Canted Antiferromagnetic Phase Research Articles

New ordered phase in geometrically frustrated generalized XY model.

Critical properties of a geometrically frustrated generalized XY model with antiferromagnetic (AFM) and third-order antinematic (AN3) couplings on a triangular lattice are studied by Monte Carlo simulation. It is found that such a generalization leads to a phase diagram consisting of three different quasi-long-range ordered (QLRO) phases. Compared to the model with the second-order antinematic (AN2) coupling, besides the AFM and AN3 phases which appear in the limits of relatively strong AFM and AN3 interactions, respectively, it includes an additional complex canted antiferromagnetic (CAFM) phase. It emerges at lower temperatures, wedged between the AFM and AN3 phases as a result of the competition between the AFM and the AN3 couplings, which is absent in the model with the AN2 coupling. The AFM-CAFM and AN3-CAFM phase transitions are concluded to belong to the weak Ising and weak three-state Potts universality classes, respectively. Additionally, all three QLRO phases also feature true LRO of the standard and generalized chiralities, which both vanish simultaneously at second-order phase transitions with non-Ising critical exponents and the critical temperatures slightly higher than the magnetic and nematic order-disorder transition temperatures.

Möbius Insulator and Higher-Order Topology in MnBi_{2n}Te_{3n+1}.

We propose MnBi_{2n}Te_{3n+1} as a magnetically tunable platform for realizing various symmetry-protected higher-order topology. Its canted antiferromagnetic phase can host exotic topological surface states with a Möbius twist that are protected by nonsymmorphic symmetry. Moreover, opposite surfaces hosting Möbius fermions are connected by one-dimensional chiral hinge modes, which offers the first material candidate of a higher-order topological Möbius insulator. We uncover a general mechanism to feasibly induce this exotic physics by applying a small in-plane magnetic field to the antiferromagnetic topological insulating phase of MnBi_{2n}Te_{3n+1}, as well as other proposed axion insulators. For other magnetic configurations, two classes of inversion-protected higher-order topological phases are ubiquitous in this system, which both manifest gapped surfaces and gapless chiral hinge modes. We systematically discuss their classification, microscopic mechanisms, and experimental signatures. Remarkably, the magnetic-field-induced transition between distinct chiral hinge mode configurations provides an effective "topological magnetic switch".

Magnetic field induced antiferromagnetic cone structure in multiferroic BiFeO3

Neutron diffraction measurements were performed under high magnetic fields up to 17 T in a multiferroic ${\mathrm{BiFeO}}_{3}$ single crystal, in which an intermediate magnetic (IM) phase has been found between the cycloid and canted antiferromagnetic phases [S. Kawachi et al., Phys. Rev. Mater. 1, 024408 (2017)]. We clearly found that the incommensurate magnetic peaks, which split perpendicular to the magnetic field in the cycloid phase, rotate by 90 deg to align parallel to the field in the IM phase. The magnetic structure in the IM phase can be best described by an antiferromagnetic cone (AF cone) structure. The transition from the cycloid to AF cone is of first order and the direction of the magnetic wave vector and the easy plane of the cycloidal component are rotated by 90 deg without changing the cycloidal modulation period, whereas the transition from the AF cone to canted antiferromagnetic phase is gradual and the cone angle becomes smaller gradually without changing the modulation period. Interestingly, the cycloidal component as well as the cone angle in the IM phase shows a large hysteresis between the field increasing and decreasing processes. This result, combined with the magnetostriction with a large hysteresis previously reported in the IM phase, suggests a strong magnetoelastic coupling.

Multiferroic behavior from synergetic response of multiple ordering parameters in BiFeO3 single crystal under high magnetic field up to 50 Tesla

BiFeO3, a typical multiferroic compound, owns complicated interactions among its charge, lattice, and spin degrees, while largely remaining a mystery. In this work, the BiFeO3 single crystal has been investigated in pulsed high magnetic fields up to 50 T. The lattice, spin, and charge orderings are found to couple with each other strongly. High magnetic field could drive the spin cycloid phase to a canted antiferromagnetic phase while accompanied by a clear magnetostriction response and weakening of ferroelectric polarization. The critical magnetic field for the magnetic phase transition was shifted to the lower magnetic field region by an external electric field over a broad temperature range, which indicates the complex interaction among magnetization, electrical polarization, and crystal lattice. This work has provided a clear picture to show the synergetic response of multiple ordering parameters during the magnetic phase transition in BiFeO3, which could benefit the design of BiFeO3 based spintronic devices and novel multiferroic materials with strong magnetoelectric coupling.

