Modeling of long-time thermal magnetization decay in interacting granular magnetic materials

We present a general method to evaluate the long-time magnetization decay in granular magnetic systems. The method is based on Arrhenius-Neel kinetics with the evaluation of the energy barriers in a multidimensional space. To establish a possible reversal mode, we suggest the use of Metropolis Monte Carlo and for the mode statistical sampling-the kinetic Monte Carlo criteria. The examples considered include long-time magnetization decay in CoCrPt low-magnetization longitudinal recording media and in a collection of Co particles with different concentrations

Ultrafast relaxation rates and reversal time in disordered ferrimagnets

In response to ultrafast laser pulses, single-phase metals have been classified as “fast” (with magnetization quenching on the time scale of the order of 100 fs and recovery in the time scale of several picoseconds and below) and “slow” (with longer characteristic time scales). Disordered ferrimagnetic alloys consisting of a combination of “fast” transition (TM) and “slow” rare-earth (RE) metals have been shown to exhibit an ultrafast all-optical switching mediated by the heat mechanism. The behavior of the characteristic time scales of coupled alloys is more complicated and is influenced by many parameters such as the intersublattice exchange, doping (RE) concentration, and the temperature. Here, the longitudinal relaxation times of each sublattice are analyzed within the Landau-Lifshitz-Bloch framework. We show that for moderate intersublattice coupling strength both materials slow down as a function of slow (RE) material concentration. For larger coupling, the fast (TM) material may become faster, while the slow (RE) one is still slower. These conclusions may have important implications in the switching time of disordered ferrimagnets such as GdFeCo with partial clustering. Using atomistic modeling, we show that in the moderately coupled case, the reversal would start in the Gd-rich region, while the situation may be reversed if the coupling strength is larger

Moving toward an atomistic reader model

With the move to recording densities up to and beyond 1 Tb/in/sup 2/, the size of read elements is continually reducing as a requirement of the scaling process. The expectation is for read elements containing magnetic films as thin as 1.5 nm, in which finite size effects, and factors such as interface mixing might be expected to become of increasing importance. Here, we review the limitations of the current (micromagnetic) approach to the theoretical modeling of thin films and develop an atomistic multiscale model capable of investigating the magnetic properties at the atomic level. Finite-size effects are found to be significant, suggesting the need for models beyond the micromagnetic approach to support the development of future read sensors

Cryptocurrencies and blockchain: history and prospects of the market, role in the modern world

Increasingly, people began to buy various goods, pay for services and transfer funds using the Internet. And for such purposes, ordinary money does not quite suit modern users. And the times when e-wallets were something new has already passed. And the most convenient and simple method of calculating Internet users became electronic payment systems, that is, money, but electronic

ПРОБЛЕМНІ ПИТАННЯ ТА ШЛЯХИ ЇХ ВИРІШЕННЯ ПІД ЧАС ДОСЛІДЖЕННЯ ПОДАТКОВОГО КРЕДИТУ З ПОДАТКУ НА ДОДАНУ ВАРТІСТЬ (оглядова стаття)

The article deals with problematic issues faced by a forensic economist in practice when conducting a forensic economic examination in relation to confirmation of violations established by tax audit reports of the State tax service of Ukraine, particularly tax credit overstatement, which in their essence are legal in nature and require not only knowledge in the field of economics, accounting, tax accounting and reporting, but also legal knowledge. The Article purpose is to highlight a number of challenging issues that arise during forensic economic examination; ways to resolve them are suggested, at the same time examples from forensic practice are offered. The analysis of judicial practice and the role of availability of a court judgment concluded between enterprises on invalidation of documents, of the results of handwriting analysis for investigative bodies while appointment of forensic economic examination is substantiated. According to the results of the carried out research, it was concluded that, in order to verify tax audit reports on violations of tax legislation, in terms of tax credit overstatement which in its essence are of a legal nature, a forensic expert should be provided not only with properly executed primary documents, but also judgment concluded between enterprises on recognition of invalid documents, court verdict on fictitious nature of the entity of economic activity, which became legally binding. Prior to appointment of forensic economic examination, it is expedient to conduct handwriting analysis (in case of signing of tax and expenditure invoices by a non-authorized person). In questions addressed to a forensic expert-economist, it is useful to take into consideration court judgment and handwriting analysis forensic report. All the above will increase the number of disclosure of economic crimes and provide money to the budget of a country.Розглянуто проблемні питання, з якими стикається судовий експерт на практиці під час проведення судової економічної експертизи щодо підтвердження порушень, визначених актами документальних перевірок контролюючих органів України (у частині завищення податкового кредиту), які за своєю сутністю мають правовий характер і потребують знань не лише у сферах економіки, бухгалтерського, податкового обліку і звітності, а й у сфері юриспруденції. Метою статті є висвітлення та шляхи вирішення проблемних питань, що виникають під час проведення судової економічної експертизи, наведено приклади з експертної практики. Проаналізовано судову практику й за результатами дослідження зроблено відповідні висновки

Ultra-fast magnetisation rates within the Landau-Lifshitz-Bloch model

The ultra-fast magnetisation relaxation rates during the laser-induced magnetisation process are analyzed in terms of the Landau-Lifshitz-Bloch (LLB) equation for different values of spin $S$. The LLB equation is equivalent in the limit $S \rightarrow \infty$ to the atomistic Landau-Lifshitz-Gilbert (LLG) Langevin dynamics and for $S=1/2$ to the M3TM model [B. Koopmans, {\em et al.} Nature Mat. \textbf{9} (2010) 259]. Within the LLB model the ultra-fast demagnetisation time ($\tau_{M}$) and the transverse damping ($\alpha_{\perp}$) are parameterized by the intrinsic coupling-to-the-bath parameter $\lambda$, defined by microscopic spin-flip rate. We show that for the phonon-mediated Elliott-Yafet mechanism, $\lambda$ is proportional to the ratio between the non-equilibrium phonon and electron temperatures. We investigate the influence of the finite spin number and the scattering rate parameter $\lambda$ on the magnetisation relaxation rates. The relation between the fs demagnetisation rate and the LLG damping, provided by the LLB theory, is checked basing on the available experimental data. A good agreement is obtained for Ni, Co and Gd favoring the idea that the same intrinsic scattering process is acting on the femtosecond and nanosecond timescale.Comment: 9 pages, 7 figure