Antiferromagnetic System Research Articles

The effect of anisotropic field on magnon numbers, magnetization and heat capacity of antiferromagnetic materials

This article provides a theoretical examination of the impact of anisotropic fields on the magnetization and heat capacity thermodynamic properties of sublattice antiferromagnetic spin systems. The analysis begins with the classical Heisenberg model and considers uniaxial anisotropic fields in the antiferromagnetic system. Quantum field theory and the double time temperature dependent Green’s function technique, which incorporates the random phase approximation, are used to decouple and diagonalize the higher order terms. The study utilizes a dispersion of uniaxial symmetric AFM crystal lattice to examine the thermodynamic parameters of magnetization and heat capacity as a function of excitation temperature at low temperatures and long wavelength approximation. The results demonstrate that the magnetization and heat capacities of AFM are sensitive to anisotropic fields, with the magnetization deviation moving up and the heat capacity maximum peak reducing with increased anisotropy. These findings may have implications for the use of antiferromagnetic materials with similar anisotropy sources and stability in real-world applications.

Antiferromagnetic interlayer exchange coupled Co68B32/Ir/Pt multilayers

Synthetic antiferromagnetic structures can exhibit the advantages of high velocity similarly to antiferromagnets with the additional benefit of being imaged and read-out through techniques applied to ferromagnets. Here, we explore the potential and limits of synthetic antiferromagnets to uncover ways to harness their valuable properties for applications. Two synthetic antiferromagnetic systems have been engineered and systematically investigated to provide an informed basis for creating devices with maximum potential for data storage, logic devices, and skyrmion racetrack memories. The two systems considered are (system 1) CoB/Ir/Pt of N repetitions with Ir inducing the negative coupling between the ferromagnetic layers and (system 2) two ferromagnetically coupled multilayers of CoB/Ir/Pt, coupled together antiferromagnetically with an Ir layer. From the hysteresis, it is found that system 1 shows stable antiferromagnetic interlayer exchange coupling between each magnetic layer up to N = 7. Using Kerr imaging, the two ferromagnetic multilayers in system 2 are shown to undergo separate maze-like switches during hysteresis. Both systems are also studied as a function of temperature and show different behaviors. Micromagnetic simulations predict that in both systems the skyrmion Hall angle is suppressed with the skyrmion velocity five times higher in system 1 than system 2.

Observation of Griffiths phase-like magnetic behavior in a frustrated antiferromagnetic system: Sr2InRuO6

An unusual observation of Griffiths phase-like magnetic behavior in an antiferromagnetic system, Sr2InRuO6, is reported. Presence of magnetic clusters and change of their properties like magnetization or concentration was found to be related to this unusual behavior.

Releasing antiferromagnetic skyrmions from local magnetic-anisotropy defects

Lattice defects may work as a kind of apparatus for catching topological excitations, preventing their escape. So, the problem of removing skyrmions from eventual local defects in magnetic materials must be closely related to new technologies such as skyrmionic. Here, we examine the conditions for drawing a skyrmion from a magnetic impurity in a two-dimensional antiferromagnetic system by applying spin-polarized currents (SPC). Two types of impurities are investigated (local easy-axis and easy-plane anisotropy defects). Also, two methods to release the skyrmion with SPC are explored. In principle, our results could be qualitatively relevant to any other type of lattice defect.

Angular and planar transport properties of antiferromagnetic V5S8

Systemically angular and planar transport investigations are performed in layered antiferromagnetic (AF) V5S8. In this AF system, obvious anomalous Hall effect (AHE) is observed with a large Hall angle of 0.1 compared to that in ferromagnetic (FM) system. It can persist to the temperatures above AF transition and exhibit strong angular field dependence. The phase diagram reveals various magnetic states by rotating the applied field. By analyzing the anisotropic transport behavior, magnon contributions are revealed and exhibit obvious angular dependence with a spin-flop vanishing line. The observed prominent planar Hall effect and anisotropic magnetoresisitivity exhibit two-fold systematical angular dependent oscillations. These behaviors are attributed to the scattering from spin–orbital coupling instead of nontrivial topological origin. Our results reveal anisotropic interactions of magnetism and electron in V5S8, suggesting potential opportunities for the AF spintronic sensor and devices.

