Pressure-induced Magnetic Phase Transition Research Articles

Pressure-induced magnetic phase and structural transition in SmSb2

Abstract Motivated by the recent discovery of unconventional superconductivity around a magnetic quantum critical point in pressurized CeSb2, here we present a high-pressure study of an isostructural antiferromagnetic (AFM) SmSb2 through electrical transport and synchrotron x-ray diffraction measurements. At P C ~2.5 GPa, we found a pressure-induced magnetic phase transition accompanied by a Cmca→P4/nmm structural phase transition. In the pristine AFM phase below P C, the AFM transition temperature of SmSb2 is insensitive to pressure; in the emergent magnetic phase above P C, however, the magnetic critical temperature increases rapidly with increasing pressure. In addition, at ambient pressure, the magnetoresistivity (MR) of SmSb2 increases suddenly upon cooling below the AFM transition temperature and presents linear nonsaturating behavior under high field at 2 K. With increasing pressure above P C, the MR behavior remains similar to that observed at ambient pressure, both in terms of temperature- and field-dependent MR. This leads us to argue an AFM-like state for SmSb2 above P C. Within the investigated pressure of up to 45.3 GPa and the temperature of down to1.8 K, we found no signature of superconductivity in SmSb2.

Pressure-induced magnetic phase transition and related physical properties in Z1-Fe3Pd alloy

A Z1-type Fe3Pd alloy with negative enthalpy of formation at ambient pressure has been discovered recently, however, its physical properties under high pressures remain unclear. In this work, the effect of pressure on the magnetic, electronic, lattice dynamic, mechanical and thermal properties of the Z1-Fe3Pd are investigated thoroughly by the first-principles methods. Under high pressures, the Z1-Fe3Pd are energetically favorable compared to other types Fe3Pd structures. A pressure-induced magnetic phase transition from ferromagnetic (FM) to ferrimagnetic (FIM) state are found, and the FM and FIM states are dynamically and mechanically stable under high pressures. The electronic density of states for both the FM and FIM states are analyzed to understand their magnetism. These two magnetic configurations are ductile, but their elastic properties and anisotropy are quite different. Additionally, the FM and FIM states have high uniaxial magnetocrystalline anisotropy, the FM state is a semi-hard magnet, and the FIM state undergoes a transition from hard magnet to semi-hard magnet with pressure. Finally, the volume and linear thermal expansion coefficients under high pressure are calculated, and the anisotropy of thermal expansion is also discussed in detail.

Coupled magnetic and structural transition in topological antiferromagnet EuAgAs under high pressure

Recently, EuAgAs and its derivatives have emerged as a promising platform for studying the interplay of transports, magnetism and topology. Herein, we report construction of a temperature-pressure phase diagram for antiferromagnetic Dirac semimetal EuAgAs, through electrical transport, synchrotron x-ray diffraction and Raman spectroscopy measurements in diamond anvil cells at high pressures up to 48.6 GPa. At Pc1∼3–5 GPa, we found a pressure-induced magnetic phase transition with accompanying a structural P63/mmc→Pnma transition. In the pristine antiferromagnetic phase, negative colossal magnetoresistance is observed mainly below the Néel temperature TN along with a field-induced metamagnetic transition; in the emergent magnetic phase, however, it is evident both above and below the magnetic critical temperature TC yet with no field-induced metamagnetic transition. These distinct features lead us to argue a ferromagnetic-like state for EuAgAs above Pc1, which is further supported by observation of a T5/3 temperature dependence of low-temperature resistance, a characteristic of marginal Fermi-liquid state expected to exist close to a ferromagnetic instability by spin fluctuations in metallic ferromagnets. At Pc2∼20 GPa, a possible phase transition of electronic origin may take place, which is revealed jointly by change of a T5/3→T5/2 temperature dependence of low-temperature resistance and change in slope of linear-in-T resistance at high temperatures.

Superconductivity beyond the Conventional Pauli Limit in High-Pressure CeSb_{2}.

We report the discovery of superconductivity at a pressure-induced magnetic quantum phase transition in the Kondo lattice system CeSb_{2}, sustained up to magnetic fields that exceed the conventional Pauli limit eightfold. Like CeRh_{2}As_{2}, CeSb_{2} is locally noncentrosymmetric around the Ce site, but the evolution of critical fields and normal state properties as CeSb_{2} is tuned through the quantum phase transition motivates a fundamentally different explanation for its resilience to applied field.