Spin reorientation transition and spin dynamics study of perovskite orthoferrite TmFeO3 detected by electron paramagnetic resonance.

The temperature-dependent spin-reorientation transition (SRT) and spin interaction mechanism of bulk TmFeO3 were studied by the electron paramagnetic resonance (EPR) method. The combined experimental results of magnetic curves and EPR spectra confirmed that there is an antiferromagnetic transition at 85 K with a reentering ferromagnetic state due to the spin-reorientation behavior. In the high-temperature region of T > 90 K, there are three distinct resonance peaks in the EPR spectrum, which indicates the presence of multiple magnetic phases (canted antiferromagnetic, weak ferromagnetic, and paramagnetic phases). In the low-temperature region (T < 85 K), the temperature dependence of the EPR linewidth, effective g-factor, and intensity can be used to infer a strong spin-lattice correlation. Different magnetic interactions such as Fe3+-Fe3+, Fe3+-Tm3+, and Tm3+-Tm3+ lead to a paramagnetic-canted antiferromagnetic phase at T > 85 K, with SRT between 85-65 K and ferromagnetic interaction at the lower temperature, respectively. Above 90 K, we find that the spin relaxation mechanism is determined by the mixture of spin-spin and spin-lattice interactions. Below 85 K, the transverse relaxation rate increases with the decrease in temperature, which is consistent with the weakening of the fluctuating internal field in this temperature region. This EPR detection provides a new method to clarify the strong spin coupling in antiferromagnetic materials.

Direct coupling of ferromagnetic moment and ferroelectric polarization in BiFeO3

The spin-driven component of electric polarization in a single crystal of multiferroic BiFeO$_{3}$ was experimentally investigated in pulsed high magnetic fields up to 41 T. Sequential measurements of electric polarization for various magnetic field directions provide clear evidence of electric polarization normal to the hexagonal $c$ axis (${\bf P}_{\rm t}$) in not only the cycloidal phase, but also the field-induced canted antiferromagnetic phase. The direction of ${\bf P}_{\rm t}$ is directly coupled with the ferromagnetic moment in the canted antiferromagnetic phase, and thus controlled by changing the direction of the applied magnetic field. This magnetoelectric coupling is reasonably reproduced by the metal-ligand hybridization model.

Structural transition, electrical and magnetic properties of Cr doped Bi0.9Sm0.1FeO3 multiferroics

The structural, vibrational, electrical and magnetic properties of Bi0.9Sm0.1Fe1-xCrxO3 (0.02 ≤ x ≤ 0.1) ceramics have been investigated in the vicinity of the morphotropic phase boundary (MPB) between the rhombohedral and orthorhombic structures. X-ray diffraction (XRD) patterns reveal a gradual formation of the orthorhombic phase and Bi14CrO24 impurity with increasing chromium concentration. The Rietveld refinement and Raman scattering analysis confirm the structural transformation from the polar R3c to the anti-polar Pnam phases. The Cole-Cole plots show two relaxation regimes which are attributed to gain and grain boundary responses above room temperature. The slim magnetic hysteresis loops are observed in samples with x = 0.02–0.08, while a robust loop with the coercivity field of Hc ≈ 1200 Oe is observed for x = 0.1 sample where the canted antiferromagnetic phase is significantly contributed to the total magnetization. This result approves that the cycloidal spin structure cannot be suppressed by Cr doping.

The Biaxial Strain Dependence of Magnetic Order in Spin Frustrated Mn3NiN Thin Films

AbstractMulticomponent magnetic phase diagrams are a key property of functional materials for a variety of uses, such as manipulation of magnetization for energy efficient memory, data storage, and cooling applications. Strong spin‐lattice coupling extends this functionality further by allowing electric‐field‐control of magnetization via strain coupling with a piezoelectric. Here this work explores the magnetic phase diagram of piezomagnetic Mn3NiN thin films, with a frustrated noncollinear antiferromagnetic (AFM) structure, as a function of the growth induced biaxial strain. Under compressive strain, the films support a canted AFM state with large coercivity of the transverse anomalous Hall resistivity, ρxy, at low temperature, that transforms at a well‐defined Néel transition temperature (TN) into a soft ferrimagnetic‐like (FIM) state at high temperatures. In stark contrast, under tensile strain, the low temperature canted AFM phase transitions to a state where ρxy is an order of magnitude smaller and therefore consistent with a low magnetization phase. Neutron scattering confirms that the high temperature FIM‐like phase of compressively strained films is magnetically ordered and the transition at TN is first‐order. The results open the field toward future exploration of electric‐field‐driven piezospintronic and thin film caloric cooling applications in both Mn3NiN itself and the broader Mn3AN family.

