Magnetic Chain Compounds Research Articles

Crystal structure and magnetic properties of two bimetallic chain compounds

AbstractTwo bimetallic magnetic chain compounds of {[Mn(dpop)(H2O)][Mn(dpop)][Fe[CN]6]•8.5H2O•0.5DMSO} n (1) and {[Mn(dpop)][Ni[CN]4]} n (2) (dpop = 2,13‐dimethyl‐3,6,9,12,18‐pentaazabicyclo‐[12.3.1]‐octadeca‐1(18),2,12,14,16‐pentaene) have been synthesized and characterized by single‐crystal X‐ray diffraction and magnetic measurements. Both complexes have cyano‐bridged chain structures, in which complex 1 is a zigzag chain, while complex 2 is nearly a straight line. The magnetic susceptibility results indicate that there is a weak ferromagnetic interaction between manganese (II) ions in complex 1, whereas the interaction is antiferromagnetic in complex 2.

Four new Mn(II) inorganic-organic hybrid frameworks with diverse inorganic magnetic chain's sequences: syntheses, structures, magnetic, NLO, and dielectric properties.

Four new inorganic-organic hybrid manganese frameworks, formulated as [Mn(Am-Hip)2]·3H2O (1), [Mn2(ip)2(H2O)]·CH3OH (2), [Mn2(OH-ip)2(DMF)]·DMF (3), and (Me2NH2)[Mn4(sdba)4(Hsdba)(H2O)]·3H2O·2DMF (4) (Am-H2ip = 5-aminoisophthalic acid, H2ip = isophthalic acid, OH-H2ip = 5-hydroxyisophthalic acid, and H2sdba = 4,4'-sulfonyldibenzoic acid), have been prepared by solvothermal reactions of Mn(II) ions with different polycarboxylate acids in the presence of LiNO3 or NH4NO3. Single-crystal X-ray diffraction studies reveal that the frameworks of 1-4 contain diverse Mn(II)-oxygen inorganic magnetic chain's sequences, -J1J1J1J1- for 1, -J1J2J1J2- for 2, -J1J1J2J2- for 3, and -J1J2J3J3- for 4. The sequence in 4 has never been seen for the magnetic chain compounds and is a new type of magnetic alternating sequence. Magnetic investigations indicate that these compounds all show weak antiferromagnetic couplings between the adjacent Mn(II) ions. Magnetostructural analyses based on the data of 1-4 and other related Mn(II) chain compounds imply that the magnitude of the magnetic coupling has some relationship with the Mn-O-Mn angle of the μ2-O bridge and the average Mn-O-C-O torsion angle of the carboxylate bridges. Compounds 2 and 4 crystallize in chiral and acentric space groups, and they both exhibit powder second harmonic generation (SHG) efficiencies approximately 0.6 and 0.9 times, respectively, that of the standard potassium dihydrogen phosphate (KDP) powder. In addition, the dielectric properties of 2 and 4 were also investigated.

Two magnetic phase transitions, driven by symmetry breaking and isostructural phase transitions, in a nickel-bis-dithiolene spin system

A one-dimensional (1-D) magnetic chain compound, [(CD3)2CN-Py][Ni(mnt)2], where (CD3)2CN-Py+ = 1-(propan-d6-2-ylideneamino)pyridinium and mnt2− = maleonitriledithiolate, was synthesized and characterized. This compound undergoes two structural phase transitions, at around 267 K and 325 K. The three phases are sequentially labeled as α (below 267 K), β (between 267 and 325 K) and γ (above 325 K). The [Ni(mnt)2]− anions form irregular stacks, with two values of neighboring Ni⋯Ni distances. The cations align in a straight and regular arrangement along the crystallographic a-axis direction in the β phase. The asymmetric unit switches from one anion–cation pair to two anion–cation pairs in the transition from the β to the α phase. This leads to a doubling of the crystallographic axis length, parallel to the anion stack. It also results in the irregular anion stack showing three non-equivalent neighboring Ni⋯Ni distances, as well as making the straight cation arrangement irregular. The β and γ phases are isostructural and exhibit quite similar packing structures. The anion stack shrinks a little with increasing temperature, with all crystallographic axes showing small reduction from the β to γ phase. The two observed magnetic phase transitions are driven by these various structural phase transitions. A thermal hysteresis loop, with a separation of ∼8 K, appears in the transition between the β and α phases. However, this is absent in the transition between the β and γ phases. A dielectric anomaly appears across the phase transition between the β and γ phases but not between the β and α phases.

