AFM Structure Research Articles

Unique magnetic structure of the vdW antiferromagnet VBr3

VBr3 is a van der Waals antiferromagnet below the Néel temperature of 26.5 K with a saturation moment of 1.2 µB/f.u. above the metamagnetic transitions detected in the in-plane and out-of-plane directions. To reveal the AFM structure of VBr3 experimentally, we performed a single-crystal neutron diffraction study on a large high-quality crystal. The collected data confirmed a slight monoclinic distortion of the high-temperature rhombohedral structure below 90 K. The magnetic structure was, nevertheless, investigated within the R-3 model. The antiferromagnetic structure propagation vector k = (1, 0, ½) was revealed. In an attempt to determine the magnetic structure, 72 non-equivalent magnetic reflections were recorded. The experimental data were confronted with the magnetic space groups dictated by the R-3 lattice symmetry and propagation vector. The best agreement between the experimental data and the magnetic structure model was obtained for the space group P-1.1′_c. The magnetic unit cell of the proposed unique antiferromagnetic structure with periodicity 6c is built from two identical triple layers antiferromagnetically coupled along the c axis. Each triple layer comprises a Néel antiferromagnetic monolayer sandwiched between two antiferromagnetically coupled ferromagnetic monolayers.

Out-of-plane weak ferromagnetism at room temperature in lattice-distortion non-collinear antiferromagnet of single-crystal Mn3Sn

Out-of-plane weak ferromagnetic (OWFM) spin arrangements with topological properties can realize a series of interesting physical properties. However, this spin structure tends to exist at low temperatures. The OWFM structure can also be induced at room temperature by hydrostatic pressure, whereas this isotropic approach tends to form helical AFM structures. We report the OWFM spin arrangement in single crystal Mn3Sn by an anisotropic strategy of high-stressconstrained compression deformation at room temperature. Both experimental and theoretical simulation results show that the alignment of the OWFM spin structure is due to the distortion of the atomic scale caused by the strain energy during deformation. The OWFM spin arrangement can significantly change the magnetic property of Mn3Sn. As a result, the remanent magnetization M r for the deformed sample (0.056 μ B/f.u.) is about eleven times that for the pre-deformed sample (0.005 μ B/f.u.), and the coercivity (H c) increases from 0 kOe (pre-deformed sample) to 6.02 kOe (deformed sample). Our findings provide a way to generate the OWFM spin structure at room temperature and may give fresh ideas for creating antiferromagnetic materials with excellent physical properties.

Magnetoelastic coupling with inverse magnetocaloric effect observed in Sr2YRuO6

Sr2YRuO6, a 4d transition metal, Ru ion based double perovskite crystallizes in monoclinic structure with Y and Ru octahedra ordering alternately. The relevance of lattice distortion to complex magnetic ground state is investigated from structural, vibrational, magnetic, transport and thermal properties. Raman modes due to monoclinic distortions are observed. From the temperature dependent magnetization studies, a magnetic transition is observed at 25 K and below that the presence of weak ferromagnetic contribution is noticed. A magnetic frustration parameter of six is evaluated from the magnetic results that suggest the presence of spin frustration on the Ru octahedra leading to geometric frustration in SYRO. Isothermal magnetization measurements are carried out for several temperatures from 8 K to 70 K in small temperature intervals to determine the magnetocaloric effect of Sr2YRuO6. The change in magnetic entropy around the Neel temperature, 25 K and Inverse magnetocaloric effect is observed in the system around this temperature. The change in isothermal magnetic entropy results indicates a canted AFM structure as the ground state. Neutron diffraction data refined using propagation vector, k = (0.5,0.5,0) reveal antiferromagnetic ordering at temperatures below 30 K down to 2 K. Variation of the lattice parameters with temperature from the neutron powder diffraction result signifies the presence of magnetoelastic coupling around 25 K. From the temperature dependent resistivity measurements, a small polaron hopping like conductivity is observed in the system. Activation energy reduces with the increase in temperature. Temperature dependent specific heat data shows no ordering, the absence of peak around magnetic transition along with magnetic contribution well above transition temperature is consistent with magnetic frustration in this system.

