Mn Exchange Research Articles

Spin-flop structure at an antiferromagnetic/ferromagnetic interface: Mn/Fe(1 0 0)

The structure and magnetic properties of manganese overlayers on Fe(1 0 0) substrates are explored using density functional theory. This system represents a model system for studying the magnetic properties of interfaces between a ferromagnet and antiferromagnet. Collinear calculations show that the Mn overlayer adopts an in-plane antiferromagnetic structure. When the constraint of spin collinearity is dropped, a spin-flop state with a nearly perpendicular direction of Fe and Mn moments is found. The exchange coupling constant between Fe and Mn moments is ferromagnetic and stronger than the antiferromagnetic Mn–Mn exchange coupling constant.

Structural, magnetic and thermal properties of CaMn 0.9957Fe 0.01O 3− δ

The polycrystalline CaMn 0.99 57Fe 0.01O 3− δ compound was studied using powder X-ray diffraction, 57Fe Mössbauer spectroscopy, ac susceptometry, dc magnetometry, specific heat and electrical resistivity measurements. X-ray diffraction measurements performed between 70 and 300 K show a thermal expansion anomaly at the Neél temperature. A weak ferromagnetic component and a spin-glass behaviour below Neél temperature are found in magnetic measurements. The Mössbauer spectroscopy measurements performed between 30 and 300 K provided the Neél temperature value of 118 K, the same as obtained from dc magnetisation and close to that derived from the specific heat (119 K). The temperature evolution of the Fe hyperfine field was analysed within a molecular field model and revealed equal strengths of the Fe–Mn and Mn–Mn exchange interactions in this compound.

Mn porphyrin-based superoxide dismutase (SOD) mimic, Mn IIITE-2-PyP 5+, targets mouse heart mitochondria

The Mn(III) meso-tetrakis( N-ethylpyridinium-2-yl)porphyrin, Mn IIITE-2-PyP 5+ (AEOL-10113) has proven effective in treating oxidative stress-induced conditions including cancer, radiation damage, diabetes, and central nervous system trauma. The ortho cationic pyridyl nitrogens of MnTE-2-PyP 5+ are essential for its high antioxidant potency. The exceptional ability of Mn IIITE-2-PyP 5+ to dismute O 2 ·− parallels its ability to reduce ONOO − and CO 3 −. Decreasing levels of these species are considered its predominant mode of action, which may also involve redox regulation of signaling pathways. Recently, Ferrer-Sueta at al. ( Free Radic. Biol. Med. 41:503–512; 2006) showed, with submitochondrial particles, that ≥3 μM Mn IIITE-2-PyP 5+ was able to protect components of the mitochondrial electron transport chain from peroxynitrite-mediated damage. Our study complements their data in showing, for the first time that micromolar mitochondrial concentrations of Mn IIITE-2-PyP 5+ are obtainable in vivo. For this study we have developed a new and sensitive method for Mn IIITE-2-PyP 5+ determination in tissues. The method is based on the exchange of porphyrin Mn 2+ with Zn 2+, followed by the HPLC/fluorescence detection of Zn IITE-2-PyP 4+. At 4 and 7 h after a single 10 mg/kg intraperitoneal administration of Mn IIITE-2-PyP 5+, the mice (8 in total) were anesthetized and perfused with saline. Mitochondria were then isolated by the method of Mela and Seitz ( Methods Enzymol. 55:39–46; 1979). We found Mn IIITE-2-PyP 5+ localized in heart mitochondria to 2.95 ng/mg protein. Given the average value of mitochondrial volume of 0.6 μL/mg protein, the calculated Mn IIITE-2-PyP 5+ concentration is 5.1 μM, which is sufficient to protect mitochondria from oxidative damage. This study establishes, for the first time, that Mn IIITE-2-PyP 5+, a highly charged metalloporphyrin, is capable of entering mitochondria in vivo at levels sufficient to exert there its antioxidant action; such a result encourages its development as a prospective therapeutic agent.

An assessment of the accuracy of soil map of Kwara state, Nigeria.

