Specific heat of decamethylferrocenium tetracyanoethanide (DMeFc)(TCNE)

Journal ArticleWe report the specific heat C(T) of (DMeFc)(TCNE) for temperatures 3 K < T < 50 K. We observe an anomaly at Tc-4.82 K corresponding to a transition to a three-dimensional (3D) macroscopic ferromagnet. A broad maximum at = 15 K corresponds to an exchange interaction of J = 35 K along the chain axis. We propose a generalized 1D Hubbard Hamiltonian to account for this feature. Below T (c) results are consistent with the opening up of a gap of approximately 2 meV in the spin-wave spectrum due to the anisotropy in the exchange interaction within the 1D chains

Photoinduced magnetization in the organic-based magnet Mn(TCNE)x.y(CH2Cl2)

Journal ArticlePhotoinduced magnetization in a magnet based on organic species is reported for the first time. Upon optical excitation in the blue region of spectrum, Mn (tetracyanoethylene)x .y(CH2Cl2) (x=2,y-0.8) exhibits increased magnetic susceptibility at temperatures as high as 75 K, accompanied with photo-induced absorption in the visible and infrared spectral regions. These effects are partially reversible by lower energy visible light and fully reversible by thermal treatment. The results suggest trapping of the photoexcited charge in a metastable state with enhanced exchange interaction

Photoinduced magnetism, dynamics, and cluster glass behavior of a molecule-based magnet

Journal ArticleThe dynamic susceptibility study of photoinduced magnetism in a molecule-based magnet, (K1-2xCo1+x [Fe(CN)6]. yH2O (0.2<_x<_0.4,y-5), is reported. Upon excitation with visible light the material has substantial changes in linear and nonlinear ac susceptibility and dc magnetization. The results demonstrate cooperative freezing of magnetic moments and absence of true long-range magnetic order. The ground and photoexcited states are described within a cluster glass model, with photoinduced increase in spin concentration leading to a shift of the dynamics to longer length and time scales and higher temperatures

Brandeis: The Legacy of a Justice

One hundred years after his appointment, Justice Louis D. Brandeis remains a distinctive and unusually influential figure in the history of the Supreme Court. Unlike many other great justices, Brandeis is not remembered for his majority opinions. Rather, what is distinctive about him is the extent to which so many of his dissents and concurring opinions continue to influence justices more than 75 years after he retired and a century after he joined the Court. Whereas justices cite majority opinions for their value as legal precedents, they invoke the dissents and concurrences of a retired justice due to the power of his or her ideas or the credibility of his or her reputation. Significantly, Brandeis\u27s successors continue to turn to his classic dissents and concurrences more often than to the discretionary opinions of other justices. Their continuing reliance on Brandeis confirms the insight of Paul Freund, one of the Justice’s most distinguished law clerks that Brandeis remains the most powerful moral teacher to have served on the Court

Magnetic properties and critical behavior of Fe(tetracyanoethylene) 2.x(CH2Cl2): a high-Tc molecule-based magnet

Journal ArticleWe report magnetic studies of Fe(TCNE)2•x(CH2Cl2), a member of the family of high-Tc molecule-based magnets, M(TCNE)x•y (solvent) (M=V, Mn, TCNE=tetracyanoethelyne). Based on extensive static and dynamic magnetic measurements we show that this system has a complex magnetic behavior, with a mixture of ferrimagnetic and random anisotropy characteristics. The constricted hysteresis curve with a spin-flop shape, the ac susceptibility in the presence of a dc field, consistent with the spin-flop picture, and the remanent magnetization suggest ferrimagnetic behavior. The ac susceptibility data in zero dc field have modest frequency dependence suggesting glassiness, while the field-cooling/zero-field-cooling magnetization data show irreversibilities, starting at -97 K, and increasing below -20 K, all consistent with the behavior of reentrant random anisotropy magnets (RAM). Ferromagneticlike scaling analyses provide a critical temperature Tc=97 K and the critical exponents B=0.45 and 8=2.5, relatively consistent with random anisotropy magnet predictions. Also, the curvature of the T<Tc data in the modified Arrott plot is characteristic for RAM. Correlating the static and dynamic magnetic studies and analyzing the similarities with other members of this family of hybrid organic/inorganic compounds, we discuss the origins of anisotropy and randomness and the possible interconnections between ferrimagnetism and RAM (sperimagnetism) in Fe(TCNE)2•x(CH2Cl2)

Optical control of magnetic order in molecule-based magnet Mn(TCNE)x.y(CH2Cl2)

Journal ArticleStudies of photoinduced magnetization and photoinduced absorption in molecule-based magnet Mn(TCNE)x•y(CH2Cl2) (x=2, y-0.8, TCNE=tetracyanoethylene) are reported. Optical excitation in the blue region of spectrum leads to increased magnetization, accompanied by changes in the electronic spectrum. These effects are preserved long after illumination, indicating formation of a highly metastable electronic state. Partial reversal of the photoinduced effects is obtained by excitation with lower energy visible light. The results suggest that the photoinduced effects are controlled by two distinct electronic transitions

Direct evidence of electron spin polarization from an organic-based magnet: [FeII(TCNE)(NCMe)2][FeIII Cl4]

Journal ArticleDirect evidence of an organic-based magnet with a finite electron spin polarization at the Fermi edge is shown from spin-resolved photoemission of the [FeII(TCNE)(NCMe)2][FeIIICl4] organic-based magnet. The 23% majority-based spin polarization at the Fermi edge is observed at 80 K in zero applied field. Ab initio calculations at the density functional level (O K) are in accord with a semiconductor with 100% majority-based electron spin polarization at the band edges, commensurate with our experimental results and model prediction for a half-semiconductor. Organic-based magnets may prove to be important for realizing polarized electron injection into semiconductors for magnetoelectronic applications

Cluster glass state and photoinduced effects on the freezing dynamics in KxCo[Fe(CN)6]y.ZH2O (x-0.16,y-0.72, z-4.4)

Journal ArticleThe magnetic properties and photoinduced magnetization of a Prussian blue analog, KxCo[Fe(Cn)6]y•ZH2O (x-0.16, y-0.72, z-4.4) were systematically studied. The frequency dependence of the linear ac susceptibility, the irreversibility in the field-cooled/ zero-field-cooled magnetization (MFC /MZFC), and the relaxation of MZFC suggest a cluster glass behavior. Illumination with red light leads to an increase in the magnetic irreversibility. While MFC is significantly increased after illumination, MZFC at low temperatures is decreased. The observed photoinduced magnetic effects are explained within a cluster glass model. The photoinduced increase in the concentration of spins leads to a shift of dynamics toward longer length and time scales, resulting in freezing of spin clusters at a higher temperature. © 2000 American Institute of Physics

Optical studies of the ultraluminous X-ray source NGC1313 X-2

NGC1313 X-2 was among the first ultraluminous X-ray sources discovered, and has been a frequent target of X-ray and optical observations. Using the HST/ACS multi-band observations, this source is identified with a unique counterpart within an error circle of 0\farcs2. The counterpart is a blue star on the edge of a young cluster of $\le10^7$ years amid a dominant old stellar population. Its spectral energy distribution is consistent with that for a Z=0.004 star with 8.5 $M_\odot$ about $5\times10^6$ years old, or for an O7 V star at solar metallicity. The counterpart exhibited significant variability of $\Delta m = 0.153\pm0.033$ mag between two F555W observations separated by three months, reminiscent of the ellipsoidal variability due to the orbital motion of this ULX binary.Comment: 21 pages, 7 figures, scheduled for the ApJ June 10, 2007, v662n 1 issu