Simple Antiferromagnet Research Articles

Giant magnetoresistance resulting from superzone gap in spin-frustrated rare-earth-based aluminide: DyFe2Al10.

The magnetic properties of orthorhombic aluminides have recently been the subject of investigation, revealing several intriguing phenomena within this class of materials. However, the exploration of their magnetic and electrical transport phenomena has remained somewhat limited. In this study, we delve into the magnetic and electrical transport characteristics of one such material from that group which is DyFe2Al10(DFA). Our findings go beyond classifying this material as a simple antiferromagnet; but it posses a short range ferromagnetic ordering apart from helical spin structure of Dy3+. It exhibits a metamagnetic transition and spin glass behavior below its Néel temperature (TN). Our analysis of electrical magnetotransport behavior indicates the emergence of an antiferromagnetic superzone gap, resulting in a significant enhancement in magnetoresistance effect. This discovery paves the way for a class of materials with complex interactions and notable magnetoresistance properties.

Topological Hall effect driven by short-range magnetic order in EuZn2As2

Short-range (SR) magnetic orders such as magnetic glass orders or fluctuations in a quantum system usually host exotic states or critical behaviors. As the long-range (LR) magnetic orders, SR magnetic orders can also break time-reversal symmetry and drive the non-zero Berry curvature leading to novel transport properties. In this work, we report that in EuZn$_2$As$_2$ compound, besides the LR A-type antiferromagnetic (AF) order, the SR magnetic order is observed in a wide temperature region. The magnetization measurements and electron spin resonance (ESR) measurements reveal the ferromagnetic (FM) correlations for this SR magnetic order which results in an obvious anomalous Hall effect above the AF transition. Moreover the ESR results reveal that this FM SR order coexists with LR AF order exhibiting anisotropic magnetic correlations below the AF transition. The interactions of LR and SR magnetism evolving with temperature and field can host non-zero spin charility and berry curvature leading the additional topological Hall contribution even in a centrosymmetric simple AF system. Our results indicate that EuZn$_2$As$_2$ is a fertile platform to investigate exotic magnetic and electronic states.

Antiferromagnetic spin Seebeck effect across the spin-flop transition: A stochastic Ginzburg-Landau simulation

We investigate the antiferromagnetic spin Seebeck effect across the spin-flop transition in a numerical simulation based on the time-dependent Ginzburg-Landau equation for a bilayer of a uniaxial insulating antiferromagnet and an adjacent metal. By directly simulating the rate of change of the conduction-electron spin density $\mathbit{s}$ in the adjacent metal layer, we demonstrate that a sign reversal of the antiferromagnetic spin Seebeck effect across the spin-flop transition occurs when the interfacial coupling of $\mathbit{s}$ to the staggered magnetization $\mathbit{n}$ of the antiferromagnet dominates, whereas no sign reversal appears when the interfacial coupling of $\mathbit{s}$ to the magnetization $\mathbit{m}$ dominates. Moreover, we show that the sign reversal is influenced by the degree of spin dephasing in the metal layer. Our result indicates that the sign reversal is not a generic property of a simple uniaxial antiferromagnet, but controlled by microscopic details of the exchange coupling at the interface and the spin dephasing in the metal layer.

A Geometrically Frustrated Family of MIIMIIIF5(H2O)2 Mixed-Metal Fluorides with Complex Magnetic Interactions.

Inverse weberites are of interest as geometrically frustrated magnetic materials due to their unique cation arrangement. We have synthesized nine isostructural materials that adopt the inverse weberite crystal structure, which consists of cross-linked kagome layers. These materials, having the general formula MIIMIIIF5(H2O)2 (MII = Co, Mn, Ni, Zn; MIII = Ga, Cr, Fe, V), were synthesized using mild hydrothermal conditions, which yielded phase-pure samples after optimization of the reaction conditions. Their crystal structures and optical, thermal, and magnetic behavior were characterized using single-crystal X-ray diffraction, UV-vis spectroscopy, thermogravimetric analysis, and measurement of the magnetic susceptibility and isothermal magnetization data, respectively. Three distinct types of magnetism were observed, including simple paramagnetism, antiferromagnetism, and canted antiferromagnetism; the last type is accompanied by a high frustration index fin the range 4.16-8.09. We demonstrated that the magnetic behavior of inverse weberites depends on the presence or absence of unpaired-electron-containing cations on the two distinct crystallographic sites, which can be employed for the prediction of the magnetic properties of other compounds in this rich and diverse family.

