magnets. Introduction of indium resulted in a higher coercivity H c of the Mn–Bi–Mg–In magnets and in a better texture of the Mn–Bi–Mg–Sn–In magnets. The former effect allowed, in particular, for a viable maximum energy product ( BH ) max of 10 MGOe to be developed in the Mn 50 Bi 46.5 Mg 3 In 0.5 magnet through annealing in a relatively low field of 15 kOe, whereas the latter effect allowed for an excellent combination of ( BH ) max = 11.6 MGOe and H c = 8.5 kOe in the Mn 50 Bi 45 Mg 3 In 0.5 Sb 1.5 magnet. The highest ( BH ) max of 12 MGOe was realized in the Mn 50 Bi 46 Mg 3 In 0.5 Sb 0.5 magnet.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Transition from an incommensurate spin density wave to a commensurate magnetic order in a triangular lattice compound Ho 2 PdAl 6 Ge 4

Rare-earth (RE) intermetallics on a triangular lattice are promising candidates for generating interesting magnetic phases due to the complex interplay between Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction and geometrical frustration. Here, in this work, we report the exotic magnetic structure of a layered compound Ho 2 PdAl 6 Ge 4 with triangular lanthanide nets. Magnetization and heat capacity measurements in zero magnetic field reveal two magnetic phase transitions at T N1 = 10.8 K and T N2 = 6.0 K. Neutron powder diffraction demonstrates a commensurate antiferromagnetic phase with k 1 = (0, 0, 1.5) below T N2 . With increasing temperature, another incommensurate vector appears and therefore, the magnetic structure of the intermediate state is identified as an unusual incommensurate spin density wave with two propagation vectors k 1 = (0, 0, 1.5) and k 2 = (0.0492, 0.0492, 1.5). The magnetic moments in the intermediate state rotate continuously and form an unusual S-shaped wave arrangement in the ab plane, sharing similarities with typical cycloid and helix magnetic orders. These results identify Ho 2 PdAl 6 Ge 4 as a candidate for exploring field-induced topological magnetic phases such as skyrmions, opening the way for further investigations on the family of RE 2 PdAl 6 Ge 4 materials.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Magnetic properties of monoclinic lanthanide orthoborates, LnBO3, Ln = Gd, Tb, Dy, Ho, Er, Yb

Highlights: • Structural and magnetic properties of lanthanide orthoborates LnBO{sub 3}, Ln = Gd, Tb, Dy, Ho, Er, Yb. • LnBO{sub 3} forms a monoclinic structure with the magnetic Ln{sup 3+} forming eclipsed triangular layers. • With the exception of Gd{sup 3+} significant single-ion anisotropy is observed for all Ln{sup 3+}. • Ordering features for LnBO{sub 3}, Ln = Gd, Tb, Dy, Er between 0.4 and 2 K, onset of magnetic ordering for YbBO{sub 3} at 0.4 K, HoBO{sub 3} forms non-magnetic singlet ground state. • GdBO{sub 3} and DyBO{sub 3} are competitive magnetocaloric materials in the liquid helium temperature regime. - Abstract: The lanthanide orthoborates, LnBO{sub 3}, Ln = Gd, Tb, Dy, Ho, Er, Yb crystallise in a monoclinic structure with the magnetic Ln{sup 3+} forming an edge-sharing triangular lattice. The triangles are scalene, however all deviations from the ideal equilateral geometry are less than 1.5%. The bulk magnetic properties are studied using magnetic susceptibility, specific heat and isothermal magnetisation measurements. Heat capacity measurements show ordering features at T ≤ 2 K for Ln = Gd, Tb, Dy, Er. No ordering is observed for YbBO{sub 3} at T ≥ 0.4 K and HoBO{sub 3} is proposed to have a non-magnetic singlet state. Isothermal magnetisation measurements indicate isotropic Gd{sup 3+} spins and strong single-ion anisotropy for the other Ln{sup 3+}. The change in magnetic entropy has been evaluated to determine the magnetocaloric effect in these materials. GdBO{sub 3} and DyBO{sub 3} are found to be competitive magnetocaloric materials in the liquid helium temperature regime.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Influence of high energy ball milling on structural parameters, cation distribution and magnetic enhancement of nanosized Co0.3Zn0.7Fe2O4

