Butterfly-shaped Hysteresis Research Articles

3d-4f heterometallic trinuclear complexes derived from amine-phenol tripodal ligands exhibiting magnetic and luminescent properties.

A new family of 3d-4f heterometallic trinuclear complexes, namely [M2LnL2]·2ClO4·H2O (H3L = tris(((2-hydroxy-3-methoxybenzy1)amino)ethyl)amine, where M = Ni, Ln = Gd (1), Dy (2), and M = Zn, Ln = Gd (3), Dy (4)) were synthesized via the reaction of H3L and Ln(NO3)3·6H2O and Ni(ClO4)2·6H2O or Zn(ClO4)2·6H2O in a 2 : 1 : 2 ratio in the solution. Complexes 1-4 consisted of three metal ions arranged in an isosceles triangle manner. Magnetic properties investigations showed that complexes 1 and 2 exhibited weak ferromagnetic coupling between the Ni(ii) and Ln(iii) ions, whereas complex 4 displayed lanthanide single-ion magnetic properties. The alternating current (ac) magnetic susceptibilities of 4 revealed that both the in-phase (χ') and out-of-phase (χ'') signals are frequency- and temperature-dependent, which are typical features of the field-induced slow relaxation of the magnetization with Ueff = 124.5 K. Complex 4 also exhibited an obvious butterfly-shaped hysteresis loop at 2 K, indicating that it is a single-ion magnet. Moreover, complex 4 showed stronger fluorescent emissions, which were typical narrow emission bands of lanthanide ions. Therefore, complex 4 can be considered as a molecular magnetic and luminescent material. Comparably, complex 2 showed very weak DyIII-based emissions because the paramagnetic NiII ions quench the fluorescence and thereby lower the population of the triplet state.

Two-dimensional frameworks formed by pentagonal bipyramidal cobalt(ii) ions and hexacyanometallates: antiferromagnetic ordering, metamagnetism and slow magnetic relaxation.

We herein report the syntheses, structures, and magnetic properties of two isostructural two-dimensional (2D) coordination polymers based on a pentagonal bipyramidal CoII unit [Co(TODA)]2+ and two hexacyanometallates, namely [MIII(CN)6]2[CoII(TODA)]3·9H2O (M = Cr (1), Co (2), TODA = 1,4,10-trioxa-7,13-diazacyclopentadecane). Structure analyses show that both complexes have 2D honeycomb structures where the [Co(TODA)]2+ units are bridged by the [MIII(CN)6]3- groups through three cyano groups in the facial positions. Magnetic investigation reveals ferromagnetic coupling between the CrIII and CoII centres through cyanides in 1. Due to the antiferromagnetic interaction between the layers, compound 1 exhibits an antiferromagnetic ordering below 11.4 K, and shows a metamagnetic phase transition under an external dc field. Due to the disorder of the TODA ligands, compound 1 shows a spin glass behavior, which leads to slow magnetic relaxation in 1. A butterfly-shaped hysteresis loop at 1.8 K can be observed with a coercive field of 720 Oe, which is quite large for cyano-bridged Cr-Co molecular magnets. For compound 2 containing the diamagnetic [CoIII(CN)6]3- unit, field-induced slow magnetic relaxation was also verified, which makes compound 2 a rare example of an SIM assembled in a 2D network. An easy-plane magnetic anisotropy with a positive D value (29.9 cm-1 by PHI and 26.5 cm-1 by Anisofit2.0) was deduced for hepta-coordinated CoII centers. These results show the efficiency of the strategy of combining cyanometallates and pentagonal bipyramidal precursors for novel molecular magnetic materials.