The variability of particle size fraction, pH, organic matter, total nitrogen, available phosphorus, exchangeable Ca, Mg, Na, exchangeable acidity, effective cation exchange capacity (CEC), base saturation, extractable Fe, Mn and Zn contents within and among the three major soil mapping units delineated in Kwara State, on the Federal Department of Agricultural Land Resources (FDALR) soil map of Nigeria was examined using some statistical measures. Sand content was the least variable (Cv=10.96-15.63%), while available phosphorus was the most Variable (CV=23.91%-181.05%) property. Except for Wilk's criterion (L), all the statistical tools used (coefficient of variation (CV), intra-class correlation coefficient (PI), Relative variance (RV), and the compliment of RV (I-RV) showed that the individual mapping units are heterogeneous. The F-ratio indicated that three mapping units were significantly different for17 out of 18 properties studied. If the usefulness of a soil map is judged by the precision with which it can predict soil conditions at any point of interest within the area covered by the map, the soil map evaluated here may not be practically accurate and its utility is limited. Nigerian Journal of Soil Science Vol. 17 2007: pp. 16-23

New photoluminescence phenomena in milled MnF2 at high pressure

This work presents a time-resolved spectroscopic study of MnF2 as grown and milled into nanoparticles. We find that high pressure (HP) induces photoluminescence (PL) at room temperature (RT) above 13 GPa in MnF2 single crystals. RT-PL occurs as a consequence of the inhibition of excitation migration processes among Mn2+ ions resulting from the HP-induced structural phase transition (SPT) to the α-PbCl2-type phase. This SPT involves important changes in the Mn– F– Mn exchange paths yielding radiative de-excitation in Mn2+, and thus also PL. As a salient result, we have found an increase of the PL-quenching temperature in nanosized milled MnF2.

The Nd–Mn exchange interaction inNd0.7Sr0.3MnO3

The Nd–Mn exchange interaction inNd0.7Sr0.3MnO3 is considered by studying its influence on the55Mn spin-echo NMR lineshape and spin–spin relaxation time. It is seen that theinteraction is of considerable strength well above the Nd spin ordering temperature(≈20 K), with a significant influence on the Mn (electron) spin dynamics.

Spin properties of charged single Mn‐doped quantum dots

AbstractThe optical properties of individual quantum dots doped with a single Mn atom and charged with a single carrier (electron or hole) are analyzed. The emission of the neutral, positively charged and negatively charged excitons coupled with a single magnetic atom are observed in the same quantum dot. The spectrum of the charged excitons in interaction with the Mn atom shows a rich pattern attributed to a strong anisotropy of the hole–Mn exchange interaction slightly perturbed by a small valence band mixing. For the positively charged exciton, the emission pattern shows that the different spin states of the hole–Mn complex remain split in the final state after the exciton recombination. This opens the possibility of storing information on a single carrier spin on a long time scale in the absence of external magnetic field. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Control of single spins in individual magnetic quantum dots

AbstractThe optical properties of individual quantum dots doped with a single Mn atom and charged with a single carrier (electron or hole) are analyzed. Bias controlled single‐carrier charging combined with photo depletion is used to control the charge state of individual Mn‐doped quantum dots. The emission of the neutral, negatively charged and positively charged excitons coupled with a single magnetic atom are observed in the same quantum dot. The emission pattern of the charged excitons differs strongly from that of the neu‐tral excitons (single and biexciton). This difference reflects the fact that the Mn spin is very sensitive to the number of electrons and holes in both the excited and the ground states of the optical transitions. The spectrum of charged excitons in interaction with the Mn atom shows a rich pattern that can be attributed to a strong anisotropy of the hole–Mn exchange interaction This opens the way of storing information on a single carrier spin on a long time scale in the absence of external magnetic field. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Interrelation between electronic structure and interatomic distances for [formula omitted] compounds

