Field-induced Magnetic Phase Transitions Research Articles

Discovery of the linear magnetoelectric effect in magnetic ferroelectric BiFeo3in a strong magnetic field

Abstract The discovery of a new magnetic field induced phase transition between the space-modulated spin structure (SMSS) and the homogeneous antiferromagnetic state (HAFS) is reported. This phase transition is accompanied by large magnetoelectric (ME) anomalies. It is well known that BiFeO, shows the ferroelectric ordering (T c = 1083 K) and antiferromagnetic ordering (T N = 673 K). ME properties of BiFeO3 so far remain a challenging experimental and theoretical problem. While the crystal symmetry of BiFeO3 allows a linear ME effect, it cannot be observed because the antiferromagnetic order of BiFeO3 is SMSS (cycloid). We show that there is a Lifshits invariant, which decreases the ground state energy and induces the SMSS. In a high magnetic field the energy of the HAFS decreases more rapidly than the energy of the SMSS. Hence the field induced phase transition between SMSS and HAFS is possible. We stress that a large variation of the ME effect is expected at the transition due to a rising linear ME contribution. To study the breaking of the SMSS by a magnetic field we measured the ME effect induced by a pulsed field up to 280 kOe at T = 10–180 K. Electric polarization components were measured with the help of electrodes attached to the faces of a BiFeO3 single crystal. The measured dependence of P(H) is quadratic at H < H, and has a jump at H = H c when the SMSS is evidently destroyed. The critical field H c is of the order 200 kOe. These conclusions agree well with the theoretical views.

Anomalous magnetic torque in UBe13: Evidence for a field-induced magnetic phase transition.

Measurements of the magnetic force and magnetic torque acting upon single-crystal and polycrystal samples of the heavy-fermion superconductor UBe[sub 13] have been made at temperatures from 60 mK to 30.0 K and in magnetic fields to 23 T using a capacitive magnetometer. The magnetic susceptibility deduced from the magnetic force is in reasonably good agreement with measurements using conventional techniques. We find that a large, anomalous contribution to the magnetic torque (AMT) appears in fields above 3--5 T at low temperature and at temperatures below about 7--12 K in high fields. The AMT coexists with the superconducting state at low temperature. We propose that the AMT reflects the existence of a field-induced magnetic phase transition. The presence of such a phase transition is consistent with specific-heat, thermopower, magnetoresistance, and Hall-effect measurements.

Phase diagram (T, H) investigation by direct measurement of dR/dT in a magnetic material

The temperature dependences of the resistance R(T) and the singular part of near the critical regime and in the presence of magnetic fields H (0-5 T) are presented in this paper. The measurements were carried out using a novel technique from which ~~i)~ can be determined directly. This quantity, being related to the transport coefficient ( j~i, is directly connected to the specific heat behavior near the phase transition. The high accuracy of our experimental data allows us to compare the critical exponents deduced from our previous mea- surements in zero field (H = 0 T) and those predicted by several models of the renormal12ation group theory. We present a complete phase diagram for a single crystal of erbium oriented along the c-axis- This constitutes the first systematic study of field-induced magnetic phase transitions using the magnetoresistance R(T, NJ and its derivative ~ji( ~ near the critical points.

Dipolar field effect on magnetic field-induced phase transitions

The concept of the intermediate state arising due to the demagnetizing field has been used in order to describe magnetic field-induced first-order reorientation transitions. Special attention is devoted to the nucleation mechanisms and their effect on the magnetization curve.

Anisotropic magnetoresistance of the semimetallic antiferromagnet EuAs3.

The Hall effect and the magnetoresistance of single crystals of ${\mathrm{EuAs}}_{3}$ have been measured in the temperature region of magnetic ordering. We observe an extreme anisotropic behavior. When the magnetic field is applied perpendicular to the buckled As layers of the ${\mathrm{EuAs}}_{3}$ crystal structure, a strong positive magnetoresistance is found, similar to the case of \ensuremath{\alpha}-As. The situation changes completely with the magnetic field parallel to [010], the direction of the ordered ${\mathrm{Eu}}^{2+}$ moments in the low-temperature AF1 phase of ${\mathrm{EuAs}}_{3}$. In this case, the magnetoresistance is much weaker and reflects the field-induced magnetic phase transitions, similar to the case of the rare-earth metals Dy and Ho. We discuss these features on the basis of superzone and spin-fluctuation scattering.

