Abstract: A giant magnetocaloric effect was found in MnAs, which undergoes a first-order ferromagnetic to paramagnetic transition at 318 K. The magnetic entropy change caused by a magnetic field of 5 T is as large as 30 J/K kg at the maximum value, which exceeds that of conventional magnetic refrigerant materials by a factor of 2–4. The adiabatic temperature change reaches 13 K in a field change of 5 T. The substitution of 10% Sb for As reduces the thermal hysteresis and lowers the Curie temperature to 280 K, while the giant magnetocaloric properties are retained.

Abstract: Magnetization of the compound LaFe11.4Si1.6 with the cubic NaZn13-type structure was measured as functions of temperature and magnetic field around its Curie temperature TC of ∼208 K. It is found that the magnetic phase transition at TC is completely reversible. Magnetic entropy change ΔS, allowing one to estimate the magnetocaloric effect, was determined based on the thermodynamic Maxwell relation. The achieved magnitude of |ΔS| reaches 19.4 J/kg K under a field of 5 T, which exceeds that of most other materials involving a reversible magnetic transition in the corresponding temperature range. The large entropy change is ascribed to the sharp change of magnetization, which is caused by a large negative lattice expansion at the TC. An asymmetrical broadening of |ΔS| peak with increasing field was observed, which is resulted from the field-induced itinerant-electron metamagnetic transition from the paramagnetic to ferromagnetic state above the TC.

Abstract: We demonstrate high-quality, highly fluorescent, ZnSe colloidal nanocrystals (or quantum dots) that are doped with paramagnetic Mn2+ impurities. We present luminescence, magnetic circular dichroism (MCD), and electron paramagnetic resonance (EPR) measurements to confirm that the Mn impurities are embedded inside the nanocrystal. Optical measurements show that by exciting the nanocrystal, efficient emission from Mn is obtained, with a quantum yield of 22% at 295 K and 75% below 50 K (relative to Stilbene 420). MCD spectra reveal an experimental Zeeman splitting in the first excited state that is large (28 meV at 2.5 T), depends on doping concentration, and saturates at modest fields. In the low field limit, the magnitude of the effective g factor is 430 times larger than in undoped nanocrystals. EPR experiments exhibit a six-line spectrum with a hyperfine splitting of 60.4 × 10-4 cm-1, consistent with Mn substituted at Zn sites in the cubic ZnSe lattice.

Abstract: Barium-filled skutterudites BayCo4Sb12 with an anomalously large filling fraction of up to y=0.44 have been synthesized. The lattice parameters increase linearly with Ba content. Magnetic susceptibility data show that Ba0.44Co4Sb12 is paramagnetic, which implies that some of the Co atoms in BayCo4Sb12 have acquired a magnetic moment. The presence of the two different valence states of Co (Co3+ and Co2+) leads to the anomalously large barium filling fraction even without extra charge compensation. All samples show n-type conduction. The electrical conductivity increases with increasing the Ba filling fraction. The lattice thermal conductivity of BayCo4Sb12 is significantly depressed as compared to unfilled Co4Sb12. The dimensionless thermoelectric figure of merit, ZT, increases with increasing temperature reaching a maximum value of 1.1 for Ba0.24Co4Sb12 at 850 K.

Abstract: We describe preparation and magnetic properties of an organic pi-conjugated polymer with very large magnetic moment and magnetic order at low temperatures. The polymer is designed with a large density of cross-links and alternating connectivity of radical modules with unequal spin quantum numbers (S), macrocyclic S = 2 and, cross-linking S = (1/2) modules, which permits large net S values for either ferromagnetic or antiferromagnetic exchange couplings between the modules. In the highly cross-linked polymer, an effective magnetic moment corresponding to an average S of about 5000 and slow reorientation of the magnetization by a small magnetic field (less than or equal to 1 oersted) below a temperature of about 10 kelvin are found. Qualitatively, this magnetic behavior is comparable to that of insulating spin glasses and blocked superparamagnets.

