Antiferromagnetic Type Research Articles

Nontransverse factorizing fields and entanglement in finite spin systems

We determine the conditions for the existence of non-transverse factorizing magnetic fields in general spin arrays with anisotropic XYZ couplings of arbitrary range. It is first shown that a uniform maximally aligned completely separable eigenstate can exist just for fields ${h}_s$ parallel to a principal plane and forming four straight lines in field space, with the alignment direction different from that of ${h}_s$ and determined by the anisotropy. Such state always becomes a non-degenerate ground state (GS) for sufficiently strong (yet finite) fields along these lines, in both ferromagnetic (FM) and antiferromagnetic (AFM) type systems. In AFM chains, this field coexists with the non-transverse factorizing field ${h}'_s$ associated with a degenerate N\'eel-type separable GS, which is shown to arise at a level crossing in a finite chain. It is also demonstrated for arbitrary spin that pairwise entanglement reaches full range in the vicinity of both ${h}_s$ and ${h}'_s$, vanishing at ${h}_s$ but approaching small yet finite side-limits at ${h}'_s$, which are analytically determined. The behavior of the block entropy and entanglement spectrum in their vicinity is also analyzed.

Magnetic and dielectric properties of Mn 2 V 2 O 7

The magnetic and dielectric properties of the manganese di-vanadate compound Mn2V2O7 are reported. The sample shows martensitic type structural transition close to room temperature which is evident both in the magnetic and dielectric data. Mn2V2O7 shows signature of antiferromagnetic type ordering around 17 K with concomitant anomaly in the dielectric properties at the same point, although no spontaneous electric polarization was found below 17 K. This clearly signifies a magnetic order driven electric anomaly and possibly it is antiferroelectric type with no net polarization. The dielectric relaxation behaviours show marked difference across the structural transition close to room temperature. Interestingly, the sample shows reversible switching behaviour across the structural transition close to 300 K between high and low dielectric states which can have important practical applications.

Coexistence of Antiferromagnetism and Superconductivity in Heavy Fermion Cerium Compound Ce3PdIn11.

Many current research efforts in strongly correlated systems focus on the interplay between magnetism and superconductivity. Here we report on coexistence of both cooperative ordered states in recently discovered stoichiometric and fully inversion symmetric heavy fermion compound Ce3PdIn11 at ambient pressure. Thermodynamic and transport measurements reveal two successive magnetic transitions at T1 = 1.67 K and TN = 1.53 K into antiferromagnetic type of ordered states. Below Tc = 0.42 K the compound enters a superconducting state. The large initial slope of dBc2/dT ≈ – 8.6 T/K indicates that heavy quasiparticles form the Cooper pairs. The origin of the two magnetic transitions and the coexistence of magnetism and superconductivity is briefly discussed in the context of the coexistence of the two inequivalent Ce-sublattices in the unit cell of Ce3PdIn11 with different Kondo couplings to the conduction electrons.

Low dimensional magnetism in MnNb2−xVxO6

The structural and magnetic properties of MnNb2−xVxO6 samples were studied. These materials belong to the AB2O6 class, which presents low-dimensional magnetism. Curie-Weiss fitting gives a negative Weiss temperature that is a characteristic of dominant antiferromagnetic interactions in paramagnetic region. Rietveld refinements of neutron diffraction data show that magnetic moments are aligned antiferromagnetically within the zig-zag chains running along the c axis. Unlike other ANb2O6 type systems crystallizing also in Pbcn space group and presenting ferromagnetic Ising chains, MnNb2−xVxO6 samples exhibit antiferromagnetic type order along the chains. At 1.5K, the Mn atoms are found to carry an ordered magnetic moment of about 4.3μB. The Mn chains are antiferromagnetic and do not present significant anisotropy. These characteristics and the high spin allowed us to model the system as weakly interacting classical Heisenberg chains, estimating the values of both intra- and interchain exchange constants evolution with x content.