Engineering the electromagnetic response and thermoelectric performance of half-functionalized stanene with [formula omitted], [formula omitted], [formula omitted], [formula omitted] and [formula omitted

We report on, for the first time, a combined density functional theory and Boltzmann-semiclassical calculations of two-dimensional stanene half-passivated with X=H,F,Cl,Br and I The thermodynamical stability is examined through the comparison of the formation energy as well as the analysis of the phonon dispersion spectrum indicating a possible experimental fabrication of these stanene derivatives. Interestingly, using generalized gradient approximation (GGA), the obtained results show that half-iodination and half-hydrogenation induce a half metallic ferromagnetic character and the magnetic moment on the unsaturated Sn atoms are 0.41μB and 0.38μB for SnSn–H and SnSn–I respectively, whereas half-decoration with fluorine, chlorine and bromine adsorbates, characterized with high electronegativity, gives rise to antiferromagnetic metallic systems. Except SnSn–I, the critical temperatures of the stanene derivatives are above room temperature. These results suggest that magnetism of stanene can be tuned by different passivation atoms. The transport properties, which result in a thermoelectric figure of merit (ZT), are very sensitive to the doping type however, less affected by the temperature variation. The highest ZT value of 0.99 is recorded for the SnSn–H conformer, while it decreases with the increase of the electronegativity. For the four compounds, the maximum figure of merit and seebeck coefficients are located at n-type doping, suggesting that these materials can be strong candidates among n-type materials for thermoelectric applications in high-temperature regions. Our findings demonstrate that half passivation with X-atoms is a feasible method to tune the properties of stanene for spin injection applications and thermoelectric cooling industry.

Discovery of ultrafast spontaneous spin switching in an antiferromagnet by femtosecond noise correlation spectroscopy

Owing to their high magnon frequencies, antiferromagnets are key materials for future high-speed spintronics. Picosecond switching of antiferromagnetic spin systems has been viewed a milestone for decades and pursued only by using ultrafast external perturbations. Here, we show that picosecond spin switching occurs spontaneously due to thermal fluctuations in the antiferromagnetic orthoferrite Sm0.7Er0.3FeO3. By analysing the correlation between the pulse-to-pulse polarisation fluctuations of two femtosecond optical probes, we extract the autocorrelation of incoherent magnon fluctuations. We observe a strong enhancement of the magnon fluctuation amplitude and the coherence time around the critical temperature of the spin reorientation transition. The spectrum shows two distinct features, one corresponding to the quasi-ferromagnetic mode and another one which has not been previously reported in pump-probe experiments. Comparison to a stochastic spin dynamics simulation reveals this new mode as smoking gun of ultrafast spontaneous spin switching within the double-well anisotropy potential.

Anisotropically suppressed frustration in antiferromagnetic systems on the kagome lattice

The influence of the interactionally generated anisotropy on the magnetic as well as thermodynamic properties of geometrically frustrated antiferromagnetic systems is investigated in the framework of the interactionally generated uniaxially-anisotropic antiferromagnetic J1−J2 spin-1/2 Ising model on the kagome lattice within the recursive lattice approximation. The exact solution of the corresponding model on the star kagome-like recursive lattice is found and the phase diagrams of the ground states of the model with and without the presence of the external magnetic field are identified from the magnetization as well as the entropy point of view. The magnetization, the entropy, and the specific heat properties of the model are investigated. It is shown that the presence of even a negligibly small interactionally generated anisotropy can lead not only to the quantitative but also to the significant qualitative changes in the magnetic and thermodynamic properties of frustrated magnetic systems, e.g., it can suppress the presence of frustration itself and, at the same time, generate the appearance of the first and second order phase transitions.

Charge-to-Spin Conversion Efficiency in Synthetic Antiferromagnetic System Using Pt–Cu/Ir/Pt–Cu Spacer Layers

Damping-like SOT efficiency (effective spin Hall angle: ξ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DL</sub> ) is investigated in synthetic antiferromagnetic (AF) systems using Pt-Cu alloy/Ir/Pt-Cu alloy spacer layers. We found AF interlayer exchange coupling through Pt-Cu alloy/Ir/Pt-Cu alloy spacer layers. We also found that the magnitude of ξ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DL</sub> for synthetic AF system using Pt <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">57</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">43</sub> alloy/Ir/Pt <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">57</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">43</sub> alloy spacer layer is larger than that for synthetic AF system using Pt/Ir/Pt spacer layer with the same magnitude of interlayer exchange coupling ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ex</sub> ), comparing to devices with nearly similar magnitudes of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ex</sub> of 0.11 mJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The observed maximum magnitude of ξ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DL</sub> is 19.9% for the synthetic AF system with Pt <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">57</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">43</sub> alloy/Ir/Pt <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">57</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">43</sub> alloy spacer layer. The use of the spacer layers with material having a large damping-like SOT efficiency and strong interlayer exchange coupling is important for increasing spin Hall angle in synthetic AF system.

