Signatures of nearly compensated magnetism and spin glass behavior in highly frustrated ß-Mn-type Mn50Fe25+xAl25-x Heusler alloys.

The present study examines the effect of Fe/Al concentration on the structural and magnetic properties of Mn-rich Mn50Fe25+xAl25-x (x = 5, 10, 15) Heusler alloys through x-ray diffraction, temperature- and field-dependent DC magnetization, thermoremanent magnetization, magnetic memory effect, AC susceptibility measurements, and DFT calculations. The samples crystallize in a cubic ß-Mn structure. The trend shows a reduction in lattice parameters (unit cell volume) with the increasing Fe proportion. These alloys exhibit strong antiferromagnetic interactions with large frustration parameters, indicating the presence of competing magnetic interactions. The DC magnetization data reveal spin glass-like features with a peak at spin glass freezing temperature (Tf). The observation of bifurcation in temperature-dependent zero-field-cooled and field-cooled magnetization curves, exponential dependence of the temperature variation of remanence and coercivity, magnetic relaxation, and magnetic memory effect below Tf support the spin-glass character of these alloys. The frequency dependence of Tf is also examined in the context of dynamic scaling laws, such as the Vogel-Fulcher law and critical slowing down model, which further supports the presence of spin glass behavior. In the theoretical DFT calculations, the electronic structure is found to be metallic and similar for both spin projections. Moreover, the antiferromagnetic arrangement of the magnetic moments, in line with the experimental observations, is stabilized by exchange interactions, resulting in an almost compensated total magnetic moment of 0.02-0.38 µB/f.u. This is probably caused by the frustrated structure and non-stoichiometric compositions of Mn50Fe25+xAl25-x.

Impression of magnetic clusters, critical behavior and magnetocaloric effect in Fe3Al alloys.

Herein, we report unusual magnetic behavior in arc melted bulk stoichiometric Fe3Al alloy with a D03 structure. The temperature variation in the magnetization measurements revealed two transitions, i.e. one at ∼763 K and another at ∼830 K. Below 763 K, it exhibits ferromagnetic ordering and the nature of the transition is second order. However, the second transition is more complex and detailed analysis of the magnetic data suggested the coexistence of ferromagnetic and paramagnetic phases (two-phase: α + D03/α + B2) and structural transitions triggered by temperature. We observed dual peaks in the magnetic entropy change curve, in accordance with the magnetization results, which corroborate the occurrence of a two-phase system. We believe that the concurrent magnetic ordering and the complex two-phase are associated with the evolution of short-range ordered magnetic clusters having a magnetic moment of ∼103µB in the host matrix. A cluster hypothesis is proposed to explain the observed intricate magnetic behavior of this alloy at high temperature. The estimated critical exponents using a modified Arrott plot, Kouvel-Fisher plot and critical isotherm analysis lie in between the 3D-Heisenberg and 3D-Ising model, indicating a short-range interaction and magnetic inhomogeneity, which again are consistent with the magnetization results. The obtained critical exponents follow the universal scaling behavior, which indicates the renormalization of interactions around the magnetic ordering transition (TC). Despite the obvious larger thermal entropy at very high temperature, our synthesized Fe3Al alloy showed enhanced magnetic entropy changes. The obtained magnetic entropy change for binary Fe3Al alloy shows twice the value of that of other binary/ternary Fe-based alloys.

Domain-wall induced large magnetoresistance effects at zero applied field in ballistic nanocontacts.

We determine magnetoresistance effects in stable and clean Permalloy nanocontacts of variable cross section, fabricated by UHV deposition and in situ electromigration. To ascertain the magnetoresistance (MR) effects originating from a magnetic domain wall, we measure the resistance values with and without such a wall at zero applied field. In the ballistic transport regime, the MR ratio reaches up to 50% and exhibits a previously unobserved sign change. Our results can be reproduced by recent atomistic calculations for different atomic configurations of the nanocontact, highlighting the importance of the detailed atomic arrangement for the MR effect.

Defect mediated mechanism in undoped, Cu and Zn-doped TiO2 nanocrystals for tailoring the band gap and magnetic properties.

Oxide based dilute magnetic semiconductor materials have been of great interest over the years due to their potential use in spintronic devices. However, the variations in the magnetic behavior of the materials have raised concerns regarding the origin of ferromagnetic properties which still needs to be explored. Manipulation of magnetic behavior in oxide based dilute magnetic semiconductors has become a challenge due to the interplay of intrinsic defects present in the material. TiO2 nanocrystals have been studied largely due to their challenging optical and magnetic properties. The present investigation studies in detail the structural, morphological, optical and magnetic behavior of non-magnetic element (Cu and Zn) doped TiO2, synthesized via a simple sol-gel technique. X-ray diffraction patterns and Raman spectra confirm the anatase phase and high resolution transmission electron microscopic results clearly indicate the formation of highly crystalline nanocrystals in all the samples with particle size ranging from 5-15 nm. Energy dispersive X-ray fluorescence spectroscopic studies reveal the compositional homogeneity of all the investigated samples. The presence of functional groups and molecular interactions were identified by Fourier transform infrared spectroscopy. Optical properties were studied through UV-visible and photoluminescence spectroscopy from which a significant reduction in band gap in Cu-doped TiO2 nanocrystals was found. X-ray photoelectron spectra confirm the presence of Ti3+, Cu2+, Cu+ and Zn2+ in Cu and Zn-doped TiO2 samples. The concept of bound magnetic polarons associated with the vacancy defects at both Ti, Cu, Zn and oxygen sites is used to explain the induced weak ferromagnetic behavior in undoped, Cu and Zn-doped TiO2 at room temperature. The overlapping of bound magnetic polarons could be the source of ferromagnetism irrespective of the non-magnetic nature of the dopant ion. The concentration of bound magnetic polarons is estimated using a Langevin fit and a detailed understanding of the variation of defect mediated magnetic properties is established with the help of PL analysis. A significant reduction in bandgap along with enhanced magnetization observed in the Cu-doped TiO2 material makes it suitable as a potential candidate for spintronics and magneto-optics applications. Room temperature magnetic properties of the Zn doped sample show a diamagnetic tail which is explained based on the defect centers and oxidation states of dopant ions present in the sample which is further verified with the help of XPS results.