Spin-orbit coupledjeff=1/2iridium moments on the geometrically frustrated fcc lattice

Motivated by experiments on the double perovskites ${\mathrm{La}}_{2}{\mathrm{ZnIrO}}_{6}$ and ${\mathrm{La}}_{2}{\mathrm{MgIrO}}_{6}$, we study the magnetism of spin-orbit coupled ${j}_{\mathrm{eff}}=1/2$ iridium moments on the three-dimensional, geometrically frustrated, face-centered cubic lattice. The symmetry-allowed nearest-neighbor interaction includes Heisenberg, Kitaev, and symmetric off-diagonal exchange. A Luttinger-Tisza analysis shows a rich variety of orders, including collinear $A$-type antiferromagnetism, stripe order with moments along the ${111}$ direction, and incommensurate noncoplanar spirals, and we use Monte Carlo simulations to determine their magnetic ordering temperatures. We argue that existing thermodynamic data on these iridates underscores the presence of a dominant Kitaev exchange, and also suggest a resolution to the puzzle of why ${\mathrm{La}}_{2}{\mathrm{ZnIrO}}_{6}$, but not ${\mathrm{La}}_{2}{\mathrm{MgIrO}}_{6}$, exhibits ``weak'' ferromagnetism.

Magnetic polarization of a Mn-doped semiconductor nanostructure controlled by an external bias

The interplay between the electric and magnetic properties in a double quantum well heterostructure doped by magnetic ions is theoretically investigated. In this material, the magnetism is mediated by the hole gas. The total magnetic polarization of the system is controllable by an external applied bias. The device has two equilibrium states (symmetric and antisymmetric configurations). In the stable configuration (anti-ferromagnetic type), the particle spin distribution is reversed in the adjacent wells. The stability of the system is investigated by simulating the interaction of the hole gas with the light. By using an ab initio method, we estimate the switching time of the device.

Magnetoresistance behavior of Ni80Fe20/Ru/Ni80Fe20 nanostripes

We present a systematic investigation on the effects of interlayer coupling on the magnetoresistance (MR) behavior of Ni80Fe20/Ru(\( t_{Ru}\)/Ni80Fe20 trilayer nanostripes (NSs) as a function of temperature T . By changing \( t_{Ru}\) from 0.8 nm to 1.7 nm, either a ferromagnetic or an antiferromagnetic (AFM) type of interlayer coupling was achieved, leading to a markedly different MR behavior. We observed that the MR response is a superimposition of AMR and GMR effects, and it is significantly dependent on temperature. For AFM coupled NSs, there is a transition from a pure AFM state to a reversed spin-flop phase due to enhanced ferromagnetic pin-hole coupling at low T. Our experimental results are in good agreement with micromagnetic simulations.

Observation of large low temperature magnetocaloric effect in HoCu2

We report the observation of large low temperature magnetocaloric effect and magnetoresistance in the rare-earth based intermetallic compound HoCu2. The compound undergoes an antiferromagnetic type ordering below about TN = 10.5 K, which is second order in nature. The magnetocaloric effect in terms of entropy change under the application of 50 kOe of field is found to have a maximum value of −19.3 J kg−1 K−1 peaking around TN, and an appreciable value of relative cooling power of 268 J kg−1 was associated with it. The sample also shows giant negative magnetoresistance with its value as high as −36.5% around TN for 50 kOe of field. Field induced second order metamagnetic transition is found to be responsible for the observed magnetocaloric and magnetoresistance behaviors in the sample. The sample is devoid of any thermal or field hysteresis by virtue of the second order nature of the transitions, which enables us to exploit large reversible magnetic cooling at cryogenic temperatures.