Structure and Unusual Magnetic Properties of Mg-Containing Solid Solutions Based on Y&lt;sub&gt;2&lt;/sub&gt;FeTaO&lt;sub&gt;7&lt;/sub&gt;

Mg-containing solid solutions based on Y2FeTaO7 and formed by various mechanisms of heterovalent substitution were synthesized and had the following compositions: Y2Fe0.55Mg0.3Ta1.15O7, Y2Fe0.625Mg0.3Ta1.075O7, Y2Fe0.7Mg0.3TaO7, Y2Fe0.7Mg0.2Ta1.1O7, Y2Fe0.85Mg0.15TaO7, Y1.85Mg0.15Fe0.925Ta1.075O7, and Y1.85Mg0.15FeTaO7. It was shown that all synthesized solid solutions have a pyrochlore-like layered structure (space group P3121), in which Fe3+ ions are distributed over three structural positions. The magnetic properties of these solid solutions are due to the presence of a small ferromagnetic component in a predominantly antiferromagnetic system and characterize a ferrimagnet or a canted antiferromagnet with the Néel transition at the Néel temperature TN above room temperature. According to the data of magnetic measurements, two magnetic phase transitions to the ordered phase occur in all the studied samples. Along with the TN transition, in weak magnetic fields and below TN, there is a second transition, which is most likely due to a spin reorientation of the Morin type. The existence of magnetic ordering at room temperature in one magnetic sublattice or an internal magnetic field (Hin) was confirmed by Mössbauer spectroscopy.

Antiferromagnetic bimeron dynamics controlled by magnetic defects

We investigate dynamics of an isolated bimeron in the antiferromagnetic system, in the presence of magnetic defects. The bimeron is driven by torques due to a spin-polarized current, which is incorporated into the Landau–Lifshitz–Gilbert (LLG) equation. We numerically solve the LLG equation, and find a breathing dynamics of the bimeron as well as its transverse motion owing to the defect potential. We also analyze the potential landscapes due to the interaction between the bimeron and a defect, and give a qualitative picture of the numerically obtained dynamics.

First principles study on the structural, elastic, electronic, optical and thermal properties of lead-free perovskites CsCaX3(X=F, Cl, Br)

The physical properties included structural, mechanical, thermal and optical features of lead-free perovskites CsCaX3 (X = F, Cl, Br) have been investigated using abـinitio computations. The optimized lattice constants correspond extremely well with experimental as well as theoretical data. Structural stability of these phases is ensured from the Goldschmidt tolerance factor (tG) and formation enthalpy. Mechanical stability of CsCaX3 (X = F, Cl, Br) is authenticated by the investigated stiffness constants. The polycrystalline parameters such as bulk modulus (B), Poisson's ratio (ν), shear modulus (G), Young's modulus (E), anisotropy factor (A), hardness and Pugh's ratio are calculated and compared with similar types of compounds. The huge Young's modulus, bulk modulus as well as hardness of CsCaF3 assured that it has a great capacity to resists the deformation of volume as well as plastic than CsCaCl3 and CsCaBr3. The CsCaBr3 material is particularly ductile which makes it excellent for usage in thin films. The density of states (DOS) and the electronic band structures have been estimated of these compounds, which demonstrate that they have direct energy band gap that reduces continually in the order of CsCaF3>CsCaCl3>CsCaBr3. The optical features of CsCaX3 (X = F, Cl, Br) are investigated. Among the studied materials, the optical features of CsCaBr3 appear to be more enhanced than the other two compounds. A combined analysis of CsCaF3, CsCaCl3 and CsCaBr3 demonstrated that these types of materials have great potential for a variety of device applications in optical, ferroelectric, antiferromagnetic systems having their wide band gaps. Very low minimum conductivity of the studied phases confirmed the use of these compounds as thermal barrier coating compounds for industrial purposes.

Implementation of logical operations using antiferromagnetic helical molecule

Abstract For the first time, we explore all possible two-input logical operations (OR, AND, NOT, NOR, NAND, XOR, and XNOR) using a single-stranded antiferromagnetic (AFM) helix system. The AFM helix produces a large amount of spin current in the presence of a transverse electric field. The spin current, considered as the output, can be tuned by the strength and direction of the electric field that are taken as the inputs of the logic gates. All the results are spin-based, which reduces the loss due to heating energy, and since the operations are reprogrammable, one can have all the gates in a single system simply by rearranging the setup. Based on the growth of experimental realization of AFM helical systems we believe that our results can be verified and may lead to a new direction in the branch of AFM spintronics.

