Abstract: Using the techniques of microelectromechanical systems, we have constructed a small low-power magnetic sensor based on alkali atoms. We use a coherent population trapping resonance to probe the interaction of the atoms’ magnetic moment with a magnetic field, and we detect changes in the magnetic flux density with a sensitivity of 50pTHz−1∕2 at 10Hz. The magnetic sensor has a size of 12mm3 and dissipates 195mW of power. Further improvements in size, power dissipation, and magnetic field sensitivity are immediately foreseeable, and such a device could provide a hand-held battery-operated magnetometer with an atom shot-noise limited sensitivity of 0.05pTHz−1∕2.

Abstract: In general, magnetic properties of bulk magnetic materials are independent of the humidity of the environment. To obtain a magnetic material that has humidity-sensitive characteristics, water vapour must penetrate the lattice and act on spin sites. Nanoporous materials composed of metal-assembled complexes1,2,3,4 may be expected to display some humidity response because materials in this category can show functionalities such as gas storage and molecular recognition. Here, we demonstrate humidity-induced reversible variations in the magnetic properties of cyano-bridged cobalt(II)–manganese(II)–chromium(III) metal assemblies. The observed magnetic humidity response is due to adsorption and desorption of a ligand water molecule on the cobalt ion, which changes cobalt (II) between a 6- and 4-fold coordination geometry and switches the magnetic interaction between ferromagnetic coupling and antiferromagnetic coupling.

Abstract: We have studied the magnetostructural phase diagram of multiferroic TbMn2O5 as a function of temperature and magnetic field by neutron diffraction. Dielectric and magnetic anomalies are found to be associated with steps in the magnetic propagation vector, including a rare example of a commensurate-incommensurate transition on cooling below 24 K, and in the structural parameters. The geometrically frustrated magnetic structure is stabilized by "canted antiferroelectric" displacements of the Mn3+ ions, an example of the magnetic Jahn-Teller effect. The Tb moments order ferromagnetically at low temperatures in an applied field, while the Mn magnetic structure is largely unchanged.

Abstract: The response of a molecule to an applied external magnetic field can be evaluated by a graphical representation of the induced magnetic field. We have applied this technique to four representative, cyclic organic molecules, that is, to aromatic (C 6 H 6 , D 6 h ), anti-aromatic (C 4 H 4 , D 2 h ) and non-aromatic (C 4 H 8 , D 4 h , and C 6 H 1 2 , D 3 d ) molecules. The results show that molecules that contain a π system possess a long-range magnetic response, while the induced magnetic field is short-range for molecules without π systems. The induced magnetic field of aromatic molecules shields the external field. In contrast, the anti-aromatic molecules increase the applied field inside the ring. Aromatic, anti-aromatic, and non-aromatic molecules can be characterized by the appearance of the magnetic response. We also show that the magnetic response is directly connected to nucleus-independent chemical shifts (NICS).

Abstract: Structural and magnetic properties have been studied for polycrystalline Zn1−xTMxO, where TM (transition metal ions)=Mn, Fe, and Co. No bulk ferromagnetism was observed for single-phase materials, contrary to the existing theories. Single-phase samples demonstrate paramagnetic Curie–Weiss behavior with antiferromagnetic interactions, similar to other diluted magnetic semiconductors. Nonoptimal synthesis conditions lead to formation of second phases that are responsible for spin-glass behavior {ZnMnO3 impurity for Zn1−xMnxO [S. Kolesnik et al., J. Supercond. 15, 251 (2002)]} or high-temperature ferromagnetic ordering [Co metal for Zn1−xCoxO with the Curie temperature TC>800 K or (Zn,Fe)3O4 for Zn1−xFexO with TC=440 K].

Abstract: In materials without spatial inversion symmetry, the spin degeneracy of the conduction electrons can be lifted by an antisymmetric spin–orbit coupling. We discuss the influence of this spin–orbit coupling on the spin susceptibility of such superconductors, with a particular emphasis on the recently discovered heavy Fermion superconductor CePt3Si. We find that, for this compound (with tetragonal crystal symmetry) irrespective of the pairing symmetry, the stable superconducting phases would give a very weak change of the spin susceptibility for fields along the c-axis and an intermediate reduction for fields in the basal plane. We also comment on the consequences for the paramagnetic limiting in this material.

