High Magnetic Field Phase Research Articles

Magnetic properties and magnetocaloric effect of R2Fe14B compounds with R = Y, Pr, Nd, Sm, Gd, Tb, Dy, Ho and High-Magnetic field phase transitions in the compounds with R = Gd, Dy

The temperature and field dependences of the: magnetization, magnetic specific heat and magnetic entropy of the R2Fe14B compounds, are studied using the mean-field two-sublattice model, where R = Y, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and B is boron. The isothermal entropy change ΔSm and the adiabatic temperature change ΔTad are calculated, for magnetic fields ≤ 5 T, by a Maxwell’s relation and a well-known integration involving the total heat capacity. The temperature range for these calculations is up to 700 K. Direct magnetocaloric effect (MCE), in all compounds, is present with maximum ΔSm and ΔTad in the range of 0.9–6.8 J/mol. K and 1.5–7.7 K, respectively, for a magnetic field change in the range of 1–5 T. The relative cooling power RCP(S) is in the range of 196–526 J/ kg. Ferrimagnetic compounds show both direct and small inverse MCE. It is found that Pr2Fe14B has the highest ΔSm of 6.8 J/mol. K and the largest ΔTad of 7.7 K at a magnetic field change of 5 T. The magnetization curves are calculated for Dy2Fe14B for temperatures in the range of 30–200 K and for Gd2Fe14B from 46 to 400 K for magnetic fields up to 300 T. It is found that these two compounds exhibit ferrimagnetic to ferromagnetic first-order phase transitions. Belov -Arrott plots, for these two compounds, show S-shaped feature which supports the occurrence of a first-order phase transition.

Anisotropy of the T vs. H phase diagram and the HO/LMAFM phase boundary in URu2−xFexSi2

The correlated f-electron compound URu2Si2 exhibits superconductivity (SC) with a critical temperature Tc = 1.5 K that coexists with the “hidden order” (HO) phase that forms below a characteristic temperature T0 = 17.5 K. The SC of URu2Si2 appears to be spin singlet chiral SC with d-wave order parameter symmetry, and the pairing of SCing electrons may involve spin excitations of the HO phase. Electrical resistance R measurements were performed on single crystal specimens of URu2−xFexSi2 with increasing x throughout the transition from the HO phase to the large moment antiferromagnetic LMAFM phase in high magnetic fields H oriented at various angles θ with respect to the tetragonal c-axis. Measurements of R(θ) at H = 20, 33, 40, and 45 T were conducted in the temperature range 0.33 ≤ T ≤ 20 K and showed θ-dependent behavior in the various phase transitions of URu2−xFexSi2 (HO, LMAFM, spin density wave, Fermi surface reconstruction, etc.). These phase transitions, as functions of T, H, and θ are plotted in a phase diagram of T vs. H//c = Hcosθ for multiple values of x and show that H//c, not θ is a tuning parameter of the URu2−xFexSi2 system throughout all Fe concentrations, as previously found by Scheereret al. for the URu2Si2 parent compound.

High-field ultrasonic study of quadrupole ordering and crystal symmetry breaking in CeRhIn5

We performed an ultrasonic measurement for the heavy-fermion compound CeRhIn$_5$ to investigate the origin of the field-induced anisotropic phase in high magnetic fields. The transverse elastic constant $C_\mathrm{T} = (C_{11} - C_{12})/2$ and the ultrasonic attenuation coefficient $\alpha_\mathrm{T}$ show clear anomaly at $B^\star = 28.5$ T, which was discussed as the electronic nematic transition point. In addition, $C_\mathrm{T}$ exhibits acoustic de Haas-van Alphen oscillation below 28.5 T. These elastic anomalies around $B^\star$ indicate an electric quadrupole ordering of $O_{x^2-y^2}$ accompanied by $B_\mathrm{1g}$ crystal symmetry breaking and Fermi surface reconstruction due to the quadrupole-strain coupling, which results from itinerant $4f$ electrons and the $p$-$f$ hybridized state.