Antiferromagnetic dispersion relations and nature of magnon pressure

We derive higher-order corrections in the magnon dispersion relations for two- and three-dimensional antiferromagnets exposed to magnetic and staggered fields that are mutually aligned. “Dressing” the magnons is the prerequisite to separate the low-temperature representation of the pressure into a piece due to noninteracting magnons and a piece that corresponds to the magnon–magnon interaction. Both in two and three spatial dimensions, the interaction in the pressure turns out to be attractive. While concrete figures refer to the spin-12 square-lattice and the spin-12 simple cubic lattice antiferromagnet, our results are valid for arbitrary bipartite geometry.

Antiferromagnetic order in CaK(Fe1−xNix)4As4 and its interplay with superconductivity

The magnetic order in CaK(Fe[1-x]Ni[x])4As4 (1144) single crystals (x = 0.051 and 0.033) has been studied by neutron diffraction. We observe magnetic Bragg peaks associated to the same propagation vectors as found for the collinear stripe antiferromagnetic (AFM) order in the related BaFe2As2 (122) compound. The AFM state in 1144 preserves tetragonal symmetry and only a commensurate, non-collinear structure with a hedgehog spin-vortex crystal (SVC) arrangement in the Fe plane and simple AFM stacking along the c direction is consistent with our observations. The SVC order is promoted by the reduced symmetry in the FeAs layer in the 1144 structure. The long-range SVC order coexists with superconductivity, however, similar to the doped 122 compounds, the ordered magnetic moment is gradually suppressed with the developing superconducting order parameter. This supports the notion that both collinear and non-collinear magnetism and superconductivity are competing for the same electrons coupled by Fermi surface nesting in iron arsenide superconductors.

High-energy magnetic excitations in lightly oxygen-doped lanthanum nickel oxides

We investigated magnetic excitations in lightly oxygen doped La2NiO4+δ (δ = 0.02 and 0.11) by inelastic neutron scattering over a wide energy range. It is known that two types of two-dimensional (2D) antiferromagnetic (AF) excitations coexist in these systems, i.e., well-defined excitations with effective exchange interactions suppressed by hole doping in the lower energy region (impurity mode) and higher energy excitations with a steep dispersion (host mode). However, details of these excitations, especially the host mode, has not been well studied so far due to the lack of information in the higher energy region. Our results reveal that host modes can be characterized by a simple 2D AF spin-wave model with the same exchange energy as that of the stoichiometric system in the δ = 0.02 phase. In the δ = 0.11 phase, although considerable broadening was observed, the upper band limit of the host modes was on the same level as that in the stoichiometric system, which implies that the magnitude of intrinsic exchange interaction is not affected by doping. The observed results can help understand the microscopic nature of doped holes in this system and other layered-transition metal oxides.

Temperature-induced phase transition from cycloidal to collinear antiferromagnetism in multiferroic Bi0.9Sm0.1FeO3 driven by f−d induced magnetic anisotropy

In multiferroic BiFeO$_3$ a cycloidal antiferromagnetic structure is coupled to a large electric polarization at room temperature, giving rise to magnetoelectric functionality that may be exploited in novel multiferroic-based devices. In this paper, we demonstrate that by substituting samarium for 10% of the bismuth ions the periodicity of the room temperature cycloid is increased, and by cooling below $\sim15$ K the magnetic structure tends towards a simple G-type antiferromagnet, which is fully established at 1.5 K. We show that this transition results from $f-d$ exchange coupling, which induces a local anisotropy on the iron magnetic moments that destroys the cycloidal order - a result of general significance regarding the stability of non-collinear magnetic structures in the presence of multiple magnetic sublattices.

