51 research outputs found
Specific heat study of magnetic excitations in a one-dimensional S =1 Heisenberg magnet with strong planar anisotropy
The results of experimental studies of the specific heat of the magnetic chain compounds Ni(C₂H₈N₂)₂Ni(CN)₄, Ni(C₁₁H₁₀N₂O)₂Ni(CN)₄, and Ni(C₁₀H₈N₂)₂Ni(CN)₄⋅H₂O are reported. All compounds are identified as S=1 planar Heisenberg magnetic chains with large planar anisotropy and different values of the in-plane anisotropy constant. The low-temperature specific heat data are interpreted assuming the existence of noninteracting excitons and antiexcitons as elementary excitations from the singlet-ground state. The extended strong-coupling model is used for analysis of the data at higher temperatures. The applicability of the models used with respect to the value of the in-plane anisotropy is discussed
Magnetocaloric Study of Spin Relaxation in `Frozen' Dipolar Spin Ice Dy2Ti2O7
The magnetocaloric effect of polycrystalline samples of pure and Y-doped
dipolar spin ice Dy2Ti2O7 was investigated at temperatures from nominally 0.3 K
to 6 K and in magnetic fields of up to 2 T. As well as being of intrinsic
interest, it is proposed that the magnetocaloric effect may be used as an
appropriate tool for the qualitative study of slow relaxation processes in the
spin ice regime. In the high temperature regime the temperature change on
adiabatic demagnetization was found to be consistent with previously published
entropy versus temperature curves. At low temperatures (T < 0.4 K) cooling by
adiabatic demagnetization was followed by an irreversible rise in temperature
that persisted after the removal of the applied field. The relaxation time
derived from this temperature rise was found to increase rapidly down to 0.3 K.
The data near to 0.3 K indicated a transition into a metastable state with much
slower relaxation, supporting recent neutron scattering results. In addition,
magnetic dilution of 50 % concentration was found to significantly prolong the
dynamical response in the milikelvin temperature range, in contrast with
results reported for higher temperatures at which the spin correlations are
suppressed. These observations are discussed in terms of defects and loop
correlations in the spin ice state.Comment: 9 figures, submitted to Phys. Rev.
Extraordinary two-dimensionality in the S=1/2 spatially anisotropic triangular quantum magnet Cu(1,3-diaminopropane)Cl2 with modulated structure
Nonlinear excitations in CsNiF3 in magnetic fields perpendicular to the easy plane
Experimental and numerical studies of the magnetic field dependence of the
specific heat and magnetization of single crystals of CsNiF3 have been
performed at 2.4 K, 2.9 K, and 4.2 K in magnetic fields up to 9 T oriented
perpendicular to the easy plane. The experimental results confirm the presence
of the theoretically predicted double peak structure in the specific heat
arising from the formation of nonlinear spin modes. The demagnetizing effects
are found to be negligible, and the overall agreement between the data and
numerical predictions is better than reported for the case when the magnetic
field was oriented in the easy plane. Demagnetizing effects might play a role
in generating the difference observed between theory and experiment in previous
work analyzing the excess specific heat using the sine-Gordon model.Comment: 6 pages, 5 figures, submitted to Phys. Rev.
· - New S = 1/2 "Sawtooth" Chain?
The results of the investigation of magnetic susceptibility, magnetization and specific heat of · (tmen = N,N,N',N'-tetramethylethane-1,2 diamine; tma = 1,3,5-benzenetricarboxylic acid) are reported. The spatial arrangement of magnetic Cu(II) ions and network of covalent bonds suggest that the studied material might be a representative of S = 1/2 sawtooth chain with moderate exchange coupling J/. The investigation of the temperature dependence of susceptibility and magnetic field dependence of magnetization yielding J/ ≈ - 0.63 K is consistent with the structural features. In addition, specific heat data reveal short-range correlations in milikelvin temperature range and indicate long-range ordering below 150 mK
Effect of Layered Structure on the Lattice Heat Capacity of the Rare Earth Molybdates
Temperature dependence of the heat capacity of layered rare earth molybdates was measured in the temperature range from 0.4 K to 23 K. It is shown that the temperature dependence of the lattice heat capacity can be described by the "T", where n ≠ 3. It is shown that differently from KDy(MoO) and CsDyEu(MoO) for CsDy(MoO) and CsGd(MoO) we obtained the temperature term with n < 3, which can be connected with the 2D behaviour, manifested also in the so-called membrane effect
Slow Magnetic Relaxation in the Highly Anisotropic Layered Crystal CsNd(MoO₄)₂
The present work is devoted to the magnetic relaxation study of the single crystal CsNd(MoO₄)₂ a layered rare-earth dimolybdate. AC susceptibility measurements performed in magnetic fields up to B=5 T applied along the easy and hard axis with frequency f ≈1 kHz revealed rather complex field-induced slow magnetic relaxation. Two relaxation regimes in different magnetic field intervals connected with magnetic interactions and possible single-ion relaxation mechanism were observed
Experimental Study of Magnetocaloric Effect in Dipolar Magnet
We report on magnetothermodynamic properties of single crystal which were investigated from nominally 0.4 K to 20 K in magnetic fields up to 4 T. Using the available specific heat data the diagram of temperature and magnetic field dependence of the total entropy was constructed. Predictions for temperature dependences of the relative temperature variations during the adiabatic demagnetization and the entropy variation during the isothermal demagnetization were calculated from the specific heat data. The obtained results suggest that unlike common refrigerants, in the quantities describing magnetic cooling remain nearly constant in the temperature range 2-10 K
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