Ferromagnetic Mn Research Articles

Synthesis, structures and magnetic properties of polynuclear mixed-valence MnIIMnIII complexes containing 3-(2-phenol)-5-(pyridin-2-yl)-1,2,4-triazole ligand

This paper reports the synthesis, crystal structures, and magnetic properties of a series of mixed-valence polynuclear manganese complexes bridged by a dianionic 1,2,4-triazole-based ligand L(2-) (H(2)L = 3-(2-phenol)-5-(pyridin-2-yl)-1,2,4-triazole). Complexes 1 to 3 show a similar binuclear structure, with the central core of [Mn(II)Mn(III)(L)(2)] and some other small molecules also coordinated to the two Mn centers. The two [Mn(II)Mn(III)(L)(2)] subunits can be further connected by different dicarboxylic acids to construct non-charged tetranuclear complexes 4 to 7. In these complexes, each deprotonated dianionic ligand L(2-) acts as a mu(2)-bridged ligand to coordinate two Mn centers via the 1,2,4-triazole ring. Bond valence sum (BVS) calculations and Mn surrounding bond lengths indicate that the Mn center coordinated to the pyridine N atoms in the +2 oxidation state, while another Mn center coordinated to the phenolic O atoms is in the +3 oxidation state. The Mn(III) centre shows Jahn-Teller elongation along one of the axes. Magnetic studies show the presence of ferromagnetic Mn(III)-Mn(II) coupling in the binuclear (1-3) and tetranuclear (4-7) complexes with the magnetic coupling constant (J) ranging from 0.58 to 1.17 cm(-1), based on the Hamiltonian H = -2JS(1) x S(2) (S(1) = 5/2 and S(2) = 2). In all cases both z'J' (intermolecular interactions) and D parameter (Zero Field Splitting of the Mn (III) ion) has been introduced to improve the corresponding fit. The relationship of the coupling interaction between the Mn(II)/Mn(III) and their electronic structures is discussed.

Effect of processing on microstructure of Si:Mn

Effect of processing of Si:Mn at up to 1270 K (HT) under enhanced hydrostatic pressure (HP, up to 1.1 GPa) for 1 h on its microstructure has been investigated by X-ray and SIMS methods. Si:Mn was prepared by implantation at 610 K of Mn + ions (dose 1 × 10 16 cm −2, energy 160 keV) into (0 0 1) oriented Czochralski (Cz-Si) or Floating zone (Fz-Si) silicon with interstitial oxygen concentration, c o = 1.5 × 10 17 cm −3 (Fz-Si) or 9 × 10 17 cm −3 (Cz-Si). The defect structure of Si:Mn depends on c o, HT and HP. The intensity of X-ray diffraction peaks originating from the ferromagnetic Mn 4Si 7 phase (with the lattice parameters a = 0.5525 nm and c = 1.7463 nm) increases with HT, up to 1070 K. Markedly shifted Mn atom concentration towards the surface is observed after processing of Si:Mn at ≥1000 K, especially under 10 5 Pa. Processing at 1270 K results in the decreased content of Mn 4Si 7; Mn diffusivity decreases with HP. Oxygen gettering within the implantation-disturbed area has been stated.

Resonant magnetic scattering of polarized X-rays at the Mn 2p edge from Mn 0.06Ge 0.94 diluted magnetic semiconductor

We have measured the X-ray resonant magnetic scattering at the 2p edge of Mn in diluted magnetic semiconductor Mn 0.06Ge 0.94/Ge(001)2 × 1 thin films. Large magnetic effects in the resonant reflectivity were observed over a wide temperature range. The asymmetry ratio of the magnetic scattering increases with increasing temperature, in accordance to the temperature dependence of the magnetization obtained from SQUID measurements. This is attributed to the contribution of ferromagnetic Mn 5Ge 3 nanoclusters present in the Mn 0.06Ge 0.94 film.

Carrier spin polarization in digital Mn/GaAs ferromagnetic structures studied with hot electron photoluminescence

The effect of ferromagnetic layers on the spin polarization of holes and electrons in digital Mn/GaAs ferromagnetic heterostructures (DFHs) is studied with hot electron photoluminescence. We show that carriers in the GaAs interlayers experience a strong exchange interaction with the ferromagnetic interfaces. This exchange field rapidly decreases with increasing distance between the ferromagnetic Mn $\ensuremath{\delta}$ layers. The relaxation of the ferromagnetic properties of the digital structures is caused by compensation of the holes mediating the ferromagnetism of DFHs by electrons originating from the GaAs interlayers. For comparison, the polarization of holes in granular MnAs:GaAs, which consists of MnAs nanocrystals embedded in a GaAs matrix, is also studied. In this case, the holes in the GaAs matrix do not experience any strong magnetic fields from the ferromagnetic MnAs nanocrystals.