The heat capacity was studied for LaMn 2 Si 2 , La 0.75 Y 0.25 Mn 2 Si 2 , La 0.7 Y 0.3 Mn 2 Si 2 , YMn 2 Si 2 and LaFe 2 Si 2 isostructural intermetallic compounds in the temperature range 1.8–360 K. The electronic, magnetic and lattice contributions to the heat capacity of the compounds were determined and analyzed. The interrelation was found between values of the electronic contribution to the heat capacity (density of states at the Fermi level) and crystal lattice parameters of R ( Mn , Fe , Ni ) 2 Si 2 compounds. The electronic contribution and the density of states at Fermi level increase with increasing lattice parameters of the compounds. The change of interlayer Mn–Mn exchange interactions with change of Y concentration in La 1 - x Y x Mn 2 Si 2 compounds is not accompanied by considerable changes in the electronic contribution to the heat capacity and density of states at the Fermi level. The performed analysis of the magnetic contribution shows that no essential differences exist between the behavior of the heat capacity of the compounds with d Mn – Mn ⩾ d c and with d Mn – Mn < d c upon various types of the magnetic phase transitions.

Shape, size, spatial distribution and composition of garnet crystals in highly deformed gneiss of the Otter Lake area, Québec, and a model for garnet crystallization

AbstractGarnet–biotite–(sillimanite) gneiss (∼700 °C, 7 kbar) of the Otter Lake area in the Western Grenville Province (Canadian Shield) occurs as granitic gneiss (group 4) that forms a large part of the Otter Complex, and as widely distributed, more heterogenous metasedimentary gneiss (group 2). In one sample of group 4 gneiss (Qtz25 Pl34 Kfs28 Bt10 Grt2.5 Sil1) the true diameter (determined by serial grinding) of subhedral garnet crystals ranges from 0.2 to 3.0 mm, with a mode at 1.0 mm. Nearest‐neighbour measurements in this sample, and in surfaces of nine additional samples (all &lt;5% garnet) confirm that garnet crystals are distributed mainly at random; slight clustering was detected in two samples. In one sample of group 4 gneiss, microprobe analyses on sections through crystal centres (obtained by serial slicing), reveal that small crystals and margins to large crystals contain more Fe and Mn and less Mg than the broad central regions of large crystals. Based on these and previous results, together with theoretical considerations, a crystallization model is proposed, in which, (i) garnet was produced by the continuous reaction, Ms + Bt + Qtz → Grt + Kfs + H2O, (ii) nucleation occurred by the random selection of randomly distributed Ms–Bt–Qtz triple junctions, (iii) the rate of linear growth remained constant, and (iv) as temperature increased, the rate of nucleation first increased slowly, then remained nearly constant, and finally declined. Within‐population compositional homogenization was followed, on cooling, by local Fe–Mg–Mn exchange with biotite.

Study of the Mn—Mn Exchange Interactions in Single Crystals of LnMn6Sn6 Compounds with Ln: Sc, Y and Lu.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Secondary bonding in a six-coordinate Mn(II) complex as a model of associative substitution

The new hexadentate, bis-pincer ligand, (dipyCH 2)MeNCH 2CH 2NMe(CH 2dipy) (dipy = 2,2′-dipyridyl-6-yl) forms a crystallographically characterized Mn(II) complex in which each half of the ligand binds a separate Mn(OAc) 2 unit. The structure consists of a distorted N 3Mn(η 2-OAc)(η 1-OAc) core with six normal coordinate bonds and a long (2.85 Å) secondary bond to a seventh ligand atom, an oxygen of the η 1-acetate. In addition to demonstrating an interesting coordination mode, the structure also mimics a predicted transition state in the associative ligand exchange of octahedral Mn(II) complexes.

