Field-induced Magnetic Phase Research Articles

Magnetic Phase Diagrams of Ce2Fe17‐xMnx—H System: A Magnetization Study.

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Anisotropic 4f-spin dynamics across theB–T phasediagram of Ce7Ni3

Longitudinal field μSR measurements in applied fields parallel and perpendicular to thec-axis of the hexagonal heavy-fermion antiferromagnetCe7Ni3 served to monitor the 4f-spin dynamics across the magnetic phase diagram in theB–T plane, which consists of an incommensurate/commensurateantiferromagnetic (AF) section below 1.9 K/0.7 K and below an applied fieldB of 0.25 T,and for B along the c-axis, of a field-induced magnetic (FIM) section forB≥0.6 T and below 0.5 K.The observed μ+ spin–lattice relaxation rates reveal persisting spin dynamics across the whole phasediagram, reflect the various phase boundaries and are interpreted to arise in the AF andFIM phases from the Ce3 sublattice (the Ce ions are located on three different sublattices)and in the intermediate phase, viewed as a short range ordered (SRO) state, also from theCe1 and Ce2 sublattices with slower fluctuation rates. In the paramagnetic regime the Ce1sublattice displays the slowest spin dynamics. In the FIM phase the fraction of relaxingμ+ appears toshrink with rising B, evidencing a possible phase separation.

Magnetostriction and electric polarization anomalies in GdFe 3(BO 3) 4 single crystals at phase transitions

Our experimental and theoretical investigation was aimed at the study of different gadolinium ferroborate single-crystal properties both at spontaneous and high magnetic field-induced phase transitions.

Peculiarities of incommensurate–commensurate phase transitions in multiferroics

Characteristic features of magnetic field-induced phase transitions incommensurate–commensurate (IC–C) phase in multiferroics are considered. An example of such substances is the ferroelectromagnet bismuth ferrite BiFeO 3. It was shown that the interaction between electric and magnetic subsystems can result in electric field induced shift of critical value for the magnetic field, at which the phase transition from spatially modulated to the homogenous antiferromagnetic state takes place. This change has value 0.5 T in the electric field 50 kV/cm. Phase diagrams in the magnetic field–electric field coordinates are plotted.

Magnetic phase diagrams of Ce 2Fe 17− xMn x–H system: A magnetization study

The field-induced magnetic phase transitions of the helical phase of Ce 2Fe 17− x Mn x alloys ( x = 1.3 and 1.7) and their hydrides of Ce 2Fe 17− x Mn x H y ( y = 1 ) were investigated by isofield magnetization curves in external magnetic fields up to H = 10 kOe. The temperature dependence of the critical fields, H C inducing phase transition between ferromagnetic (F) and helical antiferromagnetic (HAFM) state are determined. On the basis of the experimental results, the H – T phase diagrams are established. The multiple magnetic phase transitions observed in the low magnetic field are discussed in terms of competing exchange contributions within the iron magnetic sublattices. Hydrogenation leads to a considerable enhancement of ferromagnetic-like exchange interactions, which causes the increase of the Curie temperature and drastically reduces the critical field H C of a metamagnetic transition.

Pressure- and field-induced magnetic instabilities in a heavy-fermion antiferromagnet Ce 7Ni 3

We investigated ground state properties of a heavy-fermion antiferromagnet Ce 7Ni 3 under hydrostatic pressures and magnetic fields. This compound undergoes two antiferromagnetic phase transitions at T N1 = 1.9 K and T N2 = 0.7 K. Below T N1, a spin-density-wave (SDW) develops. Upon applying rather weak pressure 0.39 GPa = P c, both T N1 and T N2 vanish, and non-Fermi liquid behavior appears in the specific heat and magnetic susceptibility. The enhancement of residual resistivity along the a axis near P c is attributed to the increased spin fluctuations along the a axis. By applying fields B along the c axis, T N1 is suppressed and vanishes at 0.3 T. Magnetoresistance, specific-heat, and magnetization measurements revealed another field-induced magnetic (FIM) phase in the region B || c > 0.7 T and T < 0.5 K. Neutron diffraction experiments indicate that the magnetic unit cell in the c-plane for the FIM phase is treble that of the chemical unit cell. Moreover, this magnetic reflection intensity remains even in the region between the FIM phase and SDW phase. This observation indicates the presence of large spin fluctuations in the c-plane associated with the magnetic frustration, which should be responsible for the magnetic instability of Ce 7Ni 3.

