Magnetic Triplet Research Articles

Specific counterion effects on naphthalene solubilized in sds micelles investigated by optically detected magnetic resonance

The nature of the phosphorescence emission, optically detected magnetic resonance (ODMR) transitions and triplet state lifetime data of naphthalene (N) solubilized in frozen mixed micelles containing sodium dodecyi sulfate (NaDS) and either silver dodecyi sulfate (AgDS) or thallium dodecyi sulfate (T1DS) suggest stronger perturbation of the N triplet state by the Ag + counterion than by Tl +. Very broad ODMR transitions and a broadening of the phosphorescence for NaDS/AgDS indicate a strong specific interaction between the N probe and the Ag + counterion, absent with Tl +.

Conductive molecular crystals. Structural, magnetic, and charge-transport properties of partially oxidized (5,10,15,20-tetramethylporphyrinato)nickel(II)

(5,10,15,20-Tetramethylporphyrinato)nickel(II), Ni(tmp), has been partially oxidized by reaction with iodine. We report structural, magnetic, and charge-transport properties of single crystals of the resulting compound, Ni(tmp)I. The compound crystallizes in space group D/sup 4//sub 4h/-P4/nnc of the tetragonal system with four formula units in a cell of dimensions a = 16.610 angstrom and c = 6.932 angstrom at 114 K. Full-matrix least-squares refinement of 69 variables gives gives a final value for the R index on F/sup 2/ of 0.079 for 1418 observations. The structure consists of S/sub 4/-ruffled Ni(tmp) molecules, stacked metal-over-metal, with a Ni-Ni spacing along the stack of 3,466 angstrom. Adjacent Ni(tmp) units in the unit cell are staggered by 37/sup 0/. Severely disordered chains of iodine are located in channels surrounding the Ni(tmp) stacks. The iodine is identified as I/sub 3//sup -/ from diffuse X-ray scattering and resonance Raman spectroscopy. Splitting of the I/sub 3//sup -/ bands in the resonance Raman spectrum becomes evident at low temperature. Single-crystal room-temperature conductivity along the needle axis averages 110 ..cap omega../sup -1/ cm/sup -1/, slightly less than that of large-ring porphyrinic conductors. The temperature dependence of the conductivity of Ni(tmp)I is metal-like above 115 K and activated at lower temperatures.more » Single-crystal EPR studies indicate that the oxidation of the Ni(tmp) moiety is ligand centered. The magnetic susceptibility is metal-like, being temperature independent above 28 K but anomalously high indicative of enhanced Coulomb correlations. This susceptibility enhancement may arise from the mixing in of a magnetic triplet state that is available because of the electronic structure of small porphyrinic macrocycles. The susceptibility decreases sharply as the temperature is lowered below 28K.« less

A comparison of the dynamical susceptibility of trivalent and intermediate valent TmSe studied by inelastic neutron scattering

The inelastic neutron scattering technique has been used to measure the dynamical susceptibilities of trivalent and intermediate valent TmSe. The experiments have been performed for single-crystalline samples above and below the antiferromagnetic ordering temperatures. From the excitation spectra observed for trivalent Tm 0.87Se we have derived the crystal-field level scheme which yields a magnetic triplet ground state. For intermediate valent Tm 0.99Se there is a single dispersionless spin excitation at around 1 meV in the magnetically ordered state. Above the Néel temperature no crystal-field splittings were observed, but the energy spectra are characterized by a superposition of two quasielastic lines corresponding to slow and fast magnetic relaxation rates which almost differ by an order of magnitude.

Galvanomagnetic effects in the solid solution and precipitate phases of AuCo alloys

Abstract The electrical resistance, magnetoresistance and Hall effect in AuCo alloys containing between 1 and 15·6 at.% Co have been measured in both the quenched and over-aged states. Measurements were made in the temperature range ∼2–250 K and in flux densities up to 7 T. Supporting magnetization measurements were made to 1·6 T. The results are interpreted in terms of the standard age-hardening mechanism. The quenched state is a cluster spin-glass with magnetic triplets or larger clusters of Co ions, and the over-aged state consists of high-conductivity incoherent Co-rich precipitates. In the aged state most of the Co has effectively no influence on the electrons’ motion.