Magnetization processes and magnetocaloric effect of the Ising model on the octahedral lattice

The magnetocaloric effect and magnetization processes of the extended Ising model on the 3-dimensional octahedral lattice are studied by the classical Monte Carlo method with Metropolis algorithm. It is shown that different combinations of antiferromagnetic and ferromagnetic nearest-neighbor interactions J1 and J2 (in particular J1=−1, J2=1 and J1=−1, J2=−1) lead to the fundamentally different magnetic behaviors at nonzero temperatures, despite the fact that zero-temperature magnetization curves have exactly the same form. The reason is that the spin configurations forming zero-temperature magnetization plateaus for both J2=−1 and J2=1 are different, and different are also their temperature evolutions (controlled by calculations of in-plane and inter-plane sublattice magnetizations), which lead to different results for the magnetic entropy change (the magnetocaloric effect). Due to this fact a much higher positive entropy change is observed for the ferro-antiferromagnetic system compared to the pure antiferromagnetic system.

Comparative study between charge and spin thermoelectric figure of merits in an antiferromagnetic ring

Considering the unique and diverse characteristic features of antiferromagnetic (AFM) systems, here in our work, we explore spin-dependent thermoelectric behavior in an AFM ring geometry. A reasonably large ( ≫1 ) spin figure of merit, referred to as Z S T, is obtained under suitable input conditions. Two important prerequisites are (i) breaking the symmetry among up and down spin sub-Hamiltonians and (ii) generating different asymmetric transmission line shapes across a Fermi energy for two opposite spin electrons. Describing the physical system within a tight-binding framework, where spin-dependent scattering occurs due to the interaction of itinerant electrons with local magnetic moments via the usual spin-moment exchange interaction, we compute all the thermoelectric quantities based on Landauer integrals following the Green’s function technique. The behavior of charge figure of merit, denoted as Z C T, is also discussed along with Z S T. Though Z C T reaches above unity, it is much smaller compared to Z S T. This is the key finding of our investigation. To make the present communication a self-contained one, we compare the results with another arrangement of magnetic moments in a ring-like geometry and in a chain-like one. Our analysis gives a suitable hint that in the presence of spin-dependent scattering, much more favorable energy conversion can be substantiated.

Coexistence of Magnon-Induced and Rashba-Induced Unidirectional Magnetoresistance in Antiferromagnets.

Unidirectional magnetoresistance (UMR) has been intensively studied in ferromagnetic systems, which is mainly induced by spin-dependent and spin-flip electron scattering. Yet, UMR in antiferromagnetic (AFM) systems has not been fully understood to date. In this work, we reported UMR in a YFeO3/Pt heterostructure where YFeO3 is a typical AFM insulator. Magnetic-field dependence and temperature dependence of transport measurements indicate that magnon dynamics and interfacial Rashba splitting are two individual origins for AFM UMR, which is consistent with the UMR theory in ferromagnetic systems. We further established a comprehensive theoretical model that incorporates micromagnetic simulation, density functional theory calculation, and the tight-binding model, which explain the observed AFM UMR phenomenon well. Our work sheds light on the intrinsic transport property of the AFM system and may facilitate the development of AFM spintronic devices.

Ultrafast activation of the double-exchange interaction in antiferromagnetic manganites

In doped manganite systems, strong electronic correlations result in rich phase diagrams where electron delocalization strongly affects the magnetic order. Here, we employ a femtosecond all-optical pump-probe scheme to impulsively photodope the antiferromagnetic parent manganite system CaMnO3 and unveil the formation dynamics of a long-range ferromagnetic state. We resonantly target intense charge transfer electronic transitions in CaMnO3 to photodope the system and probe the subsequent dynamics of both charges and spins using a unique combination of time-resolved terahertz spectroscopy and time-resolved magneto-optical Faraday measurements. We demonstrate that photodoping promotes a long-lived population of delocalized electrons and induces a net magnetization, effectively promoting ferromagnetism resulting from light-induced carrier-mediated short-range double-exchange interactions. The picosecond set time of the magnetization, much longer than the electron timescale, and the presence of an excitation threshold are consistent with the formation of ferromagnetic patches in an antiferromagnetic background.

