Field-induced Magnetic Ordering Research Articles

Effect of field-induced magnetic ordering on the electrical resistance of the frustrated magnet Au80Co20

Au80Co20 platelets were produced by solid-state quenching followed by furnace annealing and characterized by X-ray diffraction. Magnetization and magnetoresistance (MR) were measured from 2 to 265K. Minima of the zero-field electrical resistance R0(T) were observed at low temperatures (Tm≈20K) in both as-quenched and annealed samples. These minima disappear upon applying a magnetic field. At low T, a negative MR is associated to strong frustration and a very short magnetic coherence length; at higher temperatures, a positive MR is also observed.

Field-induced magnetic ordering in the quantum spin systemKCuCl3

${\mathrm{KCuCl}}_{3}$ is a three-dimensional coupled spin-dimer system and has a singlet ground state with an excitation gap $\ensuremath{\Delta}{/k}_{\mathrm{B}}=31\mathrm{K}.$ High-field magnetization measurements for ${\mathrm{KCuCl}}_{3}$ have been performed in static magnetic fields of up to 30 T and in pulsed magnetic fields of up to 60 T. The entire magnetization curve including the saturation region was obtained at $T=1.3\mathrm{K}.$ From the analysis of the magnetization curve, it was found that the exchange parameters determined from the dispersion relations of the magnetic excitations should be reduced, which suggests the importance of the renormalization effect in the magnetic excitations. The field-induced magnetic ordering accompanied by the cusplike minimum of the magnetization was observed, as in the isomorphous compound ${\mathrm{TlCuCl}}_{3}.$ The phase boundary was almost independent of the field direction, and is represented by the power law. These results are consistent with the magnon Bose-Einstein condensation picture for field-induced magnetic ordering.

TRIPLET MODES IN A QUANTUM SPIN LIQUID ACROSS THE CRITICAL FIELD

S = 1/2 TlCuCl3 is a magnetic insulator with a singlet ground state and a finite spin gap to triplet excited states. At finite fields, the degeneracy of the triplet states is lifted according to the Zeeman interaction term. Field-induced magnetic ordering occurs in TlCuCl3 at the critical field Hc ~ 6 T , when the Zeeman interaction overcomes the spin gap at the antiferromagnetic zone center. A detailed characterization of the elementary excitations realized at H > Hc is obtained by means of inelastic neutron scattering on single crystals. The general framework of field-induced quantum criticality in a three-dimensional spin liquid is illustrated on the complete dynamic range for the first time.

Comparative analysis of the magnetization processes of the Gd 3Ni and Gd 3Co single crystals

The investigations and comparative analysis of the magnetization processes for Gd 3Ni and Gd 3Co single-crystal compounds are presented. The possible magnetic structures for both compounds are proposed and the features of the field-induced metamagnetic transitions are discussed on the basis of the possible magnetic structures. The anomalous behavior of the Gd 3Ni compound observed above the magnetic ordering temperature is very likely caused by the appearance of the nickel atoms magnetic moment and field-induced magnetic ordering.

Random bond effect in the quantum spin system(Tl1−xKx)CuCl3

The effect of exchange bond randomness on the ground state and the field-induced magnetic ordering was investigated through magnetization measurements in the spin-$\frac{1}{2}$ mixed quantum spin system $({\mathrm{Tl}}_{1\ensuremath{-}x}{\mathrm{K}}_{x}){\mathrm{CuCl}}_{3}$ for $x<0.36.$ Both parent compounds ${\mathrm{TlCuCl}}_{3}$ and ${\mathrm{KCuCl}}_{3}$ are coupled spin dimer systems, which have the singlet ground state with excitation gaps $\ensuremath{\Delta}{/k}_{\mathrm{B}}=7.7 \mathrm{}\mathrm{K}$ and 31 K, respectively. Due to bond randomness, the singlet ground state turns into the magnetic state with finite susceptibility, nevertheless, the excitation gap remains. Field-induced magnetic ordering, which can be described by the Bose condensation of excited triplets, magnons, was observed as in the parent systems. The phase transition temperature is suppressed by the bond randomness. This behavior may be attributed to the localization effect.

Field-induced long-range ordering in a quasi-one-dimensional Haldane system

Quantum S=1 spin chain with single-ion anisotropy in the presence of an external magnetic field is investigated by means of the finite-temperature density-matrix renormalization group. Emphasis is laid on the point that the underlying physics differs significantly with respect to magnetic-field directions. There appear various phases, which are absent in the classical counterpart studied extensively in the past. We argue possible implications of our numerical results in the field-induced magnetic long-range ordering observed experimentally in NDMAP.