Magnetic ordering in trigonal chain compounds

We present electronic structure calculations for the one-dimensional magnetic chain compounds Ca3CoRhO6 and Ca3FeRhO6. The calculations are based on density functional theory and the local density approximation. We use the augmented spherical wave (ASW) method. The observed alternation of low- and high-spin states along the Co–Rh and Fe–Rh chains is related to differences in the oxygen coordination of the transition metal sites. Due to strong hybridization the O 2p states are polarized, giving rise to extended localized magnetic moments centered at the high-spin sites. Strong metal–metal overlap along the chains leads to a substantial contribution of the low-spin Rh 4d3z2−r2 orbitals to the exchange coupling of the extended moments. Interestingly, this mechanism holds for both compounds, even though the coupling is ferromagnetic for cobalt and antiferromagnetic for the iron compound. However, our results allow to understand the different types of coupling from the filling dependence of the electronic properties.

Two Chain Compounds of [M(N3)2(HCOO)][(CH3)2NH2] (M = Fe and Co) with a Mixed Azido/Formato Bridge Displaying Metamagnetic Behavior

Two new magnetic chain compounds, where the anionic [M(N3)2(HCOO)-]n chains with a 3-fold bridge of two end-on azido and one syn-syn formato ligands are isolated by the cations of [(CH3)2NH2]+, exhibit metamagnetism because of the strong intrachain ferromagnetic coupling versus the weak interchain antiferromagnetic coupling.

Chiral and helical phase transitions in quasi-1D molecular magnets

Abstract We review recent experimental data obtained with quasi-one-dimensional (1D) molecular magnets Gd(hfac) 3 NITR. For Gd(hfac) 3 NITiPr the results can be coherently explained only in terms of the Villain’s conjecture: a chiral order at intermediate temperatures and helical order at low temperatures. In the case of weakly frustrated molecular magnetic chain compounds Gd(hfac) 3 NITPh, new specific heat measurements show the presence of a phase transition to the three-dimensional (3D) helical order, observed at T ∼ 0.63 K. In the temperature range 25–250 mK the experimental specific heat data are reproduced very well by a simple spin wave theory.

Magnetic properties of a metal-organic chain system [Co(bpdc)(H2O)2]∙H2O (bpdc=biphenyldicarboxylate)

The magnetic properties of a recently discovered metal-organic magnetic chain compound, [Co(bpdc)(H2O)2]∙H2O, were investigated using measurements of magnetic susceptibility M(T)∕H, isothermal magnetization M(H), and heat capacity C(T). The room temperature crystal structure of [Co(bpdc)(H2O)2]∙H2O is monoclinic, space group C2∕c, with lattice parameters a=6.950Å, b=31.585Å, c=6.226Å, and β=95.84°. The M(T)∕H data above 40K were fit to Curie–Weiss law with an effective moment of 5.37μB and a Curie–Weiss temperature of +26K. A spontaneous antiferromagnetic ordering with a transition temperature of 5.5K was observed in the low field M(T)∕H data. In addition, a metamagnetic transition at 500G was found in M(H), measured at 2K. The sizable anomaly observed in C(T) confirms the magnetic phase transition and the transition temperature. The total magnetic entropy removal at 5.5K is 800mJ∕molK. The nature of the magnetic properties is discussed in terms of the ferromagnetic intrachain exchange interaction between the Co(II) ions through the bridging hydrogen atoms along the magnetic chain and the antiferromagnetic Co–Co interchain coupling.

Magnetic Properties of 1D-Straight Linear Chain Chalcogenide — FePb4Sb6S14(Jamesonite)

Single crystals of Fe 2+ (d 6 ; S = 2) ID magnetic chain compound. FePb 4 Sb 6 S 14 were synthesized and the magnetic susceptibility and heat capacity measurements. The magnetic susceptibility shows a broad maximum around 33K and two anomalies at 8 and 3K. Although the dc magnetic susceptibility shows strong anisotropy. one-dimensional Heisenberg antiferromagnetic model gives better fit to the dc magnetic susceptibility data, compared with classical one-dimensional Ising model. The anomaly at 3K in the ac magnetic susceptibility shows significant frequency dependence. Heat capacity measurements manifest no long-range magnetic order down to 0.4K. However it has been still open question that FePb 4 Sb 6 S 14 is the second S = 2 Haldane compound.

