Metamagnetic State Research Articles

Complex electronic states in double-layered ruthenates(Sr1−xCax)3Ru2O7

The magnetic ground state of ${({\text{Sr}}_{1\ensuremath{-}x}{\text{Ca}}_{x})}_{3}{\text{Ru}}_{2}{\text{O}}_{7}$ $(0\ensuremath{\le}x\ensuremath{\le}1)$ is complex, ranging from an itinerant metamagnetic state $(0\ensuremath{\le}x<0.08)$ to an unusual heavy-mass nearly ferromagnetic (FM) state $(0.08<x<0.4)$, and finally to an antiferromagnetic (AFM) state $(0.4\ensuremath{\le}x\ensuremath{\le}1)$. In this report we elucidate the electronic properties for these magnetic states, and show that the electronic and magnetic properties are strongly coupled in this system. The electronic ground state evolves from an AFM quasi-two-dimensional metal for $x=1.0$ to an Anderson localized state for $0.4\ensuremath{\le}x<1.0$ (the AFM region). When the magnetic state undergoes a transition from the AFM to the nearly FM state, the electronic ground state switches to a weakly localized state induced by magnetic scattering for $0.25\ensuremath{\le}x<0.4$, and then to a magnetic metallic state with the in-plane resistivity ${\ensuremath{\rho}}_{ab}\ensuremath{\propto}{T}^{\ensuremath{\alpha}}$ $(\ensuremath{\alpha}>2)$ for $0.08<x<0.25$. The system eventually transforms into a Fermi-liquid ground state when the magnetic ground state enters the itinerant metamagnetic state for $x<0.08$. When $x$ approaches the critical composition $(x\ensuremath{\sim}0.08)$, the Fermi-liquid temperature is suppressed to zero Kelvin, and non-Fermi-liquid behavior is observed. These results demonstrate the strong interplay between the charge and spin degrees of freedom in the double-layered ruthenates.

Structural, magnetic, and electronic transport properties of (Sr0.9Ca0.1)3Ru2O7 single crystal

We have studied the structural, magnetic, and electronic transport properties of (Sr0.9Ca0.1)3Ru2O7 using single crystals grown by a floating-zone technique. The structure analysis by Rietveld refinements reveals that the Ca substitution for Sr intensifies the structure distortion; the rotation angle of the RuO6 octahedron increases. This structure change tunes magnetic and transport properties dramatically. The magnetic ground state switches from an itinerant metamagnetic state for Sr3Ru2O7 to a nearly ferromagnetic state for (Sr0.9Ca0.1)3Ru2O7. The Fermi liquid behavior occurs in Sr3Ru2O7, but is suppressed in (Sr0.9Ca0.1)3Ru2O7. These results strongly suggest that lattice, spin, and charge degrees of freedom are strongly coupled in this system. The band width narrowing caused by the structure distortion should be responsible for the enhancement of ferromagnetic correlations and the change of transport properties.

Low-temperature metamagnetic states in single crystal TbNi2B2C studied by torque magnetometry

Metamagnetic transitions in single crystal TbNi2B2C have been studied at 1.9 K with a Quantum Design torque magnetometer. The critical fields for the transitions depend strongly on the angle between the applied field and the easy axis [100]. Torque measurements have been made while changing the angular direction of the magnetic field (parallel to basal tetragonal ab-planes) at fixed field magnitude and while changing the field magnitude at fixed angular direction over a wide angular range (more than two quadrants). Torque magnetometry (sensitive only to the component of magnetization perpendicular to the field) indicates not only a different sequence of metamagnetic phases for fields near the easy axis from those near the hard axis, but also the different natures of a principal metamagnetic phase near the hard axis. Comparison of the results with longitudinal magnetization measurements is presented.

Field-induced antiferromagnetism and competition in the metamagnetic state of terbium gallium garnet

The magnetic properties of the hyperkagome system of ${\text{Tb}}_{3}{\text{Ga}}_{5}{\text{O}}_{12}$ have been investigated by neutron scattering. Evidence of antiferromagnetic long-range order of the Tb moments at ${\text{T}}_{N}\ensuremath{\le}0.35\text{ }\text{K}$ in zero field is provided. With the application of magnetic field in the paramagnetic phase, ferromagnetic peaks initially appear at nuclear Bragg reflections. With the field higher than 3 Tesla, antiferromagnetic Bragg peaks appear as well indicating that the low-temperature magnetic phase extends well beyond the phase boundary, into the paramagnetic phase, with field. The new magnetic symmetry sets in at the metamagnetic transition in this system.