Highlights: • Magnetic enhancement in mechanically activated nanosized Co{sub 0.3}Zn{sub 0.7}Fe{sub 2}O{sub 4} ferites. • Influence of crystal structure, cation distribution and stress anisotropy on magnetic and hyperfine properties. • A simple method for estimation of cation distribution of ferrites has been proposed. • Probing core-shell type magnetic structure of ferrite nanoparticles by infield Mössbauer and dc magnetic measurement. • Memory effect in the dc magnetization. - Abstract: Herein, we report the role of mechanical activation in modifying the structural, microstructural, magnetic and hyperfine parameters of nanosized Co{sub 0.3}Zn{sub 0.7}Fe{sub 2}O{sub 4} having average particle size ∼16.6 nm synthesized via coprecipitation method followed by high energy ball milling with cation distribution (Zn{sup 2+}{sub 0.61}Fe{sup 3+}{sub 0.39}){sub A} [Co{sup 2+}{sub 0.3}Zn{sup 2+}{sub 0.09}Fe{sup 3+}{sub 1.61}]{sub B}O{sub 4}. The values of the blocking temperature and Curie temperature of the sample are 220 and 270 K, respectively. The values of saturation magnetization at 300 and 5 K are 59 and 88 emu g{sup −1}and those of the coercivity at 100 and 5 K are 400 and 5000 Oe, respectively. The values of the magnetic parameters of the sample are greater than those of its counterparts synthesized by chemical methods. A model for precise estimation of the cation distribution of ferrites has been proposed. Moreover, the memory effect obtained in the dc magnetization of the sample can be used for generating, storing and retrieving binary bit pattern.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2025

Evolution of Structure and Magnetism in FeCl 2 and FeCl 3 : From Clusters to Monolayers

In this work, we address one of the most fundamental questions in cluster science─how do the structure and properties evolve from clusters to crystals? Using density functional theory (DFT), we focus our study on the evolution of structure and magnetism in iron-chloride systems, from clusters to monolayers. The choice of this system is motivated by the recent experimental confirmation of one of the author’s earlier theoretical prediction that the FeCl 2 cluster is magnetic with a spin magnetic moment of 4 μ B localized at the Fe site, while its dimer, Fe 2 Cl 4 , is antiferromagnetic. Similarly, FeCl 3 cluster is magnetic with a total spin magnetic moment of 5 μ B , with 4 μ B localized at the Fe site and 1 μ B distributed over the Cl sites. The dimer clusters Fe 2 Cl 4 and Fe 2 Cl 6 have an antiferromagnetic ground state, and upon Li-functionalization, both can be magnetically transformed from antiferromagnetic to ferromagnetic states. In contrast, FeCl 2 and FeCl 3 monolayers exhibit different magnetic ground states in their periodic forms: FeCl 2 is ferromagnetic (FM), but in FeCl 3 , the antiferromagnetic (AFM) and FM states are energetically nearly degenerate. Such a difference arises due to the different chemical coordination of the Fe atoms with the Cl atoms, caused by their different oxidation states, which is +2 in FeCl 2 and +3 in FeCl 3 , respectively. Interestingly, Li-functionalization allows both FeCl 3 and FeCl 2 monolayers to be ferromagnetic. Our study highlights that several, but not all, electronic and magnetic characteristics of isolated clusters are preserved in the extended periodic structures. This systematic investigation of iron-halide clusters is expected to inspire further experimental and theoretical exploration into the magnetism of other transition metal halides.

