Phase transitions in megagauss magnetic fields

Zvezdin, A. K.; Lubashevskii, I. A.; Levitin, R. Z.; Platonov, V.V.; Tatsenko, O. M.

doi:10.1070/pu1998v041n10abeh000465

Cited by 15 publications

(11 citation statements)

References 14 publications

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“…The high-field magnetization could be and has been measured in megagauss experiments. 54 Interestingly, the magnetization data given in Ref. 54 show pronounced features, likely related to magnetization steps, between 180 T and 400 T which could be compatible with the parameterization of Ref.…”

Section: Magnetization As Function Of Applied Fieldsupporting

confidence: 77%

Thermodynamic observables ofMn12-acetate calculated for the full spin Hamiltonian

Hanebaum

Schnack

2015

Phys. Rev. B

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35 years after its synthesis magnetic observables are calculated for the first time for the molecular nanomagnet Mn12-acetate using a spin-Hamiltonian that contains all spins. Starting from a very advanced DFT parameterization [Phys. Rev. B 89, 214422] we evaluate magnetization and specific heat for this anisotropic system of 12 manganese ions with a staggering Hilbert space dimension of 100,000,000 using the Finite-Temperature Lanczos Method.

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Section: Magnetization As Function Of Applied Fieldsupporting

confidence: 77%

Thermodynamic observables ofMn12-acetate calculated for the full spin Hamiltonian

Hanebaum

Schnack

2015

Phys. Rev. B

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“…1b) are expected to be antiferromagnetic (AF) and dominant. Most of the earlier attempts to determine the exchange parameters had focused on the temperature dependence of the magnetic susceptibility between 300 and 2 K. [33,34] This dataset is too narrow, which is illustrated by the diversity of the parameter sets in the literature, all reasonably reproducing the magnetic susceptibility. In our approach, in addition to the magnetic susceptibility, we made use of the INS results and fixed all the levels shown in Figure 3b.…”

Section: Feature Articlementioning

confidence: 98%

Single‐Molecule Magnets Under Pressure

Bircher

Chaboussant

Dobe

et al. 2006

Adv Funct Materials

149

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We feature our recent work in the field of single‐molecule magnets (SMMs) using inelastic neutron scattering (INS). The term “pressure” in the title has a triple meaning. First, there is the expectation from research‐funding agencies and the public to make some significant steps towards applications. Second, the synthesis of new compounds and the applications of physical techniques for their understanding are being pushed to their limits. And third, by applying hydrostatic pressure, valuable insight into the mechanisms behind the SMM phenomena can be gained. Examples from our research have been taken to illustrate these points. After a brief introduction to the technique, the strength of INS for the accurate determination of exchange and anisotropy interactions in SMMs is highlighted. We hope to demonstrate that, by pushing INS measurements to their limits, i.e., using the best available neutron sources and instrumentation, combined with high quality samples, new insights into the relevant physical processes in SMMs can be gained.

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“…The first experimental information was provided by magnetization measurements at very high fields using an explosive compression technique which can access magnetic fields in excess of H = 900 T. 38,39 A series of peaks is observed between 300 to 600 T in the field derivative dM / dH, suggesting important steps in the magnetization curve which may be interpreted in terms of crossovers from S =10 to S = 11, 12, . .…”

Section: Magnetic Excitationsmentioning

confidence: 99%

“…38,39 The fixed value of the weighted sum of exchange constants C 1 has a direct correspondence to the saturation field of the system, at which all bonds must be polarized ferromagnetically. The predicted T = 0 magnetization curve, by which is meant here the spin S ϳ M / g B as a function of applied field H, is shown in Fig.…”

Section: High-field Magnetizationmentioning

confidence: 99%

Exchange interactions and high-energy spin states inMn12-acetate

et al. 2004

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We perform inelastic neutron scattering measurements on the molecular nanomagnet Mn 12 -acetate to measure the excitation spectrum up to 45 meV ͑500 K͒. We isolate magnetic excitations in two groups at 5 -6.5 meV ͑60-75 K͒ and 8 -10.5 meV ͑95-120 K͒, with higher levels appearing only at 27 meV ͑310 K͒ and 31 meV ͑360 K͒. From a detailed characterization of the transition peaks we show that all of the lowenergy modes appear to be separate S = 9 excitations above the S = 10 ground state, with the peak at 27 meV ͑310 K͒ corresponding to the first S = 11 excitation. We consider a general model for the four exchange interaction parameters of the molecule. The static susceptibility is computed by high-temperature series expansion and the energy spectrum, matrix elements, and ground-state spin configuration by exact diagonalization. The theoretical results are matched with experimental observation by inclusion of cluster anisotropy parameters, revealing strong constraints on possible parameter sets. We conclude that only a model with dominant exchange couplings J 1 ϳ J 2 ϳ 5.5 meV ͑65 K͒ and small couplings J 3 ϳ J 4 ϳ 0.6 meV ͑7 K͒ is consistent with the experimental data.Mn 12 -acetate 4,16-18 is a mixed-valence ͑Mn 3+ /Mn 4+ ͒ compound where the magnetic ions are arranged in two groups: a central core composed of a tetrahedron of four Mn 4+ ions ͑S =3/2͒ and an external ring, or crown, of eight Mn 3+ ions ͑S =2͒. Figure 1 shows the Mn 12 -acetate cluster viewed along the c axis. The point group of the Mn 12 molecule in the crystal structure is S 4 . To simplify the analysis we make the additional assumption of fourfold rotation and reflection symmetry of the individual molecular clusters, and return later to a discussion of this approximation. Each cluster is only very weakly coupled to its neighbors, which are separated from each other by molecules of water and acetic acid, such that no long-range magnetic order has been found for temperatures as low as the mK range. Consequently, most of the experimental work performed at temperatures exceeding 1 K may be interpreted in terms of the properties of a single molecule. Neighboring Mn ions within a cluster are coupled in an intricate pattern by different types of -oxo bridge and by acetate bridges, as a result of which both antiferromagnetic (AFM) and ferromagnetic (FM) exchange interactions may be present in the system. A schematic representation of the exchange couplings is shown in Fig. 2. Within the approximation of fourfold cluster symmetry there are three inequivalent Mn sites with four different exchange couplings between neighboring Mn ions: J 1 (involving two -oxo bridges) and J 2 = J 2a Ϸ J 2b (one -oxo bridge) between Mn 3+ and Mn 4+ ions, J 3 between Mn 4+ ions inside the core tetrahedron (two -oxo bridges), and J 4 = J 4a Ϸ J 4b between Mn 3+ ions around the external ring (one -oxo bridge and two carboxylate groups). Inspection of the Mn-Mn distances and Mn-O-Mn angles presented in Table I suggests that the approximations J 2a Ϸ J 2b and J 4a Ϸ J 4b are emi...

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Phase transitions in megagauss magnetic fields

Abstract: ``Phase transitions in megagauss magnetic éelds.'' (2) Pustovo|¯t V I (Central Design Bureau of Unique Instrument Manufacture, Russian Academy of Sciences).`C ollinear diffraction: phenomena and devices.'' A brief presentation of the first report is given below.

Cited by 15 publications

References 14 publications

Thermodynamic observables ofMn12-acetate calculated for the full spin Hamiltonian

Thermodynamic observables ofMn12-acetate calculated for the full spin Hamiltonian

Single‐Molecule Magnets Under Pressure

Exchange interactions and high-energy spin states inMn12-acetate

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