Field-induced Magnetic Phase Research Articles

Field-induced magnetic phase transitions in ferrimagnet GdMn2Ge2: H - T magnetic phase diagrams

Magnetic properties of a two-sublattice ferrimagnet with antiferromagnetic exchange interaction inside one of the sublattices are calculated within the framework of the molecular field theory taking into account the anisotropy of unstable sublattice. The magnetization curves of single crystal GdMn2Ge2 for the magnetic field parallel and perpendicular to the c-axis at different temperatures are calculated. Field-induced magnetic phase transitions in GdMn2Ge2 are discussed. Calculated H - T magnetic phase diagrams are in fair agreement with experimental data.

Field-induced phase transitions and giant magnetoresistance in Dy Co single crystals

Electrical resistivity and calorimetric measurements on Dy 3 Coshow that below the Neel temperature (TN=44 K) the non-collinear antiferromagnetic structure exhibits field-induced magnetic phase transitions of a first-order type along all principal axes, accompanied by a strongly anisotropic giant magnetoresistance and by a change of the Sommerfeld coefficient of the specific heat. Quantum tunnelling of the magnetization appears to be possible for T < 0.6 K.

Spontaneous and field-induced magnetic phase transitions in the intermetallic compounds (Gd1−x Y x )Mn2Ge2

The magnetic properties of the intermetallic compounds Gd1−xYxMn2Ge2 (0≤x≤0.5) (tetragonal crystal structure of the type ThCr2Ge2) have been measured in fields up to 40 T in the temperature range 4.2–120 K on free powders (whose particles are free to rotate in a magnetic field), fixed powders, and polycrystalline bulk samples. The temperature dependence of the crystal structure parameters of some of these intermetallic compounds was determined from x-ray diffraction measurements. It was found that the temperatures of magnetic disordering of the gadolinium magnetic subsystem and the transition of the manganese subsystem from the ferromagnetic to the antiferromagnetic state decrease as the gadolinium content is decreased, so that in compositions with x<0.3 this transition is a first-order phase transition, and with further decrease of the gadolinium content it becomes second-order. In intermetallic compounds of this system with x=0.3 and 0.4 another spontaneous first-order transition is observed at lower temperatures. In a magnetic field the magnetization of all the investigated intermetallic compounds except for the composition x=0.5 undergo a metamagnetic transition. The T-x, H-x, and H-T magnetic phase diagrams are constructed. The experimental data are interpreted with allowance for the fact that according to the results of previous studies, the Mn-Mn exchange interaction is antiferromagnetic, and thus the examined intermetallic compounds are two-sublattice ferrimagnets with negative exchange interaction in one of the sublattices. Calculations performed within the framework of this model in the Yafet-Kittel approximation, which assumes that the sublattice with negative exchange can be divided into two sub-sublattices, permit a quantitative description of the experimental results in most cases.

Field-induced magnetic phase transitions in the Yafet-Kittel model

The Yafet-Kittel model for a two-sublattice ferrimagnet with an antiferromagnetic exchange interaction in one of the sublattices was developed to describe magnetic-field-induced phase transitions in the isotropic and Ising cases. Depending on the relative values of the exchange parameters of the inter-sublattice interaction and the intra-sublattice interaction in the isotropic case, two types of magnetic phase diagrams with two types of second-order phase transitions are possible: to the noncollinear phase and to the spin-flip phase, and, in the Ising case, three types of magnetic phase diagrams with first-order phase transitions are possible.

Magnetic and electrical properties of antiferromagnetic (Gd 1 − xY x) 3Co single crystals

Using magnetization and magnetoresistance measurements along the main axes of (Gd 1 − x Y x ) 3Co single crystals we have obtained the magnetic phase diagram of this system. The field-induced magnetic phase transitions from the antiferromagnetic (AF) to the ferromagnetic (F) state are accompanied by a giant magnetoresistance effect. The dilution of the Gd-sublattice leads to an unmonotonous change of the critical AF—F transition fields and to a change of the shape of the temperature dependencies of the electrical resistivity at high temperatures from saturation (at x = 0) to normal metallic behavior at high Y content.

Quantizing field-induced magnetic phase in a three-dimensional electron gas

Theory of magnetic-induction bifurcation in the Condon domain phase of a three-dimensional (3D) electron gas under high-magnetic field is presented. The results\char22{}the diamagnetic phase transition temperature and the induction bifurcation values\char22{}are in good agreement with nuclear magnetic resonance data in silver. The temperature dependence of the order parameter of the diamagnetic phase transition\char22{}the magnetization in each Condon domain\char22{}is obtained by a comparison of the theory with the experiment. The mean-field approach has been shown to lead to the universal behavior of an electron gas of 2D and 3D dimensionality.