Mn2MnReO6: Synthesis and Magnetic Structure Determination of a New Transition-Metal-Only Double Perovskite Canted Antiferromagnet

Transition-metal-only double perovskite oxides (A2BB′O6) are of great interest due to their strong and unusual magnetic interactions; only one compound, Mn2FeReO6, was reported in this category to date. Herein, we report the second transition-metal-only double perovskite, Mn2MnReO6, prepared at high pressure and temperature. Mn2MnReO6 crystallizes in a monoclinic P21/n structure, as established by synchrotron X-ray and powder neutron diffraction (PND) methods, with eight-coordinated A sites and rock-salt arrangement of the B and B′-site MnO6 and ReO6. Both the structural analysis and the X-ray absorption near edge spectroscopy results indicate mixed valence states of the B/B′-site in Mn2+2Mn2+/3+Re5+/6+O6. The magnetic and PND studies evidence an antiferromagnetic (AFM) transition at ∼110 K and a transition from a simple AFM to canted AFM with net ferromagnetic component at ∼50 K. The observed Efros–Shklovskii variable-range-hopping semiconducting behavior is attributed to the three (A-site Mn2+, B-site M...

Break it up

Fractional magnetic excitations naturally emerge in one-dimensional spin chains. The search for fractionalization in higher dimensions has focused on frustrated systems but evidence now suggests that it can occur in simple two-dimensional antiferromagnets.

Effect of Cu doping on the magnetic and magnetocaloric properties in the HoNiAl intermetallic compound

The magnetic properties and magnetocaloric effect of Cu doping on HoNiAl (HoNi1−xCuxAl) have been investigated. Two transitions occurred for samples with x=0 and x=0.1 induced by the combination and competition between antiferromagnetic (AFM) and ferromagnetic (FM) orderings. Simple AFM orderings were found in samples with x=0.2 to x=0.7 while FM orderings were found in samples with x=0.8–1. The magnetocaloric effect (MCE) was investigated in selected samples with x=0.3 and 0.8. Large magnetic entropy changes (ΔSM) as −29.2J/kgK at 9K and −19.7J/kgK at 9K with corresponding refrigerant capacity (RC) of 299J/kg, 309J/kg for a field change of 0–50kOe were observed. The large ΔSM and RC without hysteresis loss indicated these materials attractive candidates for magnetic refrigeration in low temperature range.

Electronic structures and ferromagnetism of SnO2 (rutile) doped with double-impurities: First-principles calculations

The electronic and magnetic properties of double-impurities-doped SnO2 (rutile) are explored using first-principles calculations within the generalized gradient approximation to examine their potential use as spintronic system. Calculations are performed for double impurities (M1 and M2) from M1 = Cr, and M2 = Mn, and Re. The origins of ferromagnetism are shown to be different in the two cases. For Sn1-2xCrxMnxO2, the hybridization between Cr-3d and O-2p results in Cr becoming ferromagnetic with a magnetic moment of about 5.0 μB per supercell. The Cr-and Mn-doped SnO2 system exhibits half-metallic ferromagnetism. The strong ferromagnetic couplings between local magnetic moments can be attributed to p-d hybridization. In contrast, in (Cr, Re) codoped TiO2, the local magnetic moments of the impurities and their oxidation states agree with the charge transfer between Cr and Re, which would lead to the ferromagnetic through the double-exchange mechanism in transition metal oxides. Since there are two possible couplings between the impurities, we studied both configurations (ferromagnetic and antiferromagnetic (AF)) for double-impurities-doped SnO2. Our calculations show that a ferromagnetic alignment of the spins is energetically always more stable than simple AF arrangements, which makes these materials possible candidates for spin injection in spintronic devices.