Effect of Cu substitution on the magnetic and dielectric properties of La2NiMnO6

In the continuation of our previous work [Biswal et al., J. Appl. Phys. 115, 194106 (2014)] of biphasic La2NiMnO6 (LNM) prepared via sol-gel technique, here we are reporting the effect of Cu substitution at Ni site of LNM. The powder x-ray diffraction results of La2Ni1−xCuxMnO6 (x = 0, 0.05, 0.1) confirm the biphasic nature (Pbnm + R-3c) for all samples along with increasing R-3c phase with Cu content in the sample. The temperature variation of magnetization (M) plot shows sharp ferromagnetic transitions of R-3c phase at 285 K, 278 K, and 270 K (obtained from dM/dT plot) and that of Pbnm phase at 165 K, 145 K, and 145 K for x = 0, 0.05, and 0.1, respectively. Weak antiferromagnetic type feature at 25 K (x = 0), is getting pronounced with Cu content in the sample and is now seen at 32 K & 266 K (for x = 0.05) and 32K & 257 K (for x = 0.1). Fitting of Curie-Weiss law in the paramagnetic region of χ−1 vs T plot results slightly lower values of corresponding Tc's of R-3 c phase (277 K, 270 K, and 260 K), thus manifesting possibility of Griffiths like singularity. The onset temperature of Griffiths singularity occurs at 295 K (x = 0) and 281 K (x = 0.05 and 0.1), such that 295–277 K in x = 0, 281–270 K in x = 0.05, and 281–260 K in x = 0.1 sample is in Griffith's phase. Temperature dependent dielectric constant (εr) shows usual step-like transitions with corresponding relaxation peaks in the dielectric loss (D) part. Cu substitution in LNM makes the entire dielectric plot shifts towards lower temperature such that high temperature plateau of step transition becomes evident. The peaks in dielectric loss for all compositions are found to obey Arrhenius law with activation energies 237 meV, 207 meV, and 180 meV for x = 0, 0.05, and 0.1, respectively.

Binuclear copper(II) complex with bis(azomethine) based on 1,3-diaminopropan-2-ol and 4-hydroxy-3-formylcoumarin: Crystal structure and magnetic properties

The binuclear copper(II) complex [Cu2(L)(Mp)(H2O)((CH3)2SO)] (Mp is 6-methoxypurinate anion) with the heterocyclic azomethine ligand, which is the condensation product of 1,3-diaminopropan-2-ol and 4-hydroxy-3-formylcoumarin (H3L), is synthesized and structurally characterized (CIF file CCDC no. 982199). The temperature dependence of the magnetic susceptibility is measured and shows a significant exchange interaction of the antiferromagnetic type (2J = −348 cm−1) in the compound. This sharply distinguishes the new complex from the earlier studied compounds with a similar exchange fragment characteristic of the ferromagnetic exchange. The antiferromagnetic exchange parameter is calculated by the quantum-chemical DFT method in the broken symmetry approximation.

First Principles Investigation of Magnetic Properties of Fe-Ni-Mn-Al Heusler Alloys

The composition dependences of crystal lattice parameters, magnetic moments and magnetic exchange parameters in FexNi2−xMn1+y Al1−y (0.0 ≤ x ≤ 2.0; 0.0 ≤ y ≤ 0.6) Heusler alloys are investigated with the help of first principles calculations. Our simulations have shown that crystal lattice parameter is decreased with Fe content (x) increasing. Our calculations show that increase of Fe content (x) leads increasing of magnetic exchange interactions between Mn atoms at regular positions and Mn atoms at Al positions and change of interaction sign from antiferromagnetic type to ferromagnetic one for Fe content x ≥ 1.4. Competitive behavior between ferromagnetic and antiferromagnetic interactions shows that these alloys have a complex magnetic structure. Calculated data for crystal lattice parameter, magnetic moment and magnetic exchange parameters for pure compounds (x = 0.0 and x = 2.0) are in an agreement with theoretical and experimental data.

A comparative study of HoSn1.1Ge0.9 and DySn1.1Ge0.9 compounds using magnetic, magneto-thermal and magneto-transport measurements

Polycrystalline HoSn1.1Ge0.9 and DySn1.1Ge0.9 compounds have been studied by means of different experimental probes. Both the compounds are antiferromagnetic and show metamagnetic transition at low temperatures. HoSn1.1Ge0.9 shows a sign change in magnetocaloric effect (MCE) and magnetoresistance (MR) with field, which is attributed to the metamagnetic transition. DySn1.1Ge0.9 shows characteristics of a typical antiferromagnet, as evidenced by magnetization, MCE and MR data. 119Sn Mössbauer studies show hyperfine splitting at low temperatures, consistent with magnetization data. Thermoelectric power and resistivity measurements reveal metallic behavior in these compounds. Magnetic, magnetocaloric and the magnetoresistance data clearly show that the antiferromagnetic coupling in DySn1.1Ge0.9 is stronger than in HoSn1.1Ge0.9.

