Magnetic Behavior of a Mixed Ising Ferrimagnetic Model in an Oscillating Magnetic Field

The magnetic behavior of a mixed Ising ferrimagnetic system on a square lattice, in which the two interpenetrating square sublattices have spins +- 1/2 and spins +-1,0, in the presence of an oscillating magnetic field has been studied with Monte Carlo techniques. The model includes nearest and next-nearest neighbor interactions, a crystal field and the oscillating external field. By studying the hysteretic response of this model to an oscillating field we found that it qualitatively reproduces the increasing of the coercive field at the compensation temperature observed in real ferrimagnets, a crucial feature for magneto-optical applications. This behavior is basically independent of the frequency of the field and the size of the system. The magnetic response of the system is related to a dynamical transition from a paramagnetic to a ferromagnetic phase and to the different temperature dependence of the relaxation times of both sublattices.Comment: 10 figures. To be published in Phys.Rev

Dc and ac magnetic properties of the two-dimensional molecular-based ferrimagnetic materials A₂M₂[Cu(opba)]₃nsolv [A⁺ = cation, M^II = Mn^II or Co^II, opba = ortho-phenylenebis(oxamato), and solv = solvent molecule]

This paper is devoted to a thorough study of the magnetic properties, both in the dc and ac modes, of two-dimensional ferrimagnetic materials. The general formula of the compounds, abbreviated as A2M2Cu3, is A2M2[Cu(opba)]3_nsolv where A+ stands for a counter cation (radical cation, alkali-metal or tetraalkylammonium), opba is ortho-phenylenebis(oxamato), MII is MnII or CoII , and solv is a solvent molecule (Me2SO or H2O). The dc magnetic susceptibility data for all compounds down to ca. 50 K are characteristic of two-dimensional ferrimagnets. In the A2Mn2Cu3 series, three classes of compounds have been distinguished. Class I has a unique representative, AV2Mn2Cu3, where AV+ is the radical cation 2-(1-methylpyridinium-4-yl )-4,4,5,5- tetramethylimadozolin-1-oxyl-3-oxide, the structure of which has already been solved. This compound is a magnet with Tc= 22.5 K. Class II corresponds to compounds with large cations (tetraethyl- and n-tetrabutylammonium). They also behave as magnets with Tc around 15 K. Class III corresponds to compounds with small cations (alkali-metal ions and tetramethylammonium). They behave as metamagnets with a long-range antiferromagnetic ordering in zero field around 15 K, and a field-induced ferromagnetic state. The critical fields are of the order of 0.15 kOe. All the A2Co2Cu3 compounds are magnets with Tc around 30 K. Furthermore, the cobalt derivatives show a very strong coercivity, with coercive fields of several kOe at 5 K. They also display a pronounced magnetic after-efect in the ordered phase. In the course of this work several peculiar features have been observed. In particular, the A2Mn2Cu3 compounds have been found to present weak but significant negative out-of-phase ac magnetic signals at temperatures just above Tc. All the observed phenomena are discussed and, in particular, a mechanism for the long-range ordering in these two-dimensional compounds has been propose

Spin distributions in antiferromagnetically coupled Mn2+Cu2+ systems: from the pair to the infinite chain

Probably the most informative description of the ground slate of a magnetic molecular species is provided by the spin density map. Such a map may be experimentally obtained from polarized neutron diffraction (PND) data or theoretically calculated using quantum chemical approaches. Density functional theory (DFT) methods have been proved to be well-adapted for this. Spin distributions in one-dimensional compounds may also be computed using the density matrix renormalization group (DMRG) formalism. These three approaches, PND, DFT, and DMRG, have been utilized to obtain new insights on the ground state of two antiferromagnetically coupled Mn2+Cu2+ compounds, namely [Mn(Me-6-[14]ane-N-4)Cu(oxpn)](CF3SO3)(2) and MnCu(pba)(H2O)(3) . 2H(2)O, with Me-6-[14]ane-N-4 = (+/-)-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, oxpn = N,N'-bis(3-aminopropyl)oxamido and pba = 1,3-propylenebis(oxamato). Three problems in particular have been investigated: the spin distribution in the mononuclear precursors [Cu(oxpn)] and [Cu(pba)](2-), the spin density maps in the two Mn2+Cu2+ compounds, and the evolution of the spin distributions on the Mn2+ and Cu2+ sites when passing from a pair to a one-dimensional ferrimagnet

Spin distributions in antiferromagnetically coupled Mn2+Cu2+ systems: from the pair to the infinite chain