Curcuma longa L. Rhizome Extract as a Poly(vinyl chloride)/Graphene Nanocomposite Green Modifier.

In this work, a method to increase the dispersion of graphene (GN) in the matrix of rigid poly(vinyl chloride) (PVC) by using a natural plant extract from Curcuma longa L. (CE) is proposed. Currently, despite the increasing number of reports on the improvement of GN dispersion in PVC blends, still there is a need to find environmentally friendly and economical dispersion stabilizers. We proposed a stabilizer that can be easily obtained from a plant offering thermal stability and high effectiveness. PVC/GN nanocomposites stabilized with the proposed extract were investigated by SEM, AFM (structure), TGA, and Congo red test (thermal properties). Additionally, static and dynamic mechanical properties and electrical resistivity were measured. The use of CE as a graphene dispersant improved its dispersion in the PVC matrix, influenced tensile properties, increased the storage modulus and glass transition temperature, and extended the thermal stability time of nanocomposites. In this work, a CE extract is proposed as an efficient eco-friendly additive for the production of nanocomposites with an improved homogeneity of a nanofiller in the matrix and promising characteristics.

Influence of Tb substitution on the structural and magnetic properties of BiFeO3 multiferroic

The effect of Tb substitution on crystal structure and magnetism in the series Bi1-xTbxFeO3 (x = 0.05, 0.10, 0.15, & 0.2) have been investigated using X-ray diffraction, neutron powder diffraction, Raman scattering and magnetization measurements. In this series, a structural transition from hexagonal (R3c) in x = 0.05 to coexisting hexagonal (R3c) and orthorhombic (Pnma) structures, is observed for compounds with x > 0.05. The magnetization studies indicate an enhancement in the ferromagnetic moment from 0.15 µB (x = 0.05) to 0.7µB (x = 0.2) at 5 K indicating a progressive increase in the canting of the AFM spins in the doped compounds. The magnetic structure of both the hexagonal and the orthorhombic phases are primarily G-type AFM structure at temperatures below 300 K. However, a canting is observed for the spins in the hexagonal phase of compositions with higher Tb content. The structural transition and the canted behaviour of the G-type AFM structure, are attributed to chemical pressure (equivalent of ∼ 5GPa) effects arising from the substitution of Bi3+ ions by Tb3+ ions (x ≤ 0.20), with lower ionic radii, leading to reduction in volume (ΔV/V ∼ 0.9 %). These observations are in agreement with earlier published DFT studies on the effect of external pressure on BiFeO3. An anomalous increase in ε’ is observed around 650 K for all the samples in the vicinity of the Néel temperature (TN ∼ 643 K) of BFO indicating magnetoelectric coupling.

Characterization of Monochromate and Hemichromate AFm Phases and Chromate-Containing Ettringite by 1H, 27Al, and 53Cr MAS NMR Spectroscopy

The calcium aluminate hydrate AFm and AFt phases formed upon hydration of Portland cement have an important role in the stabilization and solidification of hazardous chromate ions in hardened cement. AFm monochromate (Ca4[Al(OH)6]2(CrO4)·12H2O), AFm hemichromate (Ca4[Al(OH)6]2(CrO4)0.5(OH)·12H2O) and the chromate-containing AFt phase, Ca6[Al(OH)6]2-(CrO4)3·24H2O, were synthesized and investigated by 1H, 27Al, and 53Cr MAS NMR spectroscopy. 27Al quadrupolar coupling parameters (CQ, ηQ) and isotropic chemical shifts (δiso) were determined for the three phases, including two distinct Al sites in chromate-AFt, as observed by 27Al MAS and MQMAS NMR. Two dominant peaks are apparent in the 1H MAS NMR spectra of each of the phases. For the AFm phases, these resonances are assigned to framework hydroxyl groups (1.7–2.0 ppm) and water molecules/hydroxyls (5.0–5.5 ppm) in the interlayer. For chromate-AFt, the peaks are ascribed to framework hydroxyl groups in the [Ca6Al2(OH)12]6+ columns (~1.4 ppm) and water molecules (~4.8 ppm) associated with the Ca ions. 53Cr MAS NMR spectra acquired at 22.3 T for the samples show a narrow resonance for both chromate AFm phases, whereas indications of three distinct Cr resonances are apparent for the chromate AFt. The absence of any second-order quadrupolar effects in the 53Cr NMR spectra strongly suggests that the chromate ions are highly mobile in the anionic sites of the AFm and AFt structures. The NMR data reported in this work are in agreement with the reported crystal structures for the chromate AFm and AFt phases and may be useful for identification and characterization of chromate fixation in cementitious systems, complementing information gained from conventional powder X-ray diffraction studies.