Effects of the interplay between R 4f and Fe 3d on magneto-electric behavior and high field magnetization in RFe2O4 (R = Yb, Tm)

The detailed magnetization behavior of RFe2O4 (R = Yb and Tm) have been investigated in a wide range of magnetic fields. In low temperature region, the temperature dependence of magnetization shows that the strength of the interaction between R 4f and Fe 3d ions is directly related to the R3+ ions, a distinct phase transition was observed at ~53 K in YbFe2O4 and no obvious one was observed in TmFe2O4 even cooling to 1.8 K. The possible interaction between R 4f and Fe 3d ions and their evolution with magnetic field were investigated by pulsed high magnetic field. Based on the structures of both FeO5 trigonal bipyramid and RO6 octahedron of RFe2O4, the competition between ferromagnetic double-exchange and antiferromagnetic superexchange among the R-R, R-Fe and Fe-Fe, especially the interplay between R and Fe ions, are discussed. The different R-Fe magnetic interaction betweenYbFe2O4 and TmFe2O4 is experimentally verified by impedance spectroscopy and dielectric spectroscopy. Finally, the high field magnetic phase diagrams of RFe2O4 (R = Yb, Tm) are proposed.

Effects of Bi3+ doping on charge ordering and high magnetic field phase diagram of Nd0.6-xBixCa0.4MnO3

We report the doping effects and pulsed high magnetic field-induced charge ordering to ferromagnetic phase transitions in manganites Nd0.6-xBixCa0.4MnO3 (0 ≤ x ≤ 0.4). The experimental results reveal that the charge ordering is significantly enhanced upon Bi3+ doping, and the charge ordering temperature increases with increasing Bi3+ content. With applying pulsed high magnetic field, the charge ordering phase collapses into ferromagnetic phase through a metamagnetic transition. The phase diagram of Nd0.6-xBixCa0.4MnO3 has been determined by the high magnetic field studies, in which the charge ordering and ferromagnetic phase boundary is clearly figured out. The critical fields for melting the charge ordering phase of Nd0.6-xBixCa0.4MnO3 increase significantly with increasing Bi3+ content, which is revealed to reach up to 33.5 T for the sample with x = 0.3. Based on the hybridization between Bi-6s orbitals and O-2p orbitals, we assume that the 6s2 lone-pair character of Bi3+ plays a crucial role in favoring the charge ordering in Nd0.6-xBixCa0.4MnO3 (0 ≤ x ≤ 0.4).

H−T phase diagram of rare-earth–transition-metal alloys in the vicinity of the compensation point

Anomalous hysteresis loops of ferrimagnetic amorphous alloys in high magnetic field and in the vicinity of the compensation temperature have so far been explained by sample inhomogeneities. We obtain H-T magnetic phase diagram for ferrimagnetic GdFeCo alloy using a two-sublattice model in the paramagnetic rare-earth ion approximation and taking into account rare-earth (Gd) magnetic anisotropy. It is shown that if the magnetic anisotropy of the $f$-sublattice is larger than that of the $d$-sublattice, the tricritical point can be at higher temperature than the compensation point. The obtained phase diagram explains the observed anomalous hysteresis loops as a result of high-field magnetic phase transition, the order of which changes with temperature. It also implies that in the vicinity of the magnetic compensation point the shape of magnetic hysteresis loop is strongly temperature dependent.

Magnetic behavior and complete high-field magnetic phase diagram of the orthoferrite ErFeO3

