Synthesis and magnetic properties of cobalt nanocubes

Gräf, Christian P.; Birringer, R.; Michels, Andreas

doi:10.1103/physrevb.73.212401

Cited by 43 publications

(35 citation statements)

References 27 publications

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“…This behavior contrasts markedly with the behavior of isolated Ho 3 ions. NMR and SQUID magnetometry of LiHo 0:002 Y 0:998 F 4 found strong resonances at a set of longitudinal fields corresponding to nuclear hyperfine level crossings in the single-ion energy diagram [9,10]. These level crossings occur at integer multiples of 230 Oe, substantially larger than the 50 -80 Oe at which the effects discussed here emerge, and are discrete rather than continuous.…”

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Quantum Projection in an Ising Spin Liquid

et al. 2007

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A transverse magnetic field is used to scan the diagonal and off-diagonal susceptibility of the uniaxial quantum magnet, LiHo 0:045 Y 0:955 F 4 . Clusters of strongly coupled spins act as the primary source for the response functions, which result from a field-induced quantum projection of the system into a classically forbidden (meaning non-Ising) regime. Calculations based on spin pairs reproduce only some features of the data and fail to predict the measured off-diagonal response, providing evidence of a multispin collective state. DOI: 10.1103/PhysRevLett.99.057203 PACS numbers: 75.45.+j, 75.50.Dd, 75.50.Lk, 76.30.Kg A basic feature of quantum mechanics is the superposition of states and the projection of these superpositions into observable quantities. From the Stern-Gerlach experiment of 1922, where quantum projection was first demonstrated with angular momentum states in silver atoms [1], to spin echoes in nuclear magnetic resonance [2], where a series of radio frequency pulses induce the precession of nuclear spins projected into classically inaccessible states, strict experimental protocols have been derived for quantum manipulation at the atomic level. For quantum information purposes, it would be advantageous to extend these techniques to coherent clusters of atoms and to explore such effects in solids. In this Letter, we pioneer measurements of the off-diagonal susceptibility to observe quantum mixing effects in a uniaxial magnetic salt, where we are able to rotate clusters of spins into a classically forbidden (meaning non-Ising) state, transverse to the spin axis. The spins can be manipulated by a combination of ac and dc magnetic fields, detected by a multiaxis susceptometer, and parsed for their quantum-mechanical (xy) or classical (polarized along z, the Ising axis) nature by sweeping transverse magnetic field or temperature, respectively. Our technique takes full advantage of the tensor nature of the magnetic susceptibility, revealing the fundamental role played by the off-diagonal terms [3] in the Hamiltonian.Comparison of the results with calculations including only single ions and pairs of ions shows that the off-diagonal response is not only large, but that it also displays the characteristics of a quantum spin liquid [3].The results of the technique depend crucially on two properties of our system: (i) the ability to introduce quantum mechanics via a controllable, external tuning parameter, and (ii) the predilection of disorder to form spin clusters that may occur rarely but can dominate the physics. In particular, the random distribution of magnetic Ho ions in the diluted, spin-1=2 Ising system LiHo 0:045 Y 0:955 F 4 gives rise to regions where the local density of Ho is comparable to that of the pure compound, and hence are locally ferromagnetic or antiferromagnetic depending on the displacement between nearest neighbors. The Ising spins are constrained to point up or down along the crystallographic c axis, and can be controllably mixed with the application of a magnetic field H t tr...

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Quantum Projection in an Ising Spin Liquid

et al. 2007

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“…The hysteresis loops were measured first at 5 K and then at 300 K. The saturation magnetization value was determined to be 111 A m 2 /kg at 5 K and 107 A m 2 /kg at 300 K, which is significantly lower than the saturation magnetization value of 162 A m 2 /kg at 300 K for bulk hcp Co [17]. This lower value of saturation magnetization is probably due to the combination of a different crystalline structure of the Co nanocubes, the presence of many small particles which have not saturated at the highest field, and probably also a small amount of surface oxidation.…”

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confidence: 99%

“…Ref. [17] reported on the synthesis and magnetic properties of Co nanocubes, which were prepared by wet-chemistry, but these nanocubes were a mixture of hexagonal close packed (hcp) Co and e-Co [17]. In this paper, we report on the synthesis and characterization of single phase e-Co nanocubes and their assemblies.…”

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confidence: 94%

“…With recent advancements in the wet-chemical synthesis of magnetic nanoparticles with controllable sizes and shapes, several magnetic nanocubes including iron [6,7], iron oxides [8], iron-platinum [9], and manganese ferrite [10] have been synthesized. In the case of cobalt (Co) nanoparticles, although the synthesis and characterization of spherical nanoparticles and nanodisks have been well investigated [11][12][13][14][15][16], there are only few reports on Co nanocubes [13,17]. Ref.…”

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Dipolar chains formed by chemically synthesized cobalt nanocubes

Cheng¹,

Shull²,

Walker³

2009

Journal of Magnetism and Magnetic Materials

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“…From the experimental point of view, there are many methods that have been used to prepare various types of magnetic NP systems which have many applications in different types of nanotechnology areas [8][9][10][11][12]. On the other hand, the magnetic and thermodynamic properties of these NP systems have been studied by a variety of techniques, such as the mean-field theory (MFT) [13], effectivefield theory (EFT) with correlations [14][15][16][17], Green functions (GF) formalism [18], variational-cumulant expansion (VCE) [19], and Monte Carlo (MC) simulations [20][21][22].…”

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confidence: 99%