Kensuke Konishi

Bulk ferro- and antiferro-magnetic behavior in 1,5-dimethyl verdazyl radical crystals with similar molecular structure

Abstract The organic radical crystal, 3-(4-chlorophenyl)-1,5-dimethyl-6-thioxoverdazyl (p-CDTV), has been revealed to be a new and bulk ferromagnet with the second highest Curie temperature T C = (0.67 ± 0.02) K of genuine organic ferromagnets by the simultaneous measurements of heat capacity and magnetic susceptibility. On the other hand, 3-(4-bromophenyl)-1,5-dimethyl-6-thioxoverdazyl (p-BDTV) behaves as a one-dimensional antiferromagnet with an intermolecular interaction of 2J k B = −41.2 K .

Magnetic Behavior of Organic Free Radicals with Localized and Delocalized Electrons

Magnetic and thermal properties have been studied on two kinds of organic free radicals, TANOL(2,2,6,6-tetramethyl-4-piperidinol-1-oxyl) and TPV(1,3,5-triphenylverdazyl), where the unpaired electrons are localized on the NO bond in the former compound but delocalized on the larger molecular orbitals in the latter. TANOL has been confirmed magnetically as a typical one-dimensional Heisenberg system with localized quantum spins coupled with the exchange constant J / k B =-5.2 K. On the other hand, the experimental results on TPV can not reasonably be understood on the basis of a localized model with the possible paths of magnetic interactions such as a railroad trestle lattice. It is suggested that organic free radicals offer promising real systems for getting essential physical phenomena which can check model Hamiltonians for a delocalized and frustrated quantum system.

Magnetism of one-dimensional copper oxides related to HTSC

Abstract Magnetic and electronic properties of two kinds of copper oxides with the linear chains linked by planar CuO 4 , Ca 2 CuO 3 and Li 2 CuO 2 , were investigated by magnetic susceptibility (χ), specific heat ( C p ) and XPS measurements. Ca 2 CuO 3 has scarcely any magnetic contribution to χ and C p in striking contrast with Li 2 CuO 2 which shows 3D-AF magnetic ordering at 9.3 K. They are discussed on the linear chain model.

Antiferromagnetic Long-Range Ordering of Organic Free Radicals Under High Pressure

Abstract Heat capacity measurements of some organic free radicals were carried out under high pressure in the liquid helium temperature region. The magnetic phase-transition temperatures increased linearly with the applied hydrostatic pressure, and normalized slopes were much larger than those of the usual inorganic magnetic materials.

Magnetic Entropy Analysis of Commensurate Structuresin PrCo2Si2

In the commensurate phases with the wave vector k (0, 0, k ) for k =13/14 and k =7/9 in the intermetallic rare earth compound PrCo 2 Si 2 , paramagnetic ions with individual entropy k B ln 2 have been found to be immersed regularly by the direct analysis of the observed heat capacity in zero external magnetic field. The possibility of phase slipping of the sinusoidal exchange field has also been discussed as driven by the variation of temperature in zero field.

MAGNETIC PROPERTIES OF 1,5-DIMETHYLVERDAZYL RADICAL CRYSTALS. FINDING OF NEW ORGANIC FERROMAGNET, P-CDTV

Abstract Magnetic properties of organic radical crystal, 3-(4-chlorophenyl)-l,5-dimethyl-6-thioxoverdazyl (p-CDTV), have been studied by measuring heat capacity and ac susceptibility above 0.13 K in external magnetic fields of 0–30 kOe. The p-CDTV has been found to be a new and bulk ferromagnet with the second highest Curie temperature T c=0.68 ± 0.02 K of genuine organic ferromagnet. The p-CDTV behaves as a quasi-one-dimensional Heisenberg ferromagnet with the intrachain exchange interaction of 2J/k B=+12.0±0.6 K above the transition temperature T e. The interchain exchange interaction zJ/k Bwas estimated to be +0.21 ±0.02 K, where z is the number of interchain bonds per spin.

Pressure-induced reduction of the Curie temperature of the organic ferromagnet p-NPNN

Abstract Under hydrostatic pressure, a drastic reduction of the Curie temperature T C ( p ) of β-phase p-NPNN, a genuine organic ferromagnet, has been found; from T C ( p 0 ) = 0.61 K ( p = p 0 = 0.001 kbar) to T C ( p ) = 0.35 K ( p = 7.2 kbar), for example. The results are discussed in comparison with the positive effect of pressure on the Neel temperatures of organic antiferromagnets.

Prototype one-dimensional Heisenberg ferromagnetic interaction in the organic radical crystal

Abstract An experimental check of quantum statistics for the most isotropic Heisenberg ferromagnet in one dimension has been carried out with a genuine organic 1,5 dimethylverdazyl radical crystal. A prototype Heisenberg ferromagnetic behavior, including magnetic susceptibility with the critical index γ = 2.0 and field dependence of heat capacity, is observed.

Simultaneous observation of heat capacity and magnetic susceptibility of a genuine organic ferromagnet under high pressures

The magnetic interactions in β-phase p-NPNN (p-nitrophenyl nitronyl nitroxide), a prototype genuine organic ferromagnet, have been studied by simultaneous measurements of magnetic heat capacity and susceptibility under hydrostatic pressures. A drastic reduction of the Curie temperature from 0.6 K at ambient pressure to 0.35 K at 7.2 kbar has been observed. This makes a significant contrast to the pressure-induced enhancement of the Neel temperature of organic antiferromagnets. A lowering of the magnetic lattice dimensionality is also observed at temperatures slightly above the Curie temperature under pressure. These observations are interpreted in terms of the virtual charge transfer mechanism.

Thermodynamical study of the magnetic transition in commensurate phases in PrCo2Si2

Abstract In the magnetically commensurate phases in the axially anisotropic compounds PrCo 2 Si 2 , the paramagnetic ions with individual entropy k B ln 2 has been detected to be immersed regularly by the heat capacity measurement and the adiabatic magnetization experiment. The possibility of the phase-slipping of the sinusoidal exchange field has been suggested to be driven by the variation of temperature in zero field.