Magnetism of two-dimensional honeycomb layered Na2Ni2TeO6 driven by intermediate Na-layer crystal structure

The microscopic spin-spin correlations in the 2D layered spin-1 honeycomb lattice compound Na2Ni2TeO6 have been investigated by neutron diffraction and inelastic neutron scattering. The honeycomb lattice of spin-1 Ni2+ ions, within the crystallographic ab planes, are well separated along the c axis by an intermediate Na layer whose crystal structure contains chiral nuclear density distributions of Na ions. The chirality of the alternating Na layers is opposite. Such alternating chirality of the Na layer dictates the magnetic periodicity along the c axis where an up-up-down-down spin arrangement of the in-plane zigzag AFM structure is found. Besides, the above described commensurate (CM) zigzag AFM order state is found to coexist with an incommensurate (ICM) AFM state below the TN ~ 27.5 K. The ICM state is found to appear at much higher temperature ~ 50 K and persists down to lowest measured temperature of 1.7 K. Our reverse Monte Carlo (RMC) analysis divulges a two dimensional (2D) magnetic correlations (within the ab plane) of the ICM AFM state over the entire temperature range 1.7-50 K. Further, the spin-Hamiltonian has been determined by carrying out inelastic neutron scattering experiments and subsequent linear spin-wave theory analysis which reveals the presence of competing inplane exchange interactions up to 3 rd nearest neighbours consistent with the zigzag AFM ground state, and weak interplanar interaction as well as a weak single-ion-anisotropy. The values of the exchange constants yield that Na2Ni2TeO6 is situated well inside the zigzag AFM phase (spans over a wide ranges of J2/J1 and J3/J1 values) in the theoretical phase diagram. The present study, thus, provides a detailed microscopic understanding of the magnetic correlations and divulges the intertwining magneto-structural correlations.

Magnetization reversal, field-induced transitions and H–T phase diagram of Y1−x Ce x CrO3

We report a systematic study of the magnetic phase diagram in the H–T plane, negative magnetization (NM), exchange interactions and field-induced spin–flop transitions in the distorted perovskite Y1−x Ce x CrO3. Locked AFM and weak-FM configurations in Γ4(G z , F y , A x ) phase of YCrO3 (S = 3/2 ground state) unlocks into the Γ2 (F z , G y , C x ; ) phase of the canted AFM and FM structures with the dilute substitution of Ce (x ⩾ 0.05). The asymmetric and symmetric exchange interaction (J AS ∼ 0.11 meV and J S ∼ 0.85 meV) between the trivalent Ce and Cr enable the positive quartic-anisotropy field ( ∼ 2.85 × 102 Oe) along with the second order anisotropy field ( ∼ 5.93 × 102 Oe). Unlike the pristine YCrO3 compound, the Ce incorporated system exhibits a giant fourth-order anisotropy constant (K 4 = 1.35 × 105 erg/c.c.) due to the asymmetric exchange interaction between the trivalent Ce–Cr which further lifts the free energy of the system and causes lag in the onset of AFM ordering showing the significant thermal hysteresis (ΔT ∼ 10 K) in the field-cooled (FC)-warming measurement protocol as compared to the FC-cooling mode. The H–T phase diagram, mapped from the isothermal magnetization data and differential magnetic susceptibility data with different measurement protocols clearly distinguishes three prominent regions below the T N (∼150 K), viz (i) long-range canted AFM + weak FM phase (Γ4 (G z , F y , A x )), (ii) Γ24 mixed phase and (iii) robust Γ2 (F z , G y , C x ; , ) AFM + FM phases. Tunable spin–flopped transition (∼ 30 kOe), significant negative exchange-bias field (H EB ∼ 2.5 kOe), huge coercive field (H C ∼ 22 kOe) and large NM (ΔM ∼ 280 emu/mole) are the unique characteristic features of the current investigated system.

