Search

The recent discoveries of surprisingly large anomalous Hall effect (AHE) in antiferromagnets have attracted much attention due to their promising use in spintronics devices. However, such AHE‐hosting antiferromagnetic materials are rare in nature. Herein, it is demonstrated that Mn2.4Ga, a Fermi‐level‐tuned kagome antiferromagnet, has a large anomalous Hall conductivity of ≈150 Ω−1 cm−1 at room temperature that surpasses the usual high values (i.e., 20–50 Ω−1 cm−1) observed so far in two outstanding kagome antiferromagnets, Mn3Sn and Mn3Ge. Although the triangular spin structure of Mn2.4Ga shows a weak net magnetic moment of ≈0.05 µB per formula unit, it guarantees a nonzero Berry curvature in the kagome plane. Moreover, the anomalous Hall conductivity exhibits a sign reversal with the rotation of a small magnetic field that can be ascribed to the field‐controlled chirality of the spin triangular structure. This theoretical calculations further suggest that the large AHE in Mn2.4Ga originates from a significantly enhanced Berry curvature associated with the tuning of the Fermi level close to the Weyl points. These properties, together with the ability to manipulate moment orientations using a moderate external magnetic field, make Mn2.4Ga extremely exciting for future antiferromagnetic spintronics. [ABSTRACT FROM AUTHOR]

In order to improve the large anomalous Hall effect (AHE) in Mn3Sn thin films, we eliminated the co-existing Mn2Sn phase in the films by changing the composition; 50 nm thick polycrystalline Mn3+xSn thin films were fabricated on Si/SiO2 substrates by the sputtering method followed by a thermal annealing process in vacuum. The film compositions were Mn70Sn30(sample-A), Mn75Sn25(sample-B), and Mn80Sn20(sample-C) in as-deposited state and were slightly changed to be Mn75Sn25(sample-A), Mn77Sn23(sample-B), and Mn78Sn22(sample-C), respectively, after the annealing at 500 °C. From a structural analysis by X-ray diffractometry, the sample-C was considered to crystallize to Mn3Sn phase without passing the crystallization of Mn2Sn phase at 300 °C, differently from the sample-A. The saturation magnetization, $M_{\mathrm {S}}$ , of the sample-A significantly increased below 250 K, corresponding with the Curie temperature of Mn2Sn. On the other hand, $M_{\mathrm {S}}$ did not show significant changes with cooling temperature in the samples-B and -C. An AHE was observed at the room temperature in all the samples. The anomalous Hall conductivity, $\sigma _{\mathrm {AH}}$ , at the room temperature increased in magnitude, as the content of Mn increased. The sign of $\sigma _{\mathrm {AH}}$ changed from negative to positive in the sample-A with cooling temperature. On the other hand, the sign remained negative in the sample-C. These differences might be due to the elimination of co-existing Mn2Sn phase in the Mn3Sn thin films with enlarging the Mn content from the stoichiometry. Consequently, we successfully improved the large AHE in polycrystalline antiferromagnetic Mn3Sn thin films. [ABSTRACT FROM AUTHOR]

Abstract We study diluted antiferromagnetic Ising models on triangular and kagome lattices in a magnetic field, using the replica-exchange Monte Carlo method. We observe seven and five plateaus in the magnetization curve of the diluted antiferromagnetic Ising model on the triangular and kagome lattices, respectively, when a magnetic field is applied. These observations contrast with the two plateaus observed in the pure model. The origin of multiple plateaus is investigated by considering the spin configuration of triangles in the diluted models. We compare these results with those of a diluted antiferromagnetic Ising model on the three-dimensional pyrochlore lattice in a magnetic field pointing in the [111] direction, sometimes referred to as the "kagome-ice" problem. We discuss the similarity and dissimilarity of the magnetization curves of the "kagome-ice" state and the two-dimensional kagome lattice. Highlights • Calculations of diluted antiferromagnetic Ising models on triangular and kagome lattices were performed. • The origin of multiple magnetization plateaus is investigated in diluted models. • The similarity and dissimilarity of the magnetization curves of the "kagome-ice" state were discussed. [ABSTRACT FROM AUTHOR]

