Existence Of Spin-glass State Research Articles

Effect of rare earth doping on magnetic and dielectric properties of NiZnMn ferrites

In present work, RE0.01Ni0.3Zn0.4Mn0.3Fe2O4 (RE=Fe, La, Nd, Sm, Gd, Dy, Yb) ferrites with strictly controlled main composition were prepared. X-ray diffraction analysis shows that the lattice constant decreases with the increase of atomic number of rare earth. The infrared spectra demonstrate the changes of tetrahedral and octahedral bonds. The saturation magnetization is about 74 emu/g and initial permeability is about 120 for undoped ferrite. They decrease slightly after rare earth doping, but the impact of different rare earth on Ms is same. The Curie temperature of almost all samples is 262 ℃. Zero field cooling-field cooling curves demonstrate the existence of spin glass state or superparamagnetism at high temperature. Sm, Gd and Dy doped ferrites have special dielectric properties with more relaxation processes. Appropriate rare earth doping greatly improve the cut-off frequency, dielectric constant for MHz device materials and dielectric loss for GHz electromagnetic wave absorption materials.

Magnetic Properties of Co-Doped Bismuth Ferrite Nanoparticles Prepared by the Solution Method

In this work, BiFeO3 and BiCo[Formula: see text]Fe[Formula: see text]O3 nanoparticles prepared by the solution method were further investigated the magnetic properties. At room temperature, BiFeO3 reveals the antiferromagnetic order. However, Co doping achieves ferromagnetic enhancement. The room-temperature ferromagnetism and the causes are ulteriorly studied with the help of ABK plots. The stronger coercivity is due to the oxygen vacancies and stronger magnetic anisotropy caused by Co substitution. Under variable temperatures, the bifurcate curves of zero-field-cooled and field-cooled indicate the existence of spin-glass state for both samples. The weak ferromagnetism at low temperature and the spin-state transition of cobalt ions at 270[Formula: see text]K are also found.

Structural, magnetic, magnetocaloric and electrical studies of Dy0.5(Sr1−xCax)0.5MnO3 manganites

Based on sol-gel method, the Dy0.5(Sr1−xCax)0.5MnO3 (x=0 and 0.3) manganites were synthesized. Orthorhombic distortion was presented in both samples via X-ray diffraction patterns with Pnma as a space group. Magnetic measurements of both systems illustrate anomalies at around TN(Mn)∼27K for the x=0 sample and 40K for x=0.3, showing antiferromagnetic coupling among Mn-spins. Then, the AC magnetic susceptibility of these systems was investigated to demonstrate the existence of spin glass state. In order to check if these samples can be good candidates for magnetic refrigeration, relative cooling power was determined depicting that the sample with a Ca content x=0.3 can be useful for magnetic refrigeration at cryogenic temperatures with about 133.89J/kg under a magnetic field of 5T. The experimental magnetic entropy change was then treated via Landau theory showing a big discrepancy between the measured and the theoretical magnetic entropy change under 1 and 5T. The antiferromagnetic behavior, which is governed by the super exchange interactions, describes also the insulating character, thus, we discussed the electrical properties and examined the conduction mechanisms. Based on Hall effect measurements, charge careers type was determined to be electron for both samples. Eventually, both systems can be investigated also as good candidates for bolometer applications.

Thickness dependent exchange bias in co-sputter deposited Ni–Mn–Al Heusler alloy hard nanostructured thin films

In the present work thin films of off-stoichiometric Ni–Mn–Al thin films have been successfully deposited on Si substrates. The films have been deposited by DC/RF magnetron sputtering by co-sputtering of the targets of Ni, Mn and Al. The films have been studied for their structural and magnetic properties. Nanoindentation has also been done for film hardness and resistant to crack properties. It has been observed that Martensitic transformation occurs in the film exhibiting large thickness (1.5μm). All the films exhibit exchange bias at low temperature with the exchange bias field depending strongly on the thickness of the film. ac susceptibility result shows the existence of spin glass state at low temperature. The exchange bias appearing in the sample may be associated with the interface containing spin glass SG/FM phase. The appearance of exchange bias in all the samples shows that in Ni–Mn–Al system, exchange bias is independent of the occurrence of martensitic transition in the system. The existence of mixed phase (L21 and B2) is an intrinsic property of Ni–Mn–Al system and the formation of L21 phase can be controlled by using different deposition and annealing parameters. In this respect, exchange bias properties of Ni–Mn–Al may be tuned by controlling the formation of ferromagnetic L21 phase. Nanoindentation results reveal that the film exhibits high hardness (H) ~21GPa and is resistant to scratch.

Numerical Simulation of Spin Glass State in Diluted Magnetic Materials Using Ising Spin Model in 2D with Distance Dependent Interactions

In the present paper,existence of spin glass state using Ising spin model with Edwards - Anderson type of interactions has been investigated by employing numerical simulation (Monte Carlo) technique. The study shows a phase transition from paramagnetic state to spin glass statewhen far apart spins are included in addition to nearest neighbor ones using power law decaying interactions.

Electron magnetic resonance study on the surface states of La0.7Sr0.3MnO3 nanoparticles

The technique of electron magnetic resonance (EMR) with a broad temperature regime (80–400 K) was employed for studying the surface states of La0.7Sr0.3MnO3 nanoparticles, which were synthesized by sol-gel routes with three different gelification agents (grain size≈17–24nm). Our EMR results reveal that all La0.7Sr0.3MnO3 nanoparticles have two magnetic states below the Curie temperatures TC. One is attributed to the core state and the other to surface state. Furthermore, the absorption field and the linewidth of surface state have a significant temperature dependence in the sample synthesized by citric acid, which may be associated with the existence of spin-glass state on the surface of nanoparticles.

Spin-glass like behaviors in cubic VO x

Magnetic susceptibility (d.c.) measurements were performed on the well characterized cubic VO x (1.10 ⩽ x⩽1.28). A sharp cusp-like peak in χ( T) curve was analyzed in terms of spin-glass behavior and the spin-glass order parameter, q( T) was extracted from χ cusp using Sherrington-Kirkpatrick model. This analysis as well as the other characteristic behaviors strongly suggests the possible existence of spin-glass state in this material.