A.J. Van Duyneveldt

Bio: A.J. Van Duyneveldt is an academic researcher from Leiden University. The author has contributed to research in topics: Relaxation (NMR) & Antiferromagnetism. The author has an hindex of 18, co-authored 92 publications receiving 1426 citations. Previous affiliations of A.J. Van Duyneveldt include Spanish National Research Council.

Magnetic Properties of Transition Metal Compounds

Abstract: I. Paramagnetism: The Curie Law.- A. Introduction.- B. Diamagnetism and Paramagnetism.- C. Magnetic Moment of a Magnetic Ion Subsystem.- D. Some Curie Law Magnets.- E. Susceptibilities of the Lanthanides.- F. Temperature Independent Paramagnetism.- References.- II. Thermodynamics and Relaxation.- A. Introduction.- B. Thermodynamic Relations.- C. Thermal Effects.- D. Adiabatic Demagnetization.- E. Relaxation Time and Transition Probability.- F. Spin-lattice Relaxation Processes.- G. Susceptibility in Alternating Fields.- H. Adiabatic Susceptibilities.- References.- III. Paramagnetism: Zero-Field Splittings.- A. Introduction.- B. Schottky Anomalies.- C. Adiabatic Demagnetization.- D. Van Vleck's Equation.- E. Paramagnetic Anisotropy.- F. Effective Spin.- G. Direct Measurement of D.- H. Electron Paramagnetic Resonance (EPR).- References.- IV. Dimers and Clusters.- A. Introduction.- B. Energy Levels and Specific Heats.- C. Magnetic Susceptibilities.- D. Copper Acetate and Related Compounds.- E. Some Other Dimers.- F. EPR Measurements.- G. Clusters.- H. The Ising Model.- References.- V. Long-Range Order.- A. Introduction.- B. Molecular Field Theory of Ferromagnetism.- C. Thermal Effects.- D. Molecular Field Theory of Antiferromagnetism.- E. Ising, XY, and Heisenberg Models.- F. Critical Point Exponents.- G. Cu(NO3)2*21/2H2O.- H. Dipole-Dipole Interactions.- I. Exchange Effects on Paramagnetic Susceptibilities.- J. Superexchange.- References.- VI. Short-Range Order.- A. Introduction.- B. One-Dimensional or Linear Chain Systems.- C. Two-Dimensional or Planar Systems.- D. Long-Range Order.- References.- VII. Special Topics: Spin-Flop, Metamagnetism, Ferrimagnetism and Canting.- A. Introduction.- B. Phase Diagrams and Spin-Flop.- C. Metamagnetism.- D. Ferrimagnetism.- E. Canting and Weak Ferromagnetism.- References.- VIII. Selected Examples.- A. Introduction.- B. Some Single Ion Properties.- 1. Ti3+.- 2. V3+.- 3. VO2+.- 4. Cr3+.- 5. Mn2+.- 6. Fe3+.- 7. Fe2+ and Cr2+.- 8. Co2+.- 9. Ni2+.- 10. Cu2+.- 11. Lanthanides.- C. Some Examples.- 1. Iron(III) Methylammonium Sulfate.- 2. CaCu(OAc)4*6H2O.- 3. Hydrated Nickel Halides.- 4. Hydrated Nickel Nitrates.- 5. Tris Dithiocarbamates of Iron(III).- 6. Spin-3/2 Iron(III).- 7. Manganous Acetate Tetrahydrate.- 8. [M(C5H5NO)6]ClO4)2.- 9. NiX2L2.- 10. [(CH3)3NH]MX3*2H2O.- References.- Append.- A. Physical Constants.- B. Hyperbolic Functions.- Formula Index.

Activated dynamics in a two-dimensional Ising spin glass: Rb2Cu1-xCoxF4.

Abstract: The complex ac susceptibility of the two-dimensional Ising spin glass ${\mathrm{Rb}}_{2}$${\mathrm{Cu}}_{0.782}$${\mathrm{Co}}_{0.218}$${\mathrm{F}}_{4}$ is measured as a function of the temperature and frequency. The results are first analyzed in terms of the Cole-Cole formalism. It is found that the median relaxation time ${\ensuremath{\tau}}_{c}$ diverges towards ${T}_{c}$=0 K over as many as 16 decades according to activated dynamics, i.e., ${\ensuremath{\tau}}_{c}$\ensuremath{\propto}exp[(b/T${)}^{1+\ensuremath{\psi}\ensuremath{ u}}$]. The distribution of relaxation times appears to be nearly symmetric in ln\ensuremath{\tau}, covering at least 10 decades in width. These findings are corroborated with analyses based on exponential-logarithmic and stretched-exponential forms of the time decay of the spin-spin correlation function. The out-of-phase susceptibility is further found to be in conformity with activated dynamic scaling over a wide range of temperatures and frequencies. For the critical exponents the various methods of analysis yield, on the average, \ensuremath{\gamma}=4.4\ifmmode\pm\else\textpm\fi{}0.2, \ensuremath{ u}=2.4\ifmmode\pm\else\textpm\fi{}0.3, \ensuremath{\theta}=-0.41\ifmmode\pm\else\textpm\fi{}0.05, and \ensuremath{\psi}=0.8\ifmmode\pm\else\textpm\fi{}0.2.