Magnetic transitions in a single crystal of the orthoferrite ${\mathrm{ErFeO}}_{3}$ have been studied between 2 and 300 K using conventional superconducting quantum interference device measurements as well as pulsed high magnetic fields of up to 58 T. Spontaneous spin reorientations, as well as temperature and magnetic field induced spin reorientations, have been observed. At spin-reorientation transition temperatures, the ${\mathrm{Fe}}^{3+}$ sublattice exhibits a ${\mathrm{\ensuremath{\Gamma}}}_{4}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Gamma}}}_{2}$ transition where the magnetic coupling between the net magnetic moment of ${\mathrm{Fe}}^{3+}$ $3d$ and ${\mathrm{Er}}^{3+}$ $4f$ is antiferromagnetic, and the temperature dependence of the magnetization suggests that the order of magnitude of the interaction is ${J}_{\text{Er-Er}}l{J}_{\text{Er-Fe}}l{J}_{\mathrm{Fe}\text{\ensuremath{-}}\mathrm{Fe}}$. However, the magnetic coupling varies widely with temperature and/or magnetic field, which indicates that the ${\mathrm{Er}}^{3+}$ sublattice moment cannot be simply explained by the partial polarization of the paramagnetic spins due to the combination of the molecular field from the net ${\mathrm{Fe}}^{3+}$ moment and external applied magnetic fields. It is found that in a sufficiently high magnetic field, the magnetic interactions between the ${\mathrm{Fe}}^{3+}$ sublattice and the ${\mathrm{Er}}^{3+}$ sublattice are destroyed. Based on the detailed magnetization measurements, the complete high-field magnetic phase diagram has been obtained, providing an important framework for future investigations into the complicated magnetic interactions and magnetoelectric couplings in rare earth orthoferrites.

Role of band filling in tuning the high-field phases of URu2Si2

We present a detailed study of the low temperature and high magnetic field phases in the chemical substitution series URu$_2$Si$_{2-x}$P$_x$ using electrical transport and magnetization in pulsed magnetic fields up to 65T. Within the hidden order region (0 $\ x$$\ $ 0.035) the high field ordering is robust even as the hidden order temperature is suppressed. Earlier work shows that for 0.035 $\ x$ $\ $ 0.26 there is a Kondo lattice with a no-ordered state that is replaced by antiferromagnetism for 0.26 $\ x$ 0.5. We observe a simplified continuation of the high field ordering in the no-order $x$-region and an enhancement of the high field state upon the destruction of the antiferromagnetism with magnetic field. These results closely resemble what is seen for URu$_{2-x}$Rh$_x$Si$_2$\footnote{The concentration in this paper is defined as URu$_{2-x}$Rh$_x$Si$_2$ while the chemical formula in the literature is given as U(Ru$_{1-x}$Rh$_x$)$_2$Si$_2$ [24-26]}, from which we infer that charge tuning uniformly controls the ground state of URu$_2$Si$_2$, regardless of whether s/p or d-electrons are replaced. This provides guidance for determining the specific factors that lead to hidden order versus magnetism in this family of materials.

Magnetic field tuning of an excitonic insulator between the weak and strong coupling regimes in quantum limit graphite

The excitonic insulator phase has long been predicted to form in proximity to a band gap opening in the underlying band structure. The character of the pairing is conjectured to crossover from weak (BCS-like) to strong coupling (BEC-like) as the underlying band structure is tuned from the metallic to the insulating side of the gap opening. Here we report the high-magnetic field phase diagram of graphite to exhibit just such a crossover. By way of comprehensive angle-resolved magnetoresistance measurements, we demonstrate that the underlying band gap opening occurs inside the magnetic field-induced phase, paving the way for a systematic study of the BCS-BEC-like crossover by means of conventional condensed matter probes.

High magnetic field phase diagram in electron-doped manganites La(0.4)Ca(0.6)Mn(1-y)Cr(y)O3.

We report the charge-order to ferromagnetic phase transition induced by pulsed high magnetic field and impurity doping effects in manganites La0.4Ca0.6(Mn1−yCry)O3 (0 ≤ y ≤ 0.2). Significant charge-order suppression and ferromagnetic tendency upon the Cr3+-doping are evidenced, and three different ground states are identified, namely the charge-order state, the phase separated state, and the spin-glass like state. Phase diagram in the H-y plane at 4.2 K is determined by the high magnetic field study, in which the charge-order and ferromagnetic phase boundary is clearly figured out. The critical magnetic field for melting the charge-order phase of La0.4Ca0.6MnO3 is revealed to reach up to 46 T at 4.2 K. Interestingly, distinct responses of the three states to the high magnetic field are observed, indicating the special physics regarding the charge order melting process in each state. The mechanism of the doping induced charge-order suppression and ferromagnetism promotion can be understood by the competition between the antiferromagnetic interaction of Cr-Mn and local enhancement of electron hopping by Cr3+.

