The Suppression and Recovery of the Ferroelectric Phase in Multiferroic MnWO4MnWO_4

We report the discovery of a complete suppression of ferroelectricity in $MnWO_4$ by 10 % iron substitution and its restoration in external magnetic fields. The spontaneous polarization in $Mn_{0.9}Fe_{0.1}WO_4$ arises below 12 K in external fields above 4 T. The magnetic/ferroelectric phase diagram is constructed from the anomalies of the dielectric constant, polarization, magnetization, and heat capacity. The observations are qualitatively described by a mean field model with competing interactions and strong anisotropy. We propose that the magnetic field induces a non-collinear inversion symmetry breaking magnetic structure in $Mn_{0.9}Fe_{0.1}WO_4$

Robust Ferroelectric State in Multiferroic Mn1−x_{1-x}Znx_xWO4_4

We report the remarkably robust ferroelectric state in the multiferroic compound Mn$_{1-x}$Zn$_x$WO$_4$. The substitution of the magnetic Mn$^{2+}$ with nonmagnetic Zn$^{2+}$ reduces the magnetic exchange and provides control of the various magnetic and multiferroic states of MnWO$_4$. Only 5 % of Zn substitution results in a complete suppression of the frustrated collinear (paraelectric) low temperature phase. The helical magnetic and ferroelectric phase develops as the ground state. The multiferroic state is stable up to a high level of substitution of more than 50 %. The magnetic, thermodynamic, and dielectric properties as well as the ferroelectric polarization of single crystals of Mn$_{1-x}$Zn$_x$WO$_4$ are studied for different substitutions up to x=0.5. The magnetic phases have been identified in single crystal neutron scattering experiments. The ferroelectric polarization scales with the neutron intensity of the incommensurate peak of the helical phase.Comment: 6 pages, 8 figure

Polymetallic complexes: Part XXVI-Complexes of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II) and mercury(II) with chelating bis-bidentate ON NO donor bases

533-535Schiffbases synthesized by the reaction of benzoinhydrazone with salicylaldehyde and o-hydroxyacetophenone form dimeric complexes with divalent metal ions. An octahedral geometry has been assigned to the complexes of Co(II), Ni(II), Cu(II) and Zn(II) whereas a tetrahedral structure is suggested for the Cd(II) and Hg(II) complexes. The complexes are amorphous, have high melting points and are insoluble in common organic solvents. The complexes have been characterised on the basis of analytical, conductance, magnetic susceptibility, molecular weight, IR and electronic spectral data

Pressure-Temperature Phase Diagram of Multiferroic Ni3V2O8Ni_3V_2O_8

The pressure-temperature phase diagram of multiferroic $Ni_3V_2O_8$ is investigated for hydrostatic pressures up to 2 GPa. The stability range of the ferroelectric phase associated with the incommensurate helical spin order is reduced by pressure and ferroelectricity is completely suppressed at the critical pressure of 1.64 GPa at 6.2 K. Thermal expansion measurements at ambient pressure show strong step-like anomalies of the lattice parameters associated with the lock-in transition into the commensurate paraelectric phase. The expansion anomalies are highly anisotropic, the related volume change is consistent with the high-pressure phase diagram

Magnetoelectricity and Magnetostriction due to the Rare Earth Moment in TmAl3_3(BO3_3)4_4

The magnetic properties, the magnetostriction, and the magnetoelectric effect in the d-electron free rare-earth aluminum borate TmAl$_3$(BO$_3$)$_4$ are investigated between room temperature and 2 K. The magnetic susceptibility reveals a strong anisotropy with the hexagonal c-axis as the hard magnetic axis. Magnetostriction measurements show a large effect of an in-plane field reducing both, the a- and c-axis lattice parameters. The magnetoelectric polarization change in a- and c-directions reaches up to 300 $\mu$C/m$^2$ at 70 kOe with the field applied along the a-axis. The magnetoelectric polarization is proportional to the lattice contraction in magnetic field. The results of this investigation prove the existence of a significant coupling between the rare earth magnetic moment and the lattice in $R$Al$_3$(BO$_3$)$_4$ compounds ($R$ = rare earth). They further show that the rare earth moment itself will generate a large magnetoelectric effect which makes it easier to study and to understand the origin of the magnetoelectric interaction in this class of materials.Comment: 4 pages, 5 figure