Ferromagnetic Mn modulation-doped two-dimensional hole systems

Mn modulation-doped strain relaxed In 0.75Ga 0.25As/In 0.75Al 0.25As single quantum-well (SQW) structures on (0 0 1)GaAs with an embedded InAs channel are fabricated by molecular beam epitaxy. The properties of the magnetic two-dimensional hole system were investigated by magnetotransport measurements up to 19 T in the temperature range from 50 mK to room temperature. In the low-temperature regime typical features of the quantum Hall effect like quantized plateaus at the Hall resistance and Shubnikov-de Haas oscillations in the longitudinal resistance are observable. The resistance at B=0 T shows a distinct temperature dependence, and at low temperatures, a large negative magnetoresistance. Furthermore, a hysteretic behavior and jumps in the resistance below 300 mK and around B=0 T can be observed for an asymmetric QW structure.

X-ray magnetic circular dichroism characterization of GaN∕Ga1−xMnxN digital ferromagnetic heterostructure

The authors have investigated the magnetic properties of a GaN∕Ga1−xMnxN (x=0.1) digital ferromagnetic heterostructure (DFH) showing ferromagnetic behavior using soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). The Mn L2,3-edge XAS spectra were similar to those of Ga1−xMnxN random alloy thin films, indicating a substitutional doping of high concentration Mn into GaN. From the XMCD measurements, it was revealed that paramagnetic and ferromagnetic Mn atoms coexisted in the Ga1−xMnxN digital layers. Subtle differences were also found from the XMCD spectra between the electronic states of the ferromagnetic and paramagnetic Mn2+ ions. The ferromagnetic moment per Mn atom estimated from XMCD agreed well with that estimated from superconducting quantum interference device measurements, indicating that the ferromagnetic behavior of the GaN∕Ga1−xMnxN DFH sample arises only from substitutional Mn2+ ions in the Ga1−xMnxN digital layers and not from ferromagnetic precipitates.

Substituent Effect on Formation of Heterometallic Molecular Wheels: Synthesis, Crystal Structure, and Magnetic Properties

The reaction of manganese(III) Schiff bases of the type salen(2-) (N,N'-ethylenebis(salicylideneaminato)) with X-substituted (X = CH(3), Cl) pyridinecarboxamide dicyanoferrite(III) [Fe(X-bpb)(CN)(2)](-) gave rise to a series of cyanide-bridged Mn(6)Fe(6) molecular wheels, [Mn(III)(salen)](6)[Fe(III)(bpmb)(CN)(2)](6) x 7H(2)O (1), [Mn(salen)](6)[Fe(bpClb)(CN)(2)](6) x 4H(2)O x 2CH(3)OH (2), [Mn(salen)](6)[Fe(bpdmb)(CN)(2)](6) x 10H(2)O x 5CH(3)OH (3), [Mn(5-Br(salpn))](6)[Fe(bpmb)(CN)(2)](6) x 24H(2)O x 8CH(3)CN (4), and [Mn(5-Cl(salpn))](6)[Fe(bpmb)(CN)(2)](6) x 25H(2)O x 5CH(3)CN (5). Compared with [Fe(bpb)(CN)(2)](-), which always gives rise to 1D or polynuclear species when reacting with Mn(III) Schiff bases, the introduction of substituents (X) to the bpb(2-) ligand has a driving force in formation of the novel wheel structure. Magnetic studies reveal that high-spin ground state S = 15 is present in the wheel compounds originated from the ferromagnetic Mn(III)-Fe(III) coupling. For the first time, the quantum Monte Carlo study has been used to modulate the magnetic susceptibility of the huge Mn(6)Fe(6) metallomacrocycles, showing that the magnetic coupling constants J range from 3.0 to 8.0 K on the basis of the spin Hamiltonian [Formula: see text]. Hysteresis loops for 1 have been observed below 0.8 K, indicative of a single-molecule magnet with a blocking temperature (TB) of 0.8 K. Molecular wheels 2-5 exhibit frequency dependence of alternating-current magnetic susceptibility under zero direct-current magnetic field, signifying the slow magnetization relaxation similar to that of 1. Significantly, an unprecedented archlike Mn(2)Fe(2) cluster, [Mn(5-Cl(salpn))](2)[Fe(bpmb)(CN)(2)](2) x 3H(2)O x CH(3)CN (6), has been isolated as an intermediate of the Mn(6)Fe(6) wheel 5. Ferromagnetic Mn(III)-Fe(III) coupling results in a high-spin S = 5 ground state. Combination of the high-spin state and a negative magnetic anisotropy (D) results in the observation of slow magnetization relaxation in 6.