Nonvolatile Memory Based on Nonlinear Magnetoelectric Effects

The magnetoelectric effects in multiferroics have a great potential in creating next-generation memory devices. We conceive a new concept of non-volatile memories based on a type of nonlinear magnetoelectric effects showing a butterfly-shaped hysteresis loop. The principle is to utilize the states of the magnetoelectric coefficient, instead of magnetization, electric polarization or resistance, to store binary information. Our experiments in a device made of the PMN-PT/Terfenol-D multiferroic heterostructure clearly demonstrate that the sign of the magnetoelectric coefficient can be repeatedly switched between positive and negative by applying electric fields, confirming the feasibility of this principle. This kind of non-volatile memory has outstanding practical virtues such as simple structure, easy operations in writing and reading, low power, fast speed, and diverse materials available.

Effect of Ligand Substitution around the Dy(III) on the SMM Properties of Dual-Luminescent Zn-Dy and Zn-Dy-Zn Complexes with Large Anisotropy Energy Barriers: A Combined Theoretical and Experimental Magnetostructural Study.

The new dinuclear Zn(II)-Dy(III) and trinuclear Zn(II)-Dy(III)-Zn(II) complexes of formula [(LZnBrDy(ovan) (NO3)(H2O)](H2O)·0.5(MeOH) (1) and [(L(1)ZnBr)2Dy(MeOH)2](ClO4) (3) (L and L(1) are the dideprotonated forms of the N,N'-2,2-dimethylpropylenedi(3-methoxysalicylideneiminato and 2-{(E)-[(3-{[(2E,3E)-3-(hydroxyimino)butan-2-ylidene ]amino}-2,2-dimethylpropyl)imino]methyl}-6-methoxyphenol Schiff base compartmental ligands, respectively) have been prepared and magnetostructurally characterized. The X-ray structure of 1 indicates that the Dy(III) ion exhibits a DyO9 coordination sphere, which is made from four O atoms coming from the compartmental ligand (two methoxy terminal groups and two phenoxido bridging groups connecting Zn(II) and Dy(III) ions), other four atoms belonging to the chelating nitrato and ovanillin ligands, and the last one coming to the coordinated water molecule. The structure of 3 shows the central Dy(III) ion surrounded by two L(1)Zn units, so that the Dy(III) and Zn(II) ions are linked by phenoxido/oximato bridging groups. The Dy ion is eight-coordinated by the six O atoms afforded by two L(1) ligands and two O atoms coming from two methanol molecules. Alternating current (AC) dynamic magnetic measurements of 1, 3, and the previously reported dinuclear [LZnClDy(thd)2] (2) complex (where thd = 2,2,6,6-tetramethyl-3,5-heptanedionato ligand) indicate single molecule magnet (SMM) behavior for all these complexes with large thermal energy barriers for the reversal of the magnetization and butterfly-shaped hysteresis loops at 2 K. Ab initio calculations on 1-3 show a pure Ising ground state for all of them, which induces almost completely suppressed quantum tunnelling magnetization (QTM), and thermally assisted quantum tunnelling magnetization (TA-QTM) relaxations via the first excited Kramers doublet, leading to large energy barriers, thus supporting the observation of SMM behavior. The comparison between the experimental and theoretical magnetostructural data for 1-3 has allowed us to draw some conclusions about the influence of ligand substitution around the Dy(III) on the SMM properties. Finally, these SMMs exhibit metal- and ligand-centered dual emissions in the visible region, and, therefore, they can be considered as magnetoluminescent bifunctional molecular materials.

Low-voltage operation of Si-based ferroelectric field effect transistors using organic ferroelectrics, poly(vinylidene fluoride–trifluoroethylene), as a gate dielectric

Si-based metal–ferroelectric–semiconductor (MFS) capacitors have been fabricated using poly(vinylidene fluoride–trifluoroethylene) [P(VDF–TrFE)] as a ferroelectric gate. The pinhole-free P(VDF–TrFE) thin films with high resistivity were able to be prepared by spin-coating directly onto hydrogen-terminated Si. The capacitance–voltage (C–V) characteristics of the ferroelectric gate field effect transistor (FeFET) using this MFS structure clearly show butterfly-shaped hysteresis originating from the ferroelectricity, indicating carrier modulation on the Si surface at gate voltages below 2 V. The drain current–gate voltage (ID–VG) characteristics also show counterclockwise hysteresis at gate voltages below 5 V. This is the first report on the low-voltage operation of a Si-based FeFET using P(VDF–TrFE) as a gate dielectric. This organic gate FeFET without any insulator layer at the ferroelectric/Si interface should be one of the promising devices for overcoming the critical issues of the FeFET, such as depolarization field and a decrease in the gate voltage.