Noncollinear Korringa-Kohn-Rostoker Green function method: Application to3dnanostructures onNi(001)

Magnetic nanostructures on nonmagnetic or magnetic substrates have attracted strong attention due to the development of interesting experimental methods with atomic resolution. Motivated by this progress we have extended the full-potential Korringa-Kohn-Rostoker Green-function method to treat noncollinear magnetic nanostructures on surfaces. We focus on magnetic $3d$ impurity nanoclusters, sitting as adatoms on or in the first surface layer on $\mathrm{Ni}(001)$, and investigate the size and orientation of the local moments and, moreover, the stabilization of noncollinear magnetic solutions. While clusters of Fe, Co, Ni atoms are magnetically collinear, noncollinear magnetic coupling is expected for Cr and Mn clusters on surfaces of elemental ferromagnets. The origin of frustration is the competition of the antiferromagnetic exchange coupling among the Cr or Mn atoms with the antiferromagnetic (for Cr) or ferromagnetic (for Mn) exchange coupling between the impurities and the substrate. We find that Cr and Mn first-neighboring dimers and a Mn trimer on $\mathrm{Ni}(001)$ show noncollinear behavior nearly degenerate with the most stable collinear configuration. Increasing the distance between the dimer atoms leads to a collinear behavior, similar to the one of the single impurities. Finally, we compare some of the noncollinear ab initio results to those obtained within a classical Heisenberg model, where the exchange constants are fitted to total energies of the collinear states; the agreement is surprisingly good.

Study of the Mn–Mn exchange interactions in single crystals of RMn 6Sn 6 compounds with R = Sc, Y and Lu

In order to investigate the behaviour of the magnetic anisotropy and the Mn–Mn exchange interaction in RMn 6Sn 6 (R = rare earth) compounds, magnetic studies have been carried out on single crystals of RMn 6Sn 6 compounds in which R is one of the non-magnetic elements Sc, Y and Lu. The temperature dependence of the magnetization of these compounds has been measured with the field applied parallel and perpendicular to the crystallographic c-direction. Magnetic isotherms of the three compounds were measured at 4.2 K in magnetic fields up to 50 T, applied parallel and perpendicular to the c-direction, sufficiently high to reach the forced ferromagnetic state and to detect multiple field-induced transitions. For LuMn 6Sn 6, magnetic isotherms were measured also at a higher temperature of 150 K. From our results we may conclude that the magnetic anisotropy as well as the antiferromagnetic coupling strength increases in the sequence of ScMn 6Sn 6, YMn 6Sn 6 and LuMn 6Sn 6.

On the strength of the double exchange and superexchange interactions in La0.67Ca0.33Mn1–yFeyO3 – an NMR and Mössbauer study

AbstractA combined study of La0.67Ca0.33Mn0.9757Fe0.03O3 compound by means of zero field 55Mn and 57Fe NMR as well as 57Fe Mössbauer spectroscopy (MS) is reported. The 55Mn NMR spectra exhibit a single double exchange (DE) line up to the magnetic ordering temperature (T C), 200 K, determined from magnetization measurements. The hyperfine field (HFF) remains finite at the T C, which reveals discontinuous character of the transition and the occurrence of a ferromagnetic‐paramagnetic phase segregation. The 57Fe MS HFF decreases much faster with increasing temperature than the 55Mn NMR HFF. Application of a molecular field model to the temperature dependence of the 55Mn and 57Fe HFF allows to estimate values of the Mn–Mn and the Fe–Mn exchange integrals, which amount to 1.24 meV and –0.6 meV, respectively. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Optical Properties of Manganese-Doped Individual CdTe Quantum Dots

The magnetic state of a single magnetic ion (Mn) embedded in an individual quantum dot is optically probed using microspectroscopy. The fine structure of a confined exciton in the exchange field of a single Mn ion (S = 5/2) is analyzed in detail. The exciton–Mn exchange interaction shifts the energy of the exciton depending on the Mn spin component and six emission lines are observed at zero magnetic field. The emission spectra of individual quantum dots containing a single magnetic Mn atom differ strongly from dot to dot. The differences are explained by the influence of the system geometry, specifically the in-plane asymmetry of the quantum dot and the position of the Mn atom. Depending on both these parameters, one has different characteristic emission features which either reveal or hide the spin state of the magnetic atom. The observed behavior in both zero field and under magnetic field can be explained quantitatively by the interplay between the exciton–manganese exchange interaction (dependent on the Mn position) and the anisotropic part of the electron–hole exchange interaction (related to the asymmetry of the quantum dot).