Irreversible field-induced magnetic phase transitions and properties ofHo3Co

The results of magnetic susceptibility, magnetization, electrical resistivity and specific heat measurementsperformed on Ho3Co single crystals show that this compound exhibits two different antiferromagnetic structures:AFII at8 K<T<22 K andAFI belowTt≈8 K. Below the Néeltemperature TN = 22 K the application of a magnetic field along the main crystallographic directions inducesmagnetic phase transitions which are accompanied by giant magnetoresistance. AtT<Tt the field-induced phase transitions along the c- and b-axes are found to beirreversible, and a small ferromagnetic component is observed along the a-axis.These peculiarities are associated with the non-Kramers character of the Ho ionand with the presence of a complex incommensurate magnetic structure ofHo3Co belowTN. The temperature coefficient of the electrical resistivity forHo3Co aboveTN over a wide temperature range is found to differ from that observed for otherR3Co compounds. Such a behaviour is attributed to the presence of an additional contribution tothe conduction electron scattering by spin fluctuations induced by f–d exchangein the itinerant d-electron subsystem. The value of this extra contribution andits temperature range is suggested to depend on the spin value of the R ion.The excess of the effective magnetic moment per R ion, which is observed inHo3Co and inother R3M type compounds, is also attributed to spin fluctuations induced by f–d exchange.

Field-induced magnetic phase transitions in a GdSi single crystal

We report on unusual field-induced magnetic phase transitions observed in a GdSi single crystal at low temperature. The magnetization curves initially show an anisotropic character between the $b$ axis and the $ac$ plane. With increasing applied field, the magnetization measured along the $c$ axis merges with that measured along the $b$ axis through a jumplike transition at field of about $2.5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, whereas that measured along the $a$ axis gradually joins the other two at about $3.8\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. Above $3.8\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, the magnetization behaves isotropically with applied magnetic field and then reaches saturation through a jumplike transition at a field of about $19.5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. We discuss the anomalous behavior of the compound in terms of interplay between the localized $4f$ spins and the (itinerant) conduction electrons.

Link between magnetic field-induced quantum criticality and phase formation in [formula omitted

The magnetization and resistivity studies in magnetic fields up to 45 T were used to establish magnetic field versus temperature phase diagram and quantum criticality in U ( Ru 1 - x Rh x ) 2 Si 2 . For x = 4 % , the hidden order is completely destroyed, stabilizing a single field-induced phase II. A correlation between the field dependence of this phase and that of the quantum critical point, combined with the suppression of the T 2 coefficient of the resistivity within it, shows that the field-tuned quantum criticality is intimately related to the phase formation.

Magnetic-entropy change in Mn 1.1Fe 0.9P 0.7As 0.3– xGe x

We have studied the magnetic properties and magnetic-entropy changes of Mn 1.1Fe 0.9P 0.7As 0.3– x Ge x compounds with x = 0, 0.05, 0.1, 0.15 and 0.3. X-ray diffraction (XRD) study shows all the compounds crystallize in the Fe 2P-type structure. Magnetic measurements show that the Curie temperature increases from 150 K for Mn 1.1Fe 0.9P 0.7As 0.3 to 380 K for Mn 1.1Fe 0.9P 0.7Ge 0.3. A field-induced first-order magnetic phase transition is observed above the Curie temperature for the compounds with x up to 0.15. There exists an optimal composition in which the first-order phase transition is the sharpest. The optimal composition for this system is x = 0.1. The maximal magnetic-entropy change derived from the magnetization data is about 40 J/(kg K) for a field change from 0 to 3 T.

Magnetization Plateaus and Magnetic Excitations in theS= 1/2 Spin Ladder Antiferromagnet NH4CuCl3

Field-induced magnetic phases are investigated in one-dimensional S = 1/2 generalized spin ladder systems having the lattice modulation along the leg with the wavevector π/2a, a being the lattice constant, using numerical calculations. We point out that there exist cases where the 1/4- as well as the 3/4-magnetization plateaus appear but the 1/2-plateau does not, for an appropriate set of the parameters. Triplet, excitations in the plateau regions are discussed in connection with the experimental result, which provides possible implications for the important role of the interaction between triplets.