Infrared spectroscopic study on electric-field-induced dynamics of polymer chains in a ferroelectric melt-quenched cold-drawn film of nylon-12

We studied the intensity changes of the infrared bands of a ferroelectric melt-quenched, cold-drawn film of nylon-12 as a function of an external cyclic stepwise electric field with the polarization perpendicular to the draw direction. The infrared bands assigned to the NH stretching and amide I modes exhibited butterfly-shaped hysteresis loops characteristic of ferroelectric materials, whereas the intensity changes of the infrared bands assigned to the CH2 antisymmetric and symmetric stretching modes were small and showed no butterfly-shaped hysteresis loops. These results indicate that only the amide groups were inverted under the external electric field. We proposed a molecular mechanism explaining the ferroelectric properties of nylon-12: the amide groups in the antiparallel β-sheet structure are inverted by the external electric field to form new hydrogen bonds, generating two stable states in a nearly double-minimum potential.

Suspension-type tuned mass dampers with varying pendulum length to dissipate energy

Summary In this paper, an optimal energy dissipation control algorithm is applied into a semi-active suspension-type tuned mass damper (SA-STMD) to suppress excessive vibration by means of variable pendulum length. The SA-STMD mechanism consists of a mass block, a suspension rope, and a movable fulcrum that can be a short tube driven by a linear motor to vertically move along the suspension rope. As the fulcrum goes up, the pendulum length is extended, resulting in a smaller stiffness of the SA-STMD, and vice versa. Accordingly, the restoring force in the SA-STMD can be adjusted by varying the fulcrum positions. In the case where the energy dissipation ability by the original STMDs is insufficient, the movable fulcrum in the SA-STMD system can compensate the STMDs for stiffness according to the proposed optimal energy dissipation control algorithm to provide controllable restoring forces. The controllable restoring forces are designed to act as viscous dampers that can make up for the lack of energy dissipation capacity. The numerical results from the time domain and frequency domain analyses show that the proposed approach utilizing the optimal energy dissipation control algorithm to adjust the pendulum length can induce controllable restoring forces with a butterfly-shaped hysteresis loop, supplying a sufficient energy dissipation capacity to reduce responses to the unexpectedly large external vibration. Another potential benefit is cost reduction because of use of a less number of conventional viscous dampers in the STMD system. Copyright © 2016 John Wiley & Sons, Ltd.

Realization of a flux-driven memtranstor at room temperature**Project supported by the National Natural Science Foundation of China (Grants Nos. 11227405, 11534015, 11274363, and 11374347) and the Natural Science Foundation from the Chinese Academy of Sciences (Grant No. XDB07030200).

The memtranstor has been proposed to be the fourth fundamental circuit memelement in addition to the memristor, memcapacitor, and meminductor. Here, we demonstrate the memtranstor behavior at room temperature in a device made of the magnetoelectric hexaferrite (Ba0.5Sr1.5Co2Fe11AlO22) where the electric polarization is tunable by external magnetic field. This device shows a nonlinear q–φ relationship with a butterfly-shaped hysteresis loop, in agreement with the anticipated memtranstor behavior. The memtranstor, like other memelements, has a great potential in developing more advanced circuit functionalities.

Electric-Field-Induced Dynamics of Polymer Chains in a Ferroelectric Melt-Quenched Cold-Drawn Film of Nylon-11 Using Infrared Spectroscopy.