Abstract: This paper is an overview of the studies into the effect of weak magnetic fields on the structure and mechanical properties of nonmagnetic solids of various nature (ionic, covalent, molecular, and metallic crystals, polymers, etc.). The various effects and aftereffects initiated by static, pulsed, and microwave magnetic fields that have been discovered over the past 15 years are classified and critically analyzed. The thermodynamic and kinetic aspects of the magnetic-field sensitivity of real solids with structural defects containing paramagnetic centers (electrons, holes, radicals, excitons, etc.) are discussed. Possible mechanisms for the effect of a weak magnetic field on the defect structure of crystals are considered. Special attention is given to the most developed chemical-physical theory of spin-dependent reactions between mobile particles and unpaired electrons. Interpretation of magnetoplastic effects is proposed in terms of the spin, electron, molecular, and dislocation dynamics of the complex multistage processes initiated by a magnetic field in a system of metastable structural defects.

Abstract: Colloidal cobalt-doped TiO2 (anatase) nanocrystals were synthesized and studied by electronic absorption, magnetic circular dichroism, transmission electron microscopy, magnetic susceptibility, cobalt K-shell X-ray absorption spectroscopy, and extended X-ray absorption fine structure measurements. The nanocrystals were paramagnetic when isolated by surface-passivating ligands, weakly ferromagnetic (Ms = 1.5 x 10-3 mB/Co2+ at 300 K) when aggregated, and strongly ferromagnetic (up to Ms = 1.9 mB/Co2+ at 300 K) when spin-coated into nanocrystalline films. X-ray absorption data reveal that cobalt is in the Co2+ oxidation state in all samples. In addition to providing strong experimental support for the existence of intrinsic ferromagnetism in cobalt-doped TiO2, these results demonstrate the possibility of using colloidal TiO2 diluted magnetic semiconductor nanocrystals as building blocks for assembly of ferromagnetic semiconductor nanostructures with potential spintronics applications.

Abstract: Polynuclear transition metal complexes containing paramagnetic cations have caught the attention of many chemists, since they are one of the main fields of study in molecular magnetism and they play important roles in the reactivity of active sites of systems of biological interest. Theoretical methods based on density functional theory due to the possibility of handling large systems are especially indicated for studying the electronic structure of this kind of molecules. At the same time, such methods provide good accuracy to allow the calculation of the small energy differences involved in the exchange interactions. It is worth noting that theoretical methods are especially important in the study of the exchange interactions in complexes with a large number of paramagnetic centers because they can provide a more detailed analysis of the interactions than experimental data can. This fact is due to the limitations in obtaining exchange coupling constants from experimental measurements for large size systems of this kind. The knowledge of the exchange interactions that controls the ground state of the system is crucial to the understanding of magnetic properties such as the single-molecule magnet character or the reactivity of an active site in a biological system.

Abstract: A systematic study of magnetic properties of ${\mathrm{Ni}}_{2+x}{\mathrm{Mn}}_{1\ensuremath{-}x}\mathrm{Ga}$ $(0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.19)$ Heusler alloys undergoing structural martensite-austenite transformations while in the ferromagnetic state has been performed. From measurements of spontaneous magnetization, ${M}_{s}(T)$, jumps $\ensuremath{\Delta}M$ at structural phase transitions were determined. Virtual Curie temperatures of martensite were estimated from the comparison of magnetization in martensitic and austenitic phases. Both saturation magnetic moments in the ferromagnetic state and effective magnetic moments in paramagnetic state of Mn and Ni atoms were estimated and the influence of delocalization effects on magnetism in these alloys was discussed. The experimental results obtained show that the shift of martensitic transition temperature depends weakly on composition. The values of this shift are in good correspondence with the Clapeyron-Clausius formalism taking into account the experimental data on latent heat at martensite-austenite transformations.

Abstract: This paper reviews the latest developments in the field of spin chemistry with a particular focus on the effects of weak static and/or oscillating magnetic fields (typically smaller than the average hyperfine coupling) on radical recombination reactions. Anisotropic magnetic field effects and their significance in the debate about potential mechanisms controlling magnetoreception in birds are discussed.