cluster chemistry↗

DOE OSTI2025

Tuning the Magnetic Properties of CrI 3 Using Ni Thin Film Deposition for Applications in Spintronic Devices

Chromium triiodide (CrI 3 ), a van der Waals magnet, has recently been shown to host Ising ferromagnetism down to the monolayer limit. It is a potentially important material in 2D magnet-based applications, such as magnetic sensors and spintronic devices. Prior studies have revealed the coexistence of two different types of interlayer magnetic coupling, the antiferromagnetic (AFM) coupling near the surface and ferromagnetic (FM) coupling in the deep bulk layers, in pristine CrI 3 crystals below the Curie temperature. In this study, we used Ni thin film deposition to tune the surface magnetic states in bulk CrI 3 . A nanometer thickness (4 nm thick) of Ni was deposited on the surface of CrI 3 using electron-beam evaporation to form a Ni/CrI 3 heterostructure. The deposited Ni thin layer forms nanoclusters that completely cover the CrI 3 surface. Magnetic states of CrI 3 before and after Ni deposition are probed by ultralow-frequency magneto-Raman spectroscopy. Instead of seeing three spin wave branches in Raman scattering below 2 T, as in pristine bulk CrI 3 , in Ni/CrI 3 , we observe only a single spin wave branch, which is softened compared to that in pristine CrI 3 and displays a Zeeman shift under an out-of-plane magnetic field up to 7 T. This observation reveals that the AFM layers on pristine CrI 3 crystal surfaces transit into FM layers, so the entire CrI 3 crystal is in the FM state after Ni deposition. First-principles calculations show that Ni atoms tend to diffuse into the CrI 3 lattice, and the FM interlayer coupling has a much lower energy than AFM coupling in the presence of Ni atoms. As a result, our studies show that the magnetic state of CrI 3 can be modified through deposition of a thin metal layer on the surface, offering a route for controlling the spin degree of freedom in van der Waals magnets.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Strong Electronic and Magnetic Coupling in M 4 (M = Ni, Cu) Clusters via Direct Orbital Interactions between Low-Coordinate Metal Centers

In this report we present an extensive study of tetranuclear transition-metal cluster compounds M 4 (NP t Bu 3 ) 4 and [M 4 (NP t Bu 3 ) 4 ][B(C 6 F 5 ) 4 ] (M = Ni, Cu; t Bu = tert -butyl), which feature low-coordinate metal centers and direct metal-metal orbital overlap. X-ray diffraction, electrochemical, magnetic, spectroscopic, and computational analysis elucidate the nature of the bonding interactions in these clusters and the impact of these interactions on the electronic and magnetic properties. Direct orbital overlap results in strongly coupled, large-spin ground states in the [Ni 4 (NP t Bu 3 ) 4 ] +/0 clusters and fully delocalized, spin-correlated electrons. Correlated electronic structure calculations confirm the presence of ferromagnetic ground states that arise from direct exchange between magnetic orbitals, and, in the case of the neutral cluster, itinerant electron magnetism similar to that in metallic ferromagnets. The cationic nickel cluster also possesses large magnetic anisotropy exemplified by a large, positive axial zero-field splitting parameter of D = +7.95 or +9.2 cm -1 , as determined by magnetometry or electron paramagnetic resonance spectroscopy, respectively. The [Ni 4 (NP t Bu 3 ) 4 ] + cluster is also the first molecule with easy-plane magnetic anisotropy to exhibit zero-field slow magnetic relaxation, and under a small applied field, it exhibits relaxation exclusively through an Orbach mechanism with a spin relaxation barrier of 16 cm -1 . The S = 1 / 2 complex [Cu 4 (NP t Bu 3 ) 4 ] + exhibits slow magnetic relaxation via a Raman process on the millisecond time scale, supporting the presence of slow relaxation via an Orbach process in the nickel analogue. Overall, this work highlights the unique electronic and magnetic properties that can be realized in metal clusters featuring direct metal-metal orbital interactions between low-coordinate metal centers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