Ferroelectric ferromagnets are exceedingly rare, fundamentally interesting multiferroic materials that could give rise to new technologies in which the low power and high speed of field-effect electronics are combined with the permanence and routability of voltage-controlled ferromagnetism. Furthermore, the properties of the few compounds that simultaneously exhibit these phenomena are insignificant in comparison with those of useful ferroelectrics or ferromagnets: their spontaneous polarizations or magnetizations are smaller by a factor of 1,000 or more. The same holds for magnetic- or electric-field-induced multiferroics. Owing to the weak properties of single-phase multiferroics, composite and multilayer approaches involving strain-coupled piezoelectric and magnetostrictive components are the closest to application today. Recently, however, a new route to ferroelectric ferromagnets was proposed by which magnetically ordered insulators that are neither ferroelectric nor ferromagnetic are transformed into ferroelectric ferromagnets using a single control parameter, strain. The system targeted, EuTiO(3), was predicted to exhibit strong ferromagnetism (spontaneous magnetization, approximately 7 Bohr magnetons per Eu) and strong ferroelectricity (spontaneous polarization, approximately 10 microC cm(-2)) simultaneously under large biaxial compressive strain. These values are orders of magnitude higher than those of any known ferroelectric ferromagnet and rival the best materials that are solely ferroelectric or ferromagnetic. Hindered by the absence of an appropriate substrate to provide the desired compression we turned to tensile strain. Here we show both experimentally and theoretically the emergence of a multiferroic state under biaxial tension with the unexpected benefit that even lower strains are required, thereby allowing thicker high-quality crystalline films. This realization of a strong ferromagnetic ferroelectric points the way to high-temperature manifestations of this spin-lattice coupling mechanism. Our work demonstrates that a single experimental parameter, strain, simultaneously controls multiple order parameters and is a viable alternative tuning parameter to composition for creating multiferroics.

No abstract

The microscopic magnetic properties of the Cu02 planes in YBa2Cu306 63 (T, =62 K) have been investigated in Cu and 0 NMR experiments. Unlike the fully oxygenated Y-Ba-Cu-07 (T, =90 K), the various components of the Cu and 0 Knight-shift tensors show strong but identical temperature dependences in the normal state. This supports the picture that there is only one spin component in the Cu02 planes. The spin susceptibility deduced from Knight-shift results shows significant reduction with decreasing temperature in the normal state. The temperature dependences of the nuclear-spin-relaxation rates (1/T& ) are very different for the Cu and the 0 sites. 1/( T& T) at the O sites is nearly proportional to the spin susceptibility. 1/(T& T) at the Cu sites shows a broad peak around 150 K. We discuss these relaxation behaviors based on a model of the dynamical spin susceptibility proposed by Millis, Monien, and Pines.

We observe highly efficient dynamic spin injection from Y 3 Fe 5 O 12 (YIG) into NiO, an antiferromagnetic (AF) insulator, via strong coupling, and robust spin propagation in NiO up to 100-nm thickness mediated by its AF spin correlations. Strikingly, the insertion of a thin NiO layer between YIG and Pt significantly enhances the spin currents driven into Pt, suggesting exceptionally high spin transfer efficiency at both YIG/NiO and NiO/Pt interfaces. This offers a powerful platform for studying AF spin pumping and AF dynamics as well as for exploration of spin manipulation in tailored structures comprising metallic and insulating ferromagnets, antiferromagnets and nonmagnetic materials.