Crossover Behavior of Magnetic Excitations in the Anisotropic Haldane Antiferromagnet under High Magnetic Fields

Field-induced magnetic phases are investigated in the one-dimensional S = 1 Haldane system with the easy-plane anisotropy under external magnetic fields along an arbitrary direction, using the density-matrix renormalization group method. At a critical field the system exhibits the quantum phase transition from the nonmagnetic Haldane phase to a magnetic phase. It is found that the quantum analog of the classical soliton bearing system is induced except for the case where the field is applied perpendicular to the easy plane. In the exceptional case. Tomonaga-Luttiger spin-fluid state is realized. The angle dependence of the critical field is discussed in connection with two consecutive field-induced phase transitions observed in NDMAP. Possible implications for such novel transitions are given.

Field-Induced Magnetic Order of Cs3Cr2Br9and Cs3Cr2Cl9

The magnetic dimer compounds Cs 3 Cr 2 Br 9 and Cs 3 Cr 2 Cl 9 are well characterized magnetic dimer compounds. In zero field the spin 3/2 moments are bound in an hexagonal lattice of magnetic singlets, but at finite magnetic fields there are transitions to field-induced magnetic phases. In the Bromide compound this transition occurs at sufficiently low fields, ∼1.5 T, that neutron diffraction results can give details of the static and dynamic magnetic structure even in the field induced phase. High magnetic field measurements have been used to determine the equation of state up to saturation. In this paper we discuss different approaches to the calculation of the magnetization and transverse magnetic order in the two compounds. Compared to spin 1/2 dimer materials, such as TlCuCl 3 , the higher spin allows for more important effects of anisotropy, and the frustration, leads to possibily incommensurate order. Two main theoretical methods will be discussed: extension of the standard theory of Tachiki and Y...

Magnetization studies ofRMn6Ge6−xGaxsingle crystals (R=Sc,Y, Gd–Lu;0.63⩽x⩽1.00)

The magnetic properties of single crystals of rare-earth compounds of composition $R{\mathrm{Mn}}_{6}{\mathrm{Ge}}_{6\ensuremath{-}x}{\mathrm{Ga}}_{x}$ $(x\ensuremath{\approx}1)$ have been studied. In these compounds, the Mn sublattice orders ferromagnetically with a preferred moment direction perpendicular to the $c$ axis. In the compounds in which also the $R$ component carries a magnetic moment, the latter couple antiparallel to the Mn moments. Upon cooling from room temperature to cryogenic temperatures, the $R$-sublattice anisotropy becomes the dominant contribution to the total magnetocrystalline anisotropy, which leads to a spin-reorientation transition at intermediate temperatures for $R=\mathrm{Tb}\ensuremath{-}\mathrm{Yb}$. At low temperatures, the preferred moment directions are characterized by an easy axis for $R=\mathrm{Tb}$, Er, Tm, and Yb and by an easy cone for $R=\mathrm{Dy}$ and Ho. A satisfactory account of the observed preferred moment directions has been given in terms of crystal-field theory. Measurements of the magnetization in the main crystallographic directions have been made in high magnetic fields, up to about 55 T. The interplay between the antiferromagnetic intersublattice $R$-Mn coupling and the magnetocrystalline anisotropy leads to field-induced magnetic phase transitions which are particularly pronounced in the compounds with Ho, Er and Tm.

Second law implications of a magnetocaloric effect adiabatic phase transition of type I superconductor particles

The nature of the thermodynamic behaviour of type I superconductor particles having a cross-section less than the Ginzburg-Landau temperature dependent coherence length ξ(T) is discussed for a magnetic field-induced adiabatic phase transition from the superconductive state to the normal state. The magnetocaloric effect adiabatic phase transition of a particle-dimensioned specimen is characterized by a decrease in entropy, suggesting a quantum limit to traditional formulations of the second law, evidenced by attainment of a final process temperature below that resulting from the isentropic magnetocaloric effect adiabatic phase transition of a bulk dimensioned specimen.