Abstract We investigate the antiferromagnetic spin- 1 ∕ 2 Ising model in the presence of the external magnetic field on the geometrically frustrated kagome lattice using the effective field theory cluster approximation up to the size of the cluster consisting of 12 connected sites which form typical basic geometrical structure of the kagome lattice. The magnetization properties, systems of the ground states, as well as the specific heat capacity behavior of the model are investigated depending on the cluster size. It is shown that properties of the model related to the frustration, such as the formation of discrete system of ground states, strongly depend on the used cluster approximation. It is shown that besides physically relevant ground states the model also exhibits the existence of ground states which are related to the used effective field theory technique and should disappear in the limit n → ∞ of the n -site cluster approximation with simultaneous formation of physically relevant ground states of the Ising model on the kagome lattice. The unphysical origin of these ground states is also demonstrated by the low temperature behavior of the specific heat capacity which exhibits even inverse Schottky peaks with negative values of the specific heat capacity which are reduced with increasing of the cluster size approximation towards physically acceptable behavior. For completeness, the dependence of the position of the critical temperature and the behavior of the spontaneous magnetization and specific heat capacity of the ferromagnetic model in the zero external magnetic field on the size of the cluster approximation is also briefly discussed. Highlights • Dependence of magnetization properties of the model on cluster size is studied. • The formation of the magnetization plateaus for low temperatures is shown. • The existence of the single-point ground states is also shown. • Anomalies of the specific heat capacity are investigated. • Dependence of the critical temperature of the ferromagnetic model on the size of cluster approximation is studied. [ABSTRACT FROM AUTHOR]

We observe significant exchange-bias effect below ∼ 76 K in antiferromagnetic YbBaCo 4 O 7 . Exchange-bias field ( H E ) is ∼ 10 kOe for 50 kOe cooling-field ( H c o o l ) at 4 K. The H E increases considerably with H c o o l associated with the nominal increase of coercivity ( H C ) . Low H C provides high value of H E / H C ( ∼ 15) at 4 K. High H E / H C ratio and nominal increase of H C are appealing. The results suggest robust EB effect associated with the minimal occurrence of inhomogeneous micro-domains, which is potential for the applications. Magnetic phase separation between antiferromagnetic components with k 1 = (0, 0, 0) and k 2 = (1/2, 0, 0) propagation vectors of the P b n 2 1 space group is correlated with the exchange-bias effect. [ABSTRACT FROM AUTHOR]

The low temperature phases of Na2Ti3Cl8 and their phase transitions were investigated by powder neutron diffraction, heat capacity and magnetic susceptibility measurements between 1.6 K and room temperature. Aside from the previously known high temperature α-phase (R3m) and low temperature γ-phase (R3m), a new intermediate temperature β-phase was detected. It has a k = (1/4,1/4,0) superstructure and its molar volume and XT product are half way between the α- and γ-phases. The β-phase is observed between 210 K and 190 K on cooling in powder samples. Its formation is kinetically hindered in crystals. Upon heating the β→α transition occurs at 227 K. From the γ- phase, a γ→α transitions is observed on heating. Only in heat capacity measurements, a shoulder of the peak indicates an intermediate formation of the β-phase. Strong antiferromagnetic interactions between the Ti2+ ions result in the formation of triangular trimers (Ti3 clusters). In the γ-phase all Ti2+ ions are part of trimers. For the β-phase a structural model is proposed, where half of the Ti2+ ions form trimers. No longrange magnetic order was observed in Na2Ti3Cl8 down to 1.6 K. [ABSTRACT FROM AUTHOR]