The changes in intensity of the infrared bands of a ferroelectric melt-quenched, cold-drawn film of nylon-11 were measured as a function of a cyclic external electric field of 1.4 MV/cm. The infrared bands assigned to the NH stretching, amide I, NH-vicinal, and CO-vicinal CH2 scissoring modes showed butterfly-shaped hysteresis loops that are characteristic of ferroelectrics; however, the intensity changes of the infrared bands assigned to the CH2 antisymmetric and symmetric stretching modes are small and showed no butterfly-shaped hysteresis loops. These results indicate that the amide groups are inverted, while the methylene groups are not inverted under the external electric field. We propose a new molecular mechanism that explains the ferroelectric properties of nylon-11. Only the amide groups in the antiparallel β-sheet structure are inverted by the external electric field to form new hydrogen bonds; these two states form a nearly double-minimum potential.

Magnetic transitions and butterfly-shaped hysteresis of Sm-Fe-Al-based perovskite-type orthoferrite

Al doped SmFeO3 (SmFe1–xAlxO3; 0.0≤x≤0.15; step 0.05) were prepared by double sintering ceramic technique. The obtained samples were crystallized in single phase structure except the sample with x=0.15. The unit cell volume was found to decrease with increasing Al substitution in orthoferrite. The effective magnetic moment (<ι>μ</ι>eff) and the Curie constant (C) were calculated from the reciprocal of the molar magnetic susceptibility (χ−1) versus absolute temperature plot and found to attain maximum value for the parent sample. The magnetic behavior showed two different magnetic transitions, viz, Néel temperature (TN) and spin reorientation (TSR) transitions. The M-H hysteresis loop of the parent sample took butterfly-shape as a result of different contributions anisotropies. From the magnetic properties measurements, it was obviously found that B-site cation dilution resulted in a drastic decrease in the magnetization. Surprisingly large value of the coercive field was obtained for the undoped sample; Hc=6198.8 Oe. Based on the mentioned results, one can recommend the use of such orthoferrite in magnetic recording media and as pining layer in spin valve for spintronic applications.

Effect of electric field on the infrared spectrum of a ferroelectric poly(vinylidene fluoride-co-hexafluoropropylene) film

We have used infrared spectroscopy to study electric-field induced motions of polymer chains in a ferroelectric uniaxially drawn film of poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] (molar ratio, 1:0.18) consisting mainly of the polar crystalline β phase. We analyzed the observed spectra under the C2v symmetry of an infinite poly(vinylidene fluoride) (PVDF) chain. The changes in intensity of the a1 bands (2979, 1432, 1280, and 842cm−1), b1 bands (1073cm−1), and b2 bands (3017, 1168, and 880cm−1) showed butterfly-shaped hysteresis loops characteristic of ferroelectricity when the electric field was varied from 1.4 to −1.4MV/cm. The changes in intensity of the a1 and b2 bands with transition dipole moments perpendicular to the polymer chain were large, whereas those of the b1 bands with transition dipole moments parallel to the polymer chain were small. The changes in intensity of the a1 and b2 bands were mainly attributed to the inversion of the polymer chain around the polymer axis. On the other hand, the changes in intensity of the b1 band were attributed to the motion of a polar crystallite.

Three-dimensional molecular-based magnet of octacyanometalate-based tungstate(V)-cobalt(II) bimetallic assembly with TC = 26 K

A three-dimensional (3D) octacyanotungstate(V)-based molecular based magnet containing Co(II) ions, {[CoII4(H2O)6(C2O4)][WV(CN)8]2·6H2O}n (1), has been synthesized in acidic solution and structurally characterized. X-ray determination indicates that in 1 each [W(CN)8]3− structural unit is linked by seven neighboring Co(II) ions forming 2D Co–W–CN inorganic connectivity layers. Further short conjugated oxalate bridges join these neighboring 2D layers ultimately forming the 3D framework. Magnetic investigation of complex 1 reveals that long-range ferromagnetic ordering occurs below the Curie temperature of 26K. The beautiful butterfly-shaped magnetic hysteresis loop at 10K between −70KOe and 70KOe exhibits a rather high coercive field (HC=3010Oe). The remnant magnetization Mr is equal to 3055cm3mol−1. To our best knowledge, complex 1 is the first example of 3D cyano-based magnets bridged by C2O42− anions.