Unusual temperature-dependent exchange interaction in GdFe2Al10in comparison with GdRu2Al10

We investigated the magnetic properties of the antiferromagnetic (AFM) compound Gd$T$${}_{2}$Al${}_{10}$ ($T=\text{Ru}$ and Fe). Although GdRu${}_{2}$Al${}_{10}$ could be understood well as a simple AFM compound, the exchange interaction in GdFe${}_{2}$Al${}_{10}$ is found to be greatly varied with temperature. The magnitude of the AFM exchange interaction is reduced with decreasing temperature. We ascribed its origin to the exchange enhancement of the Fe ion with a decrease of temperature as was observed in YFe${}_{2}$Al${}_{10}$. The ordered moment is found to be along the [011] direction in the $bc$ plane in both compounds from the anisotropic magnetic susceptibility. The origin of the magnetic anisotropy below ${T}_{\mathrm{N}}$ could not be understood by the magnetic dipole interaction, which might come from the AFM order on the zigzag chain.

Lifetimes of Antiferromagnetic Magnons in Two and Three Dimensions: Experiment, Theory, and Numerics

A high-resolution neutron spectroscopic technique is used to measure momentum-resolved magnon lifetimes in the prototypical two- and three-dimensional antiferromagnets Rb(2)MnF(4) and MnF(2), over the full Brillouin zone and a wide range of temperatures. We rederived theories of the lifetime resulting from magnon-magnon scattering, thereby broadening their applicability beyond asymptotically small regions of wave vector and temperature. Corresponding computations, combined with a small contribution reflecting collisions with domain boundaries, yield excellent quantitative agreement with the data. Comprehensive understanding of magnon lifetimes in simple antiferromagnets provides a solid foundation for current research on more complex magnets.

Magnetoelectric responses induced by domain rearrangement and spin structural change in triangular-lattice helimagnets NiI2and CoI2

Dielectric and magnetic properties have been investigated for single crystals of triangular-lattice antiferromagnets NiI${}_{2}$ and CoI${}_{2}$. For NiI${}_{2}$, the proper screw spin order with the magnetic modulation vector $q\ensuremath{\sim}(0.138,0,1.457)$ induces electric polarization ($P$) along the in-plane direction with respect to the triangular lattice basal plane. The $P$ shows monotonic increase as a function of the poling magnetic field ($H$) along the in-plane direction, suggesting the $H$-induced rearrangement of the multiferroic domain out of six possible domains. For CoI${}_{2}$, both in-plane and out-of-plane components of $P$ emerge in the helimagnetic ground state, in which two cycloidal magnetic phases with ${q}_{1}=(\frac{1}{12},\frac{1}{12},\frac{1}{2})$ and ${q}_{2}=(\frac{1}{8},0,\frac{1}{2})$ are supposed to coexist. The application of the in-plane $H$ induces two-step metamagneticlike transitions, which probably goes through another ferroelectric helimagnetic phase as well as a paraelectric spin-collinear phase. Such distinctive magnetoelectric responses in the two simple triangular lattice antiferromagnets demonstrate that even a slight difference in the balance of magnetic interactions leads to a dramatic change of resultant magnetoelectric response in frustrated magnets.

Effect of thermal cycle on the interfacial antiferromagnetic spin configuration and exchange bias in Ni-Mn-Sb alloy

Effect of thermal cycle on the interfacial antiferromagnetic (AFM) spin configuration and exchange bias in Ni50Mn36Sb14 alloy has been investigated. The results indicate thermal cycle can induce further martensitic transition from part of arrested FM phase to AFM phase, leading to the reconstruction of interfacial antiferromagnetic spin configuration. The shape of hysteresis loops at 5 K after cooling back can be tuned from a single-shifted loop to a nearly symmetric double-shifted loop gradually accompanied with exchange bias field increasing to peak value and then decreasing. The evolutions can be illustrated intuitively by a simple AFM bidomain model.