Field-induced magnetic phase transitions

Recent trends in the field-induced magnetic phase transitions are reviewed with a short historical survey of the problems. Two new discoveries in the low-dimensional magnets, the Haldane gap quenching and field-induced frustrations produced by the J-crossover, are shown first. Applications to the highly correlated systems with conduction electrons are highlights in this field and various recent results in the heavy fermion, valence fluctuation and superconducting states are introduced. Field-induced new states in these systems are investigated.

Field Induced Phase Transitions in Systems with a Crystalline Field Singlet Ground State

Magnetic field induced phase transitions are studied in a simplified model to represent systems with a crystalline field singlet ground state such as some rare earth compounds by the mean field approximation. In the case where the magnetic field yields the level crossing of the ground and excited states in the absence of the exchange interaction, then its presence brings two types of the phase transition. One of them is a second order transition accompanied with a polarization perpendicular to the field. This is a transition found by Tsuneto and Murao, and Tachiki and Yamada. Another is a first order transition, which occurs for the ferromagnetic coupling when the perpendicular susceptibility can not be large enough to yield a spontanous polarization. The system skips over the level crossing from the lower to higher magnetization states without change of symmetry. The condition and the nature of these transitions are investigated.

Solid state physics research in megagauss fields

We present the latest results of experiments in solid state physics in very high magnetic fields in the megagauss range, which are produced by electromagnetic flux-compression and the single-turn coil technique at the megagauss laboratory in Tokyo. The topics include the infrared cyclotron resonance and magneto-optics in semiconductors, the spin-flip transition in iron garnets, the magnetic field-induced electronic phase transition in low-dimensional systems and the determination of upper critical fields of high- T c superconductors.

ChemInform Abstract: Experimental Studies of Magnetic Field Induced Phase Transitions

ChemInform Abstract: Experimental Studies of Magnetic Field Induced Phase Transitions

Differential thermal analysis of the field induced phase transitions of (TMTSF) 2ClO 4 above 1.2 K

We present some results of a differential thermal analysis of the magnetic field induced phase transitions in the organic conductor (TMTSF) 2ClO 4 above 1.2 K. This study shows that transitions between different spin density wave states are first order and that the total entropy change involved in the two detected transitions (in the temperature range 1.2–2 K) is close to that of the quasi-one-dimensional electron gas. Above 2 and 4.2 K, only a single transition has been detected in our measurements. The entropy of that transition decreases and extrapolates to zero near 5 K. We present some arguments suggesting that if longitudinal nesting (2 k F , 0, 0) is to take place in the semi-metallic SDW phase at high fields it exists only above 2 K or so.

Detection of magnetic phase transitions using the strip-line technique

The strip-line transmission spectra of suitably oriented Eu(As 1-xP x) 3 mixed crystals exhibit as a function of magnetic field several step-like changes independent of the far infrared wave length. The longitudinal magnetoresistivity of Eu(As 0.6P 0.4) 3 shows an almost identical dependence on the magnetic field strength as the strip-line transmission. A comparison with magnetization measurements reveals that both, the structures in the strip-line spectra and in the magnetoresistivity are caused by field-induced magnetic phase transitions. The magnetic phase diagram of Eu(As 0.6P 0.4) 3 has been determined using this new method of detecting magnetic phase boundaries.

Quantum oscillations and field-induced transitions in (TMTSF) 2ReO 4

We report the magnetoresistance of (TMTSF) 2ReO 4 in the metallic state at low temperature and high pressure. We find evidence for a series of magnetic field induced phase transitions. We also observe Shubnikov-de Haas oscillations both above and below the threshold for the field induced transition - an anomalous result that is not explained by present theories.

Bethe‐Peierls study of magnetic field induced phase transitions

AbstractUsing a Bethe‐Peierls like approach the thermodynamic behavior of a two‐sublattice Ising antiferromagnet is studied focusing on low temperatures and high magnetic fields portion of its phase diagram, where the system undergoes magnetic field‐induced phase transitions. The results for the H‐T phase diagram agree quite well with those from Monte Carlo calculations and show a „peculiar”︁ boundary at low temperatures and high magnetic fields separating the AF from the PM state in which, in a certain narrow range of magnetic field values, the system undergoes an AF to PM phase transition both by increasing or decreasing the temperature at constant magnetic field. The behavior of the system is investigated in this „peculiar”︁ regime by calculating the relevant thermodynamic quantities and a qualitatively symmetric behavior at the two AF to PM transition points with respect to the two directions of temperature variation at constant field is found.