Why are some hysteresis loops shaped like a butterfly?

The contribution of this paper is a framework for relating butterfly-shaped hysteresis maps to simple (single-loop) hysteresis maps, which are typically easier to model and more amenable to control design. In particular, a unimodal mapping is used to transform simple loops to butterfly loops. For the practically important class of piecewise monotone hysteresis maps, we provide conditions for producing butterfly-shaped maps and examine the properties of the resulting butterflies. Conversely, we present conditions under which butterfly-shaped maps can be converted to simple piecewise monotone hysteresis maps to facilitate hysteresis compensation and control design. Examples of a preloaded two-bar linkage mechanism and a magnetostrictive actuator illustrate the theory and its utility for understanding, modeling, and controlling systems with butterfly-shaped hysteresis.

An Organometallic Single-Ion Magnet

An organometallic single-ion magnet is synthesized with only 19 non-hydrogen atoms featuring an erbium ion sandwiched by two different aromatic ligands. This molecule displays a butterfly-shaped hysteresis loop at 1.8 K up to even 5 K. Alternating-current (ac) susceptibility measurement reveals the existence of two thermally activated magnetic relaxation processes with the energy barriers as high as 197 and 323 K, respectively.

Unusual Meissner state of the superconducting ferromagnet UCoGe revealed by differential susceptibility measurements with a polycrystalline sample

UCoGe is a ferromagnet with a Curie temperature TC∼3K at ambient pressure and superconductivity appears within the ferromagnetic phase with a superconducting transition temperature TSC∼0.8K. We have investigated magnetic properties of the ferromagnetic superconductor UCoGe in superconducting states by the differential susceptibility measurements with a polycrystalline sample. We observed unusual diamagnetic signals for magnetic field dependence of the differential susceptibility in superconducting state. We have revealed the sharp peak for the butterfly-shaped hysteresis loop of ferromagnetism observed even in Meissner state and point out the possible coexistence of ferromagnetism and superconductivity inhomogeneously in real space.

Poled composites with Nd-Mn-doped PZTfibers under bipolar electrical load

Using the sol-gel process, Nd-Mn-doped PZT fibers were produced. The PZT was doped with 2 mol% neodymium and 1.1 mol% manganese. For characterization, the fibers were embedded in a polymer. The resulting 1-3 composites were poled with constant electric field. Strain and polarization were measured by applying a bipolar sinusoidal voltage of high amplitude. Instead of the expected shifted butterfly-shaped strain hysteresis, an asymmetric strain-field relation was observed. It is characterized by a rather linear region in direction of the poling field and an inflated region without strain switching for reversed polarity. Within the temperature range from room temperature to 80 degrees C, the strain switching seems to be suppressed. Measurements of the piezoelectric coefficient at superimposed electric field prove the blocking of strain switching. Cyclation experiments with sesquipolar load show a pronounced linearity of the strain loops that declines after more than 2 x 10(4) cycles.

Nanoscale spin-dependent transport in a weak itinerant ferromagnet BaIrO3

We have performed magnetoresistance (MR) measurements for a BaIrO3 single crystal. As the magnetic field changes from 0 T to 14 T and back to 0 T, the longitudinal MR at 1.5 K traces out a butterfly-shaped hysteresis curve and the sign of the MR ratio for the field-ascending sweep changes from negative to positive near 6 T. The MR ratios for field-ascending and descending sweeps overlap each other around 13 T. A large anisotropic magnetoresistance (AMR) ratio per μb, (ρ|| - ρ ⊥)/ρ0 ∼ 400 %/μB at 1.5 K, is obtained, where ρ|| ρ⊥, and ρ0 are the longitudinal resistivity, the transverse resistivity, and the zero-field resistivity. The MR effects are interpreted based on a spin valve model considering a novel crystal structure and a local magnetic-anisotropy related to the spin-orbit coupling of this compound.

