Effects Of Mn Concentration Research Articles

Effects of Mn Concentration on Grain Boundary Pinning of 5083 Aluminum Alloy

Effects of Mn Concentration on Grain Boundary Pinning of 5083 Aluminum Alloy

Investigation on vibrational, electronic excitation entropy and magnetic moment contributions to phase stability of off-stoichiometric Ni50MnxIn50-x alloys at finite temperatures by first-principle calculations

The effects of Mn concentration and thermally excited contributions (including the vibrational, electronic excitation and magnetic contributions) on phase stability of austenite and martensite from 0 K to finite temperatures in Heusler typed Ni50MnxIn50-x shape memory alloys were studied by the first-principle calculations using exact muffin-tin orbitals with coherent potential approximation. Based on this, the martensitic transformation tendency was explored. Results show that at 0 K, the energy differences between the non-modulated martensite and the austenite become negative when extra Mn is added, indicating that the added Mn stabilizes the martensite and promotes martensitic transformation. The promoting effect increases with the increase of Mn content. At finite temperatures, the three thermal contributions (the vibrational, electronic excitation and magnetic contributions) were further calculated based on the equilibrium structure at 0 K. It was revealed that the vibrational entropies of the two phases increase with the increase of the temperature for all Mn contents. Under the two effects (temperature and Mn-content), the austenite has a larger vibrational entropy than the martensite, which indicates that the vibrational entropy contributes to promoting the martensitic transition. The Mn content and the temperature show a similar influence on the electronic entropies of the two phases. However, compared with the vibrational entropy, the contribution of the electronic entropy is much smaller. Furthermore, the influences of Mn content and temperature on the magnetic moment of both phases were simulated in their ferromagnetic state. The results show that the magnetic moments increase linearly with the Mn content, however, the influence of temperature is relatively small. Above 100 K, the magnetic moment of the austenite is higher than that of the martensite in ferromagnetic Ni50Mn29.25In20.75 alloy, suggesting that the magnetic entropy makes a similar contribution to promote the martensitic transformation, like the vibrational and electronic excitation entropies.

Effect of Mn addition on the structural and magnetic properties of Zn-ferrite nanoparticles

Abstract Super-paramagnetic, mono-dispersed and single-phased Mn-substituted Zn-ferrite nanoparticles (NPs) with a narrow size distribution were synthesized by a one-step citric acid-assisted hydrothermal method. X-ray diffraction (XRD), Scanning electron microscopy (SEM), vibrating sample magnetometry (VSM) and Fourier-transform infrared spectroscopy (FTIR) techniques were utilized to determine characteristics of the NPs. The as-prepared Zn0.3Fe2.7O4 NPs were highly crystalline with uniform size (14.5 ± 2.65) and good stability in an aqueous medium. The effects of Mn concentration (x = 0.25, 0.5, 0.75 and 1) and pH on the formation of Zn0.3MnxFe2.7−xO4 NPs were thoroughly studied. The maximum saturation magnetization of 55 emu/g was obtained for the Zn-ferrite sample substituted with x = 0.5 of Mn. Increasing x firstly resulted in an increased saturation magnetization from 47.1 emu/g (x = 0.25) to 55 emu/g (x = 0.5), followed by a decrease to 37 emu/g (x = 1). The variation of saturation magnetization was correlated with the distribution of Mn2+ ions in tetrahedral and octahedral sites.

Density functional theory study of the magnetic moment of solute Mn in bcc Fe

An unexplained discrepancy exists between the experimentally measured and theoretically calculated magnetic moments of Mn in \ensuremath{\alpha}-Fe. In this study, we use density functional theory to suggest that this discrepancy is likely due to the local strain environment of a Mn atom in the Fe structure. The ferromagnetic coupling, found by experiment, was shown to be metastable and could be stabilized by a 2% hydrostatic compressive strain. The effects of Mn concentration, vacancies, and interstitial defects on the magnetic moment of Mn are also discussed. It was found that the ground-state, antiferromagnetic (AFM) coupling of Mn to Fe requires long-range tensile relaxations of the neighboring atoms along $\ensuremath{\langle}111\ensuremath{\rangle}$ which is hindered in the presence of other Mn atoms. Vacancies and Fe interstitial defects stabilize the AFM coupling but are not expected to have a large effect on the average measured magnetic moment.