Magnetic Phases and Long-Range Ordering of the Haldane System in High Magnetic Fields

Critical properties of field-induced magnetic phases are investigated in the one-dimensional S = 1 Haldane system with planar anisotropy, using the finite-temperature density-matrix renormalization group method. We point out that the underlying physics of the properties differs significantly between cases of different field directions: The magnetic phase is characterized as the gapless Tomonaga-Luttinger regime in one case and as the gapful soliton regime in the other. In connection with the information obtained for the one-dimensional spin chain, possible implications for the field-induced magnetic long-range ordering are discussed.

Field-induced magnetic order in disordered single crystal Sr14Cu24O41: Cu-NMR study

Cu-NMR results on field-induced magnetic long-range (LR) order in structural disordered single crystal Sr14Cu24O41 (Sr14) are presented. Drastic broadening of both the ladder/Zhang Rice-NMR spectra in H∼11T occurs below TN∼20K. Meanwhile, another evidence of LR ordering is revealed in nuclear relaxation measurement. Staggered polarization originates from single-hole localization on the ladders. The growing interlayer coupling under H, as a result, leads to the appearance of the LR order as well as in the other spin-ladder compounds.

Field-induced magnetic order in quantum spin liquids.

We study magnetic-field-induced three-dimensional ordering transitions in low-dimensional quantum spin liquids, such as weakly coupled, antiferromagnetic spin- 1/2 Heisenberg dimers and ladders. Using stochastic series expansion quantum Monte Carlo simulations, we obtain the critical scaling exponents which dictate the power-law dependence of the transition temperature on the magnetic field. These are compared with recent experiments on candidate materials and with predictions for the Bose-Einstein condensation of magnons. The critical exponents deviate from isotropic mean-field theory and exhibit different scaling behavior at the lower and upper critical magnetic fields.

Field-Induced Two-Step Phase Transitions in the Singlet Ground State Triangular Antiferromagnet CsFeBr3

The ground state of the stacked triangular antiferromagnet CsFeBr$_3$ is a spin singlet due to the large single ion anisotropy $D(S^z)^2$. The field-induced magnetic ordering in this compound was investigated by the magnetic susceptibility, the magnetization process and specific heat measurements for an external field parallel to the $c$-axis. Unexpectedly, two phase transitions were observed in the magnetic field $H$ higher than 3 T. The phase diagram for temperature versus magnetic field was obtained. The mechanism leading to the successive phase transitions is discussed.

Observation of isotropic giant magnetoresistance in paramagneticAu80Fe20

Magnetization and magnetoresistance were measured at room temperature and above on ${\mathrm{Au}}_{80}{\mathrm{Fe}}_{20}$ platelets and ribbons obtained by solid-state quenching and melt spinning. The as-quenched samples contain a solid solution of Fe in Au and exhibit a paramagnetic (Curie-Weiss) behavior in the considered temperature range; magnetic data indicate very short-ranged magnetic correlation among adjacent spins, enhanced by local composition fluctuations. The solid solution is very stable. Only a very limited fraction (never exceeding 1%) of nanometer-sized, bcc Fe particles appears after long-time isothermal anneals at suitable temperatures. A negative magnetoresistance was observed at room temperature in all examined samples. The observed effect is anhysteretic, isotropic, and quadratically dependent on magnetic field H and magnetization M. The signal scales with M rather than with H, indicating that it depends on the field-induced magnetic order of the Fe moments, as it does for conventional giant magnetoresistance in granular magnetic systems. This effect derives from spin-dependent scattering of conduction electrons from single Fe spins or very small Fe clusters. The scattering centers are almost uncorrelated at a distance of the order of the electronic mean free path (of the order of 1.5 nm, or a few atomic spacings, at RT).

Specific heat study of the field-induced magnetic ordering in the spin-gap systemTlCuCl3

Specific heat measurements have been performed in the coupled dimer system TlCuCl$_3$, which has a singlet ground state with the excitation gap $\Delta \simeq 7.5$K. The cusplike anomaly indicative of the 3D magnetic ordering was clearly observed in magnetic fields higher than the critical field $H_c$ corresponding to the gap $\Delta$. The phase boundary determined by the present specific heat measurements coincides with that determined by previous magnetization measurements. The phase boundary can be described by the power law $[ H_{\rm c}(T)-H_{\rm g} ] \propto T^{\phi}$ with $\phi=2.1(1)$. This result supports the magnon Bose condensation picture for the field-induced magnetic ordering in TlCuCl$_3$ [Nikuni {\it et al}., Phys. Rev. Lett. {\bf 84} (2000) 5868].

Field-induced three- and two-dimensional freezing in a quantum spin liquid.