Metamagnetic states in single crystal HoNi2B2C at T ≈ 1.9 K: Torque magnetometry study

Metamagnetic transitions in single-crystal rare-earth nickel borocarbide HoNi2B2C have been studied at T ≈ 1.9 K with a Quantum Design torque magnetometer. With increasing field, transitions to antiferromagnetic, ferrimagnetic, non-collinear, and saturated paramagnetic states take place. The critical fields of the transitions depend crucially on the angle θ between applied field and the easy axis [110]. Measurements of torque along the c axis have been made while changing the angular direction of the magnetic field (parallel to basal tetragonal ab planes) and with changing field at fixed angle over a wide angular range. Two new phase boundaries in the region of the non-collinear phase have been observed, and the direction of the magnetization in this phase has been precisely determined. At low field the antiferromagnetic phase is observed to be multidomain. In the angular range around the hard axis (−6° ≤ ϕ ≤ 6°, where ϕ is the angle between the field and hard axis [100]) the magnetic behavior is found to be “frustrated” with a mixture of phases with different directions of the magnetization.

Torque magnetometry studies of new low temperature metamagnetic states in ErNi2B2C

The metamagnetic transitions in single-crystal ErNi2B2C have been studied at 1.9K with a Quantum Design torque magnetometer. The critical fields of the transitions depend crucially on the angle between applied field and the easy axis [100]. Torque measurements have been made while changing the angular direction of the magnetic field (parallel to basal tetragonal ab planes) in a wide angular range (more than two quadrants). Sequences of metamagnetic transitions with increasing field are found to be different for the magnetic field along (or close enough to) the easy [100] axis from that near the hard [110] axis. The study have revealed new metamagnetic states in ErNi2B2C, which were not apparent in previous longitudinal-magnetization and neutron studies.

Torque magnetometry study of metamagnetic transitions in single-crystalHoNi2B2CatT≈1.9K

Metamagnetic transitions in single-crystal rare-earth nickel borocarbide HoNi$_2$B$_2$C have been studied at T\approx 1.9 K with a Quantum Design torque magnetometer. This compound is highly anisotropic with a variety of metamagnetic states at low temperature which includes antiferromagnetic, ferrimagnetic, non-collinear and ferromagnetic-like (saturated paramagnet) states. The critical fields of the transitions depend crucially on the angle $\theta$ between applied field and the easy axis [110]. Measurements of torque along the c-axis have been made while changing the angular direction of the magnetic field (parallel to basal tetragonal $ab$-planes) and with changing field at fixed angle over a wide angular range. Two new phase boundaries in the region of the non-collinear phase have been observed, and the direction of the magnetization in this phase has been precisely determined. At low field the antiferromagnetic phase is observed to be multidomain. In the angular range very close to the hard axis [100] ($-6^{\circ} \lesssim\phi \lesssim 6^{\circ}$, where $\phi$ is the angle between field and the hard axis) the magnetic behavior is found to be ``frustrated'' with a mixture of phases with different directions of the magnetization.

Torque magnetometry: An effective tool for study of metamagnetic transitions in quaternary borocarbides RNi 2B 2C

The metamagnetic transitions in single-crystal rare-earth nickel borocarbide ErNi 2B 2C and TbNi 2B 2C have been studied at 1.9 K with a Quantum Design torque magnetometer. The critical fields of the transitions depend crucially on the angle between applied field and the easy axis [1 0 0]. Torque measurements have been made while changing angular direction of the magnetic field (parallel to basal tetragonal ab-planes) in a wide angular range (more than two quadrants). The results obtained permit discovery of new features of the metamagnetic states in these compounds, which were not revealed in previous studies. For both borocarbides the sequences of metamagnetic transitions with increasing field were different for the magnetic field along (or close enough to) the easy [1 0 0] axis from that near the hard [1 1 0] axis.