SU(5) monopoles, magnetic symmetry and confinement

The monopoles of the unified SU(5) gauge theory broken down to H E = SU(3) c ⊗ U(1) EM [or to K E = SU(3) c ⊗ SU(2) ⊗ U(1) Y], are classified. They belong to representations of a magnetic group H M(K M), which is found to be isomorphic to H E(K E). For SU(5) broken down to H E, there exists a regular and stable monopole which is a colour magnetic triplet, and carries a non-zero abelian magnetic charge. It is suggested that composite operators made out of this monopole and its antiparticle fields develop a non-zero vacuum expectation value, and so lead to a squeezing of the colour electric flux. Finally, we comment on the cosmological production of SU(5) monopoles.

Crystal fields in TmCu5

Neutron inelastic scattering experiments and specific heat experiments have been used to determine the crystal field level scheme in the cubic compound TmCu5 (AuBe5 structure). The lowest level is a non-magnetic doublet, lying in energy only slightly below a magnetic triplet level. The crystal field parameters are W=-(0.065+or-0.005) meV and x=0.95+or-0.05.

Operation of a High-Current Xenon Source

A multi-aperture Ehlers-type source has been constructed and operated to produce a 60 mA Xe/sup +1/ beam. The multi-aperture source utilizes a 13 hole aperture in a circular pattern producing a beam 25 mm in diameter. An accel--decel extraction system was used, producing a 22.5 keV beam whose normalized emittance at 29 mA was 0.027 ..pi.. cm--mrad. The neutralized beam was transported one meter through two magnetic quadrupole triplets to the entrance of a 20 cm accelerating gap consisting of five intermediate electrodes with a total voltage drop of 500 kV. The vacuum in the extraction region was held to 10/sup -5/ Torr by usng a puff valve and two 1500 1/sec turbo pumps. Multi-wire profile monitors just ahead of the column entrance measured the beam size, which was in good agreement with single-particle transport calculations.

Cooperative Jahn-Teller effect in TmZn

Specific-heat, resistivity, neutron-spectroscopy, magnetization, and magnetostriction experiments on TmZn are reported. This equiatomic metallic compound crystallizes with the cubic CsCl structure and shows a first-order Jahn-Teller transition to a tetragonal structure at ${T}_{Q}=8.55$ K. The cell distortion reaches $\frac{c}{a}\ensuremath{-}1=(\ensuremath{-}9\ifmmode\pm\else\textpm\fi{}1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$. The magnetic moment orders along a fourfold axis at ${T}_{c}=8.12$ K, its value being largely field dependent. Due to the vicinity of the transitions, they are mixed and strongly raised in temperature by (even low) applied fields as observed by the magnetization and magnetostriction experiments in the paramagnetic state. These results and the elastic constants previously published are analyzed taking into account the quadrupole-quadrupole exchange and the quadrupole-lattice term beside the Heisenberg exchange and the cubic crystal electric field (CEF) terms; the CEF parameters are ${A}_{4}〈{r}^{4}〉=\ensuremath{-}38\ifmmode\pm\else\textpm\fi{}5$ K and ${A}_{6}〈{r}_{6}〉=\ensuremath{-}19.6\ifmmode\pm\else\textpm\fi{}2$ K/atom. The ground state is the magnetic triplet ${\ensuremath{\Gamma}}_{5}^{(1)}$ in the cubic paramagnetic state. The theoretical study of the dependence of ${T}_{c}$ and ${T}_{Q}$ on the bilinear and biquadratic exchange terms reveals a complex phase diagram. In the case of TmZn, the obtained second-order coefficients allow a good description of all the physical properties now investigated.

Magnetic field modulation of geminate recombination of radical ions in a polar solvent

Measuring transient absorptions on the nanosecond time range, we observed the magnetic field ( H = 40 Oe) modulation of the pyrene triplet and pyrene anion concentrations formed through quenching of singlet excited pyrene molecules by N,N-diethylaniline in methanol at room temperature. We interpret this effect as being due to a magnetic field dependent triplet production in the geminate radical ion pair, induced by hyperfine interaction of the unpaired electrons. The discussion is based on a simple model related to the radical pair model in CIDNP theory. Moreover, the sign of the magnetic field modulation of triplets and radical ions allows to infer on the relative probability for the formation of excited and ground state molecules in ion recombination processes.