Abstract: After the dynamo experiment in November 1999 [A. Gailitis et al., Phys. Rev. Lett. 84, 4365 (2000)] had shown magnetic field self-excitation in a spiraling liquid metal flow, in a second series of experiments emphasis was placed on the magnetic field saturation regime as the next principal step in the dynamo process. The dependence of the strength of the magnetic field on the rotation rate is studied. Various features of the saturated magnetic field are outlined and possible saturation mechanisms are discussed.

Abstract: Preface.Abbreviations and Symbols.A. GENERAL PART.1. Physical Fundamentals of Electron Spin Resonance.2. Paramagnetic Organic Species and Their Generation.3. Electron-Nuclear Magnetic Interaction.4. Spin Density, Spin Population, Spin Polarization, and Spin Delocalization.5. Multiresonance.6. Taking and Analyzing ESR Spectra.B. SPEICAL PART.7. Organic Radicals Centered on One, Two, or Three Atoms.8. Conjugated Hydrocarbon Radicals.9. Conjugated Radicals with Heteroatoms.10. Saturated Hydrocarbon Radicals.11. Biradicals and Triplet-state Molecules.Appendices.References.Index.

Abstract: This lecture is aimed at providing an overview of the main phenomena which determine the magnetism of matter and the properties of magnetic materials The main interactions involved are qualitatively described in the first section The models at the basis of the interpretation of the magnetic properties of materials are presented in the second section The subtle interplay between various interactions may lead to a variety of different behaviours which are described in Sect 3 The influence of dipolar interactions on the magnetic properties at the macroscopic scale is described in Sec 4, and the concept of coercivity, important for applications is introduced in the last part of this section The last section deals with thin films and small particles, systems in which the reduction in material dimension has a drastic influence on the observed properties

Abstract: Hexagonal, nonperovskite HoMnO3 oxide, containing a triangular arrangement of Mn3+ cations, has been prepared in polycrystalline form by the thermal decomposition of metal citrates. The crystal structure has been refined from neutron powder diffraction data. Magnetic and specific-heat measurements anticipate a complex phase diagram: HoMnO3 becomes magnetically ordered at TN ≈ 72 K, and another two magnetic transitions take place at lower temperatures. Neutron powder diffraction measurements demonstrate that, below the ordering temperature, the moments of the Mn3+ cations adopt a triangular spin arrangement, the magnetic moments lying in the basal plane and parallel to the [100] axis. At T = 44.6 K, the moments suddenly reorientate within the basal plane and become aligned perpendicularly to the initial direction. Below T = 25.4 K, an ordered magnetic moment is observed on the Ho atoms at the 4b sites of the crystal structure, whereas those of the 4a site remain in a paramagnetic state. The Ho atoms adopt...

Abstract: Ising spins put onto a Barabasi-Albert scale-free network show an effective phase transition from ferromagnetism to paramagnetism upon heating, with an effective critical temperature increasing as the logarithm of the system size. Starting with all spins up and upon equilibration pinning the few most-connected spins down nucleates the phase with most of the spins down.

Abstract: For the first time, a very general theoretical method is proposed to interpret the full electron paramagnetic resonance (EPR) spectra at multiple temperatures and frequencies in the important case of S-state metal ions complexed in liquid solution. This method is illustrated by a careful analysis of the measured spectra of two Gd3+ (S = 7/2) complexes. It is shown that the electronic relaxation mechanisms at the origin of the EPR line shape arise from the combined effects of the modulation of the static crystal field by the random Brownian rotation of the complex and of the transient zero-field splitting. A detailed study of the static crystal field mechanism shows that, contrarily to the usual global models involving only second-order terms, the fourth and sixth order terms can play a non-negligible role. The obtained parameters are well interpreted in the framework of the physics of the various underlying relaxation processes. A better understanding of these mechanisms is highly valuable since they partly control the efficiency of paramagnetic metal ions in contrast agents for medical magnetic resonance imaging (MRI).