Magnetic Field Dependent Susceptibility of (TMTSF)2ClO4

Abstract The magnetic susceptibility (X)-of slowly cooled single crystals of(TMTSF)2ClO4 was measured for H/ /c* with fields up to 10 tesla and 1.7K < T < 300K. No anomaly in X is observed at the anion ordering temperature 24K, with xPauli constant for 4.2K < T < 30K. Between 4.2K and 2.2K, xPauli increases threefold in aggreement with the high field specific heat data signaling a magnetic field induced phase transition. The magnetic field dependence of the X at 4.2 and 2.0K shows the presence of ∼1500 ppm Curie spins. Such localized spins and their associated Schottky anomaly can account for a large part of the 2 tesla specific heat anomaly reported earlier by Brusetti et at.

NMR-Studies of Field-Induced Phase in (TMTSF)2ClO4

Abstract 77Se-NMR measurement on a single crystal of (TMTSF)2ClO4 is revealed to be a sensitive probe of the field-induced magnetic phase transition. A recent trial to determine the magnetic phase boundary below 1 K is described.

Magnetic Field-Induced Phase Transitions in a Thin Film of Cholesteric Liquid Crystal

A stable structure of cholesteric liquid crystal thin film in a magnetic field is explored under the boundary condition that the film is strongly anchored at one surface and kept free at the other. It is shown that the system shows a series of first order phase transitions. A step-wise change of helical pitch is obtained as a function of external magnetic field.

Magnetic field induced phase transition of a three-dimensional electron gas

It is shown within the Hartree-Fock approximation that the electron gas in a strong magnetic field undergoes a phase transition to a charge density wave (CDW) state. The transition temperature T c is calculated as a function of the magnetic field strength B. With increasing B, the nature of the electron system at T c changes from degenerate to non-degenerate. For moderate values of B a second order transition to a unidirectional CDW is obtained, and for large B a first order transition to a CDW with the symmetry of a hexagonal lattice. If material parameters are adapted to Hg .8Cd .2Te, T c is of the order of 1K for B values near 5T.

Field-induced magnetic phase transitions in dysprosium

By measuring isothermal magnetization curves in the temperature range between 4.2 K and 190 K we were able to establish a H—T-phase diagram of the spin structures of Dysprosium. The phase boundaries for the phase transitions helical—fan, helical—ferromagnetic and fan—ferromagnetic were determined in dependence of the temperature and the applied field.

Rotation and deformation of the optical indicatrix of hematite during the magnetic field-induced phase transition

It is shown from experiment that a rotaion ρ and a deformation χ of the optical indicatrix appear during the transverse field-induced phase transition in hematite. Strong dependence of ρ and χ on the temperature, magnetic field Ha and the angle Ψ corresponding to the direction of Ha with respect to the C2 axis in the basal plane are observed. During the Morin transition, the evolution of the linear magnetic birefringence is very sensitive to the magnetic phase transition and this evolution is discussed from the dependences of the analytical expressions of ρ and χ on the rotation of the antiferromagnetic vector L.

Field-induced magnetic ordering in the S = 1 singlet ground-state system Ni(C 5H 5NO) 6(ClO 4) 2 studied by specific heat

Specific-heat data on Ni(C 5H 5NO) 6(ClO 4) 2 are presented for fields 0 ⩽ H ⩽ 60 kOe and temperatures 0.1 ⩽ T ⩽ 1.3 K. In this material the S = 1 ground triplet is split by a trigonal crystal field term into a singlet and a higher lying doublet, such that ordering cannot occur in zero field. The field-induced magnetic phase transitions are studied both experimentally and theoretically, using molecular field theory, high-temperature series expansions and spin-wave theory. We obtain the values J/ k = -(0.20 ± 0.01) K and D/ k = 6.6 ± 0.2 K for the antiferromagnetic (subcritical) exchange constant and for the crystal-field splitting parameter, respectively.