Space use by foragers consuming renewable resources

We study a simple model of a forager as a walk that modifies a relaxing substrate. Within it simplicity, this provides an insight on a number of relevant and non-intuitive facts. Even without memory of the good places to feed and no explicit cost of moving, we observe the emergence of a finite home range. We characterize the walks and the use of resources in several statistical ways, involving the behavior of the average used fraction of the system, the length of the cycles followed by the walkers, and the frequency of visits to plants. Preliminary results on population effects are explored by means of a system of two non directly interacting animals. Properties of the overlap of home ranges show the existence of a set of parameters that provides the best utilization of the shared resource

1H NMR investigation of the magnetic spin configuration in the molecule-based ferrimagnet [MnTFPP][TCNE]

Journal Article1H NMR line-shape measurements have been performed in the linear chain molecule-based ferrimagnet [MnTFPP][TCNE].xPhMe (TFPP=tetrakis(4-fluorophenyl)porphinato; TCNE=tetracyanoethylene) as a function of temperature. Hyperfine shifts of opposite sign were observed indicating the presence of two oppositely hyperfine couplings, predominantly between the Mn ions and the 1H nuclei of the planar ring of the [MnTFPP]+ unit. The observation of the hyperfine shifts strongly suggests the existence of two oppositely directed [MnTFPP]+ sites. Since there is no direct exchange coupling between adjacent [MnTFPP] spins, then it can be argued that an ordered spin configuration with antiparallel components may arise from antisymmetric spin-spin exchange interactions. The field independence of the hyperfine shifts at low temperatures and for applied magnetic fields in the range 2-5 T, indicates the presence of ferromagnetic interactions in the ground state of the ferrimagnetic chain

Giant Antiferromagnetically Coupled Moments in a Molecule-Based Magnet with Interpenetrating Lattices

The molecule-based magnet [Ru$_2$(O$_2$CMe)$_4$]$_3$[Cr(CN)$_6$] contains two weakly-coupled, interpenetrating sublattices in a body-centered cubic structure. Although the field-dependent magnetization indicates a metamagnetic transition from an antiferromagnet to a paramagnet, the hysteresis loop also exhibits a substantial magnetic remanance and coercive field uncharacteristic of a typical metamagnet. We demonstrate that this material behaves like two giant moments with a weak antiferromagnetic coupling and a large energy barrier between the orientations of each moment. Because the sublattice moments only weakly depend on field in the transition region, the magnetic correlation length can be directly estimated from the magnetization.Comment: 3 figure

Reentrance in the Mn(tetracyanoethylene)x.y(CH2Cl2) high-Tc molecule-based ferrimagnet

Journal ArticleResults of static and dynamic magnetic studies of the compound Mn(TCNE)x•y(CH2Cl2) (TCNE =tetracyanoethylene) are reported. Curie-Weiss analysis of the high-temperature susceptibility data indicates a relatively strong exchange. The ac susceptibility, measured as a function of frequency and temperature, reveals frequency-independent peaks in both the in-phase and out-of-phase components of the susceptibility near 75 K. Additional peaks in both components, which are frequency dependent, are observed near 10 K. Weak irreversibilities, including a remanent moment and a bifurcation of the field-cooled (FC) and zero-field-cooled (ZFC) dc magnetizations are observed below 75 K. These irreversibilities become more pronounced below -10 K. The presence of frequency dependence in the ac susceptibility and field dependence of the FC/ZFC magnetizations near 10 K but not at 75 K strongly suggest reentrance. Static scaling analysis at the high-temperature transition and dynamic scaling analysis at the low-temperature transition provide clear evidence for ordering with a spontaneous moment at 75 K and as a spin glass below 10 K. Possible mechanisms for this behavior are discussed