Field-Dependent Switching Kinetics and Ferroelectric Hysteresis Loops Analyzed with a Phenomenological Model in Relation to Typical Experiments

A study of ferroelectric switching is performed experimentally (macroscopically and at nanoscale) and theoretically, within the framework of a lattice model based on the Gibbs-Landau-Devonshire theory. Assuming that the polarization reversal is triggered by latent nuclei sites interacting with neighboring ferroelectric units, we have simulated switching curves and hysteresis loops in the total and partial switching regime. The model parameters have been varied in order to account for the hysteresis loops of PZT samples. Negative susceptibility regions of minor loops are caused by domain inertia in a sample with a lower defect density. The linear dielectric constant calculated from this model exhibits a typical butterfly-shaped hysteresis loop, with peaks in the zero-polarization state, while the second order nonlinear dielectric constant changes its sign in line with the average polarization. The local-integral relationships of the switching process are discussed in the framework of the model, providing useful guidelines for disclosing subtle ferroelectric peculiarities from experimental data.

Phonon bottleneck effect leads to observation of quantum tunneling of the magnetization and butterfly hysteresis loops in(Et4N)3Fe2F9

A detailed investigation of the unusual dynamics of the magnetization of ${({\mathrm{Et}}_{4}\mathrm{N})}_{3}{\mathrm{Fe}}_{2}{\mathrm{F}}_{9}$ $({\mathrm{Fe}}_{2})$, containing isolated ${[{\mathrm{Fe}}_{2}{\mathrm{F}}_{9}]}^{3\ensuremath{-}}$ dimers, is presented and discussed. ${\mathrm{Fe}}_{2}$ possesses an $S=5$ ground state with an energy barrier of $2.40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ due to an axial anisotropy. Poor thermal contact between sample and bath leads to a phonon bottleneck situation, giving rise to butterfly-shaped hysteresis loops below $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ concomitant with slow decay of the magnetization for magnetic fields ${H}_{z}$ applied along the $\mathrm{Fe}\mathrm{Fe}$ axis. The butterfly curves are reproduced using a microscopic model based on the interaction of the spins with resonant phonons. The phonon bottleneck allows for the observation of resonant quantum tunneling of the magnetization at $1.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, far above the blocking temperature for spin-phonon relaxation. The latter relaxation is probed by ac magnetic susceptibility experiments at various temperatures and bias fields ${H}_{\mathrm{DC}}$. At ${H}_{\mathrm{DC}}=0$, no out-of-phase signal is detected, indicating that at $T\ensuremath{\geqslant}1.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ ${\mathrm{Fe}}_{2}$ does not behave as a single-molecule magnet. At ${H}_{\mathrm{DC}}=1\phantom{\rule{0.3em}{0ex}}\mathrm{kG}$, relaxation is observed, occurring over the barrier of the thermally accessible $S=4$ first excited state that forms a combined system with the $S=5$ state.

Butterfly hysteresis and slow relaxation of the magnetization in (Et 4N) 3Fe 2F 9: manifestations of a single-molecule magnet

(Et 4N) 3Fe 2F 9 exhibits a butterfly-shaped hysteresis below 5 K when the magnetic field is parallel to the threefold axis, in accordance with a very slow magnetization relaxation in the timescale of minutes. This is attributed to an energy barrier Δ=2.40 K resulting from the S=5 dimer ground state of [Fe 2F 9] 3− and a negative axial anisotropy. The relaxation partly occurs via thermally assisted quantum tunneling. These features of a single-molecule magnet are observable at temperatures comparable to the barrier height, due to an extremely inefficient energy exchange between the spin system and the phonons. The butterfly shape of the hysteresis arises from a phonon avalanche effect.