Single-Molecule Magnet Behavior in Heterometallic MII−MnIII2−MII Tetramers (MII = Cu, Ni) Containing MnIII Salen-Type Dinuclear Core

The linear-type heterometallic tetramers, [Mn(III)(2)(5-MeOsaltmen)(2)M(II)(2)(L)(2)](CF(3)SO(3))(2) x 2H(2)O (MII = Cu, 1a; Ni, 2a), where 5-MeOsaltmen(2-) = N,N'-(1,1,2,2-tetramethylethylene) bis(5-methoxysalicylideneiminate), and H(2)L = 3-{2-[(2-hydroxy-benzylidene)-amino]-2-methyl-propylimino}-butan-2-one oxime, have been synthesized and characterized from structural and magnetic points of view. These two compounds are isostructural and crystallize in the same monoclinic P2(1)/n space group. The structure has a [M(II)-NO-Mn(III)-(O)(2)-Mn(III)-ON-M(II)] skeleton, where -NO- is a linking oximato group derived from the non-symmetrical Schiff-base complex [M(II)(L)] and -(O)(2)- is a biphenolato bridge in the out-of-plane [Mn(2)(5-MeOsaltmen)(2)](2+) dimer. The solvent-free compounds, 1b and 2b, have also been prepared by drying of the parent compounds, 1a and 2a, respectively, at 100 degrees C under dried nitrogen. After this treatment, the crystallinity is preserved, and 1b and 2b crystallize in a monoclinic P2(1)/c space group without significant changes in their structures in comparison to 1a and 2a. Magnetic measurements on 1a and 1b revealed antiferromagnetic Mn(III)---Cu(II) interactions via the oximato group and weak ferromagnetic Mn(III)---Mn(III) interactions via the biphenolato bridge leading to an S(T) = 3 ground state. On the other hand, the diamagnetic nature of the square planar Ni(II) center generates an S(T) = 4 ground state for 2a and 2b. At low temperature, these solvated (a) and desolvated (b) compounds display single-molecule magnet behavior modulated by their spin ground state.

Ammonothermal synthesis of GaN doped with transition metal ions (Mn, Fe, Cr)

The ammonothermal technique was used to obtain GaN powders doped with various transition metal ions—Mn, Fe, Cr. The procedure of ammonothermal growth and morphology, structural, magnetic and optical investigations of magnetic GaN is described. The largest solubility limit ( x < 1%) was obtained in the case of Mn doping while the solubility of Fe and Cr occurred to be much smaller (0.03% and below 0.02%, respectively). Adding Mn into the growth zone reduces the crystallite size from 2–5 μm of pure GaN to even tens of nanometers depending on Mn amount added. Detected Mn 2+ centers are responsible for the paramagnetic behavior of GaMnN. X-ray diffraction study of GaMnN revealed presence of different Mn x N y compounds, in particular ferromagnetic Mn 4N which may be the source of additional ferromagnetic contribution. The results show substantial difficulties to obtain hole induced ferromagnetism in GaMnN. Mn reduces the luminescence efficiency of ammonothermal GaN. In the case of Fe doping we are dealing with a spectrum of different Fe centers. Ammonothermal GaN:Cr is ferromagnetic but its origin is unrecognized yet.

Cyanide-Bridged Mn(III)−Fe(III) Bimetallic Complexes Based on the Pentacyano(1-methylimidazole)ferrate(III) Building Block: Structure and Magnetic Characterizations

