Time Decay Of Thermoremanent Magnetization Research Articles

Evidence for cluster glass ground state in the potential giant dielectric constant material Ba(Fe1/2Sn1/2)O3-δ

We report the magnetic ground state of the technologically important giant dielectric constant material Ba(Fe1/2Sn1/2)O3-δ (BFSO) using detailed dc and ac magnetization and specific heat measurements. Our careful x-ray diffraction analysis confirms that BFSO is single phase and crystallizes in the cubic structure with the Pm3¯m space group. Temperature-dependent dc susceptibility measurements reveal that magnetic irreversibility sets in below Tirr ~ 18 K. In addition, the zero-field cooled susceptibility exhibits a peak at the freezing temperature Tf ~ 16 K, which is also characterized by a frequency dispersion in ac susceptibility measurements. This data also confirms to the critical slowing down model with cluster-glass transition temperature TG ~15.7 K and characteristic relaxation time τo ~10−7 s. The magnetic field dependence of the freezing temperature Tf obeys de Almeida-Thouless line in the H-T plane. The presence of aging effect and extremely slow time decay of thermoremanent magnetization is also observed below Tf. The magnetic contribution to the specific heat (Cm) exhibits a linear temperature dependence below Tf. All these observations unambiguously confirm a cluster-glass magnetic ground state in this system.

A stretched exponential-based approach for the magnetic properties of spin glasses

The spin glasses show intriguing characteristic features that are not well understood yet, as for instance its aging, rejuvenation and memory effects. Here a model based on a stretched exponential decay of its magnetization is proposed, which can describe the main magnetic features of spin glasses observed in experiments as the time-decay of thermoremanent magnetization, the relaxation of zero field cooled magnetization, the ac and dc magnetization as a function of temperature and others. In principle, the here proposed model could be adapted to describe other glassy systems.

Exchange bias in BiFeO3 and Bi0.9La0.1FeO3 nanoparticles

The exchange bias (EB) effects of BiFeO3 (BFO) and Bi0.9La0.1FeO3 nanopowders are investigated. An EB field of 152 Oe and 902 Oe at 60 K are observed for BFO and Bi0.9La0.1FeO3, respectively, when cooled in 20 kOe magnetic field. The enhancement of EB values in the case of Bi0.9La0.1FeO3 is explained based on the combination of Malozemoff’s and domain state models. Training effect measurements data fitted with Binek’s model suggested that the origin of EB lies in the interaction between the antiferromagnetic (AFM) core and the soft magnetic shell. Memory effect measurements, thermoremanent and isoremanent magnetization studies, and time decay of thermoremanent magnetization studies are done to understand the nature of the shell of both the samples. Time decay of thermoremanent magnetization of BFO is fitted with a stretched exponential based on Kohlrausch–Williams–Watt model, the obtained shape parameter value lies in the range of Heisenberg type spin-glasses. From thermoremanent and isoremanent magnetization plots, a 2D-diluted AFM shell is observed for Bi0.9La0.1FeO3. The field cooling and the temperature dependence of EB are investigated and the results are explained based on the available models of EB.

Preparation and properties of antiperovskite-type nitrides: InNNi 3 and InNCo 3

Two antiperovskite-type ternary nitrides of InN M 3 ( M=Ni, Co) have been synthesized from In 2O 3 and Ni or Co powders under NH 3 atmosphere at 600 °C. InNCo 3 is a new ternary nitride whereas InNNi 3 was previously reported as InN 0.5Ni 3 with different nitrogen content. The lattice parameters refined by Rietveld method are 3.8445(1) Å for InNNi 3 and 3.8541(7) Å for InNCo 3, respectively. Both nitrides show metallic behaviors and below 70 K the T 2 temperature dependence of resistivity was observed indicative of a Fermi liquid behavior. The temperature dependence of the field-cooling (FC) and zero-field-cooling (ZFC) magnetization and time decay of thermoremanent magnetization indicate the spin-glass-like behavior in InN M 3 ( M=Ni, Co). The freezing temperatures for this behavior, T f , are about 300 K for InNNi 3 and 10 K for InNCo 3, respectively.