Magnetic detection under high pressures using designed silicon vacancy centres in silicon carbide.

Pressure-induced magnetic phase transitions are attracting interest as a means to detect superconducting behaviour at high pressures in diamond anvil cells, but determining the local magnetic properties of samples is a challenge due to the small volumes of sample chambers. Optically detected magnetic resonance of nitrogen vacancy centres in diamond has recently been used for the in situ detection of pressure-induced phase transitions. However, owing to their four orientation axes and temperature-dependent zero-field splitting, interpreting these optically detected magnetic resonance spectra remains challenging. Here we study the optical and spin properties of implanted silicon vacancy defects in 4H-silicon carbide that exhibit single-axis and temperature-independent zero-field splitting. Using this technique, we observe the magnetic phase transition of Nd2Fe14B at about 7 GPa and map the critical temperature-pressure phase diagram of the superconductor YBa2Cu3O6.6. These results highlight the potential of silicon vacancy-based quantum sensors for in situ magnetic detection at high pressures.

Coherent Control and Magnetic Detection of Divacancy Spins in Silicon Carbide at High Pressures.

Spin defects in silicon carbide appear to be a promising tool for various quantum technologies, especially for quantum sensing. However, this technique has been used only at ambient pressure until now. Here, by combining this technique with diamond anvil cell, we systematically study the optical and spin properties of divacancy defects created at the surface of SiC at pressures up to 40 GPa. The zero-field-splitting of the divacancy spins increases linearly with pressure with a slope of 25.1 MHz/GPa, which is almost two-times larger than that of nitrogen-vacancy centers in diamond. The corresponding pressure sensing sensitivity is about 0.28 MPa/Hz-1/2. The coherent control of divacancy demonstrates that coherence time decreases as pressure increases. Based on these, the pressure-induced magnetic phase transition of Nd2Fe14B sample at high pressures was detected. These experiments pave the way to use divacancy in quantum technologies such as pressure sensing and magnetic detection at high pressures.

Raman spectroscopy investigation on the pressure-induced structural and magnetic phase transition in two-dimensional antiferromagnet FePS3

The layered van der Waals antiferromagnetic FePS3 has received considerable attention because long range magnetic ordering can remain with single atoms layer, which offers potential applications in future ultrathin devices. Here, we perform Raman spectroscopy to systematically explore the variations of lattice vibration and crystal structure under pressure up to 18.9 GPa. We observe two structural phase transitions at approximately 4 GPa and 13 GPa, respectively. Moreover, by monitoring spin-related Raman modes, we demonstrate a pressure-induced magnetic structure transition above 2 GPa. These modes disappear accompanying the second structural phase transition and insulator-to-metal transition (IMT), indicating the suppression of long-range magnetic ordering, in agreement with earlier neutron powder diffraction experiments.

Resonant inelastic x-ray scattering spectra in the hyperhoneycomb iridate β−Li2IrO3 : First-principles calculations

We studied the electronic structure of the $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ insulator within the density-functional theory using the generalized gradient approximation while taking into account strong Coulomb correlations in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band structure method. The $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ undergoes a pressure-induced structural and magnetic phase transition at ${P}_{c}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}4$ GPa with symmetry lowering to the monoclinic $C2/c$. The structural phase transition is accompanied by the formation of ${\mathrm{Ir}}_{2}$ dimers on the zigzag chains, with an Ir-Ir distance of $\ensuremath{\sim}2.66$ \AA{}, even shorter than that of metallic Ir. The strong dimerization stabilizes the bonding molecular-orbital state, leads to the collapse of the magnetism, and opens the energy gap with a concomitant electronic phase transition from a Mott insulator to band insulator. The resonant inelastic x-ray scattering spectra (RIXS) at the Ir ${L}_{3}$ edge were investigated theoretically from first principles. The calculated results are in good agreement with the experimental data. We show that the drastic reconstruction of the RIXS spectral peak at 0.7 eV associated with the structural $Fddd\ensuremath{\rightarrow}C2/c$ phase transition at ${P}_{c}$ can be related to the disappearing of the Coulomb correlations in the high-pressure $C2/c$ phase.