Thermodynamic quantities as entropy and specific heat that are of evident interest, are obtained for the nearest-neighbor antiferromagnetic Heisenberg model on kagome lattice using the linear spin-wave approach. The results are obtained for different extensions of the model with single-ion anisotropy and out-of-plane Dzyaloshinskii–Moriya (DMI) interaction. We obtain the entropy as a function of the DMI interaction, single-ion anisotropy strength and anisotropy with aim to verify the effect of these corrections that occurs in real magnetic materials on entropy and specific heat. Furthermore, we obtain the specific heat as a function of temperature T and found a discontinuity in the range of large T indicating so, a phase transition in this range of temperature. • The entropy and specific heat as a function of T and parameters of the system are calculated using the spin wave approach. • The specific heat is analyzed at limit of high-temperature and low-temperature. • The behavior of specific heat at high-temperature is analyzed. [ABSTRACT FROM AUTHOR]

Minerals of the atacamite group such as herbertsmithite and kapellasite have recently attracted enormous attention as the S = ½ Kagomé antiferromagnets for achieving the quantum spin liquid (QSL) state with diverse technological applications. Herein we report on the synthesis of the newly discovered mineral centennialite by using an unconventional 'solid-state' reaction method at 463 K. Synthetic centennialite, CaCuCl(OH)·0.73HO, has been characterized by scanning electron microscopy, electron microprobe analyses, Fourier-transform infrared spectroscopy, thermogravimetric and differential scanning calorimetric analyses, single-crystal X-ray diffraction structure refinements, and magnetic susceptibility measurements. The crystal structure of centennialite is characterized by a perfect (threefold symmetry) Kagomé layer with <5 % substitution between Ca and Cu and therefore differs from those of herbertsmithite and kapellasite, in which 15-25 % mixing between similar Zn and Cu atoms dramatically affects the QSL state. Centennialite remains antiferromagnetic down to ~7 K with a moderate spin frustration (i.e., a Weiss temperature θ = −56 K and a spin frustration parameter f = 8), but exhibits a canted antiferromagnetic ordering with a ferromagnetic component at lower temperatures. [ABSTRACT FROM AUTHOR]

We propose a method to study the magnetic properties of a disordered Ising kagome lattice. The model considers small spin clusters with infinite-range disordered couplings and short-range ferromagnetic (FE) or antiferromagnetic interactions. The correlated cluster mean-field theory is used to obtain an effective single-cluster problem. A finite disorder intensity in FE kagome lattice introduces a cluster spin-glass (CSG) phase. Nevertheless, an infinitesimal disorder stabilizes the CSG behavior in the geometrically frustrated kagome system. Entropy, magnetic susceptibility and spin–spin correlation are used to describe the interplay between disorder and geometric frustration (GF). We find that GF plays an important role in the low-disorder CSG phase. However, the increase of disorder can rule out the effect of GF. [ABSTRACT FROM AUTHOR]

Two new members of the A2B'Cu3F12 family of kagome-related materials have been prepared, in order to further understand the crystal-chemical relationships, phase transitions and magnetic behaviour within this family of potentially frustrated S = 1/2 two-dimensional quantum magnets. Cs2TiCu3F12 adopts a crystal structure with the ideal kagome lattice topology (space group R...m) at ambient temperature. Diffraction studies reveal different symmetry-lowering structural phase transitions in single crystal and polycrystalline forms at sub-ambient temperatures, with the single crystal form retaining rhombohedral symmetry and the powder form being monoclinic. In both cases, long-range antiferromagnetic order occurs in the region 16-20 K. Rb2TiCu3F12 adopts a distorted triclinic structure even at ambient temperatures. [ABSTRACT FROM AUTHOR]

Abstract: Structural and magnetic properties of the geometrically frustrated layered compound YBaCo4O7 have been studied by magnetization and neutron diffraction. A layered type crystal structure, with alternating tetrahedral layers of Kagomé and triangular types, along the c axis (hexagonal symmetry, space group P63 mc) has been found. The oxygen content of the present compound was determined by iodometric titration to be 7.00 ± 0.01. Presence of a short-range antiferromagnetic ordering (below T N ∼ 110 K) has been concluded from the appearance of an addition broad magnetic peak (at Q ∼ 1.35 Å−1) in the neutron diffraction pattern. A staggered chiral type spin structure in the Kagomé layers has been found. Presence of a significant magneto-structural coupling is concluded from the changes in lattice parameters across the magnetic ordering temperature T N ∼ 110 K. [Copyright &y& Elsevier]