Structure and magnetic transport properties of Ge doped La(Co,Si)13 intermetallics

The crystal structure and the magnetic and electronic transport properties of Ge doped LaCo10.5Si2.5−xGex (x=0–0.3) intermetallics have been investigated using powder x-ray diffraction and magnetic and electrical measurements. According to the x-ray diffraction pattern analysis, Ge as a dopant decreases the stability of the cubic LaCo 1:13 phase and stabilizes the Si based La(Co,Si) 1:13 tetragonal phase. From the authors’ structural refinement, the authors found that Ge prefers to occupy the 16l(2) position in the tetragonal phase. LaCo10.5Si2.2Ge0.3 shows ferromagnetic order with a metamagnetic state around 350K. An anomaly in resistivity is observed at around 367K, which is associated with the metamagnetic transition. The resistivity follows ρ(T)=ρo+aTn rule in the temperature range of 4–400K with n=1.17(3) for the half metallic state and n=2 for the normal metallic state, respectively. This type of discontinuity can be interpreted as a crossover from a low temperature metamagnetic half metallic state to the normal ferromagnetic-metallic state.

Torque magnetometry studies of metamagnetic transitions in single-crystal HoNi2B2C and ErNi2B2C at T≈1.9K

The metamagnetic transitions in single-crystal rare-earth nickel borocarbide HoNi2B2C and ErNi2B2C have been studied at 1.9K with a Quantum Design torque magnetometer. The critical fields of the transitions depend crucially on the angle between applied field and the easy axis [110] for HoNi2B2C and [100] for ErNi2B2C. Torque measurements have been made while changing angular direction of the magnetic field (parallel to basal tetragonal ab planes) in a wide angular range (more than two quadrants). The results are used not only to check and refine the angular diagram for metamagnetic transitions in these compounds, but also to find new features of the metamagnetic states. Among new results for the Ho borocarbide are the influence of a multidomain antiferromagnetic state, and “frustrated” behavior of the magnetic system for field directions close to the hard axis [100]. Torque measurements of the Er borocarbide clearly show that the sequence of metamagnetic transitions with increasing field (and the corresponding number of metamagnetic states) depends on the angular direction of the magnetic field relative to the easy axis.

Electronic and magnetic properties of triple-layered ruthenate Sr 4Ru 3O 10 single crystals grown by a floating-zone method

We have grown high-quality single crystals of the triple-layered perovskite ruthenate Sr 4Ru 3O 10 using a floating-zone (FZ) method and measured their electronic transport and magnetic properties. Our experiments results are consistent with those previously reported for Sr 4Ru 3O 10 flux crystals; the magnetic ground state of Sr 4Ru 3O 10 is poised between an itinerant metamagnetic and itinerant ferromagnetic state, and its electronic ground state is a Fermi liquid. In addition, we have investigated the effect of disorder on the metallic state of Sr 4Ru 3O 10. From resistivity measurements of various Sr 4Ru 3O 10 crystals with different levels of disorder, we found that disorder enhances both temperature-independent elastic scattering and also temperature-dependent inelastic scattering. The in-plane metamagnetic transition is also found to be sensitive to disorder. Disorder results in an increase in the metamagnetic transition field and different magnetic behavior above the transition. We discuss the implications of this interesting observation.

Domain walls and macroscopic spin-flip-like metamagnetism inGdxCo1−x∕GdyCo1−yexchange-coupled double layers

Amorphous ferrimagnetic ${\mathrm{Gd}}_{x}{\mathrm{Co}}_{1\ensuremath{-}x}∕{\mathrm{Gd}}_{y}{\mathrm{Co}}_{1\ensuremath{-}y}$ exchange coupled double layers (ECDL) have been prepared in order to investigate the magnetization reversal processes and the presence of stable magnetic configurations when the chemical compositions of both layers are very similar. The ECDL samples have been grown by co-sputtering from independent pure Co and Gd targets, being $100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ the thickness of each layer. The measurements have been done by the magneto-optical Kerr effect at both sides of the ECDL in the temperature interval $200\phantom{\rule{0.3em}{0ex}}\mathrm{K}--450\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and the compositions of the two layers are $x=0.22$ and $y=0.24$. A rich variety of behaviors has been found, being the most relevant of those in the temperature range between the compensation temperatures $({T}_{\mathit{comp}})$ of both layers. Some of these observed behaviors include magnetization reversal by creation/annihilation of a Bloch wall across the ECDL thickness, and a macroscopic spin-flip-like metamagnetic state where the magnetic moments form a double antiferromagnetic state with the presence of an extended Neel wall when the magnetizations of both layers are similar. A temperature phase diagram for the transition fields between different magnetic states has also been deduced, being in very good agreement with the magnetic behavior observed in the whole temperature range.

