Pablo Nieves

Verified

Pablo verified their affiliation via an institutional email.

Learn more

Verified

Pablo verified their affiliation via an institutional email.

Learn more

• Doctor of Philosophy
• PostDoc Position at University of Oviedo

The origin of magnetocrystalline anisotropic energy (MAE) guided by spin–orbit coupling in the L10-FePt alloy was analyzed. Correlation of MAE with the calculated magnetoelastic constants in the single and polycrystal model was determined by means of first-principles calculations using density functional theory (DFT). More specifically, a systemati...

Based on the idea of creating sensors sensitive to the magnetic component of terahertz electromagnetic radiation, we consider the potential possibilities of obtaining information about studied terahertz pulse by using spin-based sensors. We propose a way to analytically estimate the magnitude of the magnetic response to the action of a terahertz pu...

In this poster, we discuss about the state-of-the-art of multiscale modelling of magnetoelastic phenomena, and current challenges on this topic. Starting at the smallest spatial scale (microscopic scale), the aim is to perform a quantum mechanical characterization of the magnetoelastic constants of the material at zero temperature. For instance, th...

Picosecond ultrasonics is a fast growing and advanced research field with broad application to the imaging and characterization of nanostructured materials as well as at a fundamental level. The aim of this paper is to provide an advanced 3D model based on atomistic spin-lattice simulations of the laser-induced elastic response in ferromagnetically...

We present VelCrys, a web-based interactive tool, that allows to perform further post-processing of the elastic tensor in order to compute and plot the group velocity of the acoustic waves for any crystal symmetry. We also implemented the calculation of effective magnetic corrections to the elastic tensor and corresponding fractional change in grou...

Modern computational techniques that use a combination of electronic structure calculations, adaptive genetic algorithms, and machine learning data analysis have been recently predicting many new unknown structures that may exhibit desired physical properties. Yet, most of these theoretically discovered structures belong to the realm of virtual pha...

A convenient analytical description of an ultrashort terahertz pulse and an analysis of the influence of this pulse on the Zeeman torque dynamics are extremely important tasks due to the potential applications of terahertz radiation. The theoretical expressions proposed in this paper clarify the physics of magnetic dynamics under the action of the...

We present a methodology based on deformations of the unit cell that allows to compute the isotropic magnetoelastic constants, isotropic magnetostrictive coefficients and spontaneous volume magnetostriction associated to the exchange magnetostriction. This method is implemented in the python package MAELAS (v3.0), so that it can be used to obtain t...

We present a classical molecular-spin dynamics (MSD) methodology that enables accurate computations of the temperature dependence of the magnetocrystalline anisotropy as well as magnetoelastic properties of magnetic materials. The nonmagnetic interactions are accounted for by a spectral neighbor analysis potential (SNAP) machine-learned interatomic...

We present a methodology based on deformations of the unit cell that allows to compute the isotropic magnetoelastic constants, isotropic magnetostrictive coefficients and spontaneous volume magnetostriction associated to the exchange magnetostriction. This method is implemented in the python package MAELAS (v3.0), so that it can be used to obtain t...

In this work we computationally study the effect of microstructure on saturation magnetostriction of Terfenol-D (Tb0.27Dy0.73Fe2) by means of Finite Element Method. The model is based on the equilibrium magnetoelastic strain tensor at magnetic saturation, and shows that the crystal orientation jointly with the grain volume fraction play a more sign...

In this work, we leverage atomistic spin-lattice simulations to examine how magnetic interactions impact the propagation of sound waves through a ferromagnetic material. To achieve this, we characterize the sound wave velocity in BCC iron, a prototypical ferromagnetic material, using three different approaches that are based on the oscillations of...

In this work, we leverage atomistic spin-lattice simulations to examine how magnetic interactions impact the propagation of sound waves through a ferromagnetic material. To achieve this, we characterize the sound wave velocity in BCC iron, a prototypical ferromagnetic material, using three different approaches that are based on the oscillations of...

MAELAS is a computer program for the calculation of magnetocrystalline anisotropy energy, anisotropic magnetostrictive coefficients and magnetoelastic constants in an automated way. The method originally implemented in version 1.0 of MAELAS was based on the length optimization of the unit cell, proposed by Wu and Freeman, to calculate the anisotrop...

MAELAS is a computer program for the calculation of magnetocrystalline anisotropy energy, anisotropic magnetostrictive coefficients and magnetoelastic constants in an automated way. The method originally implemented in version 1.0 of MAELAS was based on the length optimization of the unit cell, proposed by Wu and Freeman, to calculate the anisotrop...

In this work we computationally study the effect of microstructure on saturation magnetostriction of Terfenol-D (Tb 0.27 Dy 0.73 Fe 2) by means of Finite Element Method. The model is based on the equilibrium magnetoelastic strain tensor at magnetic saturation, and shows that the crystal orientation might play a more significant role on saturation m...