Abstract: Room-temperature ferromagnetism is observed in chemically synthesized powder samples of Sn1−xCoxO2 with x=0.005 and 0.01. Magnetic hysteresis loops are observed at 300K with coercivity Hc∼630Oe, saturation magnetization Ms∼0.133μB∕Co ion, and about 31% remanence. Analyses of the magnetization data of paramagnetic samples with x=0.01 and 0.03, measured as a function of temperature (3–330K) and magnetic field (up to 65kOe), indicate the presence of Co+2 ions with spin S=3∕2. Magnetic data obtained from samples prepared at different temperatures indicate that the observed ferromagnetism for x⩽0.01 might have been triggered by changes in the oxygen stoichiometry.

Abstract: The effects of magnetic fields (of 0–5 T magnetic flux density) on iron electrodeposition were investigated in terms of current efficiency, morphology and crystal orientation. The AFM images showed that the shape of iron grains was angular in no magnetic field and roundish in magnetic fields. The occurrence of preferred orientation parallel to the substrate plane was influenced by an electric field (overpotential) and not by a magnetic field (MHD effect). By X-ray pole figure measurement, however, it was found that the biaxial texture evolution proceeded in a magnetic field while the uniaxial texture formed in no magnetic field.

Abstract: Structural and magnetic properties have been studied for polycrystalline Zn1−xMnxO (x=0.02,0.03,0.05). Low-temperature (∼500 °C) synthesis leaves unreacted starting ZnO and manganese oxides. Contrary to a recent report, no bulk ferromagnetism was observed for single-phase materials synthesized in air at temperatures above 900 °C. Single-phase samples show paramagnetic Curie–Weiss behavior.

Abstract: Rationale and Objectives:Paramagnetic Ln-DOTAMGly complexes (Ln ≠ La, Lu, and Gd) are the prototypes of a novel class of contrast agents for magnetic resonance imaging based on chemical exchange saturation transfer (CEST). Their ability to reduce the water signal intensity depends on the interplay o

Abstract: Grains consisting of finely exsolved members of the hematite-ilmenite solid-solution series, such as are present in some slowly cooled middle Proterozoic igneous and metamorphic rocks, impart unusually strong and stable remanent magnetization. TEM analysis shows multiple generations of ilmenite and hematite exsolution lamellae, with lamellar widths ranging from millimeters to nanometers. Rock-magnetic experiments suggest remanence is thermally locked to the antiferromagnetism of the hematite component of the intergrowths, yet is stronger than can be explained by canted antiferromagnetic (CAF) hematite or coexisting paramagnetic (PM) Fe-Ti-ordered ( R 3) ilmenite alone. In alternating field demagnetization to 100 mT, many samples lose little remanence, indicating that the NRM is stable over billions of years. This feature has implications for understanding magnetism of deep rocks on Earth, or on planets like Mars that no longer have a magnetic field. Atomic-scale simulations of an R 3 ilmenite lamella in a CAF hematite host, based on empirical cation-cation and spin-spin pair interaction parameters, show that contacts of the lamella are occupied by “contact layers” with a hybrid composition of Fe ions intermediate between Fe2+-rich layers in ilmenite and Fe3+-rich layers in hematite. Structural configurations dictate that each lamella has two contact layers magnetically in phase with each other, and out of phase with the magnetic moment of an odd non-self-canceling Fe3+-rich layer in the hematite host. The two contact layers and the odd hematite layer form a magnetic substructure with opposite but unequal magnetic moments: a lamellar “ferrimagnetism” made possible by the exsolution. Because it is confined to magnetic interaction involving the moments of just three ionic layers associated with each individual exsolution lamella, lamellar magnetism is unique and quite distinct from conventional ferrimagnetism. Simulation cells indicate that the magnetic moments of contact layers are locked to the magnetic moments of adjacent AF hematite layers and are parallel to the basal plane (001). Thus, lamellar magnetism is created at the temperature of chemical exsolution, and is a chemical remanent, rather than thermal remanent, magnetization. However, in thermal demagnetization experiments, too short for lamellar resorption, demagnetization temperatures are those of the CAF hematite, considerably higher than temperatures of original lamellae formation. Internal crystal structure cannot dictate that the contact layers of different lamellae will form magnetically in phase with each other to give the highest net magnetic moment, but magnetic moments of lamellae can be made to form in phase by the external force of the magnetizing field at the time of exsolution. A thesis of this paper is that an external magnetic field can dictate the magnetic moments and hence the chemical location of ilmenite lamellae in a hematite host, and that once in place, neither the location nor the magnetic moment will be easily disturbed. In an ilmenite host, the external magnetic field cannot control the chemical location of a hematite lamella, which is dictated by the enclosing ilmenite, but once lamellae have formed, the field can dictate their magnetic moments. These moments, however, are not locked chemically to the host, resulting in lower coercivity. The effectiveness of the external force in single crystals is dictated by their orientation with respect to the magnetizing field. In grains with (001) oriented parallel to the field, it would be effective in producing in-phase magnetic moments and very strong remanence. In grains with (001) normal to the field, the field would be less effective in producing in-phase magnetic moments, hence producing weak remanence. The most intense lamellar magnetism per formula unit occurs with in-phase magnetization, high lamellar yields, and the largest number of lamellae per unit volume (i.e., smallest lamellar size). Compared to the magnetic moment per formula unit ( M pfu) and magnetic moment per unit volume ( M V) of end-member magnetite ( M pfu = 4 μB, M V = 480 kA/m) and hematite ( M pfu = 0.0115 μB, M V = 2.1 kA/m), results for some atomic models reasonably tied to natural conditions are M pfu = 0.46–1.36 μB and M V = 84–250 kA/m.