Isofield low-temperature specific heat of single-crystalHo1−xYxNi2B2C(x=0,0.25,0.5,1): Probing the magnetocaloric effect inHoNi2B2C

Isofield specific heat, $C(T,H)$, of single-crystal ${\mathrm{Ho}}_{1\ensuremath{-}x}{\mathrm{Y}}_{x}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ ($x=0$, 0.25, 0.5, 1) were measured within the ranges $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}<T<50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $H(\ensuremath{\parallel}a)\ensuremath{\leqslant}60\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$. Linearized spin-wave theory is invoked to analyze the field and temperature dependence of the magnetic specific heat and entropy of ${\mathrm{HoNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ for $T<{T}_{N},H<{H}_{1}$ and $T<{T}_{N}$, $H>{H}_{3}$. Based on the known low-temperature $H\text{\ensuremath{-}}T$ phase diagram of ${\mathrm{HoNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$, this analysis identifies three distinct field regions. (i) The low-field region $(H<{H}_{1})$ where the collinear, commensurate $\ensuremath{\nearrow}\ensuremath{\swarrow}$ structure is stabilized, and ${C}_{M}(T<{T}_{N},H)$ and ${S}_{M}(T<{T}_{N},H)$ are well described by the prediction of linearized antiferromagnetic spin-wave analysis. In particular, ${(\ensuremath{\partial}{S}_{M}∕\ensuremath{\partial}H)}_{T}>0$, indicating that cooling can be effected by adiabatic magnetization. (ii) The intermediate-field region $({H}_{1}<H<{H}_{3})$, where the two metamagnetic states (namely $\ensuremath{\nearrow}\ensuremath{\nearrow}\ensuremath{\swarrow}$ at ${H}_{1}$ and $\ensuremath{\nearrow}\ensuremath{\nearrow}\ensuremath{\nwarrow}$ at ${H}_{2}$) are stabilized. Here no spin-wave analysis is attempted, but it is evident that ${(\ensuremath{\partial}{S}_{M}∕\ensuremath{\partial}H)}_{T}>0$ for $H<{H}_{2}$ while ${(\ensuremath{\partial}{S}_{M}∕\ensuremath{\partial}H)}_{T}<0$ for $H>{H}_{2}$. (iii) The high-field region $(H>{H}_{3})$ where the saturated $\ensuremath{\nearrow}\ensuremath{\nearrow}$ state is being approached. Here, both ${C}_{M}(T<{T}_{N},H)$ and ${S}_{M}(T<{T}_{N},H)$ follow the description of a ferromagnetic spin-wave analysis; furthermore, ${(\ensuremath{\partial}S∕\ensuremath{\partial}H)}_{T}<0$, indicating that cooling can be effected by adiabatic demagnetization. The magnetocaloric effect above ${T}_{N}$ as well as alloying influences on the magnetic properties are discussed.

Synthesis of MnP nanocrystals by treatment of metal carbonyl complexes with phosphines: a new, versatile route to nanoscale transition metal phosphides.

The reaction of Mn2(CO)10 with P(SiMe3)3 in coordinating solvents at T >/= 220 degrees C yields low polydispersity, highly crystalline MnP nanoparticles for the first time. The effect of dimensional limiting has resulted in the stabilization of a ferromagnetic ground state at low temperatures, rather than the metamagnetic state observed in bulk (microcrystalline) MnP. The synthetic methodology reported here is demonstrated to be general for a number of different metals and phosphine sources.

Impact of magnetic fields on anisotropy inCa3Ru2O7

${\mathrm{Ca}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ is a bilayered metallic paramagnet that orders antiferromagnetically at ${T}_{N}=56\mathrm{K}$ while remaining metallic and then undergoes a spin reorientation coincident with a metal-nonmetal transition at ${T}_{M}=48\mathrm{K},$ entering a metamagnetic state. Low-temperature specific-heat measurements in magnetic fields show that the electronic specific heat, $\ensuremath{\gamma}=44{\mathrm{m}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{}\mathrm{K}}^{2},$ is field independent above and below the 6-T critical field, whereas the first-order nature of the metamagnetic transition is reflected by a small shift in the Debye temperature. Magnetization, electrical resistivity, and specific-heat measurements were performed on high-quality single crystals, allowing construction of detailed H-T phase diagrams, which differ considerably for magnetic fields applied along the two in-plane directions. These measurements led to determination of the anisotropy field ${H}_{A}=22.4\mathrm{T}$ and exchange field ${H}_{E}=14.2\mathrm{T}.$ Evidence is presented for a possible flopside state in the region above the 41-K and 5.5-T multicritical point. Finally, superheating and supercooling are observed at temperatures and magnetic fields slightly above the multicritical point.