No abstract

We report Cu and La nuclear magnetic resonance (NMR) measurements in the title compound that reveal an inhomogeneous glassy behavior of the spin dynamics. A low temperature peak in the La spin lattice relaxation rate and the "wipeout" of Cu intensity both arise from these slow electronic spin fluctuations that reveal a distribution of activation energies. Inhomogeneous slowing of spin fluctuations appears to be a general feature of doped lanthanum cuprate. PACS 74.72.Bk, 75.30.Ds, 75.40.Gb Lanthanum cuprate, the prototypical single layer high temperature superconductor, has been extensively studied for several years to understand the origin of its unusual normal state behavior as well as the mechanism for superconductivity. Rare earth co-doped lanthanum cuprate has received attention recently because elastic neutron scattering experiments have revealed ordering of doped holes into charged stripes that constitute antiphase domain walls producing incommensurate antiferromagnetic (AF) order in the intervening undoped domains [1]. Charge stripe order is likely intimately related to the high temperature superconductivity [2][3][4][5]. Isostructural lanthanum nickelate demonstrates clear stripe order [6], and it has been shown there that both the charge order and the magnetic order are glassy [6,7]. It is also known that the magnetic order associated with charge ordering in lanthanum cuprate is glassy [8,9], but this situation is more difficult because the charge superlattice peaks are very hard to observe, presumably because the stripes tend to be dynamic. As a consequence little detail is known about the glassy behavior. Hunt et al. have observed suppression of the Cu NQR signal intensity ("wipeout") with decreasing temperature that they attribute to charge stripe order [10].NMR provides information complementary to neutron scattering because the nuclei are sensitive to the local magnetic field and the dynamic behavior of the electronic system without requiring spatial correlations. Chou et al., first proposed that the very strong peak in the 139 La nuclear spin relaxation rate displays an activated temperature dependence [13]. Furthermore, these data demonstrate a distribution P (E a ) of activation energies E a centered at E a /k B T ∼ 50 K and with a width comparable this center value indicating strongly inhomogeneous magnetic properties [13]. To understand if this inhomogeneity arises from disorder due to, e.g., substitutional dopants, we have applied this analysis to several lanthanum cuprate systems exhibiting AF order at low temperatures to allow us to explore the effect of varying the density and character of the disorder: in-plane doping by Li substitution for Cu, variation of doping density in LTT phase La 1.8−x Eu 0.2 Sr x CuO 4 : 0.01 ≤ x ≤ 0.15. Remarkably, we find that the character of the inhomogeneity, that is, the distribution of activation energies is essentially unchanged in all these cases and very similar to lightly doped La 2−x Sr x CuO 4 [11], suggesting that this inhomogeneity is intrinsi...

The use of magnetic force microscopy (MFM) to detect probe-sample interactions from superparamagnetic nanoparticles in vitro in ambient atmospheric conditions is reported here. By using both magnetic and nonmagnetic probes in dynamic lift-mode imaging and by controlling the direction and magnitude of the external magnetic field applied to the samples, it is possible to detect and identify the presence of superparamagnetic nanoparticles. The experimental results shown here are in agreement with the estimated sensitivity of the MFM technique. The potential and challenges for localizing nanoscale magnetic domains in biological samples is discussed.

We report 115 In and 59 Co Nuclear Magnetic Resonance (NMR) measurements in the heavy fermion superconductor CeCoIn5 above and below Tc. The hyperfine couplings of the 115 In and 59 Co are anisotropic and exhibit dramatic changes below 50K due to changes in the crystal field level populations of the Ce ions. Below Tc the spin susceptibility is suppressed, indicating singlet pairing. PACS Numbers: 74.70.Tx, 76.60.Cq In heavy fermion systems the interplay of magnetism and superconductivity gives rise to a diverse range of ground states including an unconventional form of superconductivity. The recently discovered family of heavy fermion compounds CeMIn 5 , where M = Co, Rh or Ir exemplifies these effects. Whereas the Rh compound undergoes a transition from antiferromagnetic to superconducting under pressure [1], the Ir [2] and Co [3] compounds superconduct at ambient pressure, with the Co system exhibiting the highest known transition temperature (2.3K) for any heavy fermion system. Evidence from heat capacity, thermal transport and µSR indicate that the pairing symmetry in the superconducting state is unconventional and that there are line nodes in the superconducting gap. [4,5] The bulk magnetic susceptibility, χ, of tetragonal CeMIn 5 displays systematic trends consistent with the diversity of observed ground states. In all three cases χ is anisotropic, and is largest for field applied along the c direction. In the ab plane, χ ab is essentially the same for all three materials. However, χ c exhibits a maximum at ∼ 10 K for CeRhIn 5 (T N = 3.8 K), whereas for the superconductors CeIrIn 5 and CeCoIn 5 χ c diverges at low temperatures until T c is reached. For both of these materials χ c also exhibits a plateau-like feature around 50 K, which is less pronounced for the Ir system. The origin of this feature and the relationship between χ c and T c have been sources of debate, however both the plateau and the divergence are intrinsic and independent of field.[3]Here we report a detailed study of site-specific magnetic shifts in CeCoIn 5 using nuclear magnetic resonance (NMR). Measurements in the normal state provide a microscopic measure of the local susceptibility and we find anomalous temperature dependencies. This behavior is likely due to the thermal depopulation of a crystal field (CEF) excitation of the Ce ions. We find remarkably strong departures from the expected proportionality between bulk susceptibility and the NMR Knight shift. We will argue that this effect is indicative of a high degree Ce moment localization, a feature that may play a role in the mechanism for superconductivity in this material. In the superconducting state the temperature dependencies of the shifts reveal a suppression of the spin susceptibility consistent with spin-singlet pairing.Crystals of CeCoIn 5 were grown from an In flux as described in [3]. The tetragonal crystal structure of CeCoIn 5 consists of alternating layers of CeIn 3 and CoIn 2 and so has two inequivalent In sites per unit cell. The In(1) site has axial symmetry ...