Magnetic phase transition and magnetic entropy change in melt-spun La 1− xNd xFe 11.5Si 1.5 ribbons

The magnetic phase transition and magnetic entropy change | Δ S m | of melt-spun La 1− x Nd x Fe 11.5Si 1.5 ( x = 0, 0.3, 0.5) ribbons were investigated by measuring the magnetization as a function of temperature. The crystal structure of all annealed ribbons is NaZn 13-type. The Curie temperature T C of the ribbons increased slightly with the increase of x. A large low-field | Δ S m | is observed in the compounds with x = 0 and 0.3, which resulted from a field-induced first-order magnetic phase transition (FOT). For the compound with x = 0.5, | Δ S m | reduced sharply and FOT disappeared at the same time. Enhancement of T C and | Δ S m | by Nd substitution suggests that La 1− x Nd x Fe 11.5Si 1.5 ( x = 0, 0.3) ribbons have great potential for applications as magnetic refrigerants working in low magnetic fields.

Mössbauer effect probe of field-induced magnetic phase transitionin LaFe13−xSix intermetallic compounds

Direct evidence of a field-induced magnetic phase transition in LaFe13−xSix intermetallics with a large magneticaloric effect was provided by Fe57 Mössbauer spectra in externally applied magnetic fields. Moreover, Mössbauer spectra demonstrate that a magnetic structure collinear to the applied field is abruptly achieved in LaFe11.7Si1.3 compound once the ferromagnetic state appears, showing a metamagnetic first-order phase transition. In the case of LaFe11.0Si2.0, the Fe magnetic moments rotate continuously from a random state to the collinear state with increasing applied field, showing that a second-order phase transition is predominant. The different types of phase transformation determine the magnetocaloric effects in response to temperature and field in these two samples.

First-order magnetic phase transition inLaFe11.7Si1.3studied using Mössbauer spectroscopy

Temperature and field induced magnetic phase transition in the magnetocaloric compound of ${\text{LaFe}}_{11.7}{\text{Si}}_{1.3}$ was investigated by means of M\"ossbauer spectroscopy and magnetization measurements. A coexistence of a magnetically split sextet and a paramagnetic doublet was observed in the temperature region of $\ensuremath{\sim}185--190\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ from zero-field M\"ossbauer spectra. A thermal hysteresis was verified between the heating and cooling processes that similar as observed in the thermomagnetic curves indicate that a first-order transition occurred in this compound. At the magnetic and paramagnetic phase coexisted region, the in-field M\"ossbauer measurements indicate that a span external fields from $\ensuremath{\sim}1$ to $\ensuremath{\sim}2\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ induced a magnetic phase transition as the temperature induced transformation. The in-field M\"ossbauer spectroscopy confirms that the field-induced magnetic phase transition is first-order phase transition as temperature-induced transition occurred in ${\text{LaFe}}_{11.7}{\text{Si}}_{1.3}$.

Universal scaling at field-induced magnetic phase transitions

We study field-induced magnetic order in cubic lattices of dimers with antiferromagnetic Heisenberg interactions. The thermal critical exponents at the quantum phase transition from a spin liquid to a magnetically ordered phase are determined from Stochastic Series Expansion Quantum Monte Carlo simulations. These exponents are independent of the interdimer coupling ratios, and converge to the value obtained by considering the transition as a Bose-Einstein condensation of magnons, alpha_(BEC) = 1.5. The scaling results are of direct relevance to the spin-dimer systems TlCuCl_3 and KCuCl_3, and explain the broad range of exponents reported for field-induced ordering transitions.

Effect of composition and cooling rate on the structure and magnetic entropy change in Gd5SixGe4−x

The effects of composition and cooling rate on the structure and the magnetic entropy change in Gd5SixGe4−x (x=1.7,2) were investigated. A large magnetic entropy change was obtained in cast and quenched Gd5Si2Ge2, which was attributed to a magnetic field-induced phase transition. This transition is significantly weakened in the slowly cooled sample, leading to a lower magnetic entropy change. The Gd5Si2Ge2-type phase in the Gd5Si2Ge2 alloy is metastable at room temperature, while it is stable in the Gd5Si1.7Ge2.3 alloy. The transition can be induced in the Gd5Si1.7Ge2.3 near room temperature by a pulsed field of 48 T.