Field-induced commensurate transverse magnetic ordering is observed in the Haldane-gap compound Ni(C(5)D(14)N(2))2N(3)(PF(6)) by means of neutron diffraction. Depending on the direction of applied field, the high-field phase is shown to be either a three-dimensional ordered Néel state or a short-range ordered state with dominant two-dimensional spin correlations. The structure of the high-field phase is determined, and properties of the observed quantum phase transition are discussed.

Field-Induced Magnetic Ordering and Bose-Einstein Condensation of Magnons in TlCuCl3

Field-Induced Magnetic Ordering and Bose-Einstein Condensation of Magnons in TlCuCl3

Field-induced three-dimensional magnetic ordering in the spin-gap system

The temperature and field variations of the magnetization have been measured for which has a singlet ground state with an excitation gap. It is found that undergoes three-dimensional ordering in magnetic fields. The phase boundaries between the paramagnetic and ordered states are determined for and . The phase boundaries for these field directions coincide when normalized by the g-factor. The excitation gap at zero temperature is re-evaluated as .

High Field Magnetization of Singlet Ground State System Cs3Cr2X9(X=Cl, Br) up to 40 T

High field magnetization measurements were performed up to 40 T in the multilevel singlet ground state systems, Cs 3 Cr 2 X 9 (X=Cl, Br), having hierarchical higher excited magnetic states. Characteristic stair structure with three steps was observed, for the first time, in the magnetization curve of Cs 3 Cr 2 Cl 9 and analysed in terms of exchange-coupled Cr 3+ dimer model with the total spin S =3. Field-induced magnetic ordering due to weak interdimer interactions is discussed and a novel type of the phase diagram composed of multiple restricted regions of magnetic ordering around the successive level-crossing fields is suggested.

Thermodynamic investigations of the field-induced spin-density wave: Significant departure from Bardeen–Cooper–Schrieffer behavior at high field

We have investigated the field-induced spin-density wave (FISDW) state of the quasi-one-dimensional organic conductor (TMTSF)2ClO4 by means of calorimetric experiments. Specific heat measurements were performed at low temperature and in fixed magnetic fields up to 10 T. The specific heat jump at the metal-FISDW transition is found to exhibit an oscillatory behavior as the field is varied: First, the jump goes through a series of discontinuities at the reentrance points of the phase diagram, corresponding to the transitions between two magnetic subphases. Next, around 10 T, a second-order phase transition occurs 1 K above the first-order line deduced from the magnetization data. Finally, in the same field range, the jump value deviates significantly from the Bardeen–Cooper–Schrieffer (BCS) prediction and rises up to about four times the BCS value at 10 T. Such a behavior appears to be in a strong departure from our present understanding of the field-induced magnetic ordering and seems to invalidate the weak-coupling limit in use up to now for the description of the Bechgaard salts.

Field-induced magnetic ordering in the singlet ground-state system Cs 3Cr 2Br 9

AC-susceptibility measurements of the dimer compound Cs 3Cr 2Br 9 show clear evidence for a field induced magnetic ordering between 1 and 2 K with field strengths ranging from 30 to 50 kG. The order is anisotropic with respect to the field direction. The results are discussed in terms of soft-mode theory in the random phase approximation as well as a static molecular-field model.

Field-induced magnetic order in bis-tetramethyltetraselenafulvalenium perchlorate(TMTSF)2ClO4

A microscopic study of the organic superconductor bis-tetramethyltetraselenafulvalenium perchlorate [${(\mathrm{TMTSF})}_{2}$Cl${\mathrm{O}}_{4}$] has been undertaken with the use of nuclear magnetic resonance techniques. Proton and selenium resonances were recorded over the field range 60-120 kOe at a temperature of 1.5 K. The proton spin-lattice relaxation-rate measurements clearly reflect both the high-field phase transition and magnetotransport anomalies. The selenium resonance is strongly attenuated above the high-field transition which indicates the onset of field-induced magnetic order. These results and their bearing on the high-field electronic properties of the Bechgaard salts are discussed.

Field-induced magnetic ordering in uniaxial nickel systems: A second example

The zero-field susceptibilities parallel and perpendicular to the tetragonal axis of NiCl2⋅4SC(NH2)2 have been measured between 1.2 and 30 K and fitted to the usual spin Hamiltonian. The resulting parameters are D/kB = 7.6±0.4 K, z0J/kB = −4.5±0.3 K, g∥ = 2.26±0.03 and g⊥ = 2.34±0.03. The susceptibility has also been measured parallel to the tetragonal axis at constant temperatures between 0.3 and 2 K as a function of external field. Magnetic ordering is found to occur, and portions of the phase boundary between paramagnetic and antiferromagnetic states have been determined.