High-field magnetic phase diagram of CsCoCl3 revised

Abstract A fine structure of high-field magnetization curves of CsCoCl 3 and related compounds is discussed. It is shown that a precursor of a high-field phase transition originates from nucleation of an intermediate high-field ferrimagnetic (IFM) phase. Since the IFM state is degenerate its growth starting from few nucleation centers gives rise to domain walls formation. Their creep also makes a contribution to the magnetization dynamics similar to slow relaxation in Ca 3 Co 2 O 6 . An experimental verification of the model is proposed.

NMR Study of the FFLO State and Magnetism in CeCoIn5

We present 115In NMR results in a novel high magnetic field and low temperature phase of CeCoIn5 where exotic superconductivity coexists with the incommensurate spin-density wave order. The quantitative analysis for the field evolution of newly-emerged low-energy quasiparticle density of states is consistent with the nodal plane formation which is expected in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. The NMR spectra also suggest that the spatially uniform spin-density wave is induced in the FFLO phase.

Magnetic phase diagram of the frustratedS=12chain magnet LiCu2O2

We present the results of the magnetization and dielectric constant measurements on untwinned single-crystal samples of the frustrated $S=1/2$ chain cuprate LiCu${}_{2}$O${}_{2}$. Magnetic phase transitions were observed. A spin-flop transition of the spiral spin plane was observed for the field orientations $\mathbit{H}\ensuremath{\parallel}\mathbit{a}$, $\mathbit{b}$. The second magnetic transition was observed at $H\ensuremath{\approx}15$ T for all three principal field directions. This high-field magnetic phase is discussed as a collinear spin-modulated phase, which is expected for an $S=1/2$ nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic chain system.

Spectroscopic and magnetooptical investigations of spin-reorientation phase transition in TbFe3(BO3)4

Spectroscopic and magnetooptical investigations of spin-reorientation transition induced by a magnetic field in antiferromagnetic terbium ferroborate TbFe3(BO3)4 were performed. In the phase-transition region, a magnetic intermediate state with a periodic alternation of domains of initial and spin-flopped magnetic phases appears. As a result, a strong light scattering by the crystal takes place. It is shown that the main mechanism of light scattering is related to an appearance of the large Faraday rotation in a high-field magnetic phase. Visual polarization investigations of the domain structure in the intermediate state were carried out. The energy of the interphase boundary between the antiferromagnetic and high-field magnetic phases was calculated. The existence domain of the intermediate magnetic state was determined in the H–T coordinates.

New high magnetic field phase of the frustrated S = 1/2 chain compound LiCuVO4

Magnetization of the frustrated $S=1/2$ chain compound LiCuVO$_4$, focusing on high magnetic field phases, is reported. Besides a spin-flop transition and the transition from a planar spiral to a spin modulated structure observed recently, an additional transition was observed just below the saturation field. This newly observed magnetic phase is considered as a spin nematic phase, which was predicted theoretically but was not observed experimentally. The critical fields of this phase and its dM/dH curve are in good agreement with calculations performed in a microscopic model (M. E. Zhitomirsky and H. Tsunetsugu, preprint, arXiv:1003.4096v2).

Neutron diffraction study of the high magnetic field phase diagram of La-doped PrB6

The high magnetic field phase diagram of lanthanum-doped PrB6 was investigated by single-crystal neutron diffraction. In this compound, a peculiar incommensurate phase denoted IC2 was observed in magnetic fields applied along directions close to [111]. Unlike the double-k IC1 phase [kIC1 = (1/4 − δ, ±1/4,1/2)] formed in zero field below TN = 7 K, IC2 is characterized by a propagation vector with two incommensurate components, kIC2 = (1/4−δ′, 1/4 − δ′, 1/2) (δ′ ≊ 0.03). The field and temperature evolutions of domain populations further indicate that, contrary to the low-field phases C and IC1, the magnetic structure in phase IC2 is single-k.

Order Parameter and Vortices in the SuperconductingQPhase ofCeCoIn5

Recently, it has been reported that the low-temperature high-magnetic field superconducting phase in CeCoIn(5) (Q phase), has spin-density wave (SDW) order that only exists within this phase. This indicates that the SDW order is the result of the development of pair density wave (PDW) order in the superconducting phase that coexists with d-wave superconductivity. Here we develop a phenomenological theory for these coexisting orders. This provides selection rules for the PDW order and further shows that the detailed structure of this order is highly constrained. We then apply our theory to the vortex phase. This reveals vortex phases in which the d-wave vortex cores exhibit charge density wave order and further reveals that the SDW order provides detailed information about the vortex phase.

