Complex Magnetic Phase Diagram Research Articles

Chemical control of interstitial iron leading to superconductivity in Fe1+xTe0.7Se0.3

The superconducting series, Fe(Te,Se), has a complex structural and magnetic phase diagram that is dependent on composition and occupancy of a secondary interstitial Fe site. In this letter, we show that superconductivity in Fe1+xTe0.7Se0.3 can be enhanced by topotactic deintercalation of the interstitial iron, demonstrating the competing roles of the two iron sites. Neutron diffraction reveals a flattening of the Fe(Te,Se)4 tetrahedron on Fe removal of iron and an increase in negative thermal expansion within the ab plane that correlates with increased lattice strain. Inelastic neutron scattering shows that a gapped excitation at 6 meV, evolves into gapless paramagnetic scattering with increasing iron; similar to the fluctuations observed for non-superconducting Fe1+xTe itself.

Heat capacity and magnetic phase diagram of the hydride CeRuSiH

The hydride CeRuSiH exhibits antiferromagnetic order with two transitions at TN1 = 7.5 and TN2 = 3.1 K. Furthermore, magnetization measurements M (H) up to H = 45 kOe shows a metamagnetic double transition at low temperatures, suggesting a complex magnetic phase diagram. Here, we present magnetization measurements and heat capacity data up to 90 kOe, which allows as to complete the magnetic phase diagram. In addition, from the analysis of the heat capacity, we propose a model for the crystal field splitting.

Magnetic order in the filled skutterudites RPt4Ge12 (R = Nd, Eu)

Rare-earth metal filled skutterudites RPt4Ge12 with R=La-Nd, and Eu exhibit a variety of different ground states, e.g., conventional and unconventional superconductivity in LaPt4Ge12 and PrPt4Ge12, respectively, and intermediate valence behavior in CePt4Ge12. In this work we investigate the magnetic state of NdPt4Ge12 and EuPt4Ge12 by specific heat, dc-susceptibility and magnetization. NdPt4Ge12 shows two magnetic phase transitions at TN1 = 0.67 K and TN2 = 0.58 K, while EuPt4Ge12 displays a complex magnetic phase diagram below the magnetic ordering temperature of 1.78 K. The specific heat indicates that in NdPt4Ge12 the crystalline electric field (CEF) ground state of the Nd3+ is a quartet and that, as expected, in EuPt4Ge12 the Eu2+ state is fully degenerate.

Pronounced basal plane anisotropy in the magnetoresistance of YbCo2Si2

AbstractWe have investigated the antiferromagnetic (AFM) state of YbCo2Si2 by means of magnetoresistance measurements for different field and current directions. We observed huge magnetoresistance effects, up to ±60% even at low fields B < 2 T, and a very rich variety of features. The results evidence a complex magnetic phase diagram, with a pronounced anisotropy even for different field directions within the basal plane. The analysis of these results gives valuable insight into the different AFM phases of YbCo2Si2.

Magnetic anisotropy in the AFM and SDW phases of CeB6

The angular dependences of magnetization and Hall resistance have been investigated both in paramagnetic and magnetically ordered phases by the technique of sample rotation in magnetic field up to 6T on the high-quality single crystals of CeB6. It has been shown that, as CeB6 undergoes the transition from the antiferromagnetic modulated (AFM) to the so-called antiferroqadrupolar phase, the easy-magnetization axis in the [110] plane changes from <100> to <110>. The behavior of the magnetization anisotropic component differs radically in these two magnetically ordered phases. The analysis provides evidence in favor of a spin density wave (SDW) state formation in cerium hexaboride in the temperature range TN ≈ 2.3K<T<TQ ≈ 3.3K. Moreover, the SDW antinodes' formation was established to be the main factor of the Hall effect renormalization and anisotropy in both AFM and SDW magnetic phases of CeB6. As a result, the complex magnetic phase diagram of CeB6 may be interpreted as caused by a competition between itinerant and 4f-antiferromagnetism in this strongly correlated electron system.

Magnetic field dependence of the antiferromagnetic phase transitions in Co-doped YbRh2Si2

We present first specific-heat data of the alloy Yb(Rh1−xCox)2Si2 at intermediate Co-contents x = 0.18, 0.27, and 0.68. The results already point to a complex magnetic phase diagram as a function of composition. Co-doping of YbRh2Si2 (Tx = 0N = 72 mK) stabilizes the magnetic phase due to the volume decrease of the crystallographic unit cell. The magnetic phase transitions are clearly visible as pronounced anomalies in C4f(T)/T and can be suppressed by applying a magnetic field. Going from x = 0.18 to x = 0.27 we observe a change from two mean-field (MF) like magnetic transitions at T0.18N = 1.1K and T0.18L = 0.65 K to one sharp λ-type transition at T0.27N = 1.3 K. Preliminary measurements under magnetic field do not confirm the field-induced first-order transition suggested in the literature. For x = 0.68 we find two transitions at T0.68N = 1.14 K and T0.68L = 1.06 K.

