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In a polar ferrimagnet GaFeO3, we have found a novel magneto-optical effect, termed x-ray nonreciprocal directional dichroism (XNDD), that the x-ray absorption at around the K edge of an Fe ion depends on whether the x-ray propagation vector is parallel or antiparallel to the outer product of the magnetization and electric-polarization vectors. The XNDD spectroscopy as demonstrated here can be a useful tool to probe the local magnetism in noncentrosymmetric systems such as magnetic interfaces and nanostructures.

Optical conductivity spectra sigma(omega) were used to investigate the effect of orbital ordering on the electronic structure of Ca2RuO4. Our LDA+U calculation predicts Ru 4d(xy) ferro-orbital ordering at the ground state, and well explains the present sigma(omega) as well as the reported O 1s x-ray absorption spectra. Variation of temperature (T) causes a large change of spectral weight over several eV as well as collapse of a charge gap accompanied by elongation of the c-axis Ru-O bond length. These results clearly indicate that the d(xy) orbital ordering plays a crucial role in the metal-insulator transition and the T-dependent electronic structure on a large energy scale.

The frequency, temperature, and dc-bias dependence of the ac-susceptibility of a high quality single crystal of the Eu0.5Sr1.5MnO4 layered manganite is investigated. Eu0.5Sr1.5MnO4 behaves like a XY spin glass with a strong basal anisotropy. Dynamical and static scalings reveal a threedimensional phase transition near Tg = 18 K, and yield critical exponent values between those of Heisenberg-and Ising-like systems, albeit slightly closer to the Ising case. Interestingly, as in the latter system, the here observed rejuvenation effects are rather weak. The origin and nature of the low temperature XY spin glass state is discussed.PACS numbers: 75.50. Lk, 75.47.Lx, 75.40.Gb, 75.40.Cx The nature of the spin-glass (SG) phase transition has been puzzling experimentalists and theoretists for about 30 years [1]. The spin-glass correlation length, as well as many other physical properties diverge at the phase transition temperature T g with characteristic exponents. The renormalization group theory categorizes phase transitions in different universality classes. Each class is characterized by its own set of critical exponents. For example, the anisotropic Ising SG and the more isotropic vector SG such as XY-and Heisenberg SG belong to different universality classes. For a long time, numerical simulations predicted a phase transition at T g = 0 K for the XY and Heisenberg systems [3]. More recently, the SG transition was investigated using Ising-like variables, namely the chiralities[4] defined by the non-collinear spin structure (with left or right handeness). A chiral-glass (CG) phase transition was found at a finite temperature. Depending on the long length-scale coupling [5] or decoupling [4] of the spins and chiralities, the CG order may or may not be accompanied by a SG order.Experimentally, a three-dimensional SG phase transition is observed in both Ising and Heisenberg systems at finite T g . For example the (Fe,Mn)TiO 3 is a model Ising system[6] with a T g near 22 K over a broad range of (Fe,Mn) compositions, while the so-called canonical SG (dilute magnetic alloys such as Au(Fe), Cu(Mn), or Ag(Mn) [7]) are typical Heisenberg-like SG with a T g depending almost linearly on the amount of the magnetic impurity. In contrast, there are few known true XY SG. The exotic chiral-glass superconductors showing the paramagnetic Meissner effect (PME) are considered as the closest experimental realization of the XY SG [8]. This glassy state is unconventional, and often referred to as an orbital-glass state [8], as it involves spontaneous orbital moments rather than spins.The magnetic and electrical properties of the R 1−x A x MnO 3 manganites (R is a rare earth and A is an alkaline earth element) are essentially controlled by the effective one-electron bandwidth [10], which characterizes the transfer of the conduction electrons between neighboring Mn sites. Thus, depending on the radii of the R and A cations, the ferromagnetic (FM) metallic phase, or the charge-and orbital-ordered (CO-OO) phase can be stabilized [9,10]. The...

Second harmonic generation (SHG) induced by spontaneous magnetization has been investigated for a polar ferromagnetic crystal of GaFeO3. The Kerr rotation of the second harmonic light becomes gigantic with decreasing temperature below the magnetic transition temperature (approximately =205 K), e.g., as large as 73 degrees at 100 K. The magnetic domains can be visualized by using that large nonlinear Kerr rotation. The spectrum of the magnetization-induced SHG as measured indicates the two-photon resonant electronic process on a Fe3+ ion in the crystal.