Magnetic and electrocatalytic properties of transition metal doped MoS2 nanocrystals

In this paper, the magnetic and electrocatalytic properties of hydrothermally grown transition metal doped (10% of Co, Ni, Fe, and Mn) 2H-MoS2 nanocrystals (NCs) with a particle size 25–30 nm are reported. The pristine 2H-MoS2 NCs showed a mixture of canted anti-ferromagnetic and ferromagnetic behavior. While Co, Ni, and Fe doped MoS2 NCs revealed room temperature ferromagnetism, Mn doped MoS2 NCs showed room temperature paramagnetism, predominantly. The ground state of all the materials is found to be canted-antiferromagnetic phase. To study electrocatalytic performance for hydrogen evolution reaction, polarization curves were measured for undoped and the doped MoS2 NCs. At the overpotential of η = −300 mV, the current densities, listed from greatest to least, are FeMoS2, CoMoS2, MoS2, NiMoS2, and MnMoS2, and the order of catalytic activity found from Tafel slopes is CoMoS2 &amp;gt; MoS2 &amp;gt; NiMoS2 &amp;gt; FeMoS2 &amp;gt; MnMoS2. The increasing number of catalytically active sites in Co doped MoS2 NCs might be responsible for their superior electrocatalytic activity. The present results show that the magnetic order-disorder behavior and catalytic activity can be modulated by choosing the suitable dopants in NCs of 2D materials.

Unsupervised machine learning account of magnetic transitions in the Hubbard model.

We employ several unsupervised machine learning techniques, including autoencoders, random trees embedding, and t-distributed stochastic neighboring ensemble (t-SNE), to reduce the dimensionality of, and therefore classify, raw (auxiliary) spin configurations generated, through Monte Carlo simulations of small clusters, for the Ising and Fermi-Hubbard models at finite temperatures. Results from a convolutional autoencoder for the three-dimensional Ising model can be shown to produce the magnetization and the susceptibility as a function of temperature with a high degree of accuracy. Quantum fluctuations distort this picture and prevent us from making such connections between the output of the autoencoder and physical observables for the Hubbard model. However, we are able to define an indicator based on the output of the t-SNE algorithm that shows a near perfect agreement with the antiferromagnetic structure factor of the model in two and three spatial dimensions in the weak-coupling regime. t-SNE also predicts a transition to the canted antiferromagnetic phase for the three-dimensional model when a strong magnetic field is present. We show that these techniques cannot be expected to work away from half filling when the "sign problem" in quantum Monte Carlo simulations is present.

Phase diagrams of the Kane-Mele-Hubbard model in the presence of an external magnetic field

We studied the Kane-Mele-Hubbard model at half filling with Zeeman magnetic field using rotationally invariant slave boson method. The competition between external magnetic field and spin orbital coupling at large Hubbard U is explored. It is found that different canted antiferromagnetic phases exist in the presence of longitudinal and transverse magnetic fields. With longitudinal external magnetic field and strong electron correlation, the z component of the local moment is preferred by the finite spin-orbital coupling.

Spin-Flop Transition and a Tilted Canted Spin Structure in a Coupled Antiferromagnet

We study a uniaxial coupled Heisenberg antiferromagnet that consists of two subsystems of classical spins with small and large lengths and spin-flop transitions in a magnetic field parallel to the magnetic easy axis. It is proved that the anisotropy of inter-subsystem coupling stabilizes an asymmetric canted antiferromagnetic phase with a tilted direction of antiferromagnetism that is not perpendicular to the magnetic field. In contrast to the conventional first-order spin-flop transition, the spin-flop transition from the Neel phase to such a tilted canted antiferromagnetic (TCAF) phase is of the second order in the absence of simple anisotropic energies in the subsystems. The transition from the TCAF phase to the high-field saturated spin phase is of the second order in the strong coupling limit of the exchange interactions J1 between the small spins, whereas when J1 is finite, it becomes first-order. Therefore, in the former case, the TCAF phase converts the Neel phase continuously into the saturated p...