Complex magnetic phases in [formula omitted

DC magnetization and AC susceptibility measurements on LuFe 2O 4 single crystals reveal a ferrimagnetic transition at 240 K followed by additional magnetic transitions at 225 K and 170 K, separating cluster glass phases, and a kinetically arrested state below 55 K. The origin of giant magnetic coercivity is attributed to the collective freezing of ferrimagnetic clusters and enhanced domain wall pinning associated with a structural transition at 170 K. Magnetocaloric effect measurements provide additional vital information about the multiple magnetic transitions and the glassy states. Our results lead to the emergence of a complex magnetic phase diagram in LuFe 2O 4.

Magnetic and superconducting properties of a pressure-induced superconductor CePd5Al2

Abstract We investigated the magnetic and electronic properties of an antiferromagnet and pressure-induced superconductor CePd5Al2 by measuring the magnetization and de Haas–van Alphen effect, together with the electrical resistivity under pressure and magnetic field. Magnetic measurements including the high field magnetization at 1.3 K reveal several magnetic transitions and quite complex magnetic phase diagram of this compound. Electrical resistivity measurements have been performed using diamond anvil cell up to 12 GPa for the magnetic fields H ∥ [ 0 0 1 ] and [1 0 0]. The upper critical field in superconductivity is anisotropic between H ∥ [ 0 0 1 ] and [1 0 0] in the tetragonal structure, reflecting the quasi-two dimensional electronic state.

Interplay of 3d and 4f magnetism in RCrSb3

RCrSb3 crystallizes in a quasi two dimensional structure with RSb and CrSb2 layers stacked along a axis. This system displays rich magnetic structure due to complex magnetic interaction between 3d moments of Cr and 4f moments of rare earth ion. In this work, we present a comparative study on the heat capacity of R(La, Ce, Pr, Nd)CrSb3 which exemplifies the interplay between two magnetic species (Cr3+ and R3+ions) leading to a complex magnetic phase diagram of RCrSb3 system. The nature of ordering of the rare earth ion is quite different in all the compounds. Moreover,the ferromagnetic ordering temperature TC of Cr spins decreases with the decrease of the size of the rare earth ion.

Anisotropic magnetism in NdCrSb3

We report anisotropic dc magnetic susceptibilityχ(T), isothermalmagnetization M(H),electrical resistivity ρ(T) and heat capacity C(T) measurements on a high quality single crystalline sample ofNdCrSb3. The crystal exhibits ferromagnetic ordering belowTC = 100 K due to ordering of Cr spins. The ferromagnetic phase is highly anisotropic. Theanisotropy becomes even more evident at low temperatures where the rare earth ion(Nd3+) gets magnetically ordered. Nd moments order ferromagneticallybelow 10 K. The magnetic interplay between these two species(Cr3+ andNd3+ ions)gives NdCrSb3 a complex magnetic phase diagram.

Anisotropic magnetism inPrCrSb3: Bulk properties of single crystals

We report anisotropic dc magnetic susceptibility $\ensuremath{\chi}(T)$, isothermal magnetization $M(H)$, electrical resistivity $\ensuremath{\rho}(T)$, and heat capacity $C(T)$ measurements on a single crystalline sample of ${\text{PrCrSb}}_{3}$. The crystal exhibits ferromagnetic ordering below ${T}_{C}=112\text{ }\text{K}$ due to ordering of Cr spins. The ferromagnetic phase is highly anisotropic. The anisotropy becomes even more evident at low temperatures at which the rare-earth ion gets magnetically ordered. Pr moments antiferromagnetically order at ${T}_{N}=12\text{ }\text{K}$. The magnetic interplay between these two species (${\text{Cr}}^{3+}$ and ${\text{Pr}}^{3+}$ ions) gives ${\text{PrCrSb}}_{3}$ a complex magnetic phase diagram.

