Existence Of Spin-glass Behaviour Research Articles

Studies on nanoconfinement effect of NiO-SiO2 spin glass within mesoporous Al2O3 template

Nanoconfinement studies in the glass system xNiO-(1-x)SiO2 having x values as 0.2 and 0.4 were carried out by preparing nanocomposites using mesoporous alumina template. These samples were studied using wide and small angle xrd data. BET analysis was conducted to find the surface area and pore size distribution of the virgin and nanocomposite samples. The microstructure and distribution of transition metal ions in the system were delineated using STEM-EDAX mapping. XPS data provide the quantitative analysis of Ni2+/Ni3+ species present in the system. Theoretical modeling using DFT simulations were implemented to understand the nanoconfinement effect which was in corroboration with the experimental findings. The theoretical model was validated using UV-Vis absorption spectrum. The magnetodielectric results were explained considering Catalan’s model having positive magnetoresistance. Nyquist plot studies were employed to visualize the realistic circuit model with contributions from different layers present in the nanocomposites. The temperature dependent resistivity data were explained using small polaron hopping model and the inter-site separation between Ni2+/Ni3+ ions was found to be larger in nano confined system than the corresponding bulk glass. Existence of more conducting species manifest a significant enhancement in percentile change of MD, MR & conductivity values for NC-2 compared to NC-1. Study of ZFC-FC magnetization curves effectively substantiate spin glass characteristics which exhibit freezing temperature at 4.1 K. The existence of spin glass behavior are well interpreted in terms of memory effect and relaxation dynamics study.

Competing magnetic interactions, low and high temperature magnetic properties of 0.3NiFe2O4–0.7Na0.5Bi0.5TiO3 nanocomposites

Abstract We report on temperature dependent magnetization and anisotropy properties, magnetic interactions at low temperatures, high temperature magnetic properties and frequency dependent dielectric properties of 0.3NiFe2O4–0.7Na0.5Bi0.5TiO3 nanocomposites. X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) techniques are employed to study the crystal structure, morphology and the chemical state of the NiFe2O4 (NFO) nanoparticles, Na0.5Bi0.5TiO3 (NBTO) nanorods and nanocomposites. XRD and Raman spectroscopy studies indicate the formation of NFO, NBTO and the nanocomposites in pure phase. SEM and TEM images indicates the presence of both nanoparticles (from NFO) and nanorods (from NBTO) in the 0.3NiFe2O4–0.7Na0.5Bi0.5TiO3 nanocomposites and the lattice planes with respect to both the phases are confirmed from the selected area diffraction pattern. Magnetization measurements at various temperatures (300 K, 40 K, 10 K and 2 K), field cooled (FC) and zero field cooled (ZFC) magnetization from 300 K to 2 K are measured for the nanocomposites. Saturation magnetization value at 300 K and 2 K for the nanocomposites is seen to be 14.62 emu/g and 16.80 emu/g respectively. Existence of spin glass behavior and competing magnetic interactions in the 0.3NiFe2O4–0.7Na0.5Bi0.5TiO3 nanocomposites is confirmed from the ZFC and FC magnetization studies. Curie temperature value for 0.3NiFe2O4–0.7Na0.5Bi0.5TiO3 nanocomposites is observed to be 900 K. Frequency dependent dielectric studies shows the relaxation behavior of the nanocomposites with two relaxation times of 5.803 × 10−2 s and 2.770 × 10−4 s arising from NFO and NBTO phases.

Effect of Ni2+(S = 1) and Cu2+(S = ½) substitution on the antiferromagnetic ordered phase Co2(OH)PO4with spin glass behaviour

The hydroxyphosphates with formula Co1.7M0.3(OH)PO4 (M = Ni, Cu) have been prepared from hydrothermal synthesis. The compounds have been characterized by X-ray powder diffraction and spectroscopic measurements. Diffuse reflectance data of both phases show bands belonging to the two chromophores, octahedral and trigonal bipyramidal, of the Co(II) ions together with others associated to the chromophores of nickel(II) and copper(II) ions. Magnetization measurements of Co1.7Ni0.3(OH)PO4 show the presence of two maxima at ca. 62 and 5 K, respectively. The first peak was attributed to a three-dimensional antiferromagnetic ordering and the second one reveals the existence of a spin glass-like state. This behaviour was confirmed from the ac measurements obtained at different frequencies and applied fields. The Co1.7Cu0.3(OH)PO4 phase exhibits only one maximum at 65 K in both χm and ac measurements associated to the three-dimensional antiferromagnetic interactions; however, the existence of spin glass behaviour is not observed. ZFC-FC curves for the cobalt–nickel and cobalt–copper compounds show irreversibility just below TN indicating the existence of higher spin decompensations than in the Co2(OH)PO4 phase. This difference and its influence in the magnetic anomalies observed at low temperatures is the more important effect in the magnetic measurements of the ordered Co2(OH)PO4 phase substituted at about 15% of the Co2+ (S = ) by Ni2+ (S = 1) or Cu2+ (S = ½) ions. The origin of the frustration, which is necessary to achieve a disordered ground state, is investigated in these kinds of spin glass compounds. Taking into account the possible magnetic exchange pathways, which are essential to install competition and ensure cooperativeness of the freezing process, correlations between structural and magnetic properties have been performed.

Magnetic properties of glassy Fe/sub 91-x/Zr/sub 7/B/sub 2/Ni/sub x/ (x=0, 5, 10, 15) alloys

We have studied the magnetization behaviour and the temperature dependence of AC-susceptibility at very low fields (5 mOe to 50 mOe) of glassy Fe/sub 91-x/Nr/sub 7/B/sub 2/Ni/sub x/ (x=0, 5, 10, 15) alloys. At zero Ni concentration our data suggests the existence of spin-glass behaviour at temperatures below 30 K. The addition of Ni drastically modifies the magnetic properties: the antiferromagnetic exchange coupling is reduced, the magnetic moment of Fe increases from 1.58 to 2.29 /spl mu//sub s/ and T/sub c/ increases from 230 to 478 K. Thus, substitution of Fe by Ni favours the increase of magnetic order in this system.