Alcaligenes faecalis metallo-β-lactamase in extensively drug-resistant Pseudomonas aeruginosa isolates

ObjectivesTo characterize Alcaligenes faecalis metallo-β-lactamase (MBL) AFM-2 and AFM-3 from clinical Pseudomonas aeruginosa isolates NDTH10366, NDTH9845 and WTJH17. MethodsClinical isolates were whole-genome sequenced using the Illumina and Oxford Nanopore platforms. MICs of clinical isolates and transformants containing MBL genes were determined using broth microdilution methods. Kinetic parameters of purified AFM and NDM-1 were measured using a spectrophotometer. The AFM structure was modelled with SWISS-MODEL. ResultsNDTH10366 and NDTH9845 were extensively drug-resistant (XDR) isolates carrying blaAFM-2 and multiple copies of blaKPC-2, whereas WTJH17 was an XDR isolate carrying blaAFM-3. The plasmid-borne blaAFM-2 and blaAFM-3 genes are associated with a novel ISCR element, ISCR29. AFM-2 and AFM-3, differing from AFM-1 by one amino acid substitution each, shared 86.2% and 86.6% amino acid sequence identity with NDM-1, respectively. Phylogenetic analysis confirmed the close relationship between AFM and NDM. Expression of AFM and NDM-1 under their native promoters in DH5α and PAO1 led to elevated MICs for all tested β-lactams except aztreonam. Comparable catalytic abilities were observed for AFM and NDM-1 when hydrolysing nitrocefin, cefepime, imipenem and biapenem, whereas for other tested β-lactams AFM displayed weaker enzymatic activities. Modelling AFM structure revealed a characteristic αβ/βα fold with two zinc-binding active sites. ConclusionsAFM from clinical P. aeruginosa isolates demonstrated β-lactamase activity comparable to NDM-1. Co-carriage of blaAFM and blaKPC renders clinical P. aeruginosa isolates non-susceptible to all antipseudomonal β-lactams. The association of blaAFM genes with translocatable genetic elements and plasmids highlights their concerning potential for dissemination.

Magnetic structures, spin-flop transition, and coupling of Eu and Mn magnetism in the Dirac semimetal EuMnBi2

We report here a comprehensive study of the AFM structures of the Eu and Mn magnetic sublattices as well as the interplay between Eu and Mn magnetism in this compound by using both polarized and non-polarized single-crystal neutron diffraction. Magnetic susceptibility, specific heat capacity measurements and the temperature dependence of magnetic diffractions suggest that the AFM ordering temperature of the Eu and Mn moments is at 22 and 337 K, respectively. The magnetic moments of both Eu and Mn ions are oriented along the crystallographic $c$ axis, and the respective magnetic propagation vector is $\textbf{k}_{Eu} = (0,0,1)$ and $\textbf{k}_{Mn}=(0,0,0)$. With proper neutron absorption correction, the ordered moments are refined at 3 K as 7.7(1) $\mu_B$ and 4.1(1) $\mu_B$ for the Eu and Mn ions, respectively. In addition, a spin-flop (SF) phase transition of the Eu moments in an applied magnetic field along the $c$ axis was confirmed to take place at a critical field of B$_c$ $\sim$ 5.3 T. The evolution of the Eu magnetic moment direction as a function of the applied magnetic field in the SF phase was also determined. Clear kinks in both field and temperature dependence of the magnetic reflections ($\pm1$, 0, 1) of Mn were observed at the onset of the SF phase transition and the AFM order of the Eu moments, respectively. This unambiguously indicates the existence of a strong coupling between Eu and Mn magnetism. The interplay between two magnetic sublattices could bring new possibilities to tune Dirac fermions via changing magnetic structures by applied fields in this class of magnetic topological semimetals.