Seven cyanide-bridged bimetallic complexes have been synthesized by the reaction of [Fe(1-CH3im)(CN)5]2- with Mn(III) Schiff base complexes. Their crystal structure and magnetic properties have been characterized. Five complexes, [Mn2(5-Brsalen)2Fe(CN)5(1-CH3im)] x H2O (1), [Mn2(5-Clsalen)2(H2O)2Fe(CN)5(1-CH3im)] x H2O (2), [Mn2(5-Clsaltn)2(H2O)2Fe(CN)5(1-CH3im)] (3), [Mn2(5-Clsaltmen)2(H2O)2Fe(CN)5(1-CH3im)] x H2O (4), and [Mn2(5-Brsaltmen)2(H2O)2Fe(CN)5(1-CH3im)] x CH3OH (5), are neutral and trinuclear with two [Mn(SB)]+ (SB2- = Schiff base ligands) and one [Fe(1-CH3im)(CN)5]2-. Complex {[Et4N][Mn(acacen)Fe(CN)5(1-CH3im)]}n x 6nH2O (6) is one-dimensional with alternate [Mn(acacen)]+ and [Fe(CN)5(1-CH3im)]2- units. The two-dimensional complex {[Mn4(saltmen)4Fe(CN)5(1-CH3im)]}n[ClO4]2n x 9nH2O (7) consists of Mn4Fe units which are further connected by the phenoxo oxygen atoms. Magnetic studies show the presence of ferromagnetic Mn(III)-Fe(III) coupling in the trinuclear compounds with the magnetic coupling constant (J) ranging from 4.5 to 6.0 cm-1, based on the Hamiltonian H = -2JSFe(SMn(1) + SMn(2)). Antiferromagnetic interaction has been observed in complex 6, whereas ferromagnetic coupling occurs in complex 7. Complexes 6 and 7 exhibit long-range magnetic ordering with a TN value of 4.0 K for 6 and Tc of 4.8 K for 7. Complex 6 shows metamagnetic behavior at 2 K, and complex 7 possesses a hysteresis loop with a coercive field of 500 Oe, typical of a soft ferromagnet.

Magnetic and structural properties ofGexMn1−xfilms: Precipitation of intermetallic nanomagnets

We present a comprehensive study relating the nanostructure of Ge_0.95Mn_0.05 films to their magnetic properties. The formation of ferromagnetic nanometer sized inclusions in a defect free Ge matrix fabricated by low temperature molecular beam epitaxy is observed down to substrate temperatures T_S as low as 70 deg. Celsius. A combined transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) analysis of the films identifies the inclusions as precipitates of the ferromagnetic compound Mn_5Ge_3. The volume and amount of these precipitates decreases with decreasing T_S. Magnetometry of the films containing precipitates reveals distinct temperature ranges: Between the characteristic ferromagnetic transition temperature of Mn_5Ge_3 at approximately room temperature and a lower, T_S dependent blocking temperature T_B the magnetic properties are dominated by superparamagnetism of the Mn_5Ge_3 precipitates. Below T_B, the magnetic signature of ferromagnetic precipitates with blocked magnetic moments is observed. At the lowest temperatures, the films show features characteristic for a metastable state.

Reconstruction Control of Magnetic Properties during Epitaxial Growth of FerromagneticMn3−δGaon Wurtzite GaN(0001)

Binary ferromagnetic Mn(3-delta)Ga (1.2<3-delta< or =1.5) crystalline thin films have been epitaxially grown on wurtzite GaN(0001) surfaces using rf N-plasma molecular beam epitaxy. The film structure is face-centered tetragonal with CuAu type-I (L1(0)) ordering with (111) orientation. The in-plane epitaxial relationship to GaN is nearly ideal with [110](MnGa) parallel[1100](GaN) and [112](MnGa) parallel[1120](GaN). We observe magnetic anisotropy along both the in-plane and out-of-plane directions. The magnetic moments are found to depend on the Mn/(Mn+Ga) flux ratio and can be controlled by observation of the surface reconstruction during growth, which varies from 1x1 to 2x2 with increasing Mn stoichiometry.

Magnetic properties ofGaN∕MnxGa1−xNdigital heterostructures: First-principles and Monte Carlo calculations

The energetic and magnetic properties of wurtzite $\mathrm{GaN}∕{\mathrm{Mn}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ digital heterostructures are investigated by first-principles total energy calculations, within the spin density-functional theory, and Monte Carlo simulations. In a wurtzite $\mathrm{GaN}$ model sample, periodic in the $c$ axis, we replace a $\mathrm{GaN}$ monolayer (a plane) by a plane with composition ${\mathrm{Mn}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$, and study its properties for varying the $\mathrm{GaN}$ spacer layer thickness and Mn concentration $x$. The 100% $\mathrm{MnN}$ monolayer possesses an antiferromagnetic (AFM) ground state when, in the periodic sample, it is isolated from the other $\mathrm{MnN}$ monolayers by more than four $\mathrm{GaN}$ spacer layers. The case of submonolayers $(x&lt;1)$ is studied by Monte Carlo simulations based on an Ising Hamiltonian, whose parameters are obtained from ab initio calculations on five configurations. At $700\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, up to the concentration of 8% Mn, the two-dimensional (2D) alloy is stable. However, above this concentration, there is a strong tendency to the formation of $\mathrm{MnN}$ clusters with an AFM ground state defined by ferromagnetic Mn rows coupled antiferromagnetically with other Mn rows. The behavior of the magnetization with the temperature is completely different in these two concentration regimes, with the 2D $\mathrm{MnN}$ cluster being very stable, whereas the 2D alloy presents low magnetic transition temperatures.