Competing multiple-q magnetic structures in HoGe3: I. Themagnetic phase diagram of HoGe3

The magnetic phase diagram of the antiferromagneticHoGe3 compound(space group Cmcm,Z = 4, TN = 11 K) has been investigated by means of magnetic measurements, specific heat and high resolutionneutron powder diffraction. The specific heat and the magnetic measurements display anomalies atTN = 11 K and indicateminor transitions at T1 = 9.5 K T2 = 8.1 K andT3 = 4.8 K (onheating). The neutron data in terms of wavevectors show three distinct regions of magnetic ordering with twomultiple-q competing magnetic structures and several transitions, besides the paramagnetic state: (i)the high temperature (HT) range is described with the wavevectors(q1,q2),q1 = (q1x,0,0) with and q2 = (q2x,0,q2z) with and and T dependent length,and the presence of q1 below T1 is not fully confirmed unlike the case for isomorphicTbGe3; (ii) the low temperature range (LT) is described with the wavevectors(q3,q4) with , , and subdivides into the lock-inLT1 range where have a constant length and theLT2 range where q3y andq4y have a lengthvariable with T; (iii) the intermediate temperature range refers to the range of coexistence of the twostructures as metastable phases in varying proportions around the first-order transitionT2. Betweenthe vectors (q1, q2)and (q3, q4) describing the HT and the LT phases there is no simple(group–subgroup) symmetry relation and the transition between them atT2 is of first order (hysteresis effects). Part I of the paper focuses on the model independentanalysis of various sets of neutron data that lead to a rather complex magneticphase diagram. A model dependent description and refinements of the underlyingmultiple-q magnetic structures will be given in part II.

Jahn-Teller distortion and magnetic transitions in perovskiteRMnO3(R=Ho, Er, Tm, Yb, and Lu)

The perovskite $R\mathrm{Mn}{\mathrm{O}}_{3}$ ($R=\mathrm{Ho}$, Er, Tm, Yb, and Lu) were prepared under high pressure and studied with heat capacity and synchrotron x-ray powder diffraction measurements. The temperature interval between the antiferromagnetic transition and the first-order transition to the presumably $E$-type structure narrows with the decreasing ionic radius of $R$, and almost closes for $R=\mathrm{Lu}$. Combined with the data for the larger rare earth $R$, the results show intricate relationship between the complex magnetic phase diagram and significant increase of Jahn-Teller distortion found for the smallest members of $R\mathrm{Mn}{\mathrm{O}}_{3}$.

The new ternary silicides RE 6Co 1.67Si 3 (RE = Ce, Nd, Gd, Tb, Dy) investigated by X-ray diffraction and magnetization measurements

These compounds crystallize in the hexagonal structure (space group P6 3/ m) related to the Gd 6Co 1.67Si 3-type. The magnetization measurements reveal that: (i) the cerium exhibits a trivalent state in Ce 6Co 1.67Si 3 but no magnetic ordering is evidenced above 1.8 K; (ii) on the contrary, two ferro(ferri)magnetic transitions are detected for Nd 6Co 1.67Si 3 (84 and 35 K) and Tb 6Co 1.67Si 3 (183 and 39 K); in both case, a remanence phenomena appears for temperatures below the higher magnetic transition; (iii) similar behavior does not exist for Gd 6Co 1.67Si 3 which shows only one ferromagnetic transition below T C = 294 K. The occurrence of a complex magnetic phase diagram for Nd 6Co 1.67Si 3 and Tb 6Co 1.67Si 3 can be correlated to the existence of two crystallographic sites for rare earth atoms in this new family of compounds.

Complex magnetic properties of Ho 3Cu 4Sn 4

The Ho 3Cu 4Sn 4 compound exhibits multiple magnetic transitions below its Néel temperature of 7.6 K. As the holmium ions occupy two different crystallographic positions (2d and 4e) a complex magnetic phase diagram was expected. Former neutron diffraction measurements revealed the existence of at least three different magnetic phases. In order to investigate the phase diagram of the Ho 3Cu 4Sn 4 compound in more detail magnetometric, specific heat, transport and high-resolution neutron diffraction measurements were carried out. The specific heat data indicate the occurrence of five magnetic transitions at temperatures of 2.3 K, 3.3 K, 4.4 K, 5.5 K and 7.6 K, which turned out to be in a strict agreement with our new neutron diffraction data. The 2d and 4e rare-earth sublattices order independently at 7.6 K and 3.3 K, respectively. The sublattices are described by different propagation vectors which change with the temperature.

Strain-induced modification of magnetic structure and new magnetic phases in rare-earth epitaxial films

Rare earths exhibit complex magnetic phase diagrams resulting from the competition between various contributions to the magnetic energy: exchange, anisotropy and magnetostriction. The epitaxy of a rare-earth film on a substrate induces (i) a clamping to the substrate and (ii) pseudomorphic strains. Both these effects are shown to lead to modifications of the magnetic properties in (0 0 1)Dy, (0 0 1)Tb and (1 1 0)Eu films. In Dy and Tb films, spectacular variations of the Curie temperature have been evidenced. Additionally, Tb films exhibit a new large wavelength magnetic modulation. In Eu films, one of the helical magnetic domains disappears at low temperature whereas the propagation vectors of the other helices are tilted. The link between structural and magnetic properties is underlined via magnetoelastic models. Moreover, molecular beam epitaxy permits the growth of Sm in a metastable dhcp phase. The magnetic structure of dhcp Sm has been elucidated for the first time. In this review, neutron scattering is shown to be a powerful technique to reveal the magnetic structures of rare-earth films.