A useful nonlinear design model for the magnetic frequency tripler

A model of the magnetic frequency triplet is described that yields useful design information at a reasonable cost. The model is based on the analysis of an ideal lossless triplet. Simple modifications are introduced to account for the effects of direct and quadrature axis losses. Similarly, a method of including a line filter network is described.

Optische Kern-Spin-Polarisation in Molekül-Kristallen

This paper deals with the polarisation of nuclei in molecular crystals due to their hyperfine interaction with optically excited triplet states and excitons, a phenomenon which is termed optical nuclear polarisation (ONP). A theory is presented which extends the mechanisms of dynamic nuclear polarisation (Overhauser effect) to the case of spin systems containing triplet states with S = 1 and nuclei with I = 1/2. In this mechanisms the optical electron polarisation (OEP) caused by symmetry selection rules for intersystem crossing to and from the magnetic triplet sublevels is assumed to be transferred to the nuclear magnetic substates by efficient hyperfine relaxation transitions. The adiabatic fast passage is used to detect the nuclear polarisation. The advantages and conditions of this technique as compared to other nmr techniques are discussed. ONP results at room temperature are given as a function of the external field H0, its orientation with respect to the crystalline axes, the intensity and frequency of the exciting light and the concentration and types of guest molecules. In phenazine crystals relative polarisation factors up to 50 are found with marked orientation dependencies even in fields as high as 11 kG. These results can be interpreted in principle in terms of the presented theory. However, in low fields (0 - 200 G) where ONP caused by hyperfine relaxation vanishes, large polarisations are found in doped crystals of fluorene and anthracene. The maximum absolute polarisation in fluorene doped with acridine is 3.6 · 10-4 at H0 = 80 G corresponding to a relative polarisation factor of ~ 104. The effect of doping is discussed.. Reference is made to a possible ONP mechanism 3 which is able to produce large nuclear polarisations at low fields

Theory of the First-Order Magnetic Phase Change in UO2

A simple model accounts semiquantitatively for the first-order magnetic phase change observed recently in UO2 by Frazer, Shirane, Cox, and Olsen. The model assumes that the electronic structure of the paramagnetic U4+ ion consists of a nonmagnetic singlet ground state and a low-lying magnetic triplet, and that only bilinear isotropic exchange interactions are present. In a molecular-field theory the triplet is split by an internal field proportional to the magnetization. If the molecular field is sufficiently strong one of the components of the triplet will lie, in the magnetic state, below the singlet, and a self-consistent magnetic solution is obtained at T=0. Increasing the temperature causes the magnetization to be reduced, and the low lying component of the triplet is raised in energy. It is shown that a ``catastrophe'' may occur at some critical temperature so that the magnetization is reduced discontinuously to zero. It is also found that, depending on the ratio of the singlet-triplet energy difference to the molecular field splitting of the triplet, one obtains either no magnetic ordering, a first-order phase change, or a second-order transition.

Theory of the First-Order Magnetic Phase Change in UO2

A simple model accounts semiquantitatively for the first-order magnetic phase change observed recently in U${\mathrm{O}}_{2}$ by Frazer, Shirane, Cox, and Olsen. The model assumes that the electronic structure of the paramagnetic ${\mathrm{U}}^{4+}$ ion consists of a nonmagnetic singlet ground state and a low-lying magnetic triplet, and that only bilinear isotropic exchange interactions are present. In a molecular-field theory the triplet is split by an internal field proportional to the magnetization. If the molecular field is sufficiently strong, one of the components of the triplet will lie, in the magnetic state, below the singlet, and a self-consistent magnetic solution is obtained at $T=0$. Increasing the temperature causes the magnetization to be reduced, and the low-lying component of the triplet is raised in energy. It is shown that a catastrophe may occur at some critical temperature so that the magnetization is reduced discontinuously to zero. It is also found that, depending on the ratio of the singlet-triplet energy difference to the molecular-field splitting of the triplet, one obtains either no magnetic ordering, a first-order phase change, or a second-order transition.

Magnetic normal triplet and preston's law

Magnetic normal triplet and preston's law