High-field Phase Research Articles

Spin-lattice coupling in a ferrimagnetic spinel: Exotic H−T phase diagram of MnCr2S4 up to 110 T

In antiferromagnets, the interplay of spin frustration and spin-lattice coupling has been extensively studied as the source of complex spin patterns and exotic magnetism. Here, we demonstrate that, although neglected in the past, the spin-lattice coupling is essential to ferrimagnetic spinels as well. We performed ultrahigh-field magnetization measurements up to 110 T on a Yafet-Kittel ferrimagnetic spinel, MnCr$_2$S$_4$, which was complemented by measurements of magnetostriction and sound velocities up to 60 T. Classical Monte Carlo calculations were performed to identify the complex high-field spin structures. Our minimal model incorporating spin-lattice coupling accounts for the experimental results and corroborates the complete phase diagram, including two new high-field phase transitions at 75 and 85 T. Magnetoelastic coupling induces striking effects: An extremely robust magnetization plateau is embedded between two unconventional spin-asymmetric phases. Ferrimagnetic spinels provide a new platform to study asymmetric and multiferroic phases stabilized by spin-lattice coupling.

High-field phase transitions in the orbitally ordered multiferroic GeV4S8

The high-field (H,T) phase diagram of the multiferroic lacunar spinel $\mathrm{Ge}{\mathrm{V}}_{4}{\mathrm{S}}_{8}$ has been studied by ultrasound, magnetization, and pyrocurrent experiments in magnetic fields up to 60 T. The title compound consists of molecular building blocks, with vanadium ${\mathrm{V}}_{4}$ clusters characterized by a unique electron density. These vanadium tetrahedra constitute a Jahn-Teller active entity, which drive an orbital-ordering transition at 30 K with the concomitant appearance of ferroelectricity. Ultrasound and magnetization experiments reveal sharp anomalies in magnetic fields of 46 T, which are associated with a first-order phase transition into an orbitally disordered state characterized by significant field and temperature hystereses. We report a sequence of complex magnetic, polar, and orbitally ordered states, i.e., the appearance of two orbitally ordered phases OO1 and OO2 for ${\ensuremath{\mu}}_{0}H<45\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ and $T<30\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Beyond the paraelectric phase we further evidenced three ferroelectric phases, FE1, FE2, and FE3. Finally, antiferromagnetic (AFM) order $(T<15\text{ K})$ and fully polarized ferromagnetic order $({\ensuremath{\mu}}_{0}H>60\phantom{\rule{0.16em}{0ex}}\mathrm{T})$ have been observed in $\mathrm{Ge}{\mathrm{V}}_{4}{\mathrm{S}}_{8}$. At low temperatures and for fields below 40 T, AFM order coexists with the polar phase FE3 identifying a multiferroic state. Our results demonstrate a fascinating competition of the different orders, which the material manifests in high magnetic fields and at low temperatures.

High-field magnetization and magnetic phase diagram of metamagnetic shape memory alloys Ni50−xCoxMn31.5Ga18.5 ( x = 9 and 9.7)

Magnetic phase diagrams of the metamagnetic shape memory alloys Ni50-xCoxMn31.5Ga18.5 (x = 9 and 9.7) were produced from high-field magnetization measurements up to 56 T. For both compounds, magnetic field induced martensitic transformations are observed at various temperatures below 300 K. Hysteresis of the field-induced transformation shows unconventional temperature dependence: it decreases with decreasing temperature after showing a peak. Magnetic susceptibility measurement, microscopy, and X-ray diffraction data suggest a model incorporating the magnetic anisotropy and Zeeman energy in two variants, which qualitatively explains the thermal and the magnetic field history dependence of the hysteresis in these alloys.

High field phase transition of cathode material Li2MnSiO4 for lithium-ion battery

The magnetic properties of the candidate lithium-ion battery cathode materials Li2MnSiO4 have been studied experimentally using static and pulsed high magnetic fields. A field-induced magnetic transition is observed in low temperature region, in which a saturation magnetization is observed above 27 T which confirms that the Mn-ion has a dominant low spin state with a saturated magnetic moment of ∼3.1 μB/Mn. With the change of temperature and magnetic field, the Li2MnSiO4 shows a complex magnetic phase transition. Considering to the coupling between spin, charge and orbital, the field-induced magnetic transition may affect the charge-discharge behavior of the cathode material, thus, the study is expected to explore the possibility and stability of the candidate lithium-ion battery cathode materials used in the low temperature and high magnetic field circumstance and its performance degradation.