Variation of magnetostriction with temperature in Tb5Si2.2Ge1.8 single crystal

The Tb5(SixGe4−x) alloy system is similar to the better known Gd5(SixGe4−x), except it has a more complex magnetic and structural phase diagram. Gd5(SixGe1−x)4 has received much attention recently due to its giant magnetocaloric effect, colossal magnetostriction and giant magnetoresistance in the vicinity of a first order combined magnetic-structural phase transition. The magnetostriction changes that accompany the phase transitions of single crystal Tb5(Si2.2Ge1.8) have been investigated at temperatures between 20 and 150K by measurements of magnetostriction along the a axis. Over this temperature range the shape and slope of the magnetostriction curves change, indicative of changes in the magnetic state, crystal structure, and magnetic anisotropy. The results appear to indicate a phase transition that occurs near 106K (onset-completion range of 116–100K). The steepness of the strain transition, its unusual hysteresis, and its temperature dependence appear to indicate a first order phase transition which is activated by applied magnetic field in addition to temperature (see Fig. 1). Magnetostriction measurements at temperature below the transition region appear to indicate a magnetostriction of small overall magnitude (about 30×10−6) but high anisotropy, with anistropy showing considerable temperature dependence.

Magnetic anisotropy in NpRhGa5 single crystals

We have investigated oriented single crystals of the antiferromagnetNpRhGa5 (TN≈37 K) by means of magnetization and specific heat measurements. Strong anisotropyeffects are observed: when magnetic fields are applied in the basal plane, theNéel temperature is barely affected. In contrast, in fields applied along thec axis, the second-order transition (magnetic ordering) is shifted to lower temperatures andmerges into the first-order transition (reorientation of the magnetic moments). A full mappingof this complex magnetic phase diagram as a function of the temperature (down to 1.6 K),applied magnetic field (up to 9 T) and crystal orientation is presented. This study showsthat antiferromagnetic order is more fragile when the magnetic field is applied along thec axis, which is similar to the situation observed for theNpCoGa5 homologue compound.

Magnetic anisotropy and phase transitions in single-crystal Tb5(Si2.2Ge1.8)

The Tb5(SixGe4−x) alloy system has many features in common with the Gd5(SixGe4−x) system although it has a more complex magnetic and structural phase diagram. This paper reports on the magnetic anisotropy and magnetic phase transition of single-crystal Tb5(Si2.2Ge1.8) which has been investigated by the measurements of M-H and M-T along the a, b, and c axes. The variation of 1∕χ vs T indicates that there is a transition from paramagnetic to ferromagnetic at Tc=110K. Below this transition temperature M-H curves show very strong anisotropy, and it is believed that this is due to the complex spin configuration. M-H measurements at T=110K show that the a axis is the easy axis, and that the saturation magnetization is 200emu∕g. The b axis is the hard axis, which needs an external magnetic field much higher than 2T to saturate the magnetization in that direction, indicating a high magnetocrystalline anisotropy. The c axis is of intermediate hardness. The magnetic properties of this material are therefore very different from those of the related Gd5Si2Ge2 system, in which the b axis was found to be the easy axis and the magnitude of the anisotropy was smaller.

Complex magnetic phase diagram of ferromagneticCeNiSb3

Measurements of electrical resistivity at applied pressures up to $55\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$ have been carried out on single crystals of the ferromagnet $\mathrm{Ce}\mathrm{Ni}{\mathrm{Sb}}_{3}$ revealing a complex magnetic phase diagram. The ferromagnetism at ambient pressure at ${T}_{c}=6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ first increases with pressure up to $25\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$, then decreases slightly for $Pg25\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$. In the pressure range $35\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}\ensuremath{\leqslant}P\ensuremath{\leqslant}55\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$, a second anomaly in the resistivity is found at ${T}_{M2}$, below another higher temperature magnetic phase that is conjectured to be different than the ferromagnetism present at lower pressure. Changes in the physical properties such as the residual resistivity, and low temperature maximum in ${\ensuremath{\rho}}_{\mathit{mag}}(T)$ suggest a modification of the electronic structure where the two magnetic phases coexist with one another above $35\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$. The critical pressure for the suppression of the lower temperature phase is estimated to be ${P}_{c}^{\mathit{mag}2}\ensuremath{\simeq}55\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$, while the increase of both the ${T}^{2}$ coefficient of the electrical resistivity $A$ and residual resistivity ${\ensuremath{\rho}}_{0}$ is suggestive of a quantum critical point associated with the higher temperature magnetic phase at ${P}_{c}^{\mathit{mag}1}\ensuremath{\sim}60\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$.