Field-temperature Phase Diagram Research Articles

Field induced effect near MPB in Pb(Zn1/3Nb2/3)O3-9%PbTiO3

Temperature dependences of the dielectric constants under the DC biasing fields along the [001]- and [111]-directions in the cubic coordinate were measured in Pb(Zn1/3Nb2/3)O3-9%PbTiO3. The temperature-field phase diagrams were clarified in the field range below 3.5 kV/cm. The existence of the critical end point at 185°C and 1.7 kV/cm was confirmed. The aspect of the temperature-field phase diagram depending on the direction of the field was discussed.

Magnetoelectric transitions of a distorted triangular-lattice antiferromagnet in a magnetic field

Large-scale Monte Carlo simulations are performed to analyze magnetoelectric transitions of a spin-lattice model in a magnetic field. The model explains well an experimental field-temperature phase diagram of RbCoBr${}_{3}$. The magnetic structure in each phase is determined. Simultaneous magnetoelectric transitions observed in the zero-field case are found to occur only in the low-field region, whereas magnetic transitions and electric transitions are decoupled in the high-field region. When the spin-lattice correlation is weak, an asymmetric ferrimagnetic state and a half-ferrimagnetic state appear. The former is the intermediate state between the partial-disordered state and the ferrimagnetic state. The latter phase is characterized by a sublattice order parameter with a $\frac{\ensuremath{\uparrow}}{2}$-$\frac{\ensuremath{\uparrow}}{2}$-$\ensuremath{\downarrow}$ ordering pattern.

Magnetic field-induced metamagnetic transitions of Pr0.5Ca0.5Mn0.97Ga0.03O3

Measurements of isothermal magnetization and electrical transport on Pr0.5Ca0.5Mn0.97Ga0.03O3 have been performed in a magnetic field up to 15 T. Two distinct metamagnetic transitions, which may relate to the collapse of the pseudo-CE-type and CE-type antiferromagnetic phases (CE, a composite antiferromagnetic structure composed of a chequeboard of alternating C and E type), have been observed in the temperature region of 2.5–140 K. Different from the traditional magnetization steps, the two metamagnetic transitions are not dependent on the field sweep rate. These peculiar features are sensitive to the microstructure of the sample. A temperature-field phase diagram has been constructed and found to exhibit a minimum critical field, similar to other phase-separated systems.

Multiple regions of quantum criticality in YbAgGe

Dilation and thermopower measurements on YbAgGe, a heavy-fermion antiferromagnet, clarify and refine the magnetic field-temperature (H-T) phase diagram and reveal a field-induced phase with T-linear resistivity. On the low-H side of this phase we find evidence for a first-order transition and suggest that YbAgGe at 4.5 T may be close to a quantum critical end point. On the high-H side our results are consistent with a second-order transition suppressed to a quantum critical point near 7.2 T. We discuss these results in light of global phase diagrams proposed for Kondo lattice systems.

High magnetic-field-induced phase transitions and refined magnetic phase diagram of Gd5Ge4

We have performed magnetization measurements of Gd5Ge4 with little or no ferromagnetic (FM) impurities under a pulsed magnetic field up to 40 T. The results reveal previously undetected transitions between 85 and 105 K, that is, a distinct second-order antiferromagnetic (AFM)-paramagnetic (PM) transition, followed by a first-order PM-ferromagnetic (FM) transition. The distinct variation of the slope of the M(H) curves is observed around the AFM-PM transition. Combining our high-field data and those reported earlier, a new magnetic field-temperature phase diagram, in which the AFM, PM, and FM states are well separated, is constructed.

Field induced phase transition in Pb(Zn 1/3Nb 2/3)O 3–8%PbTiO 3

Field induced phase transition in Pb(Zn 1/3Nb 2/3)O 3–8%PbTiO 3 (PZN–8%PT) was investigated by measuring temperature dependence of the dielectric constant under the DC biasing field. It was clarified that the critical end point exists at 172 ± 3 °C and 1.75 ± 0.25 kV/cm in the temperature–field phase diagram. The entropy change at the transition point was discussed based on the Clausius–Clapeyron relation. The phase transition in PZN–8%PT was found to be very close to the second-order.

