Andrej Zorko

A comparative study of magnetic properties of LiFePO4 and LiMnPO4

A detailed comparative study of the magnetic properties of LiFePO4 and LiMnPO4 samples is presented. Magnetic susceptibility, electron paramagnetic resonance and 7Li NMR experiments were performed on samples as prepared for electrochemical studies. The ground state of LiFePO4 seems to be that of a collinear antiferromagnet and very robust against crystal imperfections. On the other hand, our LiMnPO4 samples possess a weak ferromagnetic ground state with a transition temperature TN = 42 K. We suggest that solitons may be very important magnetic excitations in these systems and that pinning of solitons below TN together with frustration plays a decisive role in the formation of the weak ferromagnetic state in LiMnPO4. The differences between the magnetic properties of these two samples reflect also the differences between their electronic structures and may thus be important for the electrochemistry of LiFePO4 and LiMnPO4.

Unconventional Magnetism in a Nitrogen-Containing Analog of Cupric Oxide

We have investigated the magnetic properties of CuNCN, the first nitrogen-based analog of cupric oxide CuO. Our muon-spin relaxation, nuclear magnetic resonance, and electron-spin resonance studies reveal that classical magnetic ordering is absent down to the lowest temperatures. However, a large enhancement of spin correlations and an unexpected inhomogeneous magnetism have been observed below 80 K. We attribute this to a peculiar fragility of the electronic state against weak perturbations due to geometrical frustration, which selects between competing spin-liquid and more conventional frozen states.

Frustration-induced nanometre-scale inhomogeneity in a triangular antiferromagnet

Phase inhomogeneity of otherwise chemically homogenous electronic systems is an essential ingredient leading to fascinating functional properties, such as high-Tc superconductivity in cuprates, colossal magnetoresistance in manganites and giant electrostriction in relaxors. In these materials distinct phases compete and can coexist owing to intertwined ordered parameters. Charge degrees of freedom play a fundamental role, although phase-separated ground states have been envisioned theoretically also for pure spin systems with geometrical frustration that serves as a source of phase competition. Here we report a paradigmatic magnetostructurally inhomogenous ground state of the geometrically frustrated α-NaMnO2 that stems from the system’s aspiration to remove magnetic degeneracy and is possible only due to the existence of near-degenerate crystal structures. Synchrotron X-ray diffraction, nuclear magnetic resonance and muon spin relaxation show that the spin configuration of a monoclinic phase is disrupted by magnetically short-range-ordered nanoscale triclinic regions, thus revealing a novel complex state of matter.

A high-temperature quantum spin liquid with polaron spins

The existence of a quantum spin liquid (QSL) in which quantum fluctuations of spins are sufficiently strong to preclude spin ordering down to zero temperature was originally proposed theoretically more than 40 years ago, but its experimental realization turned out to be very elusive. Here we report on an almost ideal spin liquid state that appears to be realized by atomic-cluster spins on the triangular lattice of a charge-density wave state of 1T-TaS2. In this system, the charge excitations have a well-defined gap of ∼0.3 eV, while nuclear quadrupole resonance and muon-spin-relaxation experiments reveal that the spins show gapless QSL dynamics and no long-range magnetic order at least down to 70 mK. Canonical T2 power-law temperature dependence of the spin relaxation dynamics characteristic of a QSL is observed from 200 K to Tf = 55 K. Below this temperature, we observe a new gapless state with reduced density of spin excitations and high degree of local disorder signifying new quantum spin order emerging from the QSL. In the charge-density wave state of tantalum sulfide, tantalum atoms group into a Star-of-David arrangement. Experiments show that the polaron spins associated with these atomic clusters can form a quantum spin liquid.

Intrinsic paramagnetism and aggregation of manganese dopants in SrTiO3

Using local-probe magnetic-characterization techniques of muon spin relaxation (

Spin-stripe phase in a frustrated zigzag spin-1/2 chain

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Coexistence of localized and itinerant electronic states in the multiband iron-based superconductor FeSe0.42Te0.58

SR) and electron spin resonance (ESR) we have investigated the Mn-induced magnetism of the wide-bandgap perovskite SrTiO

Observation of two types of fractional excitation in the Kitaev honeycomb magnet

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Magnetic inhomogeneity on a triangular lattice: the magnetic-exchange versus the elastic energy and the role of disorder

. Our results clearly demonstrate that this diluted magnetic oxide (DMO) remains paramagnetic down to low temperatures for both doping cases, i.e., when Mn substitutes for Sr or Ti. In addition, both experimental techniques have unveiled that the distribution of individual Mn

Atomic motions in the layered copper pseudochalcogenide CuNCN indicative of a quantum spin-liquid scenario

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