Thermoelectric studies of the non-thermal equilibrium dynamics in chiral metals

The conventional pyroelectric effect is intimately connected to the symmetry, or rather lack of center of symmetry, of the material. Although the experiments we discuss involve studies of low symmetry materials, the pyroelectric currents observed are of an entirely new origin. Systems with broken-translational-symmetry phases that incorporate orbital quantization can exhibit significant departures from thermodynamic equilibrium due to a change in magnetic induction. For example, orbitally quantized field-induced spin- or charge density wave systems, in which the competition between the elastic forces of the density wave and pinning leads to a critical state analogous to the vortex phase of type II superconductors. This metastable state consists of a balance between the density-wave pinning force and the Lorentz force on the extended currents due to the drift of cyclotron orbits. This results in the establishment of a three-dimensional chiral metal that can extend deep into the bulk of the crystal. In this way the density wave pinning potential plays a similar role to the edge potential in a two-dimensional electron gas, leading to a large Hall angle and quantization of the Hall resistance. A thermal perturbation that reduces the pinning potential returns the system toward thermal equilibrium, which can only be achieved by current flow orthogonal to the surface. The observation of this new form of pyroelectric effect in the high magnetic field phase ( B > 30 T ) of the organic charge transfer salt α - ( BEDT - TTF ) 2 KHg ( SCN ) 4 is conclusive proof of the existence of a three-dimensional chiral metal.

Evolution of Ferroelectric and Antiferromagnetic Phases of TbMn2O5 Under High Magnetic Field up to 45 T

We determine high magnetic field (B//a) vs temperature phase diagram of TbMn2O5 by measurements of dielectric constant (ϵ//b) and magnetization under static and pulsed B up to 45 T, and pyroelectric/magnetoelectric currents up to 9 T. Our results reveal that a ferroelectric (FE) transition temperature at T C = 38 K at B = 0 T changes little under B up to 33 T, while incommensurate antiferromagnetic phase, characterized as increased ϵ and negative polarization below 25 K at B = 0 T, becomes unstable above B = ∼20 T at low temperatures. Furthermore, a positive FE polarization component, coined with a Tb f-spin ordering below ∼15 K at B = 0 T, abruptly disappears with Tb f-spin reorientation under B ≤ ∼2 T. Determined phase diagram shows that both magnitude of FE polarization and ϵ value are sensitively dependent on the evolution of magnetic order parameters of both Mn-d and Tb-f spins tuned by high magnetic fields.

Dimensionality of superconductivity and vortex dynamics in the infinite-layer cuprateSr0.9M0.1CuO2(M=La,Gd)

The high magnetic field phase diagram of the electron-doped infinite layer high-temperature superconducting (high-T_c) compound Sr_{0.9}La_{0.1}CuO_2 was probed by means of penetration depth and magnetization measurements in pulsed fields to 60 T. An anisotropy ratio of 8 was detected for the upper critical fields with H parallel (H_{c2}^{ab}) and perpendicular (H_{c2}^c) to the CuO_2 planes, with H_{c2}^{ab} extrapolating to near the Pauli paramagnetic limit of 160 T. The longer superconducting coherence length than the lattice constant along the c-axis indicates that the orbital degrees of freedom of the pairing wavefunction are three dimensional. By contrast, low-field magnetization and specific heat measurements of Sr_{0.9}Gd_{0.1}CuO_2 indicate a coexistence of bulk s-wave superconductivity with large moment Gd paramagnetism close to the CuO_2 planes, suggesting a strong confinement of the spin degrees of freedom of the Cooper pair to the CuO_2 planes. The region between H_{c2}^{ab} and the irreversibility line in the magnetization, H_{irr}^{ab}, is anomalously large for an electron-doped high-T_c cuprate, suggesting the existence of additional quantum fluctuations perhaps due to a competing spin-density wave order.