Abstract: A novel synthesis of the title compound, C2S3N3 (1) is reported. X- and K-band EPR spectra on dilute solutions of 1 indicate delocalisation of the unpaired spin density over both heterocyclic rings in agreement with DFT calculations. An XRPD study indicates that it crystallises in two morphologies with both phases formed during vacuum sublimation. The XRPD studies indicate that on cooling below 230 K, only the triclinic phase (P) becomes detectable, whereas on warming above 320 K, just the monoclinic phase (P21/c) becomes observed. The crystal structure of the monoclinic phase has been examined by variable temperature single crystal X-ray diffraction in the region 300–225 K and reveals a regular π-stacked structure. A crystal structure of the triclinic phase is reported at 150 K and exhibits a dimeric π-stacked motif. Susceptibility measurements show that the monoclinic phase is paramagnetic whereas the triclinic phase is diamagnetic. This radical exhibits thermal hysteresis with a wide range of bistability; EPR and magnetic susceptibility measurements indicate Tc↓ = 234 K, and Tc↑ = 317 K. The magnetic behaviour of the monoclinic phase is consistent with strong antiferromagnetic exchange interactions between open shell doublet states (J = −320 K) along the π-stacking direction, although significant inter-stack interactions are required to model the data adequately. In contrast the dimeric phase is essentially diamagnetic, with the residual paramagnetism indicating a very large singlet–triplet separation (|2J| > 2000 K). The magnetic exchange interactions in both phases are probed through a series of DFT calculations using the broken-symmetry approach. These confirm the presence of strong magnetic exchange interactions along the π-stacking direction in the high temperature phase (2J = −182 K), but with additional interstack interactions which are an order of magnitude smaller. Calculations on the triclinic phase indicate that it is best considered as a dimer with an open-shell singlet state with a very large singlet–triplet separation (2J = −2657 K). The magnitude of J for both phases from theory and experiment are in good agreement. The origin of the thermal hysteresis is attributed to the presence of two energetically similar structures which have a low energy barrier to interconversion. The thermodynamic parameters associated with the interconversion process have been probed by DSC studies. It confirms the first order nature of the transition with Tc↓ = 232.3 K (ΔH↓ = 1.41 kJ mol−1, ΔS↓ = 6.0 J mol−1 K−1) and Tc↑ = 320.5 K (ΔH↑ = 1.86 kJ mol−1, ΔS↑ = 5.8 J mol−1 K−1).

Abstract: Lectures.- to Magnetism and Magnetic Materials.- Spectroscopy and Magnetism: An Introduction.- Instrumentation Developments for Polarization Dependent X-ray Spectroscopies.- Dichroism in X-ray Absorption.- A Photoemission Primer.- Micromagnetics: Dynamical Aspects.- Magnetization Reversal of Nano-particles.- Molecular Magnetism: Design of High-TC Prussian Blue Molecule Based Magnets.- Spin-Resolved Circularly Polarised Resonant Photoemission: Cu2+ as a Model System.- X-ray Magnetic Circular Dichroism at Low Temperature.- High-Pressure Magnetism and Magnetic Circular Dichroism.- Resonant Inelastic X-ray Scattering.- Some Nuclear Techniques in Experimental Magnetism: Mossbauer Effect, Neutron Scattering and Nuclear Magnetic Resonance.- Linear and Non-linear Magneto-optical Effects: Magnetism of Thin Film Structures.- Topical Cases.- Relation Between X-ray Magnetic Linear Dichroism and Magnetocrystalline Anisotropy.- Field Induced Magnetic Circular Dichroism in Paramagnetic Solids.- X-ray Magnetic Circular Dichroism in the Investigation of Magnetisation Dynamics in the Nanosecond Time Scale.- Magnetism in Nanoscale Fe Clusters Studied by Dichroism in X-ray Absorption and Photoemission.- X-ray Spectromicroscopy and Applications to Magnetic Materials.- Magnetic Ordering and Resonance Process in Sm Epitaxial Films and Superlattices: An RXMS Study.- X-ray Gyrotropy Related Spectroscopies: Natural Circular Dichroism and Non-reciprocal Linear Dichroism.- Synchrotron-Based Mossbauer Spectroscopy at Iron Islands and Clusters on Tungsten (110).