Specific heat of single-crystal PrMnO3

The specific heat of single-crystalPrMnO3 was investigated from 2 to 200 K under different magnetic fields up to 8 T. ASchottky-like anomaly observed at low temperature was gradually shiftedto higher temperatures by magnetic fields. The first four singlets of thePr3+ 3H4 groundmultiplet in PrMnO3 are given for the first time by fitting the specific heat ofPr3+ ions below 40 K under zero field. By analysing the field dependence of the first singlet ofPr3+ ions,the Pr–Mn exchange field is found to be negligible, which is consistent with the magnetic anisotropyof Pr3+ ions revealed in the magnetic measurement. AtTN, the cooperative antiferromagnetic ordering ofMn3+ spinsshows up as λ-shaped anomaly, which is lowered and broadened in magnetic fields. The magnetic entropy nearTN is estimated by subtracting the contributions to specific heat fromPr3+ ions and lattice vibrations. It was found that the fraction of entropy aboveTN in the total entropy increases with the fields due to the enhancement of spin fluctuations bymagnetic field.

Change of easy magnetization direction in TmMn 6Sn 6− xGa x (0.00 < x < 1.22) studied in high magnetic fields

Single crystals of TmMn 6Sn 6− x Ga x compounds (0 ≤ x ≤ 1.22) obtained in a tin flux have been studied by thermomagnetic and high-field magnetization measurements. A collinear-antiferro to heli-magnetic transition at 324 K has been observed in TmMn 6Sn 6. Spin-reorientation transitions at low temperature are found in the compounds with x = 0.66 and 1.22. The magnetization curves in high fields at 4.2 K are interpreted to result from the competition between the Tm–Mn exchange interaction and the magnetocrystalline anisotropy of the Tm and Mn sublattices. A strong easy-plane anisotropy is favored for the Ga-poor compounds and a strong easy-axis anisotropy for the Ga-rich compounds while the compounds of intermediate Ga content (0.51 ≤ x ≤ 0.66) display rather weak magnetocrystalline anisotropy.

Optical probing of the spin state of a single magnetic ion in an individual quantum dot

AbstractThe magnetic state of a single magnetic ion (Mn2+) embedded in an individual quantum dot is optically probed using micro‐spectroscopy. The fine structure of a confined exciton in the exchange field of the single Mn2+ ion is analyzed in detail. At zero magnetic field, the exciton–Mn exchange coupling lifts the degeneracy of the six Mn spin projections. Under magnetic field, the electron–Mn interaction induces a mixing of the bright and dark exciton states. Magneto‐optic measurements reveals that the polarisation of the Mn2+ spin distribution is controlled by the magnetic field and an effective manganese temperature depending on both the lattice temperature and the density of photo‐created carriers. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

First-principles study of exchange interactions and Curie temperatures of half-metallic ferrimagnetic fullHeusler alloys Mn2V Z (Z = Al,Ge)

We report the parameter-free, density functional theory calculations of interatomic exchangeinteractions and Curie temperatures of half-metallic ferrimagnetic full Heusler alloysMn2V Z (Z = Al,Ge). To calculate the interatomic exchange interactions we employ the frozen-magnonapproach. The Curie temperatures are calculated within the mean-fieldapproximation to the classical Heisenberg Hamiltonian by solving a matrixequation for a multi-sublattice system. Our calculations show that, although alarge magnetic moment is carried by Mn atoms, competing ferromagnetic(inter-sublattice) and antiferromagnetic (intra-sublattice) Mn–Mn interactions inMn2V Al almost cancel each other in the mean-field experienced by the Mn atoms. InMn2V Ge the leading Mn–Mn exchange interaction is antiferromagnetic. In bothcompounds the ferromagnetism of the Mn subsystem is favoured by strongantiferromagnetic Mn–V interactions. The obtained value of the Curie temperature ofMn2V Al is in good agreementwith experiment. For Mn2V Ge there is no experimental information available and our calculation is a prediction.