Emergence of helical edge conduction in graphene at theν=0quantum Hall state

The conductance of graphene subject to a strong, tilted magnetic field exhibits a dramatic change from insulating to conducting behavior with tilt-angle, regarded as evidence for the transition from a canted antiferromagnetic (CAF) to a ferromagnetic (FM) \nu=0 quantum Hall state. We develop a theory for the electric transport in this system based on the spin-charge connection, whereby the evolution in the nature of collective spin excitations is reflected in the charge-carrying modes. To this end, we derive an effective field theoretical description of the low-energy excitations, associated with quantum fluctuations of the spin-valley domain wall ground-state configuration which characterizes the two-dimensional (2D) system with an edge. This analysis yields a model describing a one-dimensional charged edge mode coupled to charge-neutral spin-wave excitations in the 2D bulk. Focusing particularly on the FM phase, naively expected to exhibit perfect conductance, we study a mechanism whereby the coupling to these bulk excitations assists in generating back-scattering. Our theory yields the conductance as a function of temperature and the Zeeman energy - the parameter that tunes the transition between the FM and CAF phases - with behavior in qualitative agreement with experiment.

Strong ferromagnetism induced by canted antiferromagnetic order in double perovskite iridates(La1−xSrx)2ZnIrO6

Iridates represent a unique material system that possesses both strong spin-orbit coupling and electron correlation. The interplay between spin-orbit coupling and correlation could facilitate the emergence of novel electronic and magnetic states. In this work, we report on a systematic study of magnetism in the double perovskite iridate ${\mathrm{La}}_{2}{\mathrm{ZnIrO}}_{6}$ and its hole-doped compounds $({\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}){}_{2}{\mathrm{ZnIrO}}_{6}$ via dc magnetization measurement, heat capacity characterization, electron spin resonance spectroscopy, and simple modeling. Undoped ${\mathrm{La}}_{2}{\mathrm{ZnIrO}}_{6}$ undergoes two magnetic transitions, at ${T}_{1}\ensuremath{\sim}7.3$ K and ${T}_{2}\ensuremath{\sim}8.5$ K, respectively. While magnetic hysteresis loops with large remnant moments are observed below these two transition temperatures, the corresponding magnetic states are shown to be canted antiferromagnetic by the linear increase in magnetization in the high field region along with the observation of antiferromagnetic resonance. The nature of the canted antiferromagnetic states with large canting angles can be understood by a simple model that includes both the Heisenberg exchange interaction and the Dzyaloshinskii-Moriya interaction. With the introduction of ${\mathrm{Ir}}^{5+}$ by ${\mathrm{Sr}}^{2+}$ doping, the canted antiferromagnetic phases are suppressed, accompanied by an enhancement of electrical conductivity.

Magnetization Reversal in PrCrO&lt;sub&gt;3&lt;/sub&gt;

PrCrO3(PCO) samples were prepared by Citric acid route .The samples were characterized by XRD and SEM. The sample exhibits a single phase orthorhombic structure with Pbnm space group. The temperature dependent and field dependent magnetic measurements were measured in the range of 5K-400K at 100 Oe field and 0 to 5T field at 5K and RT respectively .The temperature dependence of dc magnetic properties show that the ZFC and FC magnetization curves are irreversible strongly and nearly symmetrical below 240K .There appears a novel magnetization behavior with negative magnetization characteristic in ZFC, the diamagnetism like behavior .This behavior exhibits the coexistence of canted anti-ferromagnetic and weak ferromagnetic phase and the existence of competition mechanism below 240K . This behavior can be interpreted from the interaction between Pr3+and Cr3+moments .The field and temperature dependent magnetization indicates the phase transition from canted anti ferromagnetic to paramagnetic occurred below 240K. In the region of higher temperature above 240K, PrCrO3behaved as a typical Curie-Weiss paramagnetic.Keywords: Orthochromites ,Multiferroics ,Neel temperature.PACS: 75.85 +t, 75.60 d, 75.50.Ee,75.30 Et,76.30 Kg

Nuclear magnetometry studies of spin dynamics in quantum Hall systems

We performed a nuclear magnetometry study on quantum Hall ferromagnet with a bilayer total filling factor of $\nu_{\rm{tot}} = 2$. We found not only a rapid nuclear relaxation but also a sudden change in the nuclear spin polarization distribution after a one-second interaction with a canted antiferromagnetic phase. We discuss the possibility of observing cooperative phenomena coming from nuclear spin ensemble triggered by electrons with collective spin interactions.