Nano-second timescale high-field phase transition in hydrogenated amorphous silicon

In this work, we report the phase transition behavior of hydrogenated amorphous silicon on the application of nanosecond timescale high-field pulse electrical stress. The transition of amorphous silicon to nanocrystalline silicon, confirmed through Raman spectroscopy, is marked by an abrupt change in the pulse I-V characteristics. The mechanism of the phase transition at high electric field involving the avalanche generation of charge carriers and optical phonon generation is discussed. The role of defect states in optical phonon localization and eventual phase transition is explored. The phase transition in the case of devices with a drain-gate underlap is also studied. The role of self-heating in accelerating the phase transition has also been explored. The impact of channel dimensions on the onset of the phase transition is also discussed. Characterization of the resultant nc-Si is done through deconvolution of the Raman spectra, and the quality of nc-Si created is found comparable to earlier studies.

Microscopic evidence of a quantum magnetization process in the S=12 triangular-lattice Heisenberg-like antiferromagnet Ba3CoSb2O9

We report results of the neutron scattering investigations of frustrated quantum magnet ${\mathrm{Ba}}_{3}{\mathrm{CoSb}}_{2}{\mathrm{O}}_{9}$ in magnetic fields up to 25.9 T. Contrary to other materials, ${\mathrm{Ba}}_{3}{\mathrm{CoSb}}_{2}{\mathrm{O}}_{9}$ exhibits properties typical of an ideal $S=\frac{1}{2}$ triangular lattice Heisenberg antiferromagnet, making it a perfect model system for testing theoretical predictions. In this work, we looked into the magnetization process in ${\mathrm{Ba}}_{3}{\mathrm{CoSb}}_{2}{\mathrm{O}}_{9}$ on a microscopic scale with a magnetic field applied in plane. A sequence of magnetic phase transitions, including the new high-field phase at 22.5 T reported recently has been followed at low temperatures as a function of field and modeled using the large-size cluster mean-field plus scaling method. Showing good agreement with the model, our results bridge the theory and the experiment providing microscopic information about the high-field spin ordering in $S=\frac{1}{2}$ triangular lattice Heisenberg-like antiferromagnet ${\mathrm{Ba}}_{3}{\mathrm{CoSb}}_{2}{\mathrm{O}}_{9}$.

High-field expansion approach to kagome antiferromagnets with Dzyaloshinskii-Moriya interactions

We apply linked cluster expansion techniques to study the polarized high-field phase of a spin-half antiferromagnet on the Kagome lattice with Heisenberg and Dzyaloshinskii-Moriya interactions (DMI). We find that the Dirac points of the single-magnon spectrum without DMI are robust against arbitrary DMI when the magnetic field lies in the Kagome plane. Unlike the typical case where DMI gaps the spectrum, here we find that varying the DMI merely shifts the location of the Dirac points. In contrast, a magnetic field with a component out of the Kagome plane gaps the spectrum, leading to topological magnon bands. We map out a topological phase diagram as the couplings are varied by computing the band Chern numbers. A pair of phase transitions are observed and we find an enhanced thermal Hall conductivity near the phase boundary.

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.

Putative spin-nematic phase in BaCdVO(PO4)2

We report neutron scattering and AC magnetic susceptibility measurements of the 2D spin-1/2 frustrated magnet BaCdVO(PO$_{4}$)$_{2}$. At temperatures well below $T_{\sf N}\approx 1K$, we show that only 34 % of the spin moment orders in an up-up-down-down strip structure. Dominant magnetic diffuse scattering and comparison to published $\mu$sr measurements indicates that the remaining 66 % is fluctuating. This demonstrates the presence of strong frustration, associated with competing ferromagnetic and antiferromagnetic interactions, and points to a subtle ordering mechanism driven by magnon interactions. On applying magnetic field, we find that at $T=0.1$ K the magnetic order vanishes at 3.8 T, whereas magnetic saturation is reached only above 4.5 T. We argue that the putative high-field phase is a realization of the long-sought bond-spin-nematic state.

Giant Anisotropic Magnetoresistance due to Purely Orbital Rearrangement in the Quadrupolar Heavy Fermion Superconductor PrV_{2}Al_{20}.

We report the discovery of giant and anisotropic magnetoresistance due to the orbital rearrangement in a non magnetic correlated metal. In particular, we measured the magnetoresistance under fields up to 31.4T in the cubic Pr-based heavy fermion superconductor PrV_{2}Al_{20} with a non magnetic Γ_{3} doublet ground state, exhibiting antiferroquadrupole ordering below 0.7K. For the [100] direction, we find that the high-field phase appears between 12 and 25T, accompanied by a large jump at 12T in the magnetoresistance (ΔMR∼100%) and in the anisotropic magnetoresistivity ratio by ∼20%. These observations indicate that the strong hybridization between the conduction electrons and anisotropic quadrupole moments leads to the Fermi surface reconstruction upon crossing the field-induced antiferroquadrupole (orbital) rearrangement.