From an ST = 3 Single-Molecule Magnet to Diamagnetic Ground State Depending on the Molecular Packing of MnIIIsalen-type Dimers Decorated by N,N‘-Dicyano-1,4-naphthoquinonediiminate Radicals

Two manganese(III) tetradentate Schiff-base dimers to which N,N'-dicyano-1,4-naphthoquinonediiminate (DCNNQI) radicals are attached have been selectively synthesized by varying the solvents used in the reactions: [Mn2(5-MeOsaltmen)2(DCNNQI)2].MeOH (1) and [Mn2(5-MeOsaltmen)(2)(DCNNQI)(2)] x 2CH2Cl2.2CH3CN (2) [5-MeOsaltmen2- = N,N'-(1,1,2,2-tetramethylethylene)bis(5-methoxysalicylideneiminate)]. These two complexes share the same molecular core, [(DCNNQI.-)-Mn(III)-(O)2-Mn(III)-(DCNNQI.-)], where -(O)2- is a biphenolate bridge in the out-of-plane dimerized [Mn(2)(5-MeOsaltmen)2]2+ moiety. However, their packing arrangements are completely different. Whereas complex 1 is found to be relatively isolated, strong intermolecular dimerization of the DCNNQI moieties (with the nearest contact being approximately 3.0 A) is observed in 2, forming a one-dimensional chain of [-Mn(III)-(O)2-Mn(III)-(DCNNQI.-)2-](infinity). The magnetic susceptibility of 1 can be modeled with an [S = 1/2, 2, 2, 1/2] four-spin system including strong antiferromagnetic Mn(III)/DCNNQI radical coupling (J(Mn/rad)/kB = -23 K) and ferromagnetic Mn(III)/Mn(III) coupling through the biphenolate bridge (J(Mn/Mn)/kB = +2.0 K). These interactions lead to an ST = 3 ground state that possesses significant uniaxial anisotropy (D(S=3)/kB = -2.1 K). Low-temperature ac and dc magnetic data of 1 reveal its single-molecule magnet behavior with quantum tunneling of the magnetization. By contrast, 2 possesses the diamagnetic ground state induced by dominating Mn(III)-Mn(III) antiferromagnetic interactions mediated by the diamagnetic DCNNQI dimers and/or pi-pi contact along the b axis.

Characterization of room temperature ferromagnetic Mn–Si compound synthesized on SiC substrate

Manganese silicide (Mn–Si) related compound with a Curie temperature (TC) of 300K was synthesized on a 4H-SiC homoepitaxial wafer. Thin Mn layer was deposited on the SiC wafer, and then annealing was performed to diffuse the Mn atoms into the SiC epitaxial layer. Transmission magnetic circular dichroism spectra reflected that of the SiC wafer, although the structural investigations suggested that the dominant phase of the synthesized layer was paramagnetic Mn5Si2. At this stage, two possible explanations are considered the origin of the observed ferromagnetism. One is that a small amount of carbon (C) incorporated into the Mn5Si2 host induced the ferromagnetic order in Mn5Si2. On the other hand, the partial formation of a ferromagnetic SiC-related component at the vicinity of the lower side of the interface between SiC and Mn5Si2 layers is considered the other possible explanation.

Ferromagnetic ordering and magnetic anisotropy of a Mn monolayer on Nb(001)

Through density functional full-potential linearized augmented-plane-wave calculations, we found that it is possible to materialize a ferromagnetic Mn monolayer on nonmagnetic Nb(001). It was obtained that the surface Nb atom has a large induced magnetic moment of $\ensuremath{-}0.56{\ensuremath{\mu}}_{B}$ and the Nb has an antiferromagnetic exchange interaction with the Mn adlayer. We attribute this antiferromagnetic exchange interaction between Mn and Nb atoms to the realization of a ferromagnetic ground state in a Mn monolayer on the Nb(001) surface. We also present the calculated results of x-ray magnetic circular dichroism and magnetic anisotropy. It was observed that $\mathrm{Mn}∕\mathrm{Nb}(001)$ has weak perpendicular magnetocrystalline anisotropy, but the easy axis is in plane due to the shape anisotropy.