Dynamical behavior of the susceptibility around the freezing temperature in (Eu,Sr)S

Abstract: New measurements of the ac susceptibility in zero field for a (${\mathrm{Eu}}_{0.2}$${\mathrm{Sr}}_{0.8}$)S single crystal are reported. For the first time in a spin-glass we can resolve the frequency dependence of the inphase component ${\ensuremath{\chi}}^{\ensuremath{'}}$ (dispersion) as well as the out-of-phase component ${\ensuremath{\chi}}^{\ensuremath{'}\ensuremath{'}}$ (absorption). From these studies a clear change in the dynamic behavior of the system around the freezing temperature is found, which can be related to large ferromagnetic clusters. The susceptibility behavior is described in terms of a wide distribution of relaxation times characterizing the intercluster interactions.

Frequency and field dependence of the ac susceptibility of the Au Mn spin-glass

Abstract: We have measured the ac susceptibility for $\mathrm{Au}\mathrm{Mn}$ containing 2.98 at.% Mn. Below the spin-glass freezing temperature ${T}_{f}$ a small frequency dependence of $\ensuremath{\chi}$ is found. The application of an external magnetic field near ${T}_{f}$ shows a distinct reduction of ${\ensuremath{\chi}}^{\ensuremath{'}}$. A comparison of the susceptibility behavior with that of other metallic spin-glass alloys containing manganese is made.

Long-Range Order

Abstract: We now expand the concept of exchange to include interactions throughout a three-dimensional (3-d) crystalline lattice. The interactions are not necessarily long-range, and probably are important only for first through fourth nearest neighbors, but the effects are observed over large distances in a sample. Transitions to such long-range order are characterized by both characteristic specific heat anomalies and susceptibility behavior quite different from what has been described above. In other words, the transition to an ordered state is in fact a phase transition.

Spin glasses: Experimental facts, theoretical concepts, and open questions

Abstract: This review summarizes recent developments in the theory of spin glasses, as well as pertinent experimental data. The most characteristic properties of spin glass systems are described, and related phenomena in other glassy systems (dielectric and orientational glasses) are mentioned. The Edwards-Anderson model of spin glasses and its treatment within the replica method and mean-field theory are outlined, and concepts such as "frustration," "broken replica symmetry," "broken ergodicity," etc., are discussed. The dynamic approach to describing the spin glass transition is emphasized. Monte Carlo simulations of spin glasses and the insight gained by them are described. Other topics discussed include site-disorder models, phenomenological theories for the frozen phase and its excitations, phase diagrams in which spin glass order and ferromagnetism or antiferromagnetism compete, the Ne\'el model of superparamagnetism and related approaches, and possible connections between spin glasses and other topics in the theory of disordered condensed-matter systems.

Nonexponential relaxations in strong and fragile glass formers

Abstract: Deviations from thermally activated and from exponential response are typical features of the vitrification phenomenon and previously have been studied using viscoelastic, dielectric, calorimetric, optical, and other techniques. Linear response data from literature on about 70 covalent glass formers, ionic melts, supercooled liquids, amorphous polymers, and glassy crystals are surveyed. Except for orientational glasses and monohydric aliphatic alcohols a distinct but broad correlation of non‐Debye behavior with non‐Arrhenius relaxations is found. Within the broad trend several groups of materials, distinguished by their respective molecular complexity, can be identified and are shown to exhibit narrow correlations. At a given degree of deviation from Arrhenius behavior externally imposed stresses are relaxed with a departure from exponential behavior which is stronger the more the molecular or atomic subunits of the glassforming material are interconnected with each other.

Proximity effects in superconductor-ferromagnet heterostructures

Abstract: The proximity effect at superconductor-ferromagnet interfaces produces damped oscillatory behavior of the Cooper pair wave function within the ferromagnetic medium. This is analogous to the inhomogeneous superconductivity, predicted long ago by Fulde and Ferrell (P. Fulde and R. A. Ferrell, 1964, ``Superconductivity in a strong spin-exchange field,'' Phys. Rev. 135, A550--A563), and by Larkin and Ovchinnikov (A. I. Larkin and Y. N. Ovchinnikov, 1964, ``Inhomogeneous state of superconductors,'' Zh. Eksp. Teor. Fiz. 47, 1136--1146 [Sov. Phys. JETP 20, 762--769 (1965)]), and sought by condensed-matter experimentalists ever since. This article offers a qualitative analysis of the proximity effect in the presence of an exchange field and then provides a description of the properties of superconductor-ferromagnet heterostructures. Special attention is paid to the striking nonmonotonic dependence of the critical temperature of multilayers and bilayers on the ferromagnetic layer thickness as well as to the conditions under which ``$\ensuremath{\pi}$'' Josephson junctions are realized. Recent progress in the preparation of high-quality hybrid systems has permitted the observation of many interesting experimental effects, which are also discussed. Finally, the author analyzes the phenomenon of domain-wall superconductivity and the influence of superconductivity on the magnetic structure in superconductor-ferromagnet bilayers.