Nonequilibrium magnons from hot electrons in antiferromagnetic systems

Nonequilibrium magnons from hot electrons in antiferromagnetic systems

Evolution of the inverse magnetocaloric effect for random-field to spin-glass crossover in SmCaCoMnO6−SmMnO3 nanocomposite

We observe an enhancement of inverse magnetocaloric effect (MCE) in $\mathrm{Sm}\mathrm{Ca}\mathrm{Co}\mathrm{Mn}{\mathrm{O}}_{6}$ (94%) and $\mathrm{Sm}\mathrm{Mn}{\mathrm{O}}_{3}$ (6%) nanocomposite due to uniform external field-induced random field (RF) to spin glass (SG) crossover. RF is generally observed in diluted antiferromagnet and dilute dipole-coupled Ising ferromagnet systems. Under the application of magnetic-field ($H$), such systems may show a crossover from RF to SG at low temperatures ($T$). Here, we report a similar type of crossover but in ferrimagnetic $\mathrm{Sm}\mathrm{Ca}\mathrm{Co}\mathrm{Mn}{\mathrm{O}}_{6}$ and antiferromagnetic $\mathrm{Sm}\mathrm{Mn}{\mathrm{O}}_{3}$ nanocomposite. A model of site dilution of the ferrimagnetic phase by the embedded antiferromagnetic regions is proposed. In this composite system, the RF appears at $T&lt;35$ K, which shows a crossover to SG at $T&lt;15$ K under the applied field. The enhanced inverse MCE (with an entropy change, $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}\ensuremath{\sim}\ensuremath{-}0.95$ J ${\mathrm{Kg}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ for a change in $H\ensuremath{\sim}70$ kOe at $T\ensuremath{\sim}7.5$ K) due to the SG state is the consequence of field-induced RF-SG crossover giving highly $H$-dependent $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}$ in the SG regime, a requisite for large MCE.

Weak trimerization in the frustrated two-dimensional triangular Heisenberg antiferromagnet LuyY1−yMnO3

To understand the 2D triangular Heisenberg antiferromagnetic system, we investigated the magnetic structures and the dynamics of ${\mathrm{Lu}}_{y}{\mathrm{Y}}_{1\ensuremath{-}y}{\mathrm{MnO}}_{3}$ in detail. The substitutions are adjusted to the Mn atomic position close to ${x}_{\text{Mn}}=\frac{1}{3}$. The neutron powder diffraction data claims that the magnetic structure of ${\mathrm{Lu}}_{y}{\mathrm{Y}}_{1\ensuremath{-}y}{\mathrm{MnO}}_{3}$ is described as a mixture of ${\mathrm{\ensuremath{\Gamma}}}_{3}$ ($P{6}_{3}^{\ensuremath{'}}c{m}^{\ensuremath{'}}$) and ${\mathrm{\ensuremath{\Gamma}}}_{4}$ ($P{6}_{3}^{\ensuremath{'}}{c}^{\ensuremath{'}}m$) at the ${x}_{\text{Mn}}$ position for $y=0.15$, 0.30, and 0.45. The ratio of ${\mathrm{\ensuremath{\Gamma}}}_{3}$ and ${\mathrm{\ensuremath{\Gamma}}}_{4}$ depends on temperature and composition and the fraction of ${\mathrm{\ensuremath{\Gamma}}}_{3}$ increases upon cooling, while no clear trimerization was observed at the ${x}_{\text{Mn}}$ position. We estimated exchange parameters from the analysis of the low-energy part of the spin waves. The results showed a weak trimerization effect on cooling because the nearest-neighbor exchange interaction is slightly enhanced. The temperature dependence of the spin-wave dispersion around the $\mathrm{\ensuremath{\Gamma}}$ point shows that the spin gap closes with increasing temperature because the exchange interactions in the nearest Mn-Mn neighbor become smaller. Gapless diffusive magnetic excitation from a Mn triangular lattice has been observed in a wide range in $Q$ and $E$ space of ${\mathrm{Lu}}_{y}{\mathrm{Y}}_{1\ensuremath{-}y}{\mathrm{MnO}}_{3}$. We found that ${\mathrm{Lu}}_{0.7}{\mathrm{Y}}_{0.3}{\mathrm{MnO}}_{3}$ could be an ideal case to investigate the trimerization, frustrated magnetism, and magnetoelastic coupling often observed in two-dimensional triangular lattice Heisenberg antiferromagnet systems.