Magnetization processes of polycrystalline La 0.7Pb 0.3Mn 1−xFe xO 3

A systematic investigation of the magnetic properties in the perovskite materials La 0.7Pb 0.3Mn 1− x Fe x O 3 is presented in this study. The distortion induced by Mn-site substitution is not obvious as radii of Fe and Mn are similar for low Fe-content samples. Powder X-ray diffraction patterns show the same crystallographic phase of rhombohedral symmetry with space group R 3 ¯ c for x⩽0.4 and change to orthorhombic symmetry with space group Pnma for x⩾0.6. The zero field cooling–field cooling curves and the values of temperature-dependence magnetization indicate ferromagnetic Mn 3+–O 2−–Mn 4+ double-exchage interaction would be gradually replaced by antiferromagnetic Fe 3+–O 2−–Mn 4+ and Fe 3+–O 2−–Fe 4+ exchange coupling for x = 0.6 and 0.8 and would be completely replaced by Fe 3+–O 2−–Fe 4+ for x = 1.0 . From the results of experiments, the substitution of Mn by Fe suppresses the double-exchange interaction, weakens the ferromagnetism and consequently decreases the ferromagnetic transition temperature T C and saturation magnetization M S.

Properties of wurtzite w-MnN and of w-MnN inclusions in (Ga,Mn)N

Mn ions in (Ga,Mn)N exhibit a tendency to form pairs, which is enhanced by ferromagnetic Mn–Mn coupling. We also find that segregation of Mn to form MnN clusters in the wurtzite structure of host GaN is energetically favorable. However, our first-principles calculations show that both w-MnN inclusions stretched to fit the lattice constant of GaN, and relaxed ones with the equilibrium lattice constant of MnN are antiferromagnetic, and thus they are not responsible for the high temperature ferromagnetism reported for (Ga,Mn)N. Incorporation of Mn on the N sites is prohibited by the high formation energy of MnN.

Large magnetic moments and anomalous exchange coupling in As-doped Mn clusters

We report electronic and magnetic properties of pure and arsenic-doped manganese clusters from density functional theory using spin-polarized generalized gradient approximation for the exchange-correlation energy. We see for both the cases, noncollinear treatment of spins are indeed necessary. The arsenic atom stabilizes manganese clusters, which is further accompanied by the ferromagnetic $\mathrm{Mn}\text{\ensuremath{-}}\mathrm{Mn}$ coupling for ${\mathrm{Mn}}_{2}\mathrm{As}$ and ${\mathrm{Mn}}_{4}\mathrm{As}$ clusters, resulting in large cluster magnetic moments, 9 and $17\phantom{\rule{0.3em}{0ex}}{\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$, respectively. We show in doped clusters, exchange coupling are anomalous and behave quite differently from the Ruderman-Kittel-Kasuya-Yosida-type predictions. Finally, it is suggested that, if grown in the low temperature MBE, the giant magnetic moments due to ferromagnetic Mn ordering and their large enough exchange coupling parameter in ${\mathrm{Mn}}_{2}\mathrm{As}$ and ${\mathrm{Mn}}_{4}\mathrm{As}$ could play an important role on the ferromagnetism and on the observed large variation in the Curie temperature of the Mn-doped III-V semiconductors.

Synthesis, Structure, and Magnetic Properties of Li-Doped Manganese-Phthalocyanine, Lix[MnPc] (0 ⩽x⩽ 4)

We report on the first synthesis of Li-intercalated manganese-phthalocyanine (MnPc) in the bulk form and on the evolution of the structural and magnetic properties as a function of Li concentration, x. We find that solid beta-MnPc, which comprises rodlike assemblies of individual planar molecules, is best described as a glassy one-dimensional ferromagnet without three-dimensional ordering and that it can be quasi-continuously intercalated with Li up to x = 4, forming an isosymmetrical series of Li(x)[MnPc] phases. Inserted Li+ ions strongly bond to pyrrole-bridging nitrogen atoms of the Pc rings, thereby disrupting the ferromagnetic Mn-N(a)...Mn superexchange pathways. This gradually induces a crossover of the intrachain exchange interactions from ferromagnetic to antiferromagnetic as the doping level, x, increases coupled with a spin-state transition of the Mn2+ ions from intermediate spin, S = 3/2, to high spin, S = 5/2.