Magnetic moments and chemical bonding in isolated BiNCoM clusters

Out-of-focus spatial map imaging of magnetically deflected sodium ammonia clusters

This paper introduces out-of-focus spatial map imaging (SMI) as a detection method for magnetic deflection of molecular/cluster beams, using Nam(NH3)n to illustrate its capabilities. This method enables imaging of the complete spatial distribution, simplifying measurements and allowing for cluster-size-resolved analysis by shifting away from traditional in-focus SMI conditions. Incorporating out-of-focus SMI with TOF-MS and velocity map imaging into a single setup allows for direct assessment of clusters' magnetic moments without needing to pre-select velocities. Key findings include a slower relaxation for Na(NH3)4 compared to Na(NH3)3 and Na(NH3)5, unexpectedly high deflection for larger clusters up to Na(NH3)9, hinting at changes in cluster dynamics as the first solvation shell closes. The study also covers the first measurements of Na2(NH3)1 and Na3(NH3)n, showing distinct deflection behaviors and underscoring the improved capabilities of the new detection method.

Comparison of Magnetic Deflection among Neutral Sodium-Doped Clusters: Na(H2O)n, Na(NH3)n, Na(MeOH)n, and Na(DME)n

Using a pulsed Stern-Gerlach deflection experiment, we present the results of a comparative study on the magnetic properties of neutral sodium-doped solvent clusters Na(Sol)n with n = 1-4 (Sol: H2O, NH3, CH3OH, CH3OCH3). Experimental deflection ratios are compared with values calculated from molecular dynamics simulations. NaNH3 and NaH2O are deflected as a spin 1/2 system, consistent with spin transitions occurring on a time scale significantly longer than 100 μs. For all other clusters, reduced deflection is observed. The observed magnetic deflection behavior is correlated to the number of thermally populated rotational states in the clusters. We discuss that spin-rotational couplings allow for avoided crossings and a reduction in the effective magnetic moment of the cluster. This work attempts to understand the evolution of magnetic properties in isolated weakly bound clusters and is relevant to diamagnetic and paramagnetic species expected to exist in solvated electron systems.

Fourth generation cryogenic neutral cluster beam apparatus for studying fundamental properties of metallic clusters

A cryogenic beam apparatus for studying neutral clusters has been built and tested. The lowest beam temperature reaches less than 9 K at a repetition rate of 20 Hz. Mechanical decoupling from the refrigerator avoids misalignment during temperature ramping. Adopting a permanent magnet based magnetic deflector eliminates the hysteresis and electric noise of the traditional electromagnet and offers excellent reproducibility of the applied magnetic field. The mass spectrometer can operate in either Mass Spectroscopy Time-Of-Flight mode or Position-Sensitive Time-Of-Flight mode with spatial resolution better than 7 μm. Its performance is demonstrated with niobium and cobalt clusters.

Magnetic deflection of neutral sodium-doped ammonia clusters

A new Stern–Gerlach setup elucidates the spin relaxation dynamics of small weakly-bound Na(NH₃)_n clusters.

Geometrical and electronic structures of small Co–Mo nanoclusters

The geometries, energetics and electronic structures of Co₁₃, Mo₁₃, Co₁₂Mo and Mo₁₂Co clusters are systematically investigated by using the first principles method combined with a genetic algorithm.

An improved time-of-flight method for cluster deposition and ion-scattering experiments

A molecular beam apparatus has been developed for deposition and scattering experiments of size-selected clusters. The new setup combines a bimetallic laser ablation cluster source with a collinear time-of-flight mass spectrometer. Mass selection is achieved with a pulsed electrostatic mirror. A significantly improved transmission in combination with a reduction of the kinetic energy distribution of the mass selected clusters has been obtained. Without further modification of the apparatus, surface-induced dissociation of mass selected tin clusters has been investigated, demonstrating the possibility to combine cluster beam deposition and scattering experiments.

Magnetic moments of bare and benzene-capped cobalt clusters

Magnetic moments of bare cobalt clusters Co(n) (n=7-32) and benzene-capped cobalt clusters Co(n)(bz)(m) have been measured at temperatures ranging from 54 to 150 K using a molecular beam deflection method. It was observed that Co(12-32) produced at temperatures greater than approximately 100 K display high-field-seeking behavior at all temperatures in the range investigated, indicating that they are superparamagnetic species. At temperatures below approximately 100 K, the field-on beam profiles of Co(7-11) and some larger clusters displayed substantial symmetric broadening, indicating that some fraction of the clusters in the beam were no longer superparamagnetic, but rather were in a blocked (locked-moment) state. In the superparamagnetic regime (T=150 K) Co(n) clusters in the n=7-32 size range were found to possess per-atom moments ranging from 1.96+/-0.04 micro(b)(Co(24)) to 2.53+/-0.04 micro(b)(Co(16)), significantly above the bulk value of 1.72 micro(b). Locked-moment isomers were found to display moments of approximately 1 micro(b) per atom. Cobalt clusters containing a layer of adsorbed benzene molecules were found to possess significantly lower moments per cobalt atom than the corresponding bare cobalt clusters.

Magnetic enhancement in cobalt-manganese alloy clusters

Magnetic moments of Co(N)Mn(M) and Co(N)V(M) clusters (N < or = 60; M < or = N/3) are measured in molecular beams using the Stern-Gerlach deflection method. Surprisingly, the per atom average moments of Co(N)Mn(M) clusters are found to increase with Mn concentration, in contrast to bulk CoMn. The enhancement with Mn doping is found to be independent of cluster size and composition in the size range studied. Meanwhile, Co(N)V(M) clusters show reduction of average moments with increasing V doping, consistent with what is expected in bulk CoV. The results are discussed within the virtual bound states model.

Magnetic moments and adiabatic magnetization of free cobalt clusters

Magnetizations and magnetic moments of free cobalt clusters Co(N) (12 < N < 200) in a cryogenic (25 K < or = T < or = 100 K) molecular beam were determined from Stern-Gerlach deflections. All clusters preferentially deflect in the direction of the increasing field and the average magnetization resembles the Langevin function for all cluster sizes even at low temperatures. We demonstrate in the avoided crossing model that the average magnetization may result from adiabatic processes of rotating and vibrating clusters in the magnetic field and that spin relaxation is not involved. This resolves a long-standing problem in the interpretation of cluster beam deflection experiments with implications for nanomagnetic systems in general.

Spin relaxation in isolated molecules and clusters: The interpretation of Stern-Gerlach experiments

Intramolecular spin relaxation may occur in isolated molecules or clusters provided that the density of rovibrational eigenstates is sufficiently high to serve as an energy bath and angular momentum is conserved. In the coupled, zero-field limit, total angular momentum (J) is the sum of spin (S) and rotational (N) momenta such that J and M(J) are good angular momentum quantum numbers. In the coupled limit, transitions between Zeeman levels (Delta M(J)++0) cannot occur in the absence of an external torque. However, in the high-field limit, J and M(J) are no longer good quantum numbers, as N and S are decoupled and only their projections on the z axis defined by the external field are invariant. In this case M(N) and M(S) remain as good quantum numbers so that angular momentum conserving transitions can occur subject to the selection rule Delta M(N)=-Delta M(S). Determination of the magnetic moments of isolated molecules and clusters via a thermodynamics-based analysis requires that their magnetizations are measured at sufficiently large fields that spin-rotation effects become negligible and the Zeeman level structure approaches the free-spin case.