Vacancy and substitutional impurities in the spin-density wave state of Cr from first principles

Density functional theory (DFT) calculations are carried out to study magnetic and energetic properties of vacancy, and magnetic and nonmagnetic substitutional impurities (respectively Fe and Cu) in the ground state of bcc Cr, i.e., spin-density wave (SDW). We find the lowest energy site for all the defects to be around a magnetic node, as compared with the high-spin SDW sites and (100)-layered antiferromagnetic (AF) and nonmagnetic (NM) phases. The corresponding differences for vacancy formation energy are 0.29, 0.32, and 0.23 eV, respectively. The migration of a vacancy is revealed to be highly anisotropic in the SDW state, mainly confined in the nodal and adjacent planes. The energy barrier for such a quasi-bidimensional motion is indeed 0.52 eV lower than that for migration in perpendicular directions. Regarding magnetic modifications of the SDW introduced by point defects, they are confirmed to be weak and rather local at low defect concentrations ($0.27%$ and $0.55%$). Cu behaves similarly to a vacancy-inducing magnetic moment enhancement on neighboring Cr atoms. On the other side, the presence of Fe atoms leads to multiple energy minima with different local magnetic arrangements, particularly around a node, due to competition between neighboring Fe-Cr, Cr-Cr, and Fe-Fe magnetic coupling tendencies. The present results strongly suggest that simple AF and NM phases may not allow an accurate description of defect properties in the ground state of Cr. Instead, an explicit SDW representation is required. In addition, we point out that the presence of vacancy and both Cu and Fe may promote a migration of SDW nodes, which may activate the SDW-to-AF phase transition through a node-annihilation mechanism as proposed in previous works.

Anomalous Magnetic Phase Diagram of CeRu2Al10

We measured the magnetization of CeRu 2 Al 10 single crystal with a good quality along all the crystal axes and disccused the results from the standpoint of the antiferromagnetic (AFM) order recently proposed by Khalyavin et al. χ along all the crystal axes shows a clear thermally activated temperature dependence below T 0 . These results are dificult to be explained at least by a simple AFM order. We propose the possible existence of a spin singlet nature below T 0 even when the AFM order takes place.

Electrical and Magnetic Properties of CeAu2Si2

We succeeded in growing a high-quality single-crystal of CeAu 2 Si 2 , which was previously reported to be highly sample-dependent in terms of electrical and magnetic properties. CeAu 2 Si 2 is not a simple AF1-type antiferromagnet, but reveals three antiferromagnetic transitions in a narrow temperature range from the Neel temperature T N1 =9.6 K to T N3 =8.0 K. A clear metamagnetic transition with two steps was observed at H c1 =53 kOe and H c2 =55 kOe in the magnetization curve below 5 K for the magnetic field along an antiferromagnetic easy-axis, namely, the tetragonal [001] direction, with a saturation moment of 1.53 µ B /Ce. The magnetic susceptibility and magnetization are anisotropic, which are well explained by results of crystalline electric field analyses. We also studied the de Haas–van Alphen (dHvA) effect. The detected dHvA branches are found to be consistent with those of a non-4 f reference compound such as YCu 2 Si 2 .

Magnetism of Fe ion in FeSr2YCu2O6+δ superconductor

FeSr2YCu2O6+δ compounds with various oxygen contents, 6 + δ = 7.02 ∼ 7.55 and FeSr2Y(Cu0.95Zn0.05)2O7.55 compound were synthesized and studied by the magnetization measurement. FeSr2YCu2O7.55 compound shows superconductivity below TC = 56 K and a broad peak at 20 K, which corresponds to the magnetic ordering of Fe ion, in the magnetization measurement. The Curie constants and the asymptotic Curie temperature strongly depend on the oxygen content. Increasing the oxygen contents, the Curie constants and the absolute values of the asymptotic Curie temperature are increased. Since the asymptotic Curie temperature is negative value, the interaction between Fe ions is mainly antiferromagnetic. A hysteresis is observed in the magnetization curve of non-superconducting FeSr2Y(Cu0.95Zn0.05)2O7.55 compound. It implies that the magnetism of Fe ion is not simple antiferromagnetism.