Abstract: We report the preparation, crystallization, and solid-state characterization of ethyl (3)- and butyl (4)-substituted spiro-biphenalenyl radicals. Both of these compounds are found to be conducting face-to-face π-dimers in the solid state but with different room-temperature magnetic ground states. At room temperature, 4 exists as a diamagnetic π-dimer (interplanar separation of ∼3.1 A), whereas 3 is a paramagnetic π-dimer (interplanar separation of ∼3.3 A), and both compounds show phase transitions between the paramagnetic and diamagnetic forms. Electrical resistivity measurements of single crystals of 3 and 4 show that the transition from the high-temperature paramagnetic π-dimer form to the low-temperature diamagnetic π-dimer structure is accompanied by an increase in conductivity by about 2 orders of magnitude. This behavior is unprecedented and is very difficult to reconcile with the usual understanding of a Peierls dimerization, which inevitably leads to an insulating ground state. We tentatively assi...

Abstract: The physical mechanism of the optical transmission of magnetic fluid films under perpendicular magnetic fields is investigated in this work. Under perpendicular magnetic fields, originally dispersed magnetic particles agglomerate to form magnetic columns. The liquid phase is transparent, whereas the columns are opaque. Hence, the liquid phase dominates the optical transmission of the magnetic fluid film. When the field strength is raised, more columns are formed, and the area of the liquid phase is reduced. This leads to the decrease in the optical transmission of the film under higher field strength. The variation in the concentration of the liquid phase under various field strengths also contributes to the transmission of the film. By taking account of the variations of the effective concentration and the area ratio of the liquid phase in the magnetic fluid film under magnetic fields, the resultant magnetic field dependence of the optical transmission was calculated and found to be consistent with the experimental results. This provides evidence for the origin of the field-dependent optical transmission of the magnetic fluid film under external fields.

Abstract: Periodic magnetic nanodot arrays have been produced on an area as large as 1 cm×1 cm by direct nanolithography using interferometric laser radiation. The dots are formed by the local annealing of sputtered amorphous Co–C films in regions where the laser intensity is highest. At room temperature the dots exhibit ferromagnetic order and are embedded in a paramagnetic matrix. The onset of room-temperature ferromagnetism is caused by nanoscale chemical and morphological changes during dot formation and reflects the phase separation of magnetic Co-rich clusters. The present single-step nanolithography is potentially an efficient method for fabrication of patterned magnetic arrays.

Abstract: Measurements of the thermal conductivity as a function of temperature and magnetic field in the 2D dimer spin system ${\mathrm{SrCu}}_{2}({\mathrm{BO}}_{3}{)}_{2}$ are presented. In zero magnetic field the thermal conductivity along and perpendicular to the magnetic planes shows a pronounced double-peak structure as a function of temperature. The low-temperature maximum is drastically suppressed with increasing magnetic field. Our quantitative analysis reveals that the heat current is due to phonons and that the double-peak structure arises from pronounced resonant scattering of phonons by magnetic excitations.

Abstract: A complete theory for paramagnetic relaxation enhancement (PRE) and its dependence on the magnetic field is developed for systems with electron spin S = 1, 3/2, 2, 5/2, 3 and 7/2, characterised by the presence of zero-field splitting (ZFS). The electron spin interacts through dipole–dipole coupling with the nuclear spin residing in the paramagnetic complex (the inner-sphere case) as well as outside of it (the outer-sphere case). The earlier theory for S = 1 and inner-sphere interaction only is included as a special case of the present, more general approach. The theory assumes a slow reorientation of the paramagnetic complex and a lack of correlation between the rotation and translation of the complex and the electron spin dynamics. The electron spin energy level structure is determined by a combination of the Zeeman interaction and the static ZFS, and depends thus on the orientation of the complex in the magnetic field. The electron spin relaxation is described by a Redfield formulation, using the pseudorotation model for the modulation of the transient zero-field splitting. Illustrative calculations are presented, showing that the typical field dependences of the inner- and outer-sphere relaxation enhancements are in general different. The static ZFS is demonstrated to influence the magnetic field dependences by affecting the frequencies occurring in the expressions for spectral densities. The model is applied to interpret the PRE of a slowly-rotating gadolinium(III) complex, a potential magnetic resonance imaging (MRI) contrast agent.

