arXiv subjects

C. Ritter

Publications and source records attributed to C. Ritter.

76 records · Page 5Linked to original sources

arXiv2002

First Order Transition in the Spin Dynamics of Geometrically Frustrated Yb2Ti2O7

Using neutron diffraction, 170Yb Mossbauer and muSR spectroscopies, we have examined the pyrochlore Yb2Ti2O7 where the Yb3+ S'=1/2 ground state has planar anisotropy. Below ~0.24K, the temperature of the known specific heat lambda transition, there is no long range magnetic order. We show that the transition corresponds to a first order change in the fluctuation rate of the Yb3+ spins. Above the transition temperature, the rate, in the GHz range, follows a thermal excitation law, whereas below, the rate, in the MHz range, is essentially temperature independent indicative of a quantum fluctuation regime.

cond-mat.str-el↗

arXiv2001

Correlation Functions and Corner Transfer Matrix of the Chiral Potts Model

We use the Density Matrix Renormalization Group technique to compute correlation functions of the Z_3-chiral Potts quantum chain in the massive regimes. Chains of up to 70 sites are used and a clear oscillatory behavior is found. We also check the relation between the density matrix spectrum and the Corner Transfer Matrix spectrum pointed out by Nishino and Okunishi, using Baxter's low-temperature formulae for the chiral Potts Corner Transfer Matrix eigenvalues. We find very good agreement.

cond-mat↗

arXiv2001

Magnetic-field -induced structural changes in the electron doped manganites: CaxSm1-xMnO3 (x = 0.8, 0.85)

We studied the correlation between magnetic, electrical, structural, and magnetostriction properties of the electron doped manganites Ca$_x$Sm$_{1-x}$MnO$_3$ (x = 0.85, 0.8). The paramagnetic to antiferromagnetic transition in both the compounds while cooling is accompanied by an abrupt increase of the spontaneous volume thermal expansion ($Δ$V/V = 0.07 % for x = 0.85 and 0.25 % for x = 0.2). The x = 0.15 exhibits multiple phase separation at 5 K: G-type, and C-type antiferromagnetic phases in orthorhombic (\QTR{it}{Pnma}) and monoclinic (\QTR{it}{P2}$_1$\QTR{it}{/m}) structures respectively. Magnetic study on x = 0.85 also suggest ferromagnetic regions possibly in $Pnma$ structure coexist with the antiferromagnetic phases. The magnetization (M = 1.2 $μ_B$) of x = 0.85 does not reach the value expected for the complete alignment of Mn spins even at 12 T and at 12 K. Metamagnetic transitions (C-type to Ferromagnetic) in both compounds are accompanied by contraction of volumes under high magnetic fields. We suggest that a high magnetic field induces \QTR{it}{P2}$_1$\QTR{it}{/m} (high volume) to \QTR{it}{Pnma} (low volume) structural transition. This is also supported by the neutron diffraction study.

cond-mat.mtrl-sci↗

arXiv2000

Magnetic and structural properties of the double-perovskite Ca_2FeReO_6

We suceeded in the preparation of polycrystalline Ca_2FeReO_6 which has a Curie temperature of 540 K, the highest value of all magnetic perovskites investigated up to now. This material has been characterised by X-ray and neutron powder diffraction. We found at 548 K a monoclinic unit cell (space group P2_1/n) with a=5.4366(5) A, b=5.5393(5) A, c=7.7344(5) A, and beta=90.044(4) deg. For low temperatures a phase separation in two monoclinic phases with identical cell volume is observed in neutron scattering. The two phases possess different magnetic structure and coercivity. 57-Fe-Moessbauer spectroscopy measurements show the presence of four different Fe(3+) positions indicating two different phases at room temperature, indistinguishable in the diffraction experiments. The conductivity is thermally activated for all temperatures and no significant magnetoresistivity is observed.

cond-mat.mtrl-sci↗