The electric memory properties of azo-chalcone derivatives based on different film forming processes

The azo chalcone derivative 3-(4-(dimethylamino)phenyl)diazenyl)phenyl)-1- (2-nitrophenyl)prop-2-en-1-one (AZOC-2N) was designed and synthesized. The active layer was prepared by solution spin coating and vacuum evaporation methods, respectively. The accumulation of molecular film was studied by AFM and crystalline structure. It was found that the device had a non-volatile binary write once read many (WORM) memory performance and device in which form by vacuum evaporation with a higher threshold voltage -2.1 V. Finally, the electrical memory performance of the device is analysed by theoretical calculation simulation.

Gradual pressure-induced enhancement of magnon excitations in CeCoSi

CeCoSi is an intermetallic antiferromagnet with a very unusual temperature-pressure phase diagram: at ambient pressure it orders below $T_{\mathrm{N}} = 8.8$ K, while application of hydrostatic pressure induces a new magnetically ordered phase with exceptionally high transition temperature of $\sim40$ K at 1.5 GPa. We studied the magnetic properties and the pressure-induced magnetic phase of CeCoSi by means of elastic and inelastic neutron scattering (INS) and heat capacity measurements. At ambient pressure CeCoSi orders into a simple commensurate AFM structure with a reduced ordered moment of only $m_{\mathrm{Ce}} = 0.37(6)$ $\mu_{\mathrm{B}}$. Specific heat and low-energy INS indicate a significant gap in the low-energy magnon excitation spectrum in the antiferromagnetic phase, with the CEF excitations located above 10 meV. Hydrostatic pressure gradually shifts the energy of the magnon band towards higher energies, and the temperature dependence of the magnons measured at 1.5 GPa is consistent with the phase diagram. Moreover, the CEF excitations are also drastically modified under pressure.

Spontaneous antisymmetric spin splitting in noncollinear antiferromagnets without spin-orbit coupling

We propose a realization of an antisymmetric spin-split band structure through magnetic phase transitions without spin-orbit coupling. It enables us to utilize for a variety of magnetic-order-driven cross-correlated and nonreciprocal transport phenomena as similar to those in the spin-orbit-coupling oriented systems. We unveil its general condition as an emergence of a bond-type magnetic toroidal multipole (polar tensor) in the triangular unit with the noncollinear 120$^{\circ}$-AFM structures. By using the concept of augmented multipoles, we systematically analyze the phenomena in terms of an effective multipole coupling. Our multipole description is ubiquitously applied to any trigonal and hexagonal structures including the triangular, kagome, and breathing kagome structures, which provides how to design and engineer materials with a giant antisymmetric spin splitting and its physical responses even without the spin-orbit coupling.

Fixation of borate-anions in lamellar AFm-phases in the system CaO–Al2O3–B2O3–H2O at 20 ​°C, 40 ​°C and 50 ​°C

Synthesis of boron containing lamellar calcium aluminum hydroxy salts were performed at different relative humidities and the behaviour and properties of the lamellar phases were investigated. The following AFm compound could be synthesized in pure form and their properties were determined:AFm-phase: 3CaOAl2O3CaHBO3.nH2O.With excess boron an Ettringite-compound AFt with the following composition is coexisting in the investigated system:Ettringite-phase: 3CaOAl2O32Ca[B(OH)4]2Ca(OH)2·30H2O.The incorporation of boron in the interlayer of LDH-phases under the influence of OH-ions at different temperatures were investigated. Carbonate was excluded by using a glove box to get definite lattice parameters. Different boron containing AFm-phases, using pure phase compositions in the system OH-lamellar AFm phase and the boron containing AFm phase, were synthesized. The solid solution between the so called compounds Monoborate and Monohydroxide at different temperatures and different relative humidities, with careful control of the different water contents of the lamellar phases, was investigated. Boron contents in solution and the uptake in the interlayer of the AFm-phases was studied [13]. The uptake of boron from pure solutions and the newly formed relevant phases with AFm structure and at higher boron contents of the ettringite structure were determined.