Anomalous Hall effect triggered by pressure-induced magnetic phase transition in α -Mn

Recent interest in topological nature in condensed matter physics has revealed the essential role of Berry curvature in anomalous Hall effect (AHE). However, since large Hall response originating from Berry curvature has been reported in quite limited materials, the detailed mechanism remains unclear at present. Here, we report the discovery of a large AHE triggered by a pressure-induced magnetic phase transition in elemental $\alpha$-Mn. The AHE is absent in the non-collinear antiferromagnetic phase at ambient pressure, whereas a large AHE is observed in the weak ferromagnetic phase under high pressure despite the small averaged moment of $\sim 0.02 \mu_B$/Mn. Our results indicate that the emergence of the AHE in $\alpha$-Mn is governed by the symmetry of the underlying magnetic structure, providing a direct evidence of a switch between a zero and non-zero contribution of the Berry curvature across the phase boundary. $\alpha$-Mn can be an elemental and tunable platform to reveal the role of Berry curvature in AHE.

Pressure-induced magnetic phase transitions of intermetallic Fe2AlB2

Pressure-dependent magnetic properties and magneto-structural phase transitions of the intermetallic Fe2AlB2 compound have been investigated by using spin-polarized density functional theory calculations. From the enthalpy calculations, possible phase transitions are predicted. It is seen that a phase transition from ferromagnetic (FM) to antiferromagnetic (AFM) occurs at 40 GPa, and the other one is from AFM to nonmagnetic (NM) occurs at 96 GPa. To investigate the source of the magneto-structural phase transitions, atomic bonding characteristics, and possible pressure effects on the physical properties of the compound are calculated. And, the structural, electronic, and mechanical properties of FM-, AFM- and NM-phases are considered as a function of pressure on the 0–120 GPa range. Subsequently, the spin-polarized partial and total density of states (DOS), projections of the charge densities, integrated spin densities, magnetization (or net magnetic moment), DOSs at the Fermi level, Mulliken bond overlap populations are studied to present a compact pressure analysis for Fe2AlB2. It is observed that there are sudden changes and discontinuities in the structural and magnetic properties at 40, 54, 59, and 96 GPa pressures as well as the other physical properties, which support the magneto-structural phase transitions.

Navigating the Trends in the Proximity to Magnetic Quantum Critical Point and Superconductivity for Ce-Based Heavy-Fermion Compounds

Pressure-induced magnetic quantum phase transition of CeRhIn$_5$ is described from first principles based on a realistic Kondo lattice model. Simulations of CeRhIn$_5$ above ambient pressure up to P=5 [GPa] show that it is driven from an antiferromagnetic phase into the paramagnetic phase crossing the possible QCP around P=2 [GPa], being consistent with the experimental trends. Our calculations suggest a possibility for a coexistence phase around $P\stackrel{<}{\sim} 3$ [GPa]. On the basis of the data from our realistic simulations, a comprehensive materials navigator is compiled including pressure dependent CeRhIn5 to possibly provide a guideline for further discovery of Ce-based heavy fermion superconductors.

Magnetic Sensing inside a Diamond Anvil Cell via Nitrogen-Vacancy Center Spins**Supported by the National Basic Research Program of China under Grant No 2015CB921103, the National Key R&D Program of China under Grant No 2016YFA0401503, the Strategic Priority Research Program of Chinese Academy of Sciences under Grant No XDB28000000, the National Natural Science Foundation of China under Grant Nos 11574386, 11575288

The diamond anvil cell-based high-pressure technique is a unique tool for creating new states of matter and for understanding the physics underlying some exotic phenomena. In situ sensing of spin and charge properties under high pressure is crucially important but remains technically challenging. While the nitrogen-vacancy (NV) center in diamond is a promising quantum sensor under extreme conditions, its spin dynamics and the quantum control of its spin states under high pressure remain elusive. In this study, we demonstrate coherent control, spin relaxation, and spin dephasing measurements for ensemble NV centers up to 32.8 GPa. With this in situ quantum sensor, we investigate the pressure-induced magnetic phase transition of a micron-size permanent magnet Nd2Fe14B sample in a diamond anvil cell, with a spatial resolution of ∼2 μm, and sensitivity of ∼20 μT/Hz1/2. This scheme could be generalized to measure other parameters such as temperature, pressure and their gradients under extreme conditions. This will be beneficial for frontier research of condensed matter physics and geophysics.