Exchange bias effect in polycrystalline SR2IrO4

We report the presence of an exchange bias effect in a layered iridate compound, Sr2IrO4, in polycrystalline form. The Rietveld refinement of the x-ray diffraction pattern shows that Sr2IrO4 crystallizes in a tetragonal structure (I41acd). The temperature dependence of zero-field cooled (ZFC) and field cooled (FC) magnetization measurements show a magnetic ordering temperature of ~240 K, which is considered as its canted antiferromagnetic ordering temperature. An irreversibility between ZFC and FC curves is observed at Tirr, which decreases with an increasing field (H). The Tirr vs. H2/3 plot follows the Almeida-Thouless (AT) line. The presence of an AT line and a significant amount of coercivity (~0.3 T) at 5 K hint a cluster-glass like behaviour in Sr2IrO4 polycrystals. A negative exchange bias effect has been observed at 5 K with an exchange bias field of 0.018 T, which is attributed to an interfacial exchange interaction between a canted antiferromagnetic phase and a probable cluster-glass phase. This is the first report on the observation of an exchange bias effect in Sr2IrO4. Further studies are underway for a detailed understanding.

Spectrum of edge states in theν=0quantum Hall phases in graphene

Edge excitations of the $\ensuremath{\nu}=0$ quantum Hall state in monolayer graphene are studied within the mean-field theory with different symmetry-breaking terms. The analytical expressions for the continuum (Dirac) model wave functions are obtained for the charge density wave, Kekul\'e distortion, ferromagnetic, and (canted) antiferromagnetic phases. The dispersion equations for each phase and boundary type (zigzag and armchair) are derived, numerically solved, and compared to the results of the corresponding effective tight-binding model. The effect of the next-to-nearest neighbor hopping parameter on the edge state spectrum is studied and revealed to be essential. The criteria for the existence of gapless edge states are established for each phase and edge type.

Terahertz–infrared electrodynamics of overdoped manganites La1–xCaxMnO3

We have measured low-temperature terahertz and infrared spectra of La1–xCa xMnO3 with x = 0.5; 0.6; 2/3, 0.7; 3/4, 0.85; 0.9; 0.95; 0.98 and x = 1 in the form of ceramics and epitaxial films. In the charge-ordered state for commensurate dopings (x = 2/3 and 3/4), we observed an absorption band at frequencies corresponding to the position of the lowest energy van Hove singularity in the folded Brillouin zone. The band is assigned to the boson peak. We observed qualitatively the same boson peak in Raman spectra of La1/3Ca2/3MnO3 ceramics. In antiferromagnetic phase, for the 0.5 ≤ x < 0.85 range of doping, the conductivity mechanism gradually changes from a hopping-like transport at low temperatures to the Drude behavior at elevated temperatures in the paramagnetic phase. For 0.85 ≤ x < 1 (canted antiferromagnetic phase), the electrons behave as Drude-like carriers in the whole temperature interval 5–300 K.

Investigation of magnetic and electrical transport properties of Dy2Ni2Sn

The magnetic and transport properties of the ternary rare-earth compound Dy2Ni2Sn are reported. The compound undergoes a long range antiferromagnetic ordering below TN=43K with a collinear structure. A second transition is observed below about Tt=28K, where spin canting takes place. We find clear thermal hysteresis in our magnetization data between 20 and 45K, indicating the first order nature of the magnetic transitions occurring at TN and Tt. Clear signature of metamagnetism is observed in the canted antiferromagnetic phase. The change in entropy on the application of magnetic field (magnetocaloric effect) was calculated from the isothermal magnetization data and it shows negative and positive peaks at TN and Tt respectively. The thermal variation of resistivity shows clear peak like signature near TN, which gets suppressed under applied magnetic field resulting negative magnetoresistance. The low temperature resistivity (below Tt) can be well fitted with the model available for spin dependent s–f scattering in antiferromagnetic system having well localized moments. The data also indicate short range correlations well above the antiferromagnetic transition point, which might be related to the two dimensional spin–spin correlations in this layered compound.