We present a methodology based on the Néel model to build a classical spin-lattice Hamiltonian for cubic crystals capable of describing magnetic properties induced by the spin-orbit coupling like magnetocrystalline anisotropy and anisotropic magnetostriction, as well as exchange magnetostriction. Taking advantage of the analytical solutions of the...

In this work, we present the program MAELAS to calculate magnetocrystalline anisotropy energy, anisotropic magnetostrictive coefficients and magnetoelastic constants in an automated way by Density Functional Theory calculations. The program is based on the length optimization of the unit cell proposed by Wu and Freeman to calculate the magnetostric...

Recent experiments on magnetic nanoparticle hyperthermia show that the heat dissipated by particles must be considered locally instead of characterizing it as a global quantity. Here we show theoretically that the complex energy transfer between nanoparticles interacting via magnetic dipolar fields can lead to negative local hysteresis loops and do...

We present a methodology based on the N\'eel model to build spin-lattice models for cubic crystals capable of describing magnetic properties induced by the spin-orbit coupling like magnetocrystalline anisotropy and anisotropic magnetostriction. The dipole and quadrupole terms of the N\'eel model are parameterized through the Bethe-Slater curve. We...

The design of new materials for technological applications is increasingly being assisted by online computational tools that facilitate the study of their properties. In this work, based on modern web application frameworks, the online app MAELASviewer has been developed to visualize and analyze magnetostriction via a user-friendly interactive grap...

In this work, we present the program MAELAS to calculate magnetocrystalline anisotropy energy, anisotropic magnetostrictive coefficients and magnetoelastic constants in an automated way by Density Functional Theory calculations. The program is based on the length optimization of the unit cell proposed by Wu and Freeman to calculate the magnetostric...

In this paper, we perform a systematic calculation of the Fe-Ta phase diagram to discover hard magnetic phases. By using structure prediction methods based on evolutionary algorithms, we identify two energetically stable magnetic structures: a tetragonal Fe3Ta (space group 122) and a cubic Fe5Ta (space group 216) binary phase. The tetragonal struct...

Multiscale simulation is a key research tool in the quest for new permanent magnets. Starting with first principles methods, a sequence of simulation methods can be applied to calculate the maximum possible coercive field and expected energy density product of a magnet made from a novel magnetic material composition. Iron (Fe)-rich magnetic phases...

In this work we perform a systematic calculation of the Fe-Ta phase diagram to discover novel hard magnetic phases. By using structure prediction methods based on evolutionary algorithms, we identify two new energetically stable magnetic structures: a tetragonal Fe$_3$Ta (space group 122) and cubic Fe$_5$Ta (space group 216) binary phases. The tetr...

In this paper, we use a multiscale approach to describe a realistic model of a permanent magnet based on MnAl τ-phase and elucidate how the antiphase boundary defects present in this material affect the energy product. We show how the extrinsic properties of a microstructure depend on the intrinsic properties of a structure with defects by performi...

This paper describes the open Novamag database that has been developed for the design of novel Rare-Earth free/lean permanent magnets. Its main features as software technologies, friendly graphical user interface, advanced search mode, plotting tool and available data are explained in detail. Following the philosophy and standards of Materials Geno...

Multiscale simulation is a key research tool for the quest for new permanent magnets. Starting with first principles methods, a sequence of simulation methods can be applied to calculate the maximum possible coercive field and expected energy density product of a magnet made from a novel magnetic material composition. Fe-rich magnetic phases suitab...

In this work we use a multiscale approach toward a realistic design of a permanent magnet based on MnAl $\tau$-phase and elucidate how the antiphase boundary defects present in this material affect the energy product. We show how the extrinsic properties of a microstructure depend on the intrinsic properties of a structure with defects by performin...

This paper describes the open Novamag database that has been developed for the design of novel Rare-Earth free/lean permanent magnets. The database software technologies, its friendly graphical user interface, advanced search tools and available data are explained in detail. Following the philosophy and standards of Materials Genome Initiative, it...

We study the capability of a structure predicting method based on genetic/evolutionary algorithm for a high-throughput exploration of magnetic materials. We use the USPEX and VASP codes to predict stable and generate low-energy meta-stable structures for a set of representative magnetic structures comprising intermetallic alloys, oxides, interstiti...

DOI:https://doi.org/10.1103/PhysRevB.97.019901

In this work we develop an atomistic spin dynamics model for the ideal Mn50Al50τ-phase by means of first-principles calculations. The model is applied to study the domain wall and antiphase boundary phenomenology. In particular, it allows us to obtain the dependence on the interfacial exchange coupling of the nucleation and depinning fields, as wel...

Advances in theoretical and computational condensed matter physics have opened the possibility to predict and design magnetic materials for specific technological applications. In this paper, we use the adaptive-genetic algorithm technique for exploring the low-energy crystal structure configurations of Co <sub xmlns:mml="http://www.w3.org/1998/Mat...