Probably the most informative description of the ground slate of a magnetic molecular species is provided by the spin density map. Such a map may be experimentally obtained from polarized neutron diffraction (PND) data or theoretically calculated using quantum chemical approaches. Density functional theory (DFT) methods have been proved to be well-adapted for this. Spin distributions in one-dimensional compounds may also be computed using the density matrix renormalization group (DMRG) formalism. These three approaches, PND, DFT, and DMRG, have been utilized to obtain new insights on the ground state of two antiferromagnetically coupled Mn2+Cu2+ compounds, namely [Mn(Me-6-[14]ane-N-4)Cu(oxpn)](CF3SO3)(2) and MnCu(pba)(H2O)(3) . 2H(2)O, with Me-6-[14]ane-N-4 = (+/-)-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, oxpn = N,N\u27-bis(3-aminopropyl)oxamido and pba = 1,3-propylenebis(oxamato). Three problems in particular have been investigated: the spin distribution in the mononuclear precursors [Cu(oxpn)] and [Cu(pba)](2-), the spin density maps in the two Mn2+Cu2+ compounds, and the evolution of the spin distributions on the Mn2+ and Cu2+ sites when passing from a pair to a one-dimensional ferrimagnet

CCDC 146391: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

CCDC 181307: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

Spin density maps for the ferrimagnetic chain compound MnCu(pba)(H2O)(3)center dot 2H(2)O (pba equals 1,2-propylenebis(oxamato)): Polarized neutron diffraction and theoretical studies

This paper is devoted to the determination of the spin density in the ferrimagnetic ground state of the bimetallic chain compound MnCu(pba)(H2O)(3) . 2H(2)O, with pba = 1,3-propylenebis(oxamato). The crystal structure, previously determined at room temperature through X-ray diffraction, was redetermined at 10 K through unpolarized neutron diffraction (orthorhombic system, space group Pnma, a = 12.727(11) Angstrom, b = 21.352(19) Angstrom, c = 5.153(3) Angstrom, Z = 4). The experimental spin density has been deduced from polarized neutron diffraction data recorded at 10 K under 50 kOe. Positive spin densities were observed on the manganese side and negative spin densities on the copper side. The delocalization of the spin density from the metal centers toward the oxamato bridging ligand was found to be more pronounced on the copper side than on the manganese side, so that the nodal surface (of zero spin density) is closer to manganese than to copper. The experimental spin distribution has been compared to the theoretical distributions deduced from density functional theory (DFT) calculations, using both DGauss and DMol programs. The experimental results for the title chain compound have also been compared to the spin distribution for the binuclear compound [Mn(Me-6-[14]ane-N-4)Cu(oxpn)](CF3SO3)(2) with Me-6-[14]ane-N-4 = (+/-)-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, and oxpn = N,N\u27-bis(3-aminopropyl)oxamido, recently reported. The most striking difference between pair and chain compounds concerns the positive P+ and negative P- spin populations carried by the manganese and copper sides, respectively. For the pair compound P+ was found as 4.67(8) mu(B), and P- as -0.67(8) mu(B) while for the chain compound these values are 5.05(7) mu(B) and -1.05(10) mu(B), respectively. The spin distribution for the ferrimagnetic chain compound is very close to a Neel state (P+ = 5 mu(B) and P- = -1 mu(B))

Spin density maps for the ferrimagnetic chain compound MnCu(pba)(H2O)(3)center dot 2H(2)O (pba equals 1,2-propylenebis(oxamato)): Polarized neutron diffraction and theoretical studies

This paper is devoted to the determination of the spin density in the ferrimagnetic ground state of the bimetallic chain compound MnCu(pba)(H2O)(3) . 2H(2)O, with pba = 1,3-propylenebis(oxamato). The crystal structure, previously determined at room temperature through X-ray diffraction, was redetermined at 10 K through unpolarized neutron diffraction (orthorhombic system, space group Pnma, a = 12.727(11) Angstrom, b = 21.352(19) Angstrom, c = 5.153(3) Angstrom, Z = 4). The experimental spin density has been deduced from polarized neutron diffraction data recorded at 10 K under 50 kOe. Positive spin densities were observed on the manganese side and negative spin densities on the copper side. The delocalization of the spin density from the metal centers toward the oxamato bridging ligand was found to be more pronounced on the copper side than on the manganese side, so that the nodal surface (of zero spin density) is closer to manganese than to copper. The experimental spin distribution has been compared to the theoretical distributions deduced from density functional theory (DFT) calculations, using both DGauss and DMol programs. The experimental results for the title chain compound have also been compared to the spin distribution for the binuclear compound [Mn(Me-6-[14]ane-N-4)Cu(oxpn)](CF3SO3)(2) with Me-6-[14]ane-N-4 = (+/-)-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, and oxpn = N,N\u27-bis(3-aminopropyl)oxamido, recently reported. The most striking difference between pair and chain compounds concerns the positive P+ and negative P- spin populations carried by the manganese and copper sides, respectively. For the pair compound P+ was found as 4.67(8) mu(B), and P- as -0.67(8) mu(B) while for the chain compound these values are 5.05(7) mu(B) and -1.05(10) mu(B), respectively. The spin distribution for the ferrimagnetic chain compound is very close to a Neel state (P+ = 5 mu(B) and P- = -1 mu(B))