Thermal and magnetic properties of spin-1 magnetic chain compounds with large single-ion and in-plane anisotropies

The thermal and magnetic properties of spin-1 magnetic chain compounds with large single-ion and in-plane anisotropies are investigated via the integrable $su(3)$ model in terms of the quantum transfer matrix method and the recently developed high temperature expansion method for exactly solved models. It is shown that large single-ion anisotropy may result in a singlet gapped phase in the spin-$1$ chain which is significantly different from the standard Haldane phase. A large in-plane anisotropy may destroy the gapped phase. On the other hand, in the vicinity of the critical point a weak in-plane anisotropy leads to a different phase transition than the Pokrovsky-Talapov transition. The magnetic susceptibility, specific heat, and magnetization evaluated from the free energy are in excellent agreement with the experimental data for the compounds ${\mathrm{Ni}(\mathrm{C}}_{2}{\mathrm{H}}_{8}{\mathrm{N}}_{2}{)}_{2}\mathrm{Ni}{(\mathrm{CN})}_{4}$ and ${\mathrm{Ni}(\mathrm{C}}_{10}{\mathrm{H}}_{8}{\mathrm{N}}_{2}{)}_{2}\mathrm{Ni}{(\mathrm{CN})}_{4}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{H}}_{2}\mathrm{O}$.

Extended moment formation and magnetic ordering in the trigonal chain compound Ca 3Co 2O 6

The results of electronic structure calculations for the one-dimensional magnetic chain compound Ca 3Co 2O 6 are presented. The calculations are based on density functional theory and the local density approximation and used the augmented spherical wave (ASW) method. Our results allow for deeper understanding of recent experimental findings. In particular, alternation of Co 3d low- and high-spin states along the characteristic chains is related to differences in the oxygen coordination at the inequivalent cobalt sites. Strong hybridization of the d states with the O 2p states lays ground for polarization of the latter and the formation of extended localized magnetic moments centered at the high-spin sites. In contrast, strong metal–metal overlap along the chains gives rise to intrachain ferromagnetic exchange coupling of the extended moments via the d 3z 2–r 2 orbitals of the low-spin cobalt atoms.

Specific heat study of magnetic excitations in a one-dimensional S=1 Heisenberg magnet with strong planar anisotropy

The results of experimental studies of the specific heat of the magnetic chain compounds Ni(C2H8N2)2Ni(CN)4, Ni(C11H10N2O)2Ni(CN)4, and Ni(C10H8N2)2Ni(CN)4⋅H2O are reported. All compounds are identified as S=1 planar Heisenberg magnetic chains with large planar anisotropy and different values of the in-plane anisotropy constant. The low-temperature specific heat data are interpreted assuming the existence of noninteracting excitons and antiexcitons as elementary excitations from the singlet-ground state. The extended strong-coupling model is used for analysis of the data at higher temperatures. The applicability of the models used with respect to the value of the in-plane anisotropy is discussed.

Role of dipolar interactions in three-dimensional magnetic ordering of chain compounds with very large interchain spacing

A model that takes into account the dipolar interaction between quantum spin chains is proposed to explain the occurrence of three-dimensional (3D) ordering in magnetic chain compounds, where superexchange interaction can be neglected because of large interchain spacing. The divergence of the in-chain correlation length at low temperature promotes correlated spin blocks that can interact from chain to chain through sizeable dipole-dipole coupling. Using a modified mean-field approach we show that the strength of this interaction is large enough to induce 3D magnetic ordering. The model is applied to the Mn-porphyrin-based magnets exhibiting ferrimagnetic chains well separated in space (up to 30 \AA{} apart). Different ground-state spin alignments are analyzed. In the framework of the proposed approach, the ordering temperatures that are calculated compare well with the experimental findings. It is shown that the rate of increase of the correlation length at low temperature is the essential parameter in order to reach the observed transition temperatures. Indeed an exponential divergence of the 1D correlation length is required, which implies the existence of single-ion anisotropy, whereas the power-law divergence for 1D Heisenberg coupled spins yields transition temperatures one order of magnitude smaller than observed.

