P. K. Mukhopadhyay

Magnetic and hyperfine properties of nanocrystalline Ni0.2Zn0.6Cu0.2Fe2O4 prepared by a chemical route

Nanoparticles of Ni0.2Zn0.6Cu0.2Fe2O4 were prepared by the standard co- precipitation method. The formation of nanocrystalline mixed spinel phase has been confirmed by x-ray diffractograms. The sizes of the nanoparticles were estimated in the range 7-30 nm, which was confirmed by transmission electron microscopy. Thermal variations of the real part of AC magnetic susceptibilities measured from 450 K down to 80 K and Mossbauer effect measurements at room temperature and down to 20 K clearly indicate the presence of superparamagnetic particle si n allthe samples. Specific saturation magnetizations measured by VSM are found to increase steadily with the increase of average particle size. The coercive field obtained from low frequency measurements shows that in all the samples a small fraction of particles is not relaxed within the measuring time. For samples showing a less dominating superparamagnetic behaviour, AC magnetic susceptibility data showed the expected increase of blocking temperature with increase in particle size. Magnetic anisotropy energy constants of the nanoparticles were estimated from the blocking temperature and the values cannot be directly correlated with their particle sizes.

Structural, magnetic, and transport properties of nanoparticles of the manganite Pr0.5Ca0.5MnO3

In this paper we report the structural, magnetic, and transport properties of nanoparticles of Pr0.5Ca0.5MnO3(PCMO). On comparing our results with that of bulk PCMO, we find that there is a likely destabilization of charge ordering in nanoparticles of PCMO. The investigation has been done with particle sizes as small as 15nm synthesized by polyol route. The size reduction (by keeping the chemical composition unchanged) reduces the orthorhombic c axis preferentially and thus reduces the orthorhombic distortion. The size reduction to 15nm enhances the ferromagnetic moment at low temperatures and strongly suppresses the activated charge transport which is seen in the bulk samples of charge ordered PCMO.

Magnetoresistance behavior of ferromagnetic shape memory alloy Ni 1.75 Mn 1.25 Ga

A negative-positive-negative switching behavior of magnetoresistance (MR) with temperature is observed in a ferromagnetic shape memory alloy

Variation of magnetoresistance in Ni2+xMn1−xGa with composition

{\text{Ni}}_{1.75}{\text{Mn}}_{1.25}\text{Ga}

Magnetic transition in NiPt alloy systems: experiment and theory

. In the austenitic phase between 300 and 120 K, MR is negative due to

Effect of nanosize modulation of granular La0.67Sr0.33MnO3 manganites on temperature-dependent low-field spin-polarized tunneling magnetoresistance

s\text{\ensuremath{-}}d

The elastic manifestation of a spin-glass transition: a low-frequency study

scattering. Curiously, below 120 K MR is positive, while at still lower temperatures in the martensitic phase, MR is negative again. The positive MR cannot be explained by Lorentz contribution and is related to a magnetic transition. Evidence for this is obtained from ab initio density-functional theory, a decrease in magnetization and resistivity upturn at 120 K. Theory shows that a ferrimagnetic state with antiferromagnetic alignment between the local magnetic moments of the Mn atoms is the energetically favored ground state. In the martensitic phase, there are two competing factors that govern the MR behavior: a dominant negative trend up to the saturation field due to the decrease in electron scattering at twin and domain boundaries and a weaker positive trend due to the ferrimagnetic nature of the magnetic state. MR exhibits a hysteresis between heating and cooling that is related to the first-order nature of the martensitic phase transition.

Crossover of spin glass characteristics as a function of field in an NiMnSnAl alloy

The magnetoresistance (MR) of Ni2+xMn1−xGa (−1≤x≤0.35) ferromagnetic shape memory alloy shows a large increase in magnitude at room temperature (RT) with increasing x. For Mn2NiGa (x=−1), MR at 8 T is −0.2%, while for Ni2.35Mn0.65Ga (x=0.35), it is −7.3%. Thus, MR of Ni2+xMn1−xGa can be varied over one order of magnitude by changing composition (x). Considering that the Curie temperature (TC) varies with x, the MR behavior in the austenitic phase is explained on the basis of the s−d scattering model. By fitting the MR at 8 T in the austenitic phase for different x and T, a (T/TC)6 power law dependence is obtained. In contrast to the monotonic MR variation with x, the magnetization at RT is highest for Ni2MnGa (x=0) and decreases for both Ni and Mn excess compositions.

Magnetic properties and magnetocaloric effect in Pt doped Ni-Mn-Ga

We report here the preparation and measurements on the susceptibility, sound velocity and internal friction for NiPt systems. We then compare these experimental results with the first principle theoretical predictions and show that there is reasonable agreement with experiment and theory.

A simple vibrating reed apparatus for use at low temperatures

We have investigated magnetotransport behaviors of a series of single-phase, nanocrystalline La0.67Sr0.33MnO3 (LSMO) samples having grain sizes in the nanometric regime (14, 22, and 26 nm), all synthesized through chemical route “pyrophoric reaction process.” The motivation behind the present investigation is to study the effects of nanometric grain size on magnetoresistance (MR), specially its temperature and magnetic-field dependences. Magnetoresistance measurements show that in all samples there is a large negative MR at very low fields (LFMR), followed by a slower varying negative MR at comparatively high fields (HFMR), in the ferromagnetic regime. Surprisingly, we observed that at both low- and high-field regimes, the magnitude of MR remains constant up to sufficiently high temperature and then drops sharply with temperature. This temperature-dependent MR behavior gets enhanced with the decrease in particle size. Most interestingly, we found a considerable low-field MR (14%) persisting even at 200 K,...