Linear chain ferromagnetic charge transfer compounds

Journal ArticleCharge transfer complexes possessing a ... DADA ... structure with both the donor, D, and acceptor, A, being S = 1/2 radicals may exhibit cooperative magnetic phenomena. The complex [Fe(C5Me5)2]+ [TCNQ]-. exhibits metamagnetic behavior. The similarly structured [TCNE]-. and [C4(CN)6]-. complexes are ferromagnets, whereas the [DDQ]-. salt is a paramagnet. The high temperature magnetic susceptibility obeys the Curie-Weiss expression with 0 = + 30, + 30, and + 3 for the [TCNE]-., [C4(CN)6]-., and [TCNQ]-. salts, respectively. The ferromagnetic [TCNE]-. salt exhibits zero field Zeeman split 57Fe Mossbauer spectra with an internal field of 425.6 kOe at 4.23 K. After reviewing the current papers discussing ferromagnetism in molecular (organic) compounds, a qualitative model consistent with the necessary bulk spin alignment required for a ferromagnet is presented

Magnetic phase diagram of a molecule-based ferrimagnet: weak ferromagnetism and multiple dimensionality crossovers

Journal ArticleA detailed study of the magnetic behavior of the molecule-based magnet, [MnOEP][HCBD], (OEP=mesooctaethylporphyrinato, HCBD=hexacyanobutadiene) from 1.7 to 20 K was performed. The earlier reported magnetic transition at 19.6 K, ascribed to a crossover from a one-dimensional Heisenberg-like ferrimagnet to a two-dimensional Ising-like antiferromagnet, is further probed via ac-dc magnetic studies consisting of dc magnetization as a function of field at various temperatures, and magnetization as a function of temperature with both field cooling and zero-field cooling. In addition, the ac susceptibility was measured as a function of temperature and applied dc field. The appearance of a nonzero out-of-phase component of the ac susceptibility in zero dc field at 8 K accompanied by a shoulder in the in-phase component indicates the presence of a magnetic transition near that temperature. Irreversibilities and a spontaneous moment observed below 4.2 K indicate an additional lower temperature transition. The ac and dc data allow a determination of the temperature-field phase boundaries around these transitions. Evidence of a tricritical point at 2 kOe and 19.6 K and a multicritical point at 9.5 kOe and 8 K is presented. The nature of the ordered states, along with the possible mechanisms responsible for the transitions, including dipole-dipole interactions, are analyzed. [S0163-1829(97)02446-6

Lattice- and spin-dimensionality crossovers in a linear-chain-molecule-based ferrimagnet with weak spin anisotropy

Journal Article[MnOEP][HCBD], a member of the metalloporphyrin family of donor-acceptor molecule-based magnets, consists of isolated ferrimagnetic chains of alternating S=2, [MnOEP], and s=1/2, [HCBD] units (OEP=octaethylporphyrinato and HCBD=hexacyanobutadiene). Analysis of the exchange pathways reveals an exchange along one interchain axis (Jinter) almost 3 orders of magnitude weaker than the intrachain exchange (Jintra), and a negligible exchange along the other interchain axis. From the susceptibility and magnetization data we determine Jintra and Jinter to be antiferromagnetic with values of -172 K and -0.4 K, respectively. At 19.6 K, the system undergoes both lattice and spin dimensionality crossovers in which the ferrimagnetic chains couple antiferromagnetically as two-dimensional Ising sheets. [S0163-1829(97)01625-1

Thermoelectric-power studies of (N-Methylphenazinium)x(Phenazine)1-x(Tetracyanoquinodimethanide), (0.5 <_ x <_ 1.0)

Journal ArticleTemperature-dependent thermoelectric-power (S) studies of (N-methylphenaziniurn)(x)- (phenazine) (1-x) (tetracyanoquinodimethanide) [(NMP)x(phen) (1-x)(TCNQ) 1 show that for x = 0.5, S(T) is indentical to that of (quinolinium) (TCNQ)2. S(T) for 0.5 70 K

Potential technology directions of molecular metals

Journal ArticleIn the past decade, anisotropic molecular conductors have been found which possess unusual electrical, optical, magnetic, and in some cases mechanical properties. Exploiting these properties for specific devices is inevitable, and a number of diverse applications of molecular metals have been reported over the past few years