Surface modification of Ti6Al4V by forming hybrid self-assembled monolayers and its effect on collagen-I adsorption, osteoblast adhesion and integrin expression

Silanization is a widely explored chemical technique to modify surfaces for tailoring physio-chemical properties like surface chemistry and wettability but its impact on bio-interfaces interaction i.e. protein adsorption and cellular responses is not well understood. This work focusses on modulating surface properties of Ti6Al4V to study their behavior towards collagen-I (Col-I) adsorption and subsequently on osteoblast adhesion and integrin expression. The moderate hydrophobic Ti6Al4V surfaces (θ = 78 ± 3°) were prepared by forming hybrid self-assembled monolayers (SAMs), which contain both hydrophobic and hydrophilic moieties on the same SAM molecule and were characterized using different techniques. The experimental adsorbed amounts of Col-1 were compared with the predicted ones using the Gibbs equation, which were overestimated but linearly related. AFM and secondary structure analyses of the adsorbed Col-I revealed globular morphology with significant change only in helical content. Cells adhered to hybrid surface pre-adsorbed with Col-1 exhibited better cell adhesion (~100%) and spreading area (1127 µm2) as compared to cells adhered to hybrid surface without (adhesion of 69% and cell area of 509 µm2) and with (adhesion of 94% and cell area of 908 µm2) FBS in cell culture media. Further, integrin expression was analyzed using ELISA based integrin assay to elucidate the cellular adhesion. We observed higher expression of α1 and α2 integrins on surfaces with pre-adsorbed Col-I and were correlated with the increase in nuclei area indicating α1 and α2 mediated cell adhesion promoted the cell proliferation. Overall, cell-surface interactions were improved on hybrid surfaces with pre-adsorbed Col-I, which designated the potential applications of the modified Ti6Al4V especially in metallic orthopedic implants.

Soft Magnetic Switching in a FeSr2YCu2O7.85 Superconductor with Unusually High Iron Valence.

Ozone oxidation has allowed the stabilization of a very high iron oxidation state in the FeSr2YCu2O7.85 cuprate, in which a long-range magnetic ordering of the high valent iron cations coexists with the superconducting interactions (magnetic ordering temperature TN = 110 K > superconducting critical temperature Tc = 70 K). The somewhat unexpected A-type AFM structure, with a μ(Fe) ∼ 2 μB magnetic saturation moment associated with the hypervalent iron sublattice, suggests an unusual low spin state for the iron cations, while the low dimensionality of the magnetic structure results in a soft switching toward ferromagnetism under small external magnetic fields. The role of the crystal structure and of the high charge concentration in the stabilization of this unusual electronic configuration for the iron cations is discussed.

Two dimensional electron gas in the -doped iridates with strong spin–orbit coupling: LaSr2IrO4

Iridates are of considerable current interest because of the strong spin–orbit coupling that leads to a variety of new phenomena. Using density-functional studies, we predict the formation of a spin-orbital entangled two dimensional electron gas (2DEG) in the -doped iridate LaSr2IrO4, where a single SrO layer is replaced by a LaO layer. The extra La electron resides close to the -doped layer, partially occupying the upper Hubbard band and thereby making the interface metallic. The magnetic structure of the bulk is destroyed near the interface, with the Ir0 layer closest to the interface becoming non-magnetic, while the next layer (Ir1) continues to maintain the AFM structure of the bulk, but with a reduced magnetic moment. The Fermi surface consists of a hole pocket and an electron pocket, located in two different Ir layers (Ir0 and Ir1), with both carriers derived from the upper Hubbard band. The presence of both electrons and holes at the -doped interface suggests unusual transport properties, leading to possible device applications.