Realization of extreme tunnel magnetoresistance with a molecule-magnet-dimer junction

By means of the Rate equation approach in the sequential tunneling regime, we study spin-polarized transport through a molecule magnet dimer of both ferromagnetic (FM) and antiferromagnetic (AFM) types, which is weakly coupled to collinear FM leads. We pay particular attention to the effect of spin exchange interactions between electron spin and the molecule magnet on the tunnel magnetoresistance (TMR). Giant positive TMR is found in the positive bias with the AFM dimer. Particularly we are able to realize the negative TMR of theoretical lowest limit. And thus the molecule dimer device acts as an ideal valve to blockade completely the current channel of parallel configuration of electrode polarizations.

Manganese(II) coordination polymer with simultaneous azide, tetrazolate and carboxylate bridges: Synthesis, structure and magnetism

The reaction of a pyridinium-containing ligand precursor with manganese(II) chloride and sodium azide yielded a Mn(II) coordination polymer, [MnLN3]n·1.5nH2O, where L is 1-(tetrazolato-5-methyl)pyridinium-4-carboxylate, a bifunctional zwitterionic ligand generated in situ from a non-coordinative precursor via two organic reactions (cyano-to-azide cycloaddition and ester hydrolysis). In the compound, metal ions are connected into uniform chains by the triple bridges consisting of μ-1,1-azide, μ-2,3-tetrazolate and μ-1,3-carboxylate, and the formally anionic chains are charge compensated and interlinked into 2D layers by the cationic 1-methylenepyridinium backbone of the L ligand. The compound displays typical 1D antiferromagnetism with J=−2.37cm−1 through the triple bridges. Magneto-structural analysis indicates the antiferromagnetic interaction increases as the Mn–N–Mn angle of the azide bridge decreases.

Magnetic and Fermi Surface Properties of Antiferromagnet EuCd11

We succeeded in growing a high-quality single crystal of EuCd11 with the BaCd11-type tetragonal structure by the Cd self-flux method, and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization, and de Haas–van Alphen (dHvA) oscillations, together with the electrical resistivity under high pressures up to 8 GPa. The antiferromagnetic ordering was confirmed to occur at the Néel temperature TN = 2.7 K, and the antiferromagnetic state was found to change into the field-induced ferromagnetic state with 7 μB/Eu above a critical field Hc \( \simeq \) 15 kOe for both the magnetic fields H || [100] and [001], revealing a typical Eu-divalent antiferromagnet. Reflecting the large lattice parameters of a = 11.93 Å and c = 7.682 Å with the caged structure, where each Eu atom is surrounded by a polyhedron of 22 Cd atoms, the Brillouin zone and the corresponding Fermi surfaces are small in volume. The detected dHvA branches are well explained by the full potential linear augmented plane wave (FLAPW) energy band calculations for the non-4f reference compound SrCd11, revealing ellipsoidal Fermi surfaces with complicated concave and convex shapes. The present Eu-divalent electronic state is found to be robust against high pressures up to 8 GPa, and does not change into the Eu-trivalent state.