Field-Induced Magnetic Phase Transition of FeRh1-xPdx Alloy with Body-Centered Tetragonal Structure

Field-Induced Magnetic Phase Transition of FeRh1-xPdx Alloy with Body-Centered Tetragonal Structure

Study of spin-Peierls CuGeO 3 by high-field ESR

An inorganic spin-Peierls compound CuGeO 3 has been studied by high-field ESR combining pulsed magnetic fields and far-infrared lasers. In EPR measurements under megagauss fields, an exchange splitting is observed and the interchain exchange coupling is evaluated. In the dimerized spin-Peierls phase, a direct transition between the singlet ground and the triplet excited states is observed. This result supports the existence of the second gap between the triplet state and the continuum. Collective spin wave modes in the field-induced magnetic phase and in the antiferromagnetic phase of the impurity-doped system have been also studied.

Evidence of mixed magnetic phases inTbRu2Ge2

In compounds with normal rare earths at the same crystallographic site, mixed magnetic phases with two distinct rare-earth magnetic states, namely, a zero moment one and another with a high moment, can be stabilized at low temperature not only in zero applied field but also in different field-induced magnetic phases of a metamagnetic process. These characteristics are observed in tetragonal ${\mathrm{TbRu}}_{2}{\mathrm{Ge}}_{2}$ from neutron diffraction and magnetization measurements on a single crystal. It is shown that such magnetic structures may originate from a moment instability due to the crystal field in the presence of frustrated exchange interactions. Numerical simulations using the periodic-field model allowed us to satisfactorily account for the observed properties and emphasize the crucial role played by the crystal field.

ESR study of the field-induced magnetic phase of spin-Peierls CuGeO 3 and MEM(TCNQ) 2

ESR measurements have been performed in high magnetic fields up to 30 T on the spin-Peierls compounds CuGeO 3 and MEM(TCNQ) 2 to examine the magnetic excitation in the magnetic phase (M phase) induced by external fields. Discontinuous changes in the resonance fields have been observed around the phase boundary between the dimerized spin-Peierls phase and the M phase for both CuGeO 3 and MEM(TCNQ) 2. Anisotropic AFMR modes are observed in the M phase of CuGeO 3.

Magnetic Field-Induced Phase Transition in the Quasi Two-Dimensional Organic Superconductor (BEDO-TTF)2ReO4 .H2O

Transverse magnetoresistance of the two-dimensional (2D) organic superconductor (BEDO-TTF) 2 ReO 4 . H 2 O has been measured in pulsed magnetic fields up to 52 T and in the temperature range from 1.7 K to 4.2 K. For magnetic field lower than ∼15 T, applied perpendicularly to the conducting planes, the data are in good agreement with previous studies, namely, the two Shubnikov-de Haas oscillation series with frequency F 1 = (38 ± 2) T and F 2 = (74 ± 2) T attributed to electron and hole orbits, respectively, are observed. However, as the magnetic field is rotated in the plane perpendicular to the best conductivity direction, the behaviour of the oscillations is not consistent with a perfect 2D picture. In addition, a new oscillation series with frequency about twice F2 (F4 = (150 ± 10) T) rises up, at high magnetic field while the amplitude of the oscillations with the F2 frequency decreases. Furthermore, magnetic fields higher than 10 T, applied parallel to the conducting planes, yield negative magnetoresistance. These features are discussed on the basis of the available Fermi surface calculations.

Magnetic Field-Induced Phase Transitions in Ferrofluid Emulsion

Two field-induced phase transition regimes are found in a ferrofluid emulsion system, which are defined by three critical fields, Hc1&lt;HC2&lt;Hc3. The first regime, which starts at Hc1 and finishes at Hc2, is the transition from a gas to induced Nematic liquid crystal phase. In the second regime, or Hc2&lt;H&lt;Hc3, induced Nematic liquid crystal transits to columnar solid structure. A phase diagram is drawn and is explained well by a scaling calculation, which gives Hc1~Φ−1/2, Hc2~Φ−1/4, and Hc3~Φγ exp (πG/Φγ/2), where Φ is the volume fraction, γ=0.172 and G=1.44.

Evidence for Mixed State in Terbium

Evidence for the existance of a previously unresolved additional mixed state in terbium single crystals is obtained in the temperature range 190 to 220 K. Magnetoresistance measurements are reported in an applied magnetic field, continuously changing to a maximum of 23 kOe, and in the temperature range 80 to 300 K. Longitudinal and transverse measurements were made with the current and the field in the [0001], [10\\overline10], and [2\\overline1\\overline10] directions. Anomalies in the magnetoresistance are correlated here with field-induced magnetic phase modifications. Certain details of the measurement techniques employed have been found to be of importance: It is essential that the samples' internal magnetic fields have high homogeneity and that the specimen is mounted in such a way as to provide for the relief of thermal and magnetostrictive stresses.

