Magnetism and Magnetic Isomers in Chromium Clusters

Bloomfield, L. A.; Deng, Jun; Zhang, H.; Emmert, J. W.

doi:10.1142/9789812793805_0016

Cited by 15 publications

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“…This remarkably magnetic form of chromium exists for all clusters from Cr 34 up to at least Cr 133 , and it is possible that it exists for smaller clusters as well. While preliminary measurements showed evidence for the high-moment cluster all the way down to Cr 9 , [35] the more careful measurements presented here were only able to confirm the existence of a high-moment species for Cr 30 .…”

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confidence: 66%

Magnetism and Magnetic Isomers in Free Chromium Clusters

2006

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We have used the Stern-Gerlach deflection technique to study magnetism in chromium clusters of 20-133 atoms. Between 60 K and 100 K, we observe that these clusters have large magnetic moments and respond superparamagnetically to applied magnetic fields. Using superparamagnetic theory, we have determined the moment per atom for each cluster size and find that it often far exceeds the moment per atom present anywhere in the bulk antiferromagnetic lattice. Remarkably, our cluster beam contains two magnetically distinguishable forms of each cluster size with ≥ 34 atoms. We attribute this observation to structural isomers. Even before the rise of nanoscience, atomic clusters were of keen interest to people trying to understand how the physical properties of atoms and molecules evolve with size and shape into those of bulk materials. Clusters are true many-body quantum systems, too large for exact solutions in ordinary space and too small for exact solutions in momentum space, and the properties they exhibit are often rich and complex.One such property, magnetism, offers unparalleled insight into clusters because it is sensitive to electronic and spatial structure, quantum size effects, surface to volume ratio, symmetry, and even temperature. Magnetism has been studied in low-dimensional supported systems (e.g., powders, granular metals, surfaces, and films) since Neel's pioneering work in the late 1940s and in isolated clusters since 1990. Even more dramatic enhancements of magnetism were predicted in clusters of rhodium [12,13] and manganese, [14] 4d and 3d transition metals that are merely paramagnetic in the bulk.Experimental measurements of isolated rhodium and manganese clusters find large magnetic moments in small clusters of these two elements. [15,16,17] Chromium, another of the 3d transition metals, is an itinerant antiferromagnet in the bulk. Below its ∼311 K Néel temperature, bulk chromium exhibits a transverse spin-density wave (SDW) that becomes a longitudinal spin-density wave below ∼123 K.[18] At zero temperature, chromium's SDW has a moment per atom of 0.43 µ B rms and 0.62 µ B peak.If chromium clusters had this same itinerant antiferromagnetic order, as though they were simply portions of the bulk bcc lattice, their moments per atom could not exceed 0.62 µ B .Even 0.62 µ B per atom is small compared to what is observed in iron, cobalt, and nickel clusters. [6,8,9,19] It came as no surprise then when an early study in our laboratory was unable to detect magnetism in chromium clusters of 9-31 atoms and set an upper limit of 0.77 µ B per atom for their magnetic moments. [20] More recently, chromium clusters supported on Au surfaces were shown to be antiferromagnetic.[21] Nonetheless, several theoretical studies predicted that small chromium clusters should be magnetic. [22,23,24,25,26,27]

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confidence: 66%

Magnetism and Magnetic Isomers in Free Chromium Clusters

2006

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“…Transition metal (TM) clusters are of particular interest resulting from their great diversity in geometrical structure, electronic configuration, and spin state . For example, Cr and Mn are both antiferromagnetic in the bulk phase; however, net magnetic moments have been found in chromium (Cr 8–156 ) and manganese (Mn 5–22 ) clusters. , Remarkable magnetic moments were also detected in the clusters of Rh 9–60 and Sc 5–20 , even though their corresponding bulks are paramagnetic. , Another well-known example is gold, whose clusters show exceptional chemical activity toward CO at low temperature while their bulk is inert …”