Crystalline field effect and magnetic ordering in the heavy fermion Kondo lattice Ce6Pd12In5

Results of magnetic, specific heat, electric and thermal transport studies carried out on the novel hexagonal-type structure Ce6Pd12In5 compound, with a unique site for Ce, two sites for In and four sites for Pd are reported. The compound exhibits long-range order, probably of antiferromagnetic type, below TN=1.6K in spite of a moment reducing Kondo effect acting on the magnetic Ce3+ ions. A strong influence of magnetic field on the low temperature dependencies of susceptibility, specific heat and electrical resistivity is observed. The crystal-electric field effect, CEF, plays an influential role in the ground state of this compound. The CEF parameters have been estimated. Based upon the low-temperature specific heat we observe heavy fermion behavior with the electronic specific heat coefficient that is enhanced to the value of γ=132mJ/Ce-molK2. In the electrical resistivity, a logarithmic character ρ4f(T)∼-lnT is observed that arises from incoherent Kondo scattering. Towards low temperature this behavior evolves into Kondo lattice formation with a coherence temperature Tcoh≃5.3K, before long-range order takes place. We propose that Ce6Pd12In5 presents a new case study for competing Kondo and magnetic ordering in a high-symmetry lattice, with CEF and magnetocrystalline anisotropy further impacting upon the cooperative magnetic behavior.

Co-existence of ferromagnetic and antiferromagnetic interactions in Mn3Ga(1−x)SnxC

The magnetic properties of the , antiperovskite compounds have been investigated in detail. Though all compounds of this series crystallize in a cubic structure, the Ga rich compounds transform, via a first-order transformation, to an antiferromagnetic ground state and the Sn rich compounds exhibit dominant ferromagnetic interactions at low temperature. In the intermediate range co-existence of ferromagnetic and antiferromagnetic interactions can be seen. The results have been explained to be due to growth of ferromagnetic sub-lattice at the expense of antiferromagnetic sub-lattice with increasing Sn concentration in . This growth occurs to a point where the first-order transition is altered from a ferromagnetic–antiferromagnetic type in Ga rich compounds to a paramagnetic–ferrimagnetic type in .

Antiferromagnetism and Low Magnetostriction in <inline-formula> <tex-math notation="TeX">${\rm Fe}_{100-{\rm x}}{\rm Mn}_{\rm x}$ </tex-math></inline-formula> (<inline-formula> <tex-math notation="TeX">${\rm x}={38}$ </tex-math></inline-formula>, 42, 46, 50, and 55) Alloys

The structural and magnetic properties of polycrystalline Fe100-xMnx alloys with x = 38, 42, 46, 50, and 55 atomic percent were investigated after a heat treatment and a cold rolling process. According to X-ray diffraction (XRD), all samples crystallize into a y -phase. For cold rolled alloys x = 38 and 42, XRD analysis using pole figures showed no texture formation whereas cold rolled alloys with x = 46 and 50 exhibited texture components {110} and with x = 55, {011} . Magnetization measurements clearly demonstrate an antiferromagnetic type of ordering. For both the as-cast as well as the cold rolled materials, magnetostriction measurements at room temperature gave nearly zero magnetostriction.

Exchange bias in Ferromagnetic/Antiferromagnetic bilayer systems with varying microstructure and sequence of layer deposition

Correlations of the exchange bias and surface roughness in bilayer structures of a ferromagnetic (Ni80Fe20)/antiferromagnetic (Ir25Mn75) type (F/AF structures) with varying thickness and sequence of deposition of the AF layer are studied using the angular dependence of the resonance field of the ferromagnetic resonance (FMR). It is found that the roughness of the samples in structures with an AF layer deposited on top of an F layer (TS type) is higher than in structures with an AF layer located at the bottom (BS type). The possible causes of differences in the behavior of the exchange bias as a function of surface roughness in samples with the different location of the AF layer are discussed.

Structure, magnetic, and electric properties of bismuth niobates doped with d-elements: IX. State of nickel in the Bi2BaNi x Nb2−x O9−δ solid solutions with layered perovskite-like structure

The study of magnetic susceptibility of the Bi2BaNi x Nb2−x O9−δ solid solutions has shown that paramagnetic nickel atoms are present in diluted solutions as exchange-bound dimers formed by Ni(III) atoms in the high-spin state and characterized by the exchange parameter J of 12 cm−1. As the concentration of the solid solutions increases, clusters consisting of pairs of ferromagnetic Ni(III) dimers with antiferromagnetic exchange type and J = −170 cm−1 are formed.