The Critical End Point in Pb(Zn1/3Nb2/3)O3–8%PbTiO3

Temperature dependence of the dielectric constant under the DC biasing field was measured in Pb(Zn1/3Nb2/3)O3–8%PbTiO3. The temperature-field phase diagram was clarified in the field range below 2.5 kV. The existence of the critical end point at 172 ± 3°C and 1.75 ± 0.25 kV/cm was confirmed.

Field Tuning and Quantum Criticality in Ytterbium Based Heavy Electron Compounds

We review here the results of magnetization, specific heat, and inelastic neutron scattering measurements conducted on Yb3Pt4, Yb2Pt2Pb, Yb5Pt9, and YbRh2Pb, which indicate that the Yb moments in these heavy electron compounds are appreciably localized, at least in their paramagnetic states. The magnetic ground states in each are isolated magnetic doublets, and we show that magnetic fields suppress long ranged magnetic order and lead to a characteristic magnetic field-temperature phase diagram where order vanishes suddenly above a critical value for the field. We argue that the stability of magnetic order in these compounds arises from the competition between the Zeeman splitting gμBH of the ground state doublet, which favors a spin polarized state with minimal entropy and without long range order, and the exchange splitting Δ of the doublet, which enables long ranged magnetic order.

Two-dimensional square-latticeS=12antiferromagnetCu(pz)2(ClO4)2

We present an experimental study of the two-dimensional $S=\frac{1}{2}$ square-lattice antiferromagnet $\text{Cu}{(\text{pz})}_{2}{({\text{ClO}}_{4})}_{2}$ (pz denotes pyrazine-${\text{C}}_{4}{\text{H}}_{4}{\text{N}}_{2}$) using specific-heat measurements, neutron diffraction, and cold-neutron spectroscopy. The magnetic field dependence of the magnetic ordering temperature was determined from specific-heat measurements for fields perpendicular and parallel to the square-lattice planes, showing identical field-temperature phase diagrams. This suggest that spin anisotropies in $\text{Cu}{(\text{pz})}_{2}{({\text{ClO}}_{4})}_{2}$ are small. The ordered antiferromagnetic structure is a collinear arrangement with the magnetic moments along either the crystallographic $b$ or $c$ axis. The estimated ordered magnetic moment at zero field is ${m}_{0}=0.47(5){\ensuremath{\mu}}_{\text{B}}$ and thus much smaller than the available single-ion magnetic moment. This is evidence for strong quantum fluctuations in the ordered magnetic phase of $\text{Cu}{(\text{pz})}_{2}{({\text{ClO}}_{4})}_{2}$. Magnetic fields applied perpendicular to the square-lattice planes lead to an increase in the antiferromagnetically ordered moment to ${m}_{0}=0.93(5){\ensuremath{\mu}}_{\text{B}}$ at ${\ensuremath{\mu}}_{0}H=13.5\text{ }\text{T}$ evidence that magnetic fields quench quantum fluctuations. Neutron spectroscopy reveals the presence of a gapped spin excitations at the antiferromagnetic zone center and it can be explained with a slightly anisotropic nearest-neighbor exchange coupling described by ${J}_{1}^{\text{xy}}=1.563(13)\text{ }\text{meV}$ and ${J}_{1}^{\text{z}}=0.9979(2){J}_{1}^{\text{xy}}$.

Field re-entrant hidden-order phase under pressure inURu2Si2

We succeeded in growing high quality single crystals ofURu2Si2 and performed thermal expansion measurements under pressure. Applying a magnetic field along the[001] direction in the tetragonal structure, the so-called hidden-order phase reappearsafter the suppression of the antiferromagnetic phase above the critical pressurePx. We determined the pressure–temperature–field phase diagram for the paramagnetic,hidden-order and antiferromagnetic states for the direction. We also present the temperature dependence of the upper critical fieldHc2 for and [100] determined by the AC specific heat measurements, corresponding to the bulksuperconductivity in a high quality single crystal.