Section: Introductionmentioning

confidence: 99%

Comparative ab Initio Study of CO Adsorption on Sc_n and Sc_nO (n = 2–13) Clusters

Wang¹,

Wu²,

Du³

et al. 2011

J. Phys. Chem. A

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Using a cluster model, we investigated the similarities and differences in chemical activity and the magnetic properties of Sc(n) clusters (n = 2-13) and their oxides, Sc(n)O, toward CO molecule adsorption via a spin-polarized density functional theory approach. The Sc(n) and Sc(n)O clusters have similar chemical activity at small sizes of n = 2-10, whereas remarkable differences are observed at large sizes of n = 11-13. More interestingly, different magnetic responses are found in the Sc(n) and Sc(n)O clusters with the presence of CO molecule: The magnetic moment is attenuated significantly for Sc(n) with n = 2, 4, 12, and 13, whereas for Sc(n)O, it is enhanced at n = 4 and 13 and is reduced for n = 7, 8, 10, and 11. In particular, the magnetic moment remarkably increases from 7 μ(B) of Sc(13)O to 13 μ(B) of Sc(13)OCO, whereas it reduces from 19 μ(B) of Sc(13) to 5 μ(B) of Sc(13)CO.

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“…The study of structures and magnetic properties on free transition metal (TM) clusters and their oxides has motivated remarkable research activity in the past years. , In this kind of system, the lowered dimensionality and coordination number, as well as high symmetry, are expected to produce nonzero magnetization in clusters when bulk materials are nonmagnetic or to enhance the magnetic moments when the bulk counterpart is already magnetic. For example, enhanced magnetic moments have been found in small iron and cobalt clusters, and ferromagnetic or ferrimagnetic ordering has been observed in chromium and manganese clusters, even though chromium and manganese are both antiferromagnetic in the bulk phase. − …”

Section: Introductionmentioning

confidence: 99%

Theoretical Study of Y_nO₂ and Y_nO₂⁻ (n = 1−8) Clusters

Yang

Xiong

2009

J. Phys. Chem. A

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The structural, electronic, and magnetic properties of Y(n)O(2) and Y(n)O(2)(-) clusters, up to n = 8, have been systematically investigated by using the density-functional approach. Our theoretical results show that the geometries of the ground-state neutral and anionic clusters are similar, except for n = 2. For the lowest-energy structures of the two systems, a two-dimensional to three-dimensional structural transition is identified. In addition, the ionization potentials, electron affinities, electron detachment energies, and gaps are carefully investigated. Here, the calculated electron affinities and electron detachment energies are in good agreement with the experimental data, implying that the predictions of the ground-state configurations of these clusters are reliable. On the basis of the optimized structures, we investigate and discuss the magnetic properties of the two systems for the first time. (PACS numbers: 75.50.Xx. 36.40.Cg,73.22.-f.).

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Magnetism and Magnetic Isomers in Chromium Clusters

Cited by 15 publications

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Magnetism and Magnetic Isomers in Free Chromium Clusters

Magnetism and Magnetic Isomers in Free Chromium Clusters

Comparative ab Initio Study of CO Adsorption on Sc_n and Sc_nO (n = 2–13) Clusters

Theoretical Study of Y_nO₂ and Y_nO₂⁻ (n = 1−8) Clusters

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Magnetism and Magnetic Isomers in Chromium Clusters

Cited by 15 publications

References 0 publications

Magnetism and Magnetic Isomers in Free Chromium Clusters

Magnetism and Magnetic Isomers in Free Chromium Clusters

Comparative ab Initio Study of CO Adsorption on Scn and ScnO (n = 2–13) Clusters

Theoretical Study of YnO2 and YnO2− (n = 1−8) Clusters

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Comparative ab Initio Study of CO Adsorption on Sc_n and Sc_nO (n = 2–13) Clusters

Theoretical Study of Y_nO₂ and Y_nO₂⁻ (n = 1−8) Clusters