Cooperative magnetic behavior of self-assembled iron(II) chelate chain compounds

The magnetic characterization of two different magnetic chain compounds containing the same Schiff base ligand L but different axially coordinated ligands is reported: The spin crossover complex [Fe(L)(HIm) 1.80] and the magnetic compound [Fe(L)(MeOH) 1.83]. (L=diethyl (E,E)-2,2′-[1,2-phenylenebis(iminomethylidyne)]-bis[3-oxobutanoate], MeOH=methanol, HIm=imidazole.) The compound [Fe(L)(HIm) 1.80] displays a cooperative spin crossover phenomenon (high-spin↔low-spin transition) centered at T 1/2=330 K, and the high-spin compound [Fe(L)(MeOH) 1.83] shows a weak spontaneous magnetization below T c=9.5 K. Both complexes are chemically connected via strong hydrogen bonds which influences the magnetic properties of both compounds.

Magnetic and thermodynamic properties ofNi(C10H8N2)2Ni(CN)4⋅H2O:AS=1Heisenberg antiferromagnetic chain with strong in-plane anisotropy and subcritical exchange coupling

The results of experimental studies of the magnetic and thermodynamic quantities and ESR data of a magnetic chain compound $\mathrm{Ni}({\mathrm{C}}_{10}{\mathrm{H}}_{8}{\mathrm{N}}_{2}{)}_{2}\mathrm{Ni}(\mathrm{CN}{)}_{4}\ensuremath{\cdot}{\mathrm{H}}_{2}\mathrm{O}$ are reported. The system is identified as an $S=1$ planar Heisenberg antiferromagnetic chain with subcritical exchange coupling and strong in-plane anisotropy. The influence of in-plane anisotropy is discussed with respect to the validity of a theoretical model proposed for $S=1$ Heisenberg chains with strong planar anisotropy. The analysis suggests that in-plane anisotropy should be considered in any attempt to find a compound potentially located at the boundary between the Haldane and large-$D$ phases.

New Magnetic Iron(II) Chelate and Iron(III) Chelate TCNE− Complexes with a Tc of 10 K

The high spin iron(II) chelate complex Fe1×2MeOH as well as its 1:1 derivative with TCNE have been investigated with respect to cooperative magnetic properties. Fe1×2MeOH represents a magnetic chain compound, wherein an intermolecular interaction via hydrogen bonds between the CH-groups of axially coordinated methanol and the ester groups located on the ligand periphery is observed. The weak spontaneous magnetization below approximately 10 K indicates cooperative magnetic behavior. The reaction of the iron(II) chelate complex with the electron acceptor TCNE leads to a 1:1 charge-transfer complex. The spontaneous magnetization occurs here below 10 K and is significantly higher compared to the magnetic iron(II) chelate chain compound.

A neutron investigation of the soliton regime in the one-dimensional planar antiferromagnet (CD3)4NMnCl3

The authors present a detailed quantitative experimental analysis of the soliton regime in a magnetic chain compound. The experiments described were performed on the one-dimensional antiferromagnet TMMC ((CD3)4NMnCl3) which is known to be a planar system below 5K. By applying a magnetic field in the plane perpendicular to the chain axis one can create solitons which correspond to the solutions of a sine-Gordon equation. An intense quasi-elastic (central) peak is observed, the width of which results from the flipping of the spins associated with the sublattices each time a soliton passes by. This feature is characteristic of antiferromagnetic chains. Together with a detailed neutron analysis it allows the authors to develop a quantitative study of the soliton regime. This is made by varying both the magnetic field (H approximately=0-50 kOe) and the temperature (T approximately=1.5-5K). A characteristic exponential dependence as a function of H/T is established for both the energy and wavevector widths of the central peak. The soliton energy is determined with very good accuracy and it is shown that quantum corrections are important in TMMC.

Mössbauer measurements on the rectangular Ising compounds RbFeCl3·2H2O and CsFeCl3·2H2O

Mössbauer experiments are reported on two magnetic chain compounds. Estimates of the crystal field splittings and the sign of Vzz are presented. The temperature dependence of the hyperfine field fits well by the 2D S = 12 rectangular Ising model. The low temperature value and orientation of the hyperfine field are discussed.