Anisotropic phase diagram of the frustrated spin dimer compoundBa3Mn2O8

Heat capacity and magnetic torque measurements are used to probe the anisotropic temperature-field phase diagram of the frustrated spin dimer compound Ba3Mn2O8 in the field range from 0T to 18T. For fields oriented along the c axis a single magnetically ordered phase is found in this field range, whereas for fields oriented along the a axis two distinct phases are observed. The present measurements reveal a surprising non-monotonic evolution of the phase diagram as the magnetic field is rotated in the [001]-[100] plane. The angle dependence of the critical field (Hc1) that marks the closing of the spin gap can be quantitatively accounted for using a minimal spin Hamiltonian comprising superexchange between nearest and next nearest Mn ions, the Zeeman energy and single ion anisotropy. This Hamiltonian also predicts a non-monotonic evolution of the transition between the two ordered states as the field is rotated in the a-c plane. However, the observed effect is found to be significantly larger in magnitude, implying that either this minimal spin Hamiltonian is incomplete or that the magnetically ordered states have a slightly different structure than previously proposed.

High-field metamagnetism in the antiferromagnetCeRh2Si2

A study of the antiferromagnet CeRh$_2$Si$_2$ by torque, magnetostriction, and transport in pulsed magnetic fields up to 50 Tesla and by thermal expansion in static fields up to 13 Tesla is presented. The magnetic field-temperature phase diagram of CeRh$_2$Si$_2$, where the magnetic field is applied along the easy axis $\mathbf{c}$, is deduced from these measurements. The second-order phase transition temperature $T_{N}$ and the first-order phase transition temperature $T_{1,2}$ (=~36 K and 26 K at zero-field, respectively) decrease with increasing field. The field-induced antiferromagnetic-to-paramagnetic borderline $H_c$, which equals 26 T at 1.5 K, goes from first-order at low temperature to second-order at high temperature. The magnetic field-temperature phase diagram is found to be composed of (at least) three different antiferromagnetic phases. These are separated by the first-order lines $H_{1,2}$, corresponding to $T_{1,2}$ at H=0, and $H_{2,3}$, which equals 25.5 T at 1.5 K. A maximum of the $T^2$-coefficient $A$ of the resistivity is observed at the onset of the high-field polarized regime, which is interpreted as the signature of an enhanced effective mass at the field-induced quantum instability. The magnetic field dependence of the $A$ coefficient in CeRh$_2$Si$_2$ is compared with its pressure dependence, and also with the field dependence of $A$ in the prototypal heavy-fermion system CeRu$_2$Si$_2$.

A study on the antiferromagnetic behavior of the hydride CeRuGeH adopting theZrCuSiAs-type structure

The non-magnetic heavy fermion behavior of CeRuGe is destroyed by hydrogen insertion.The resulting hydride CeRuGeH, investigated by magnetization, thermoelectric, electricalresistivity and specific heat measurements, exhibits an antiferromagnetic ordering belowTN = 4.0(2) K weakly influenced by the Kondo effect. BelowTN, a metamagnetic double transition induced by an applied magnetic field was evidenced forCeRuGeH. This hydride presents a simple field–temperature phase diagram in comparisonto that determined for the equivalent compound CeRuSiH.

Pressure Dependence of the Magnetic and Quadrupolar Ordering in YbRu2Ge2

We have investigated the pressure dependence of the magnetic field-temperature phase-diagram of the tetragonal compound YbRu2Ge2 by electrical resistivity measurements in the pressure range up to 10 GPa and for magnetic fields up to 14 T.

Two-Dimensional Kagome Correlations and Field Induced Order in the FerromagneticXYPyrochloreYb2Ti2O7

Neutron scattering measurements show the ferromagnetic XY pyrochlore Yb2Ti2O7 to display strong quasi-two-dimensional (2D) spin correlations at low temperature, which give way to long range order (LRO) under the application of modest magnetic fields. Rods of scattering along 111 directions due to these 2D spin correlations imply a magnetic decomposition of the cubic pyrochlore system into decoupled kagome planes. A magnetic field of approximately 0.5 T applied along the [110] direction induces a transition to a 3D LRO state characterized by long-lived, dispersive spin waves. Our measurements map out a complex low temperature-field phase diagram for this exotic pyrochlore magnet.