Signatures of spin-glass freezing in NiO nanoparticles

We present a detailed study of the magnetic properties of sol-gel prepared nickel oxide nanoparticles of different sizes. We report various measurements such as frequency, field and temperature dependence of ac susceptibility, temperature and field dependence of dc magnetization and time decay of thermoremanent magnetization. Our results and analysis show that the system behaves as a spin glass.

Magnetic relaxation of YBa 2Cu 3O 7− δ ceramics in an intergrain-ordered phase

Magnetic relaxation is studied in YBa 2Cu 3O 7− δ ceramics consisting of weakly coupled submicron grains. In the system, the ordering proceeds successively from the intragrain ordered state to the intergrain one at zero field. Below the intergrain ordering point T c2, the time decay of thermoremanent magnetization could be well fitted to a stretched exponential function. Waiting time dependence of the time decay is noticed below T c2, suggesting a glassy phase below T c2 in the present system.

Time decay of thermoremanent magnetization and relaxation spectra in the cluster glass of itinerant magnetic Fe xTiS 2

Time decays of the thermoremanent magnetization (TRM) in the cluster-glass (CG) phase of Fe x TiS 2 ( x= 1 3 , T g=53 K) have been measured using the anomalous Hall effect at three fixed temperatures 24.3, 29.3, and 34.3 K, over the time range 10 −1–10 4 s with the cooling-fields H FC=0.005–0.14 T. For a low field-cooling ( H FC⩽0.035 T), the Hall resistivity or TRM decays according to the power law ρ H( t)= At − m in a short time range and the overall decay curves over the wide time range can be reproduced by an existing domain theory. By comparing the theory with experiments, we have obtained the equilibrium relaxation spectrum Q( τ) for x= 1 3 , which is much wider and smaller than those for another CG system ( x= 1 4 ) and a spin-glass one ( x=0.20). For a higher field-cooling ( H FC⩾0.07 T), we have observed the unusual decay profiles that cannot be explained by the domain theory. For these dynamical properties of Fe 1/3TiS 2, we have made qualitative discussions by considering a random distribution of Fe atoms with up- and down-spins in the two-dimensional hexagonal layer of Fe x TiS 2, where the formation and decomposition of some percolated cluster formed by the nearest and next-nearest interactions play an important role in the time decay profiles that depend on Fe concentration, cooling-field, and temperature.

Time decay of thermoremanent magnetization in cluster-glass phase of intercalation compound Fe xTiS 2 studied by use of anomalous Hall effect

Time decay of Hall resistivity ρ H after field-cooling under magnetic fields H FC = 0.035–0.14 T for a cluster-glass phase of Fe x TiS 2 ( x = 1 4 , T g = 53 K ) has been measured over the temperature range 4.2–35 K and time range 10 −1–10 3 s. After the magnetic field is switched off to zero at time t = 0, the Hall voltage decays with time obeying the power law ρ H( t) = At − m in a short time range up to t d, beyond which the decay becomes faster than a power law. The temperature and magnetic field dependences of the exponents m are analyzed to obtain a universal relation for the thermoremanent magnetization (TRM), m = Dξ, where ξ is a characteristic quantity, defined by ξ = 1 − M(0)/ M FC( T → 0); M FC( T → 0) is the magnetization at H = H FC extrapolated to T = 0 and M(0) the remanent magnetization at time t = 0. Comparison with the present field-cooled and the zero-field case (isothermal remanent magnetization, IRM) is made to emphasize the dependence of relaxation behavior on the magnetic history.

Time dependence of magnetization decay in spin glasses

A gamma distribution of relaxation times integrates to a modified Bessel function time dependence. It is suggested that it be used in analyzing the time decay of thermoremanent magnetization, or other complex systems of exponential decays.