The effects of Mn concentration on the tribocorrosion resistance of Al–Mn alloys

An increase in the complexity and severity of service conditions demands improvements in the design of new engineering materials that are resistant to the effects of tribocorrosion. Unfortunately, there is typically a tradeoff between wear and corrosion resistance, even for important passive metals such as Al alloys. In this work, it was shown that alloying Al with Mn in supersaturated solid solution simultaneously increased the wear resistance of the Al as well as the protectiveness of the passive layer, thus improving the overall tribocorrosion resistance. Specifically, the effects of Mn alloying on the tribocorrosion behavior of magnetron-sputtered Al- Mn thin films with 5.2at% and 20.5at% Mn were investigated in a 0.6M NaCl aqueous solution. Tribocorrosion resistance was found to be strongly affected by the alloying concentration and applied potential. Higher Mn content increased the ratio of hardness to elastic modulus (H/E) and promoted the formation of denser and more compact passive film, hence improving tribocorrosion resistance of Al. In particular, alloying with 20.5at% Mn led to an increase of the corrosion resistance by ~10 times and the hardness by ~8 times compared to pure Al. The total material loss during tribocorrosion was found to increase with the anodic shift of the applied potential. A galvanic cell model was used to investigate the depassivation-repassivation kinetics during tribocorrosion. It was found that alloying with 5.2at% Mn led to more than 10-fold reduction in the current density required to re-passivate similar worn areas of pure Al. Finally, the origin of wear-corrosion synergy was discussed based on these observations.

Mn-doping effects on structural, optical and magnetic properties of BaSn1-xMnxO3

Polycrystalline bulk samples of BaSn1-xMnxO3 with x=0, 0.05, 0.10 and 0.13 are prepared by the conventional solid state reaction method. The effects of Mn concentration on crystal structural, optical and magnetic properties of BaSn1-xMnxO3 are investigated systematically. Powder X-ray diffraction (XRD) shows that each of these compounds presens a perovskite structure (with the space group Pm3m) without the secondary crystalline phase. The Mn ions take the Sn sites which is revealed by the XRD, diffusion reflectance spectrum (DRS) and Raman scattering. With the increase of doping level x, the optical absorption edge shifts towards higher wavelength and is smoothened gradually, meanwhile the Raman spectrum shows that Raman mode is also changed. The photoluminescence spectrum under magnetic field shows that near-infrared luminescence is probably related to Sn ions. The magnetization measurement demonstrates that Mn-doped BaSnO3 system exhibits ferromagnetism at low temperature, which can be explained by the F-center exchange (FCE) mechanism.

The effects of Mn concentration on structural and magnetic properties of Ge1−xMnx diluted magnetic semiconductors

Reflexion high-energy electron diffraction (RHEED), transmission electron microscopy (TEM) along with physical property measurement system (PPMS) were used to investigate the growth kinetics of Ge1−xMnx diluted magnetic semiconductors (DMS) grown on Ge(001) by means of molecular beam epitaxy (MBE). At a given intermediate growth temperature of 130 °C, we have identified the formation of successive heterogeneous phases when increasing the Mn concentration from 1 to 14 %: DMS phase containing nanosized Mn-rich clusters for x below 2%, DMS phase containing high Curie temperature (TC) nanocolumns for x ranging from 5 to 6 %, DMS phase in which GeMn nanocolumns and Mn5Ge3 clusters coexist and then finally DMS containing mainly Mn5Ge3 clusters at Mn concentration higher than 12%. Our results confirm that the low solubility of Mn in Ge is the main origin of the formation of heterogeneous phases and provide evidence that it is extremely difficult to form a homogenous GeMn DMS even for Mn concentrations being below 2%. We also demonstrate that high-TC nanocolumns and Mn5Ge3 clusters are competing processes and the process window corresponding to the stabilisation of high-TC nanocolumns remains extremely tight.