Magnetoresistance and the field-induced magnetic phase transitions in the re-entrant superconductor HoNi 2B 2C

Magnetoresistivity isotherms of polycrystalline HoNi 2B 2C indicate, for T < T N, a cascade of field-induced magnetic phase transitions. These transitions (and the recently reported H- T phase diagram) are interpreted as follows: an external field transforms, at H c2, the superconducting antiferromagnetic ground state into a non-superconducting distorted helical state. On increasing the field further, such a distorted helical state is transformed into the ferromagnetic state via two types of fan-like spin structures. Furthermore, a discussion is given regarding the following characteristic low- T features of HoNi 2B 2C (i) the driving mechanism behind the formation of the helical state (ii) the spontaneous transformation of the helical state into the commensurate AFM state and (iii) the influence of the magnetic field and impurities on the helical state.

Magnetic phase transitions and magnetoresistance in easy-plane antiferromagnets HoGa 2 and DyGa 2

The results of the magnetization and magnetoresistance studies performed on single crystals of hexagonal HoGa 2 and DyGa 2 compounds are presented. They have an antiferromagnetic alignment of the magnetic moments of R-ions in the basal plane below the Néel temperatures 7.6 and 11 K respectively. The field-induced multi-step magnetic phase transitions in the basal plane are accompanied by the great changes in the electrical resistivity of both compounds. Using data on the magnetoresistance, two field-induced intermediate phases in HoGa 2 are found, when the field was applied along the a axis, which is of easy magnetization. The magnetic phase diagram of HoGa 2 along a axes is determined.

Neutron-diffraction study of multi-step metamagnetism in a TbRu 2Si 2 single crystal

Neutron-diffraction measurements in magnetic fields up to 5 T have been performed on a TbRu 2Si 2 single crystal, which has a six-step metamagnetic process, down to 2.5 K. The field-induced magnetic phases have the same propagation vector k = (0.23,0,0) as the antiferromagnetic phase at H = 0 with the higher harmonics depending on magnetic field. The existence of a non-magnetic Tb ion is suggested.

Magnetic state of Dy 3Co

Using data on magnetization, magnetoresistance, a.c. susceptibility and specific heat, magnetic phase diagrams of the compound Dy 3Co were obtained for the main crystallographic axis. The different antiferromagnetic (AF) structures exist below T N = 44 K: AF 1 exists at T < T t = 32 K and AF 2 exists at the temperatures T t < T < T N. The field-induced magnetic phase transitions observed along the three main axes are associated with a complex non-collinear antiferromagnetic structure and are accompanied by a significant change in the electrical resistivity (Δ ρ/ρ up to −40%) owing to the appearance or disappearance of the energy gaps on superzone boundaries. At the phase transitions along a- and c-axes, large hysteresis loops are observed at low temperatures. At T < 4 K the single crystal of Dy 3Co remains in a magnetized state after the application and removal of a magnetic field along the c-axis.

Influence of the f-d exchange interaction on the field-induced magnetic phase transitions in the Y 1− tGd tCo 3 intermetallics

A metamagnetic transition of the itinerant Co-sublattice induced by an external ( t < 0.25) or an intersublattice molecular ( t ≈ 0.25) field was studied in the Y 1− t Gd t Co 3 system by magnetization measurements up to 40 T. In the range 0.50 ⩽ t ⩽ 0.55 field-induced non-collinear magnetic structures were observed. The strength of the intersublattice molecular field is discussed.

Investigation of the magnetic properties and 57Fe Mössbauer effect in DyFe 4Ge 2

The magnetic properties of the compound DyFe 4Ge 2 have been studied using 57Fe Mössbauer spectroscopy and using magnetic measurements in high magnetic fields. The compound DyFe 4Ge 2 orders magnetically below 65 K. At 4.2 K it displays a strong field-induced first order magnetic phase transition at B crit = 1.6 T and a second weaker transition at B crit = 6.0 T .

Investigation of the magnetic properties and 57Fe Mössbauer Effect in DyFe 4Ge 2

The magnetic properties of the compound DyFe 4Ge 2 have been studied by 57Fe Mössbauer spectroscopy and by magnetic measurements in high magnetic fields. The compound DyFe 4Ge 2 orders magnetically below 65 K. At 4.2 K it displays a strong field-induced first-order magnetic phase transition at B crit = 1.6 T and a second weaker transition at B crit = 6.0 T .