A. A. Nugroho

Colossal dielectric constant up to gigahertz at room temperature

The search for new materials with extremely high (colossal) dielectric constants, required for future electronics, is one of the most active fields of modern materials science. However, the applicability of the colossal-epsilon materials, discovered so far, suffers from the fact that their dielectric constant, epsilon, only is huge in a limited frequency range below about 1 MHz. In the present report, we show that the dielectric properties of La15/8Sr1/8NiO4 surpass those of other materials. Especially, epsilon retains its colossal magnitude of >10000 well into the GHz range. This material is prone to charge order and this spontaneous ordering process of the electronic subsystem can be assumed to play an important role in the generation of the observed unusual dielectric properties.

Magnetodielectric coupling in frustrated spin systems: the spinels MCr2O4 (M = Mn, Co and Ni)

We have studied the magnetodieletric coupling of polycrystalline samples of the spinels MCr(2)O(4) (M = Mn, Co and Ni). Dielectric anomalies are clearly observed at the onset of the magnetic spiral structure (T(s)) and at the lock-in transition (T(f)) in MnCr(2)O(4) and CoCr(2)O(4), and also at the onset of the canted structure (T(s)) in NiCr(2)O(4). The strength of the magnetodielectric coupling in this system can be explained by spin-orbit coupling. Moreover, the dielectric response in an applied magnetic field scales with the square of the magnetization for all three samples. Thus, the magnetodielectric coupling in this state appears to originate from the P(2)M(2) term in the free energy.

Spin-Orbital Short-Range Order on a Honeycomb-Based Lattice

Going to Ground Frustrated systems, in which the geometry of the crystal lattice stands in the way of achieving an energetic minimum on all lattice sites simultaneously, have the potential to remain disordered down to the lowest temperatures. Numerous experimental efforts to find a material with a truly fluctuating ground state have failed because ordering often sets in at a finite temperature owing to symmetry breaking. Nakatsuji et al. (p. 559; see the Perspective by Balents) identify the compound Ba3CuSb2O9 as a promising candidate for this state; the Cu-Sb dipoles reside on a hexagonal structure, forming fluctuating spin singlets. Multiple lines of evidence suggest that the material does not order down to the millikelvin temperature range, remaining magnetically isotropic. Magnetic measurements indicate that a material remains disordered to millikelvin temperatures, thanks to its unusual lattice structure. Frustrated magnetic materials, in which local conditions for energy minimization are incompatible because of the lattice structure, can remain disordered to the lowest temperatures. Such is the case for Ba3CuSb2O9, which is magnetically anisotropic at the atomic scale but curiously isotropic on mesoscopic length and time scales. We find that the frustration of Wannier’s Ising model on the triangular lattice is imprinted in a nanostructured honeycomb lattice of Cu2+ ions that resists a coherent static Jahn-Teller distortion. The resulting two-dimensional random-bond spin-1/2 system on the honeycomb lattice has a broad spectrum of spin-dimer–like excitations and low-energy spin degrees of freedom that retain overall hexagonal symmetry.

Spectroscopic evidence for exceptionally high orbital moment induced by local distortions in α-CoV2O6

N. Hollmann, S. Agrestini, Z. Hu, Z. He, M. Schmidt, C.-Y. Kuo, M. Rotter, A. A. Nugroho, V. Sessi, A. Tanaka, N. B. Brookes, and L. H. Tjeng Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Str. 40, 01187 Dresden, Germany State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jl. Ganesha 10, Bandung 40132, Indonesia European Synchrotron Radiation Facility, Bôıte Postale 220, F-38043 Grenoble Cédex, France Department of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima 739-8530, Japan (Dated: May 11, 2014)

Evidence for magnetic Weyl fermions in a correlated metal

Weyl fermions have been observed as three-dimensional, gapless topological excitations in weakly correlated, inversion-symmetry-breaking semimetals. However, their realization in spontaneously time-reversal-symmetry-breaking phases of strongly correlated materials has so far remained hypothetical. Here, we report experimental evidence for magnetic Weyl fermions in Mn3Sn, a non-collinear antiferromagnet that exhibits a large anomalous Hall effect, even at room temperature. Detailed comparison between angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory (DFT) calculations reveals significant bandwidth renormalization and damping effects due to the strong correlation among Mn 3d electrons. Magnetotransport measurements provide strong evidence for the chiral anomaly of Weyl fermions-namely, the emergence of positive magnetoconductance only in the presence of parallel electric and magnetic fields. Since weak magnetic fields (approximately 10u2009mT) are adequate to control the distribution of Weyl points and the large fictitious fields (equivalent to approximately a few hundred T) produced by them in momentum space, our discovery lays the foundation for a new field of science and technology involving the magnetic Weyl excitations of strongly correlated electron systems such as Mn3Sn.

Observation of large refrigerant capacity in the HoVO3 vanadate single crystal

The HoVO3 orthovanadate undergoes a large negative and conventional magnetocaloric effects around 4u2009K and 15u2009K, respectively. The partly overlapping of the magnetic transition at 15u2009K and the structural transition occurring at 40u2009K, as well as the large magnetization, give rise to a giant refrigerant capacity without hysteresis loss. For a magnetic field variation of 7u2009T, the refrigerant capacity is evaluated to be 620u2009J/kg, which is larger than that for any known RMnO3 manganite. These results should inspire and open new ways for the improvement of magnetocaloric properties of ABO3 type-oxides.

Spin-wave excitations in the ferromagnetic metallic and in the charge-, orbital-, and spin-ordered states in Nd 1 − x Sr x MnO 3 with x ≈ 0.5

We report inelastic neutron-scattering experiments on single crystals of Nd

Dynamics of photo-excited electrons in magnetically ordered TbMnO3

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Mn-dopant-induced effects in Zn1−xMnxO compounds

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Probing orbital fluctuations in RVO3 (R = Y, Gd, or Ce) by ellipsometry

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