• A frustrated antiferromagnetic system in MFT approximations is studied. • Dependence of magnetization of the model of a cluster of the 12 sites is studied. • The formation of the magnetization plateaus for low temperatures is shown. • Appearance of magnetic charges in the Kagome lattice is found. In this work, we investigate the magnetic properties using the hybrid Hamiltonian (spin/charge) in the Ising spin-1/2 antiferromagnetic model in the kagome lattice, which presents geometric frustration. The study was carried out using the Mean-Field theory obtained from the generalization of Callen's identity to obtain expressions for the magnitude magnetization as a function of temperature and an external field. In the presence of an external field the model exhibits the characteristics of a frustrated system through the appearance of magnetization plateaus on the magnetization curves. As geometric frustration in magnetic materials can provide exotic states of matter, in our investigations it was possible to verify the appearance of magnetic charges in the kagome lattice through a hexagonal sublattice using the spin/charge hybrid model. [ABSTRACT FROM AUTHOR]

Herein, the spin dynamics for various magnetic configurations arranged on a Kagome lattice is investigated. Using a Holstein–Primakoff expansion of the isotropic Heisenberg Hamiltonian with multiple exchange parameters, the development and evolution of magnetic Dirac nodes with both anisotropy and magnetic field are examined. From the classical energies, the phase diagrams for the ferromagnetic (FM), antiferrimagnetic (AfM), and the 120° phases are shown as functions of J1, J2, J3, and anisotropy. Furthermore, the production of bosonic Dirac and Weyl nodes in the spin‐wave spectra is shown. Through frustration of the magnetic geometry, a connection to the asymmetric properties of the Kagome lattice and the various antiferromagnetic configurations is discerned. Most interesting is the 120° phase, which does not have Dirac nodes when considering only J1 due to the formation of an analogous antiferromagnetic honeycomb lattice, but gains Dirac symmetry with next‐nearest neighbor interactions. Additionally, the presence of flat modes that are characteristic of cluster excitations is shown. Further study of external frustrations from a magnetic field and anisotropy reveals a tunability of the exchange interactions and nodal points. [ABSTRACT FROM AUTHOR]

The entropy properties of the antiferromagnetic spin- 1 ∕ 2 Ising model in the presence of the external magnetic field on the kagome lattice are studied in the framework of various effective-field theory cluster approximations up to the size of the cluster consisting of 12 connected sites, which form typical basic star-like geometrical structure of the kagome lattice. The dependence of the entropy on the reduced temperature is studied for various specific values of the external magnetic field and the corresponding residual entropies are found. It is shown that the effective-field theory cluster approximation technique is suitable for description of the entropy properties of the model for values of the magnetic field in which real single-point ground states are formed. In this case, obtained values of the residual entropies are even in very good quantitative accordance with the known exact result for the model in the zero external magnetic field. On the other hand, in the intervals of the magnetic field, in which the artificial plateau and single-point ground states are formed, the entropy demonstrates strong low-temperature dependence on the used cluster approximation and, moreover, it can also exhibit the unphysical reentrant behavior, i.e., the existence of temperature intervals in which the entropy decreases with increasing temperature. It is shown, however, that this nonstandard low-temperature behavior of the entropy naturally explains the formation of artificial low-temperature inverse Schottky peaks in the temperature behavior of the specific heat capacity observed and discussed recently in Jurčišinová and Jurčišin (2019) and is reduced with increasing the size of the used cluster approximation towards the physically acceptable behavior. • EFT is used for analysis of entropy properties of a frustrated system. • Dependence of entropy properties of the model on the cluster size is studied. • The residual entropies of ground states of the model are determined. • Anomalies in the low-temperature behavior of the entropy are discussed. [ABSTRACT FROM AUTHOR]