Abstract: Zn 1− x Mn x Fe 2 O 4 nanoparticles were synthesized through a hydrothermal process at 180°C. X-ray diffraction (XRD) and transmission electron microscope (TEM) studies show an increase in particle size with the increasing of Mn concentration. The saturation magnetization ( M s ) of Zn 1− x Mn x Fe 2 O 4 measured by vibrating sample magnetometer (VSM) is found to increase rapidly at first and then slowly augments with the increasing of Mn concentration. Mossbauer spectroscopy analysis reveals that the spectra change from a paramagnetic double peak to hyperfine magnetic sextets and the Zn 0.2 Mn 0.8 Fe 2 O 4 nanoparticles have 43% inversion occupancy on the tetrahedral sites by Fe 3+ cations, while this value increases to 47% in the MnFe 2 O 4 sample. The results show that the occupancy of cations on A and B sites affects magnetic properties of spinel ferrite nanoparticles.

Abstract: Peculiarities of synthesis of chain polymeric, copper(II) hexafluoroacetylacetonate based complexes with stable nitroxyl radicals and the results of studies on correlations between the magnetic properties and structure of these compounds are summarized. Temperature variation causes structural rearrangements in the solid phases of the compounds, accompanied by the magnetic effects similar to spin crossover phenomena. Magnetic anomalies induced by phase transitions originate from specific motions in the Jahn—Teller coordination units containing two types of exchange clusters, Cu2+—O·—N N—·O—Cu2+—O·—N<, and are accompanied by significant changes in the crystal volume after multiple cooling/heating cycles. Chemical methods of controlling the character and temperature of spin transitions by both the formation of solid solutions of mixed metal hexafluoroacetylacetonates with the same nitroxyl radical, {Cu1−xMx(hfac)2L} (M = Mn, Ni, Co), and by the formation of solid solutions based on copper(II) hexafluoroacetylacetonate with different nitroxyl radicals, {Cu(hfac)2LxL′1−x}, are discussed. Specific influence of isotope substitution CH3 → CD3 in the paramagnetic ligand on both the structure of the heterospin polymer chain and the temperature of the magnetic anomaly is discussed.

Abstract: Three ion pair complexes, [4-R-benzylpyridinium][bis(maleodinitriledithiolato)platinum(III)] (abbreviated as [RBzPy][Pt(mnt)(2)]; R = Cl (1), Br (2), or NO(2) (3)), have been synthesized. The cations and anions stack into well-separated columns in the solid state, and the Pt(III) ions form a 1-D zigzag chain within a [Pt(mnt)(2)](-) column through Pt...S, S...S, and Pt...S...Pt interactions. The chain is uniform in 1 and 2, while it alternates in 3. Unusual magnetic phase transitions from paramagnetism to diamagnetism were observed in these three complexes at approximately 275 K for 1, approximately 269 K for 2, and approximately 184 K for 3. These phase transitions were also found in DSC measurements for 1 and 2. The overall magnetic behaviors for 1-3 indicate the presence of antiferromagnetic exchange interactions in the high-temperature phase and spin-gapped systems in the low-temperature phase. Below 50 K, 2 exhibits weak ferromagnetism. The spontaneous moments are nearly repressed by a field of 1.0 T. The crystal structure of 2 at 173 K reveals that there are two crystallographically independent [Pt(mnt)(2)](-) entries in an asymmetric unit. These two crystallographically independent [Pt(mnt)(2)](-) entries satisfy the spin-canting condition, and the EPR spectra measured at room temperature exhibit anisotropic character. Therefore, the weak ferromagnetic behavior in the low-temperature region for 2 can be attributed to the spin-canting phenomenon.