Abstract: The partial density of vibrational states has been measured for Fe in compressed FeO (wustite) using nuclear resonant inelastic x-ray scattering. Substantial changes have been observed in the overall shape of the density of states close to the magnetic transition around 20 GPa from the paramagnetic (low pressure) to the antiferromagnetic (high pressure) state. The results indicate that strong magnetoelastic coupling in FeO is the driving force behind the changes in the phonon spectrum of FeO. The paper presents the first observation of changes in the density of terahertz acoustic phonon states under magnetic transition at high pressure. The study of the electronic and magnetic properties of simple transition-metal compounds is an important topic in diverse fields ranging from solid-state physics to Earth sciences. Iron oxide FeO (wustite) belongs to the group of highly correlated transition metal oxides, being an archetypal insulating antiferromagnetic material at zero temperature. NiO, CoO, and MnO fall in the same group of materials, which are still not well understood by theory. Here we present a study of the vibrational density of states of isotope-enriched Fe0.947O using high-resolution nuclear resonant inelastic x-ray scattering. We observe changes in the density of states that are consistent with the softening of the aggregate shear sound wave velocity of wustite under pressure [1], which we associate with the phase transition from the cubic paramagnetic phase to the rhombohedrally distorted antiferromagnetic phase stable at higher pressures. We show that the phonon density of states is affected by magnetoelastic coupling between phonon and spin subsystems in FeO. The influence of magnetoelastic interaction on sound velocity is well studied up to GHz frequency range. This Letter presents the first observation of changes in density of Terahertz acoustic phonons in the vicinity of the magnetic transition under pressure. Experiments were performed at the synchrotron beam line SRI-CAT 3ID of the Advanced Photon Source (APS), Argonne National Laboratory. The details of the diamond cell and the experimental setup are reported elsewhere [2]. The sample was 25 mm in diameter (loaded without pressure medium), and diamonds with flat 400 mm culets were used. The maximum counting rate in the phonon wing ranged from 10 cps at 0.9 GPa to 2 cps at 48 GPa. The measured spectra, i.e., count rate as a function of the

Abstract: The transient current response following a stepwise decrease of potential from the rest potential is studied for solutions of Ag + , Zn 2+ , Cu 2+ , and Bi 3+ , comparing the behavior in the presence and absence of a 0.5 T magnetic field. In all cases, regardless of whether ions are paramagnetic (Cu 2+ ) or diamagnetic (Ag + , Zn 2+ , Bi 3+ ), the plating current with a field increases in the long-time limit when the potential is stepped into the mass-transport-limited region. The results support the Aogaki model of mass-transport enhancement due to disruption of the diffusion layer by the Lorentz force j X B. There is no effect of the magnetic field on the diffusion coefficient D derived from the Cottrell plots.

Abstract: Examples of the confinement of electrogenerated paramagnetic species in magnetic field gradients surrounding magnetized disk- and cylinder-shaped Fe microelectrodes (250 μm radius) are reported. Magnetization of the Fe microelectrodes in a uniform magnetic field (0.25 T) creates a field gradient in the local vicinity of the electrodes. The force acting on the redox molecule in this region is given by F∇ = 2(m*2/kT)(B·∇)B, where m* is the magnetic dipole of the molecule and B is the magnetic flux density. As anticipated, the distribution of paramagnetic molecules in the solution surrounding the electrode (recorded using video microscopy) is shown to be proportional to the quantity (B·∇)B; i.e., paramagnetic molecules are trapped in regions of space where the product of the field and field gradient is largest. Voltammetric measurements and video images illustrate the effectiveness of the gradient force in trapping paramagnetic molecules at the Fe microelectrodes and are compared with results obtained using ...