Pressure-induced first-order magnetic phase transition and Yb ordered moment in YbCu2Si2

We report on high-pressure x-ray absorption near edge structure and x-ray magnetic circular dichroism (XMCD) measurements at the Yb ${L}_{3}$ edge on ${\mathrm{YbCu}}_{2}{\mathrm{Si}}_{2}$. This intermetallic is a well-known intermediate valence compound which shows a pressure-induced paramagnetic-ferromagnetic phase transition at about 8 GPa. The pressure dependence of the Yb magnetization has been determined by following the evolution with pressure of the maximum of the dichroic signal at the energy corresponding to the electric quadrupole ($2{p}_{3/2}\ensuremath{-}4f$) transitions. The observed XMCD deduced magnetization curves confirm the ferromagnetic nature of the high-pressure phase as well as the first-order nature of the transition. The Yb ordered moment deduced from XMCD which amounts to about $1.25{\ensuremath{\mu}}_{B}$ at 8.7 GPa and 2.7 K is in very good agreement with the one estimated by M\"ossbauer spectroscopy for the magnetically ordered component of the spectra. This observation indicates that the paramagnetic and ferromagnetic phases coexist only in a narrow pressure range in our XMCD experiment. This is not the case for the M\"ossbauer measurements, which show that the paramagnetic component vanishes only at 20 GPa. Our results clarify the existing discrepancy with dc magnetization measurements that reported values of the Yb moment more than two times smaller. We propose that these apparent contradictory results are due to different experimental conditions which influence the range of coexistence of the paramagnetic and ferromagnetic phases, as found in many similar situations and frequently addressed in the literature.

Pressure-induced magnetic transition in Nd2Fe14B based on two-sublattice model

To analyze the magnetic properties of Nd2Fe14B compound under high pressure, an improved two-sublattice molecular field model coupled with equivalent stress field was applied to study the effect of pressure on magnetization, magnetostriction coefficient, susceptibility and Curie temperature. The calculation results show that the pressure has a stronger effect on the magnetization of Fe sublattice compared to that of Nd sublattice at varied temperatures when the external magnetic field is parallel to the alignment direction. Saturated magnetization, initial susceptibility and magnetic moment of Nd2Fe14B compound are found to decrease gradually with pressure increasing, and the Curie temperature of Nd2Fe14B decreases to about 298 K under an applied pressure of 1.15 GPa. The results suggest that the pressure-induced magnetic phase transition of Nd2Fe14B occurs under 1.15 GPa at room temperature.

Electronic structure and x-ray magnetic circular dichroism in the hyperhoneycomb iridate β−Li2IrO3

We studied the electronic, magnetic, and optical properties of $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ insulator within the density-functional theory using the generalized gradient approximation taking into account strong Coulomb correlations (GGA+$U$) in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. The x-ray absorption spectra and x-ray magnetic circular dichroism (XMCD) at the Ir ${L}_{2,3}$ edges were investigated theoretically from first principles. The calculated results are in good agreement with experimental data. We found that the GGA+$U$ approach with Hubbard ${U}_{\text{eff}}=1.5\phantom{\rule{4pt}{0ex}}\mathrm{eV}$ well describes the optical spectra and XMCD spectra at the Ir ${L}_{2,3}$ edges. We investigated the electronic structure of $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ under pressure from first principles. The hyperhoneycomb iridate $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ is on the border of the magnetic ordering with relatively weak Coulomb electron-electron correlations. The $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ undergoes a pressure-induced structural and magnetic phase transitions at ${P}_{c}=4.4$ GPa with symmetry lowering to the monoclinic $C2/c$. The structural phase transition is accompanied by a dimerization of the previously equally long $x/y$ Ir-Ir bonds. We find remarkable nonmagnetic ground states of $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ at ${P}_{c}$, with a concomitant electronic phase transition from a Mott insulator to band insulators. We found that ${J}_{\text{eff}}=1/2$ states are still dominant in the low-energy region in high-pressure monoclinic $C2/c$ structure.

Pressure-induced dimerization and valence bond crystal formation in the Kitaev-Heisenberg magnet α−RuCl3

Magnetization and high-resolution x-ray diffraction measurements of the Kitaev-Heisenberg material alpha-RuCl3 reveal a pressure-induced crystallographic and magnetic phase transition at a hydrostatic pressure of p=0.2 GPa. This structural transition into a triclinic phase is characterized by a very strong dimerization of the Ru-Ru bonds, accompanied by a collapse of the magnetic susceptibility. Ab initio quantum-chemistry calculations disclose a pressure-induced enhancement of the direct 4d-4d bonding on particular Ru-Ru links, causing a sharp increase of the antiferromagnetic exchange interactions. These combined experimental and computational data show that the Kitaev spin liquid phase in alpha-RuCl3 strongly competes with the crystallization of spin singlets into a valence bond solid.