The uncertainty in rare-earth market resulted in worldwide efforts to develop rare-earth-lean/free permanent magnets. In this paper, we discuss about this problem and analyse how advances in computational and theoretical condensed matter physics could be essential in the development of a new generation of high-performance permanent magnets via high...

Several recently reported exciting phenomena such as spin caloritronics or ultrafast laser-induced spin dynamics involve the action of temperature on spin dynamics. However, the inverse effect of magnetization dynamics on temperature change is very frequently ignored. Based on the density matrix approach, in this work we derive a self-consistent mo...

Manipulation of magnetization with ultrashort laser pulses is promising for information storage device applications. The dynamic of the magnetization response depends on the energy transfer from the photons to the spins during the initial laser excitation. A material of special interest for magnetic storage is FePt nanoparticles , on which optical...

Manipulation of magnetization with ultrashort laser pulses is promising for information storage device applications. The dynamic of the magnetization response depends on the energy transfer from the photons to the spins during the initial laser excitation. A material of special interest for magnetic storage is FePt nanoparticles , on which optical...

We perform atomistic modeling of Co/CoO nanoparticles with a diameter of a few nanometers and realistic values of the exchange and anisotropy parameters in order to study the field-dependent energy barriers under forward and backward reversal of the magnetization. The barriers are extracted from the constrained energy minimization using the integra...

The switching of magnetization by ultrafast lasers alone in FePt could open a technological perspective for magnetic recording technology. Recent experimental results [D. Lambert et al., Science 345, 1337 (2014)] indicate a dynamical magnetization response in FePt under circularly polarized laser pulses. Using high-temperature micromagnetic modelin...

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" t...

The recently derived Landau-Lifshitz-Bloch equation of motion for two-component magnetic systems, including ferri- ferro- and antiferromagnets, provides a framework to analyze species dependent ultra fast demagnetization rates. In agreement with reported experimental observations, we show that Gd sublattice demagnetizes slower then FeCo in GdFeCo....

Micromagnetic modeling has proved itself as a widely used tool, complimentary in many respects to experimental measurements. The Landau-Lifshitz equation provides a basis for this modeling, especially where the dynamical behaviour is concerned. However, this approach is strictly valid only for zero temperature and for high temperatures must be repl...

A hierarchical multiscale approach to model the magnetization dynamics of ferromagnetic random alloys is presented. First-principles calculations of the Heisenberg exchange integrals are linked to atomistic spin models based upon the stochastic Landau-Lifshitz-Gilbert (LLG) equation to calculate temperature-dependent parameters (e.g., effective exc...

Several recently appeared applications such as spin-caloritronics, heat-assisted magnetic recording or ultra-fast laser induced magnetization dynamics involve high temperatures. The standard micro-magnetic approach is known to fail there due to the conservation of the magnetization length. Recently proposed micromagnetics based on the Landau-Lifshi...

DOI:https://doi.org/10.1103/PhysRevB.92.019901

A hierarchical multiscale approach to model the magnetization dynamics of ferromagnetic ran- dom alloys is presented. First-principles calculations of the Heisenberg exchange integrals are linked to atomistic spin models based upon the stochastic Landau-Lifshitz-Gilbert (LLG) equation to calculate temperature-dependent parameters (e.g., effective e...

The Landau-Lifshitz-Bloch equation provides a micromagnetic framework for large-scale modeling of the ultrafast magnetization dynamics in ferromagnets. Here we present a detailed discussion of the LLB equation with a quantum spin number S. As an example, we present our recently numerical results of the ultrafast demagnetization dynamics in FePt thi...

The detailed derivation of the quantum Landau-Lifshitz-Bloch (qLLB) equation for simple spin-flip scattering mechanisms based on spin-phonon and spin-electron interactions is presented and the approximations are discussed. The qLLB equation is written in the form, suitable for comparison with its classical counterpart. The temperature dependence of...

Magnetization manipulation is essential for basic research and applications. A fundamental question is, how fast can the magnetization be reversed in nanoscale magnetic storage media. When subject to an ultrafast laser pulse, the speed of the magnetization dynamics depends on the nature of the energy transfer pathway. The order of the spin system c...

Magnetization manipulation is becoming an indispensable tool for both basic and applied research. Theory predicts two types of ultrafast demagnetization dynamics classified as type I and type II. In type II materials, a second slower process takes place after the initial fast drop of magnetization. In this letter we investigate this behavior for Fe...

We derive the Landau-Lifshitz-Bloch (LLB) equation for a two-component magnetic system valid up to the Curie temperature. As an example, we consider disordered GdFeCo ferrimagnet where the ultrafast optically induced magnetization switching under the action of heat alone has been recently reported. The two-component LLB equation contains the longit...