Effects of Mn concentration on the ac magnetically induced heating characteristics of superparamagnetic MnxZn1−xFe2O4 nanoparticles for hyperthermia

The effects of Mn2+ cation concentration on the ac magnetically induced heating characteristics and the magnetic properties of superparamagnetic MnxZn1−xFe2O4 nanoparticles (SPNPs) were investigated to explore the biotechnical feasibility as a hyperthermia agent. Among the MnxZn1−xFe2O4 SPNPs, the Mn0.5Zn0.5Fe2O4 SPNP showed the highest ac magnetically induced heating temperature (ΔTac,mag), the highest specific absorption rate (SAR), and the highest biocompatibility. The higher out of phase susceptibility (χm″) value and the higher chemical stability systematically controlled by the replacement of Zn2+ cations by the Mn2+ cations on the A-site (tetrahedral site) are the primary physical reason for the promising biotechnical properties of Mn0.5Zn0.5Fe2O4 SPNP.

The effects of Mn concentration on spin-polarized transport through ZnSe/ZnMnSe/ZnSe heterostructures

We have studied the effects of Mn concentration on the ballistic spin-polarized transport through diluted magnetic semiconductor heterostructures with a single paramagnetic layer. Using a fitted function for zero-field conduction band offset based on the experimental data, we found that the spin current densities strongly depend on the Mn concentration. The magnitude as well as the sign of the electron-spin polarization and the tunnel magnetoresistance can be tuned by varying the Mn concentration, the width of the paramagnetic layer, and the external magnetic field. By an appropriate choice of the Mn concentration and the width of the paramagnetic layer, the degree of spin polarization for the output current can reach 100% and the device can be used as a spin filter.

Effects of Mn concentration and deposition temperature on the giant magnetoresistive properties of ion-beam-deposited PtMn spin valves

We studied the effects of Mn concentration (C/sub Mn/) in PtMn antiferromagnets (AFs) and the deposition temperature (T/sub s/) of PtMn in bottom PtMn spin valves. The exchange coupling field (H/sub ua/) and the critical thickness of PtMn were found to depend strongly on C/sub Mn/. Spin valves made with the optimum C/sub Mn/ (51%) show an H/sub ua/ value of around 410 Oe even with 125-/spl Aring/-thick PtMn, compared to the saturation value of about 500 Oe for the spin valves with much thicker PtMn. For the T/sub s/ dependence study, the NiFeCr-NiFe underlayer, PtMn AF layer, and part of the CoFe pinned layer were deposited at T/sub s/ up to 300/spl deg/C, and the rest of the layers were deposited after cooling the spin valve down to ambient temperature. The spin valves deposited at T/sub s/>250/spl deg/C and with >150-/spl Aring/-thick PtMn show H/sub ua/ of around 250 Oe, as deposited (without postannealing). The H/sub ua/ values increase upon postannealing for the spin valves deposited at all the T/sub s/ studied (25/spl deg/C-300/spl deg/C). However, the ferromagnetic coupling field (H/sub f/) also increases with repetitive postannealing, the rate of H/sub f/ increase being lower for the spin valves deposited at higher T/sub s/. The sheet resistance of PtMn spin valves was found to increase both after postannealing and with increasing T/sub s/, consistent with the higher resistivity observed for thin PtMn films deposited at higher T/sub s/. These results are attributed to the smaller grain size and the higher degree of chemical ordering for PtMn in the postannealed spin valves deposited initially at higher T/sub s/, as deduced from X-ray diffraction.