Low-temperature thermal conductivity and magnetic transitions of the kagome-staircase compound Ni3V2O8

The kagome-staircase compound ${\mathrm{Ni}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ is an attractive multiferroic material exhibiting rich phase diagrams. However, the magnetic properties and magnetic transitions have been studied only above 1.3 K. In this work, we study the thermal conductivity $\ensuremath{\kappa}$ of ${\mathrm{Ni}}_{3}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$ single crystals at low temperatures down to 0.3 K and in magnetic fields up to 14 T. In zero field, the magnetic transitions from the low-temperature incommensurate (LTI) phase to the commensurate phase (C) and then to a second commensurate phase $({\mathrm{C}}^{\ensuremath{'}})$ yield anomalies in $\ensuremath{\kappa}(T)$ curves at ${T}_{\mathrm{LC}}=3.7$ K and ${T}_{{\mathrm{CC}}^{\ensuremath{'}}}=2.0$ K, respectively, which indicates a significant phonon scattering by the critical spin fluctuations. When the field is applied along the $a$ axis, the field dependence of $\ensuremath{\kappa}$ displays four anomalies associated with different magnetic transitions and reveals an undetected magnetic state at subkelvin temperatures. In addition, the $\ensuremath{\kappa}(B)$ curves are found to depend not only on the history but also on the magnitude of the applied field. When the field is applied along the $b$ axis, a high-field phase located above the LTI and high-temperature incommensurate phases is revealed.

Frustration-free spatially anisotropic S=1 square-lattice antiferromagnet Ni[SC(NH2)2]6Br2

Kagom\'{e}-staircase compound Ni$_3$V$_2$O$_8$ is an attractive multiferroic material exhibiting rich phase diagrams. However, the magnetic properties and magnetic transitions have been studied only above 1.3 K. In this work, we study the thermal conductivity ($\kappa$) of Ni$_3$V$_2$O$_8$ single crystals at low temperatures down to 0.3 K and in magnetic fields up to 14 T. In zero field, the magnetic transitions from the low-temperature incommensurate (LTI) phase to the commensurate phase (C) and then to a second commensurate phase (C') yield anomalies in $\kappa(T)$ curves at $T\rm_{LC}$ = 3.7 K and $T\rm_{CC'}$ = 2.0 K, respectively, which indicates a significant phonon scattering by the critical spin fluctuations. When the field is applied along the $a$ axis, the field dependence of $\kappa$ displays four anomalies associated with different magnetic transitions and reveals an undetected magnetic state at subKelvin temperatures. In addition, the $\kappa(B)$ curves are found to depend not only on the history but also on the magnitude of applying field. When the field is applied along the $b$ axis, a high-field phase locating above the LTI and high-temperature incommensurate (HTI) phases is revealed.

Even- and Odd-Frequency Superconductivity in Q1D Organic Superconductors Under Magnetic Field

One of the quasi-one-dimensional organic superconductors $$(\hbox {TMTSF})_2X$$ , called Bechgaard salts, has attracted a lot of interest since its discovery in 1980. These compounds have high critical magnetic field $$H_{\mathrm {c}2}$$ in the direction parallel to the layers, and their pairing symmetries seem to be different between low-field phase and high-field phase. In addition, recently, the possibility of the realization of odd-frequency superconductivity was pointed out. Therefore, we study pairing symmetries of Bechgaard salts under magnetic field with frequency-dependent pairing interaction due to spin and charge fluctuation. The model is given by the extended Hubbard model on a quasi-one-dimensional square lattice, and the spin susceptibility and charge susceptibility for the effective pairing interactions are derived by random-phase approximation under magnetic field. The odd-frequency s-wave and even-frequency f-wave regions expand as the magnetic field is increased.

High-field nonlinear optical response and phase control in a dielectric laser accelerator

Advances in ultrafast laser technology and nanofabrication have enabled a new class of particle accelerator based upon miniaturized laser-driven photonic structures. However, developing a useful accelerator based on this approach requires control of the particle dynamics at field intensities approaching the damage limit. We measure acceleration in a fused silica dielectric laser accelerator driven by fields of up to 9 GV m−1 and observe a record 1.8 GV m−1 in the accelerating mode. At these intensities the dielectric is driven beyond its linear response and self-phase modulation changes the phase velocity of the accelerating mode, reducing the average gradient to 850 MeV m−1. We show that free-space optics can be used to compensate this dephasing and demonstrate that tailoring the laser phase and amplitude can facilitate optimization of the beam dynamics. This could enable MeV scale energy gain in a single stage and pave the way towards applications in scientific, industrial, and medical fields.