MCM-41 Nanoparticles for Brain Delivery: Better Choline-Esterase and Amyloid Formation Inhibition with Improved Kinetics.

The present study was aimed at delivering a low bioavailability drug, rivastigmine hydrogen tartrate (RTG), to the brain through its encapsulation in mesoporous silica nanoparticles (MSNs) and targeted to amyloid inhibition in the brain. MSNs were characterized for size, zeta potential, and drug entrapment using SEM, TEM, HR-TEM, FT-IR, and PXRD. Drug-loaded MSNs were assessed for in vitro release kinetics and ex vivo followed by animal studies. The average size of the prepared blank (MCM-41B) and drug-loaded MSNs (MCM-41L) was 114 ± 2.0 and 145 ± 0.4 nm with the zeta potential of approximately -43.5 ± 1.1 and -37.6 ± 1.4 mV, respectively. MCM-41L exhibited an average entrapment efficiency of 88%. In vitro release studies exhibited early surge followed by a sluggish persistent or constant release (biphasic pattern). Hemolytic studies proved that the developed MCM-41L NPs are less hemolytic compared to RTG. A reduced ThT fluorescence was observed with MCM-41L compared to MCM-41B and RTG in the amyloid inhibition studies. A significant (p < 0.05) inhibition of AChE (acetycholinesterase) was observed for MCM-41L (80 ± 4.98%), RTG (62 ± 3.25%), and MCM-41B (54 ± 4.25%). In vivo pharmacokinetics in Wistar rats revealed that the AUC and mean residence time (MRT) for MCM-41L was sustained and significantly higher (p < 0.05) (780 ± 3.30 ng/L; 5.49 ± 0.25 h) compared to RTG solution (430 ± 3.50 ng/L; 0.768 ± 0.17 h). Similarly, the half-life was found to be significantly higher in case of MCM-41L. The promising result was brain delivery of RTG in Wistar rats which was enhanced almost 127 folds in vivo, using MCM-41L nanoparticles. MCM-41L nanoparticles effectively enhanced the bioavailability of RTG. Conclusively, these can be used for the administration of RTG and other related low bioavailability drugs for improved brain delivery.

Elemental composition in mud crab Scylla serrata from Mahanadi estuary, India: in situ irradiation analysis by external PIXE.

During the present study concentration of nine elements (K, Ca, Mn, Fe, Cu, Zn, Se, Br and Pb) in different tissues of mud crab Scylla serrata from Mahanadi estuary, India were determined by the external PIXE set up at Institute of Physics, Bhubaneswar, India. The study demonstrates the effectiveness of the technique in analyzing both soft and hard tissue samples from marine organisms and opens the door for non-destructive, multi-elemental analysis of tissue samples with a very little sample preparation by direct irradiation. This technique can be well utilized for analyzing the tissue samples for environmental, toxicological and nutritional purposes. The study also demonstrates the elemental concentrations from tissue samples of any crustaceans from Mahanadi estuary for the first time. Sex based difference in the elemental concentration of the mud crabs were marked, which may be related to the growth rate and other biological activities. No significant difference in the concentration of elements (Ca, Mn, Fe, Cu and Zn) in the tissues of juveniles and adults of respective sex is observed, which indicated the active regulation of these elements by S. serrata.

Trace element-based food value evaluation in soft and hard shelled mud crabs.

Concentrations of 10 elements were studied from the pre-moult hard shelled and newly moulted (soft shelled) crabs (Scylla serrata) by the (Energy Dispersive X-ray Fluorescence) EDXRF technique. The study evaluated the composition of all 10 elements from the body tissues and the exuvium of soft shelled and the carapace of pre-moulted hard-shelled crabs in order to evaluate the food value from nutritional and safety point of view for human consumption. The essential elements like K, Ca, Mn, Cu, etc., get reabsorbed from the carapace to the body tissues in order to meet the further requirement in the soft shelled crabs and are also utilized to some extent during the formation of new carapace, toxic element like Pb gets excreted during exuviation and element like Zn gets regulated, as and when become higher in bioavailable form. This study gives evidence that, the freshly moulted soft shelled crabs are more safe and nutritious than the hard-shelled crabs.