Sharing the Risks of Bankruptcy: \u3ci\u3eTimbers\u3c/i\u3e, \u3ci\u3eAhlers\u3c/i\u3e, and Beyond

Bankruptcy policy appears to be in disarray. Recent decisions by the United States Supreme Court have only served to reinforce the uncertainties that mar the bankruptcy process. In United Savings Association of Texas v. Timbers of Inwood Forest Associates, Ltd., the Court held that an undersecured creditor was not entitled to interest on its collateral as compensation for the opportunity costs of delay caused by the bankruptcy process. Timbers thus supports the argument that secured creditors should be forced to share the burdens of bankruptcy with other claimants. Conversely, in Norwest Bank Worthington v. Ahlers, the Court held that the proposed contribution of future labor on the family farm could not trump the absolute priority rule that bars a debtor\u27s retention of an equity interest over the objections of senior creditors. Thus, Ahlers rejects the claim that secured creditors should be forced to share the burdens of bankruptcy through a liberalized contribution rule. Can these decisions be reconciled? And what light do they shed on the future of bankruptcy sharing? There are a number of ways to rationalize the results in Timbers and Ahlers through careful statutory and doctrinal analyses. The fact that this article does not address them does not belittle the value of careful allegiance to the Bankruptcy Code and prior case law in seeking to predict the future of bankruptcy law. Nevertheless, few would doubt that the Court could have written carefully reasoned opinions justifying the opposite result in each case. Thus, it seems probable that unacknowledged and unexpressed policy considerations may have influenced the Court. This article examines precisely what those policy goals are and what they imply for the future of federal bankruptcy. Part I of the article analyzes the traditional objectives of the bankruptcy process in terms of the techniques of contemporary legal analysis. This exercise is principally one of translation, the time-honored task of pouring old wine into new bottles. By attempting to recharacterize old truths in contemporary terms, I mean to clarify what those truths really mean. Thereafter, Part II sketches a theory that rationalizes the apparently conflicting objectives of bankruptcy law. The theory suggests that the Court\u27s decisions in Timbers and Ahlers are, in fact, entirely consistent and complementary. This approach thus provides a convenient benchmark for assessing how the burdens of bankruptcy ought best to be shared between various claimants of different classes

Magnetoelectric Effect and Spontaneous Polarization in HoFe3_3(BO3_3)4_4 and Ho0.5_{0.5}Nd0.5_{0.5}Fe3_3(BO3_3)4_4

The thermodynamic, magnetic, dielectric, and magnetoelectric properties of HoFe$_3$(BO$_3$)$_4$ and Ho$_{0.5}$Nd$_{0.5}$Fe$_3$(BO$_3$)$_4$ are investigated. Both compounds show a second order Ne\'{e}l transition above 30 K and a first order spin reorientation transition below 10 K. HoFe$_3$(BO$_3$)$_4$ develops a spontaneous electrical polarization below the Ne\'{e}l temperature (T$_N$) which is diminished in external magnetic fields. No magnetoelectric effect could be observed in HoFe$_3$(BO$_3$)$_4$. In contrast, the solid solution Ho$_{0.5}$Nd$_{0.5}$Fe$_3$(BO$_3$)$_4$ exhibits both, a spontaneous polarization below T$_N$ and a magnetoelectric effect at higher fields that extends to high temperatures. The superposition of spontaneous polarization, induced by the internal magnetic field in the ordered state, and the magnetoelectric polarizations due to the external field results in a complex behavior of the total polarization measured as a function of temperature and field.Comment: 12 pages, 15 figure