Observation of two critical points linked to the high-field phase B in CeCu2Si2

We present thermal expansion and magnetostriction measurements on a CeCu2Si2 single crystal of A/S-type up to 17.9T magnetic field applied along the crystallographic a-direction (Delta L ll a ll H) and down to 0.015K temperature. We identify clear thermodynamic anomalies at the superconducting transition T_c and at two second order transitions T_A,B into ordered phases A and B. Our measurements establish for the first time the boundary of phase B at high field and low temperature. No evidence for additional high field phases above B is found up to the maximum field. We speculate based on our experimental results that i) phase B is similar to phase A of spin-density wave type and ii) the first order phase transition between A and B is caused by Fermi surface reconstruction. We furthermore identify a new quantum critical point at H_c ~ 17T, where T_B is suppresssed to zero, and a bicritical point at (0.35K, 7.0T), where phase lines T_A(H) and T_B(H) meet.

Effect of uniaxial stress on the magnetic phases of CeAuSb2

We present results of measurements of resistivity of \CAS{} under the combination of $c$-axis magnetic field and in-plane uniaxial stress. In unstressed \CAS{} there are two magnetic phases. The low-field A phase is a single-component spin-density wave (SDW), with $\mathbf{q} = (\eta, \pm \eta, 1/2)$, and the high-field B phase consists of microscopically coexisting $(\eta, \eta, 1/2)$ and $(\eta, -\eta, 1/2)$ spin-density waves. Pressure along a $\langle 100 \rangle$ lattice direction is a transverse field to both of these phases, and so initially has little effect, however eventually induces new low- and high-field phases in which the principal axes of the SDW components appear to have rotated to the $\langle 100 \rangle$ directions. Under this strong $\langle 100 \rangle$ compression, the field evolution of the resistivity is much smoother than at zero strain: In zero strain, there is a strong first-order transition, while under strong $\langle 100 \rangle$ it becomes much broader. We hypothesize that this is a consequence of the uniaxial stress lifting the degeneracy between the (100) and (010) directions.

Field-induced ordering in a random-bond quantum spin ladder compound with weak anisotropy

The field induced quantum phase transitions in the disorder-free and disordered samples of the spin ladder material (CH_3)_2CHNH_3Cu(Cl_{1-x}Br_x)_3 are studied using magnetic calorimetry and magnetic neutron diffraction on single crystal samples. Drastically different critical indexes and correlation lengths in the high field phase are found for two different orientations of the applied field. It is argued that for a field applied along the crystallographic c axis, as in previous studies [1], the transition is best described as an Ising transition in random field and anisotropy, rather than as a magnetic Bose Glass to Bose Condensate transition. [1] Tao Hong, A. Zheludev, H. Manaka, and L.- P. Regnault, Phys. Rev. B 81, 060410 (2010).

Mermin-Wagner physics, (H,T) phase diagram, and candidate quantum spin-liquid phase in the spin- 12 triangular-lattice antiferromagnet Ba8CoNb6O24

Ba$_8$CoNb$_6$O$_{24}$ presents a system whose Co$^{2+}$ ions have an effective spin 1/2 and construct a regular triangular-lattice antiferromagnet (TLAFM) with a very large interlayer spacing, ensuring purely two-dimensional character. We exploit this ideal realization to perform a detailed experimental analysis of the $S = 1/2$ TLAFM, which is one of the keystone models in frustrated quantum magnetism. We find strong low-energy spin fluctuations and no magnetic ordering, but a diverging correlation length down to 0.1 K, indicating a Mermin-Wagner trend towards zero-temperature order. Below 0.1 K, however, our low-field measurements show an nexpected magnetically disordered state, which is a candidate quantum spin liquid. We establish the $(H,T)$ phase diagram, mapping in detail the quantum fluctuation corrections to the available theoretical analysis. These include a strong upshift in field of the maximum ordering temperature, qualitative changes to both low- and high-field phase boundaries, and an ordered regime apparently dominated by the collinear "up-up-down" state. Ba$_8$CoNb$_6$O$_{24}$ therefore offers fresh input for the development of theoretical approaches to the field-induced quantum phase transitions of the $S = 1/2$ Heisenberg TLAFM.