Contrasting the magnetism in La2−xSrxFeCoO6(x=0,1,2) double perovskites: The role of electronic and cationic disorder

The magnetism of the double perovskite compounds \SLFCOx\ ($x$ = 0, 1, 2) are contrasted using magnetization, neutron diffraction and electron paramagnetic resonance with the support from density functional theory calculations. \LFCO\ is identified as a long-range ordered antiferromagnet displaying a near-room temperature transition at $T_N$ = 270~K, accompanied by a low temperature structural phase transition at $T_S$ = 200~K. The structural phase transformation at $T_S$ occurs from $R\overline{3}c$ at 300~K to $Pnma$ at 200~K. The density functional theory calculations support an insulating non-compensated AFM structure. The long-range ordered magnetism of \LFCO\ transforms to short-range glassy magnetism as La is replaced with Sr in the other two compounds. The magnetism of \LFCO\ is differentiated from the non-equilibrium glassy features of \SFCO\ and \SLFCO\ using the {\em cooling-and-heating-in-unequal-fields} (CHUF) magnetization protocols. This contransting magnetism in the \SLFCOx\ series is evidenced in electron paramegnetic resonance studies. The electronic density-of-states estimated using the density functional theory calculations contrast the insulating feature of \LFCO\ from the metallic nature of \SFCO. From the present suite of experimental and computational results on \SLFCOx, it emerges that the electronic degrees of freedom, along with antisite disorder, play an important role in controlling the magnetism observed in double perovskites.

Thermodynamic modelling of temperature effects on the mineralogy of Portland cement systems containing chloride

Thermodynamic equilibrium based modelling was carried out to quantify the influence of temperature on the mineralogy of hydrated ordinary Portland cement. In typical Portland cement system hydrated at 25 °C interlayer sites in the AFm phase are occupied by OH, SO4 or CO3 ions. Chloride which can be added as a set accelerating admixture or ingress from the outside environment, has the ability to displace hydroxide, sulfate and carbonate from the AFm structure leading to the formation of ‘Friedel's salt’ (Cl-AFm). However temperature variations may cause important compositional changes or even destabilization of Friedel's salt. A description of phase relations and changing balances between AFm and AFt (ettringite) phases is presented in a range of temperatures between 5 and 85 °C. With an increasing temperature Friedel's salt is predicted to decompose at the expense of monosulfoaluminate (SO4-AFm) formation. Due to the higher stability of hydroxy- AFm (OH-AFm) at lower temperature the OH substitution in the Friedel's salt is expected to be slightly higher as compared to room temperature.

Phase transformation in crystal and magnetic structure and improved dielectric and magnetic properties of Ho substituted BiFeO3multiferroics

The changes in crystal and magnetic structure of BiFeO3 produced by partial substitution of Bi ions by Ho ions has been studied with powder X-ray diffraction, neutron powder diffraction, dielectric and magnetization techniques. The present study demonstrates that Bi1-xHoxFeO3(x = 0.05, 0.10, 0.15, & 0.2) multiferroics shows change in crystal structure at x > 0.05. The sample with x = 0.05 exhibits rhombohedral structure (space group R3c), while the other three samples (x > 0.05) exhibit mixed phase with coexisting rhombohedral (R3c) and Orthorhombic (Pnma) structure. This change in the crystal structure is attributed to the distortion of FeO6 octahedra via substitution of Ho at phase boundaries. The magnetization studies indicate that doping of Ho in pristine BiFeO3 leads to enhancement in the ferromagnetic moment. We find that doping of Ho breaks the spin cycloid phase of BiFeO3 and creates a canted G-type antiferromagnetic structure in the hexagonal phase whereas the orthorhombic phase exhibits a collinear G-type AFM structure. The canting angle increases with increase in doping with Ho, leading to an enhancement in the ferromagnetic component in magnetization. Dielectric constant (ε′) and loss factor (tanδ) are measured in frequency range 1 kHz to 7 MHz and ε′ and tanδ show dispersion behaviour at low frequencies. The significant improvement in magnetization and dielectric properties is achieved by Ho substitution which in turn enhances the potential of BiFeO3 for multiferroics applications.