Abstract: The title compounds were prepared by direct reactions of the corresponding elements at high temperature. They are isostructural with each other (monoclinic, P21/m, Z = 2; Na8BaPb6, a = 13.116(4), b = 5.351(1), and c = 16.166(5) A, β = 108.07(2)°; Na8BaSn6, a = 12.897(4), b = 5.362(1), and c = 16.826(5) A, β = 108.19(2)°; Na8EuSn6, a = 12.912(2), b = 5.220(1), and c = 15.721(2) A, β = 108.09(1)°) and contain isolated, flat, and aromatic pentagonal rings of Sn56- and Pb56- as well as isolated anions of Sn4- and Pb4-. According to four-probe conductivity measurements, the tin compounds, Na8BaSn6 and Na8EuSn6, are semiconducting with band gaps of 0.11 and 0.09 eV, respectively, and are therefore electronically balanced. Magnetic measurements show that Na8BaSn6 is diamagnetic while Na8EuSn6 is paramagnetic and undergoes two transitions at low temperatures.

Abstract: The design of cyanide-bridged transition-metal clusters is one of the leading topics in the field of molecular magnetism. Two of the main reasons for this high interest are 1) cyanide chemistry easily lends itself to a building-block approach and 2) the nature (ferromagnetic versus antiferromagnetic) of magnetic exchange interactions through a linear cyanide ligand is largely predictable. These attributes have inspired numerous research groups to pursue the synthesis of highspin, magnetically anisotropic metal cyanide molecules with the goal of engendering slow paramagnetic relaxation of the magnetization, a phenomenon that has been likened to the behavior of single-domain particles. This “superparamagnetic-like” magnetic behavior of molecules, commonly referred to as “single-molecule magnetism”, has been observed for paramagnetic clusters that exhibit a large spin ground state combined with an appreciable degree of anisotropy (i.e., a negative zero-field splitting parameter D). 10,11] Singlemolecule magnet (SMM) behavior was first noted over ten years ago for an {Mn12} cluster of the oxide family, [10,11] and many new examples of oxide-based SMMs have been prepared in the ensuing years. 12] Progress in this area has been only incremental, however, in terms of raising the blocking temperature of the magnetization. One of the main reasons for this situation is that it is difficult to control the sign and magnitude of D. This limitation to realizing high-temperature SMMs is one of the focal points of research in the field. One approach to increasing the magnetic anisotropy of paramagnetic clusters is to incorporate heavier transition elements, such as 5d metal ions, which exhibit strong spin– orbit coupling effects that can induce anisotropic magneticexchange interactions. In this vein, we have been investigating the use of the paramagnetic Re anion complex [Re(triphos)(CN)3] (triphos= 1,1,1-tris(diphenylphosphanylmethyl)ethane) as a building block for high nuclearity clusters with unusual magnetic properties. As a backdrop for these studies, we undertook a full investigation of the magnetic behavior and theoretical modeling of [Et4N][Re (triphos)(CN)3], which revealed that the compound exhibits an unusually strong temperature-independent paramagnetism due to spin–orbit coupling of the S= 1/2 ground state and low-lying excited states. Given these intriguing findings, we proceeded to explore reactions of [Re(triphos)(CN)3] with complementary building blocks including MCl2 reagents (M= 3d metal ion). The results of these studies with Fe and Co chlorides are reported herein. Single-crystal X-ray studies revealed the products to be distorted molecular cubes composed of both sixand fourcoordinate vertices (Figure 1). The triphos ligands act as

Abstract: Cantilever magnetometry has been used to measure the upper critical magnetic field H c 2 of the quasi-one-dimensional molecular organic superconductor (TMTSF) 2 ClO 4 . From simultaneous resistivity and torque magnetizationexperiments conducted under precise field alignment, H c 2 at low temperature is shown to reach 5 T, nearly twice the Pauli paramagnetic limit imposed on spin singlet superconductors. These results constitute the first thermodynamic evidence for a large H c 2 in this system and provide support for spin triplet pairing in this unconventional superconductor.