A First-Principles Investigation of the Structural and Magnetic Stability of Fe/GaAs(001)

The electronic properties of the interface of Fe/GaAs(001) have been investigated by using first-principles and molecular-dynamics techniques. While the ground state is ferromagnetic for all structures considered, a ferrimagnetic spin structure is found to be very close in energy (<1 meV). The observed lowering of the magnetic moments when relaxing the atomic positions is believed to be connected to this close in energy lying metamagnetic state. On the other hand, the magnetic moments of the Fe atoms at the interface are large, which can be explained by the bulk-like behavior of the density ot states of interface atoms.

Specific Heat of Field-dependent Magnetic Orderings in HoNi2B2C

We have investigated the low-temperature specific heat of HoNi 2 B 2 C down to T = 1 K in various magnetic fields from 0 T to 5 T. At zero field, the specific heat exhibits a large peak at T N = 5.1 K, which is due to commensurate antiferromagnetic ordering, and other smaller peak at T 1 = 5.5 K, which is related to incommensurate ordering. As the field is increased up to 0.5 T, the first peak broadens and moves to a lower temperature, while the other peak at T 1 moves to a higher temperature, which indicates that the phase between T N and T 1 is more favored in magnetic fields. Among possible candidates for the phase, the a -axis modulation phase, which is an extension of a low temperature metamagnetic state, is the most probable. In the high-field region above 1 T, the two-peak feature is replaced by a broad-hill one that fades away with increasing fields, which is the typical smearing feature of the magnetic order at high fields.

Magnetic phase diagram and reentrant superconductivity in DyNi 2B 2C single crystals

In order to investigate the interaction between superconductivity and magnetic ordering resistivity, magnetisation measurements were performed on DyNi 2B 2C single crystals for T=0.05–15 K and for B=0–5 T in the crystallographic ab-plane. Measurements of the magnetisation with a torque cantilever magnetometer give strong evidence for metamagnetic states built of different ordered ferromagnetic domains. For B ‖ [1 0 0], an anomalous large hysteresis effect of the metamagnetic transitions and also of the superconducting transitions were observed in the low-temperature range ( T<2 K). In some extreme cases, the metamagnetic state can be frozen after a field cycle sweeping up to 2 T and down to zero at 50 mK. In this case, superconductivity is totally suppressed. The superconducting state can be restored in two ways: Either with increasing temperature, or by applying a small field with the opposite field direction.

Relation of magnetic and structural factors in the course of phase transitions in MnAs-based alloys

A phenomenological analysis of the magnetic and structural phase states observed in the manganese arsenide-based alloys over a wide range of temperatures and pressures has been performed. The unique first-order phase transitions from the paramagnetic and metamagnetic states to the ferromagnetic state are studied experimentally. It is found that these transitions exhibit characteristic features associated with the magnetostriction suppression of nucleation when the lability boundary of the paramagnetic phase is absent and the transition from the metamagnetic state is not thermodynamically “forbidden.” The phase behavior of manganese arsenide-based alloys is interpreted within the proposed model. This model accounts for the interrelation of the magnetic, structural, and elastic properties of alloys and also the specific features of phase transformations in real crystals.

Ordering wave vectors of metamagnetic states inHoNi2B2C:One dimension is not enough

Elastic neutron-diffraction measurements have been preformed in each of the metamagnetic states of ${\mathrm{HoNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ for an applied field applied in the tetragonal basal plane making an angle of approximately $15\ifmmode^\circ\else\textdegree\fi{}$ with the $[110]$ axis. Whereas these data are in excellent quantitative agreement with earlier thermodynamic studies of the ${H}_{\mathrm{app}}\ensuremath{-}\ensuremath{\theta}$ phase diagram of ${\mathrm{HoNi}}_{2}{\mathrm{B}}_{2}\mathrm{C},$ the magnetic wave vector of the metamagnetic state, $\ensuremath{\approx}{4/7a}^{\ensuremath{\star}},$ is in stark contradiction with the predictions of two, one-dimensional theoretical models developed for this system. On the other hand, simple energetic arguments which are consistent with the existence of the ${a}^{\ensuremath{\star}}$ phase are presented.