Field-Induced Bose-Einstein Condensation of Triplons up to 8 K inSr3Cr2O8

Single crystals of the spin dimer system Sr(3)Cr(2)O(8) have been grown for the first time. Magnetization, heat capacity, and magnetocaloric effect data up to 65 T reveal magnetic order between applied fields of H(c1) approximately 30.4 T and H(c2) approximately 62 T. This field-induced order persists up to T(c)(max) approximately 8 K at H approximately 44 T, the highest observed in any quantum magnet where H(c2) is experimentally accessible. We fit the temperature-field phase diagram boundary close to H(c1) using the expression T(c) = A(H-H(c1))(nu). The exponent nu = 0.65(2), obtained at temperatures much smaller than T(c)(max), is that of the 3D Bose-Einstein condensate (BEC) universality class. This finding strongly suggests that Sr(3)Cr(2)O(8) is a new realization of a triplon BEC where the universal regimes corresponding to both H(c1) and H(c2) are accessible at (4)He temperatures.

A pinning model and universal pinning regimes in [formula omitted] superconducting films

A model for vortex pinning at boundaries with modulated pinning potentials is developed for high-quality YBa2Cu3O7 superconducting films and multilayers. This model accurately describes the experimentally obtained Jc(Ba) behavior in different films over the entire field and temperature (T) ranges. Deviations are observed at high fields and temperatures due to the thermally activated depinning which is not accounted for by the model. A supplementary “model-free” analysis of the temperature dependent Jc curves leads to the four regions in the field-temperature phase diagram which are attributable to the well-known pinning regimes of collective pinning theory. The results obtained indicate the universality of the pinning model developed, which incorporates the universal pinning regimes and the ability to describe Jc(Ba,T) dependences.

Observation of large magnetoresistance in Gd2Al

The magneto-transport properties of Gd2Al compound are reported. The sample orders antiferromagnetically below the long range ordering temperature, To = 47 K, and under an applied magnetic field transforms into a ferromagnetic state. We observe a sharp decrease in resistivity at this field-induced transition, and the associated magnetoresistance is found to be −58% at 6.5 K for the field changing from 26 to 36 kOe. The metamagnetic transition appears to be first order in nature, at least at low temperatures (below 15 K), with a clear signature of field hysteresis. The sample shows an interesting field–temperature phase diagram with the distinct nature of the paramagnetic–antiferromagnetic and paramagnetic–ferromagnetic phase boundaries.

MWA and scanning-probe study of argon-ion irradiation effects on superconducting properties of Bi 2Sr 2CaCu 2O 8 thin films

Bi 2Sr 2CaCu 2O 8 films with thickness of 200 and 800 nm were irradiated with monovalent argon ions with an energy of 40 keV and a dose ranging between 10 14 and 10 17 ion/cm 2. The dose dependences of (i) the superconducting transition temperature, (ii) the critical current density value and (iii) the irreversibility line position on the magnetic field-temperature phase diagram were determined for two series of samples of different thickness. Atomic force microscopy images of the irradiated samples showed an appearance of defects in the form of surface holes. The obtained data were used to establish conditions for improving properties of thin-film superconducting materials. Firstly, the irradiation dose should be at least 10 16 ion/cm 2 to form embedded gas bubbles and surface holes serving as artificial pinning centers. Secondly, the film thickness and the average depth of the defect formation should be of a comparable value and sufficiently exceed the thickness of the surface layer sputtered as a result of irradiation.

Magnetization measurement of a possible high-temperature superconducting state in amorphous carbon doped with sulfur

Magnetization M(T,H) measurements performed on thoroughly characterized commercial amorphous carbon powder doped with sulfur (AC-S), revealed the occurrence of an inhomogeneous superconductivity (SC) below T_c = 38 K. The constructed magnetic field-temperature (H-T) phase diagram resembles that of type-II superconductors. However, AC-S demonstrates a number of anomalies. In particular, we observed (1) a non-monotonic behavior of the lower critical field H_c1(T); (2) a pronounced positive curvature of the "upper critical field boundary" that we associated with the flux lattice melting line Hm(T); (3) a spontaneous ferromagnetic-like magnetization M0 coexisting with SC. Based on the analysis of experimental results we propose a nonstandard SC state in AC-S.