Phase diagrams in the plane of rA (the average ionic radius, related to one-electron bandwidth W ) and σ 2 (the ionic radius variance, measuring the quenched disorder), or "bandwidth-disorder phase diagrams", have been established for perovskite manganites, with three-dimensional (3D) Mn-O network. Here we establish the intrinsic bandwidth-disorder phase diagram of half-doped layered manganites with the two-dimensional (2D) Mn-O network, examining in detail the "mother state" of the colossal magnetoresistance (CMR) phenomenon in crystals without ferromagnetic instability. The consequences of the reduced dimensionality, from 3D to 2D, on the order-disorder phenomena in the charge-orbital sectors are also highlighted.

Inflammatory bowel disease (IBD), which encompasses ulcerative colitis (UC) and Crohn's disease (CD), is a complicated, uncontrolled, and multifactorial disorder characterized by chronic, relapsing, or progressive inflammatory conditions that may involve the entire gastrointestinal tract. The protracted nature has imposed enormous economic burdens on patients with IBD, and the treatment is far from optimal due to the currently limited comprehension of IBD pathogenesis. In spite of the exact etiology still remaining an enigma, four identified components, including personal genetic susceptibility, external environment, internal gut microbiota, and the host immune response, are responsible for IBD pathogenesis, and compelling evidence has suggested that IBD may be triggered by aberrant and continuing immune responses to gut microbiota in genetically susceptibility individuals. The past decade has witnessed the flourishing of research on genetics, gut microbiota, and immunity in patients with IBD. Therefore, in this review, we will comprehensively exhibit a series of novel findings and update the major advances regarding these three fields. Undoubtedly, these novel findings have opened a new horizon and shed bright light on the causality research of IBD.

The electrical, magnetic, and structural properties of Sr3(Ru1−xMnx)2O7 (0 ≤ x ≤ 0.2) are investigated. The parent compound Sr3Ru2O7 is a paramagnetic metal, critically close to magnetic order. We have found that, with a Ru-site doping by only a few percent of Mn, the ground state is switched from a paramagnetic metal to an antiferromagnetic insulator. Optical conductivity measurements show the opening of a gap as large as 0.1 eV, indicating that the metal-to-insulator transition is driven by the electron correlation. The complex low-temperature antiferromagnetic spin arrangement, reminiscent of those observed in some nickelates and manganites, suggests a long range orbital order.PACS numbers: 74.70. Pq, 71.27.+a, 71.30.+h The Ruddelson-Popper-type Sr n+1 Ru n O 3n+1 series show metallic properties, as well as exotic superconductivity and spin/orbital order. SrRuO 3 (n = ∞, perovskite) and Sr 4 Ru 3 O 10 (n = 3) are itinerant ferromagnets with Curie temperatures (T c ) around 160 K and 100 K respectively [1,2]. In contrast, the single-layered Sr 2 RuO 4 (n = 1) and double-layered Sr 3 Ru 2 O 7 (n = 2) do not show ferromagnetism (FM). Sr 2 RuO 4 is a well known superconductor, which displays the unconventional spin-triplet pairing [3]. Sr 3 Ru 2 O 7 (Ru 4+ , 4d 4 ) is essentially paramagnetic[4] although there is some controversy in the literature related to the presence of ferromagnetic SrRuO 3 and Sr 4 Ru 3 O 10 impurities. A metamagnetic transition is observed at low temperatures in large magnetic fields [5,6], indicating the presence of quantum criticality. Another signature of this phase competition is found in hydrostatic pressure experiments [8] or Sr-site doping by Ca [7] of Sr 3 Ru 2 O 7 , which stabilizes the antiferromagnetic (AFM) state. In the case of Ca 3 Ru 2 O 7 , which has a lattice structure closely related to that of Sr 3 Ru 2 O 7 , the AFM ordering is observed at low temperature (∼ 56 K). The system remains metallic below this temperature, but near 48 K, a first-order-like transition to a less conductive state is observed [9].In this article, we investigate the effects of the Rusite doping by Mn of Sr 3 Ru 2 O 7 . A metal-to-insulator transition is observed as the Mn content increases. Optical conductivity measurements reveal the opening of a Mott-like gap [10]. Neutron diffraction experiments show that the low temperature insulating state is associated with a novel antiferromagnetic spin arrangement, which suggests some complex orbital order. Interestingly, while there are many observations of insulator-to-metal transitions upon tuning of one-electron bandwidth or bandfilling by doping [11], there are few reports of the opposite, i.e. of the formation of a Mott-like insulating state upon addition of impurities in a metal. One example of such impurity doping effects is found in the Mott insulator V 2 O 3 . As V 3+ is replaced by Ti 3+/4+ , the system becomes metallic by modification of the band filling and/or bandwidth [12]. However, the replacement of V 3+by Cr 3+ instead strengthens the e...