Substitution- and strain-induced magnetic phase transition in iron carbide

Cementite-type carbides are of interest for magnetocaloric applications owing to their temperature- or pressure-induced magnetic phase transition. Here, using first-principles calculations, we investigate the magnetism and the magnetic phase transition in iron carbide (Fe3C) with the substitution of Cr atoms at Fe sites with the strain effect. The presence of Cr atoms is found to give rise to a second-order magnetic phase transition from a ferromagnetic phase for Fe3C to a nonmagnetic phase in chromium carbide (Cr3C).While the ternary Fe2CrC and Cr2FeC compounds prefer the ferrimagnetic ground state, the magnitudes of both the Fe and Cr spin moments, which are antiparallel in orientation, decrease as x increases in Fe3-xCrxC (x = 0, 1, 2, and 3). Furthermore, the fixed spin-moment calculations indicate that the magnetization of Fe3-xCrxC compounds can be delicately altered via the strain effect and that the magnetic-nonmagnetic phase transition occurs at an early stage of Cr substitution, x = 2.

Magnetic-field- and pressure-induced quantum phase transition inCsFeCl3proved via magnetization measurements

We have performed magnetization measurements of the gapped quantum magnet CsFeCl$_3$ at temperatures ($T$) down to 0.5\,K at ambient pressure and down to 1.8\,K at hydrostatic pressures ($P$) of up to 1.5\,GPa. The lower-field ($H$) phase boundary of the field-induced ordered phase at ambient pressure is found to follow the power-law behavior expressed by the formula $H_{\rm N}(T)$\,$-$\,$H_{\rm c}$\,$\propto$\,$T_{\rm N}^{\phi}$. The application of pressure extends the phase boundary to both a lower field and higher temperature. Above the critical pressure $P_{\rm c}$\,$\sim$\,0.9\,GPa, the transition field $H_{\rm N}$ associated with the excitation gap becomes zero, and a signature of the magnetic phase transition is found in the $T$-dependence of magnetization in a very low applied field. This suggests that CsFeCl$_3$ exhibits a pressure-induced magnetic phase transition at $P_{\rm c}$.

Pressure-induced electronic and magnetic phase transitions in a Mott insulator: Ti-dopedCa3Ru2O7bilayer ruthenate

We report the hydrostatic pressure-induced electronic and magnetic phase transitions in a Mott insulator, a bilayer ruthenate $\mathrm{C}{\mathrm{a}}_{3}{(\mathrm{R}{\mathrm{u}}_{0.97}\mathrm{T}{\mathrm{i}}_{0.03})}_{2}{\mathrm{O}}_{7}$, via electronic transport and single crystal neutron diffraction measurements. The system undergoes an insulator-metal transition at a very small hydrostatic pressure \ensuremath{\approx}0.04 GPa, followed by a magnetic phase transition around 0.3 GPa, suggesting that the low energy charge fluctuation and magnetic ordering couple to the pressure separately in this compound. The $ab$ initio calculations show that the suppressed $\mathrm{Ru}{\mathrm{O}}_{6}$ flattening induced by the pressure reduces the orbital polarization and gives rise to an insulator-metal transition preceding the magnetic phase transition.

First-principles investigation of the magnetic structures and pressure-induced magnetic phase transition in magnetocaloric MnRhAs

Density functional theory was applied to investigate the magnetic orderings and pressure-induced magnetic phase transition of hexagonal, Fe2P-type MnRhAs. Effective exchange parameters were evaluated to measure the strength of pair-wise metal–metal magnetic couplings. Results indicate that indirect Mn⋅⋅⋅Mn exchange couplings dominate in MnRhAs. Weak direct exchange couplings for near-neighbor Rh–Rh and Rh–Mn contacts are caused by small moments on the Rh atoms. In addition, RKKY and superexchange mechanisms were used to analyze indirect Mn⋅⋅⋅Mn exchange couplings in MnRhAs. The relationship between inter-layer Mn–Mn magnetic couplings and volume changes in MnRhAs was examined to understand the pressure-induced magnetic phase transition.