Carmen R. Kmety

Magnetic Phase Transitions in MII[N(CN)2]2

Abstract We summarize the magnetic behavior of MII[N(CN)2]2 (M ˭ Co, Ni, Mn and Zn). Analyses of the DC magnetization and AC susceptibility data demonstrate that α-CoII[N(CN)2]2 (1a) and NiII[N(CN)2]2 (2) are ferromagnets below Tc, while β-CoII[N(CN)2]2 (1b) and MnII[N(CN)2]2 (3) are canted antiferromagnets below TN. ZnII[N(CN)2]2 (4) is diamagnetic. Specific heat and neutron powder diffraction results clearly define the transition temperatures for 1a, 1b, 2 and 3. Crystal structure determination from high-resolution neutron powder data for 1a, 2 and 3 shows that the three systems are isomorphous and crystallize in the orthorhombic space group Pnnm with Z = 2. Single crystal X-ray diffraction shows that 4 crystallizes in the orthorhombic space group Pnma with Z = 4. We solved the magnetic structures of 1a, 2 and 3 from neutron powder diffraction experiments. All low-temperature measurements are consistent with high-spin 1b, 2, 3 and 4, though 1a exhibits an effective J′ = 1/2 behavior.

Electronic Structure of Transition-Metal Dicyanamides Me(N(CN)2)2 (Me = Mn, Fe, Co, Ni, Cu)

The electronic structure of Me[N(CN)

New High Tc Molecule-Based Magnets - Magnetic Behavior of M(TCNE)2·x(CH2Cl2) (M ˭ Mn, Fe)

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Structure and magnetic ordering of MII[N(CN)2]2 (M = Co, Ni)

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Noncollinear antiferromagnetic structure of the molecule-based magnet Mn [ N ( CN ) 2 ] 2

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Low-Field Remanent Magnetization in the Weak Ferromagnet Mn[N(CN)2]2. Evidence for Spin-Flop Behavior

(Me=Mn, Fe, Co, Ni, Cu) molecular magnets has been investigated using x-ray emission spectroscopy (XES) and x-ray photoelectron spectroscopy (XPS) as well as theoretical density-functional-based methods. Both theory and experiments show that the top of the valence band is dominated by Me 3d bands, while a strong hybridization between C 2p and N 2p states determines the valence band electronic structure away from the top. The 2p contributions from non-equivalent nitrogen sites have been identified using resonant inelastic x-ray scattering spectroscopy with the excitation energy tuned near the N 1s threshold. The binding energy of the Me 3d bands and the hybridization between N 2p and Me 3d states both increase in going across the row from Me = Mn to Me = Cu. Localization of the Cu 3d states also leads to weak screening of Cu 2p and 3s states, which accounts for shifts in the core 2p and 3s spectra of the transition metal atoms. Calculations indicate that the ground-state magnetic ordering, which varies across the series is largely dependent on the occupation of the metal 3d shell and that structural differences in the superexchange pathways for different compounds play a secondary role.

Collinear ferromagnetism and spin orientation in the molecule-based magnets M[N(CN){sub 2}]{sub 2} (M=Co,Ni)

Abstract We report and review studies of new partially crystalline members of the high-Tc molecule-based magnets family, M(TCNE)2·x(CH2Cl2), (M ˭ Fe, Mn, TCNE ˭ tetracyanoethylene). Remanent magnetization revealed high critical temperatures, Tc = 97 K for M ˭ Fe and 75 K for M ˭ Mn. Hysteresis curves for the Fe compound, for 5 ≤ T ≤ 80 K, have a spin-flop shape, indicating ferrimagnetic behavior. Field-cooled and zero-field-cooled magnetization reveals magnetic irreversibilities below Tc for both compounds. Static and dynamic scaling analyses of the dc magnetization and ac susceptibility for M ˭ Mn show a transition to a 3D ferrimagnetic state at Tc = 75 K, followed by a reentrant transition, to a spin glass state at Tg = 2.5 K. For M ˭ Fe static scaling analyses are consistent with a high-T transition to a correlated sperimagnet, while below ∼20 K there is a crossover to sperimagnetic behavior.