Field-induced Ferromagnetic State Research Articles

Intrinsic insulating transport characteristics in low-carrier density EuCd2As2 films

Searching for an ideal magnetic Weyl semimetal hosting only a single pair of Weyl points has been a focal point for systematic clarification of its unique magnetotransport derived from the interplay between topology and magnetization. Among the candidates, triangular-lattice antiferromagnet EuCd2As2 has been attracting special attention due to the prediction of the ideal Weyl semimetal phase in the ferromagnetic state; however, transport properties of low-carrier density samples have remained elusive. Here, we report molecular beam epitaxy growth of EuCd2As2 films, achieving low-hole density in the range of 1015–1016 cm−3 at low temperature. Transport measurements of such low-carrier density films reveal an insulating behavior with an activation gap of about 200 meV, which persists even in the field-induced ferromagnetic state. Our work provides an important experimental clue that EuCd2As2 is intrinsically insulating, contrary to the previous prediction.

Emergence of 1/3 magnetization plateau and successive magnetic transitions in Zintl phase Eu3InAs3

Single crystals of ${\mathrm{Eu}}_{3}{\mathrm{InAs}}_{3}$ have been successfully synthesized by indium flux reactions. ${\mathrm{Eu}}_{3}{\mathrm{InAs}}_{3}$ crystallizes in the ${\mathrm{Ca}}_{3}\mathrm{Al}{\mathrm{As}}_{3}$-type structure with an orthorhombic space-group $Pnma$. Theoretical calculations indicate that ${\mathrm{Eu}}_{3}{\mathrm{InAs}}_{3}$ is a semiconductor with a direct band gap of 0.3 eV. ${\mathrm{Eu}}_{3}{\mathrm{InAs}}_{3}$ has large negative Seebeck coefficients in the range of 300--450 \ensuremath{\mu}V/K at room temperature. ${\mathrm{Eu}}_{3}{\mathrm{InAs}}_{3}$ displays two antiferromagnetic transitions (${T}_{N1}=13$ and ${T}_{N2}=10$ K) for both $H\ensuremath{\parallel}b$ and $H\ensuremath{\perp}b$ which can be suppressed by magnetic fields. At 2 K, field-induced ferromagnetic states are reached for both $H\ensuremath{\parallel}b$ and $H\ensuremath{\perp}b$. Particularly, the $H\ensuremath{\parallel}b$ magnetization curves show a plateau at 1/3 of the saturated magnetization and an anomaly at 2/3 of the saturated magnetization. ${\mathrm{Eu}}_{3}{\mathrm{InAs}}_{3}$ is a Zintl phase material showing a 1/3 magnetization plateau here.

Interlayer electronic coupling on demand in a 2D magnetic semiconductor.

When monolayers of two-dimensional (2D) materials are stacked into van der Waals structures, interlayer electronic coupling can introduce entirely new properties, as exemplified by recent discoveries of moiré bands that host highly correlated electronic states and quantum dot-like interlayer exciton lattices. Here we show the magnetic control of interlayer electronic coupling, as manifested in tunable excitonic transitions, in an A-type antiferromagnetic 2D semiconductor CrSBr. Excitonic transitions in bilayers and above can be drastically changed when the magnetic order is switched from the layered antiferromagnetic ground state to a field-induced ferromagnetic state, an effect attributed to the spin-allowed interlayer hybridization of electron and hole orbitals in the latter, as revealed by Green's function-Bethe-Salpeter equation (GW-BSE) calculations. Our work uncovers a magnetic approach to engineer electronic and excitonic effects in layered magnetic semiconductors.

Anomalous magnetoresistance in centrosymmetric skyrmion-lattice magnet Gd2PdSi3

We performed a systematic study of the temperature- and field-dependence of magnetization and resistivity of Gd2PdSi3, which is a centrosymmetric skyrmion crystal. We show that a phase diagram can be constructed based on the anomalous magnetoresistance with one-to-one correspondence among all the feature, while the DC magnetization behavior is consistent with the reported phase diagram based on AC susceptibility. In addition, the crossover boundary from a paramagnetic state into the field-induced ferromagnetic state is also identified. Our results suggest that the ferromagnetic spin fluctuations above the Néel temperature play a key role in the high sensitivity of the resistivity anomalies to magnetic field, pointing to the rich interplay of different magnetic correlations at zero and finite wave vectors underlying the skyrmion lattice in this frustrated itinerant magnet.

Tailoring the ferrimagnetic-to-ferromagnetic transition field by interstitial and substitutional atoms in the R–Fe compounds

Fundamental characteristics of rare-earth (R) – iron intermetallics R2Fe14B are highly sensitive to the atomic substitutions and interstitial absorption of light elements. We studied a combined influence of the substitutions in the rare-earth sublattice and hydrogen absorption on the magnetization behavior in magnetic fields up to 60 T Er2Fe14B and Tm2Fe14B ferrimagnets chosen for the study showed that the substitution of Nd for Er or Tm increases the saturation magnetization as a result of ferromagnetic ordering of Nd and Fe moments. Under sufficiently high magnetic fields the magnetic moments rotate and the field-induced ferromagnetic state may be observed. The field at which a transition occurs is related to the strength of the inter-sublattice exchange interaction. The role of hydrogen is primarily to weaken the inter-sublattice ferrimagnetic coupling so that the reorientation becomes achievable at the available magnetic field strength (in hydrides Tm2Fe14BH5.5 and (Tm0.5Nd0.5)2Fe14BH5.5). We analyze the volume dependence of the R–Fe magnetic interaction in R2Fe14B and compare it with other R–Fe compounds.

De Haas–van Alphen Experiment and Fermi Surface Properties in Field-Induced Ferromagnetic State of MnP

MnP is a prototype 3d-itinerant magnet but still a compound under considerable study. This is based on the characteristic magnetic phases including the helical, cone, and fan structures and a varie...

Magnetic phase diagram and magnetoresistance of Gd–Tb–Dy–Ho–Lu hexagonal high-entropy alloy

We present a study of the magnetic phase diagram and the magnetoresistance of a Gd–Tb–Dy–Ho–Lu "ideal" hexagonal high-entropy alloy (HEA), composed of the elements from the heavy half of the rare earth series only. The phase diagram contains an antiferromagnetic (AFM) state, a field-induced ferromagnetic (FM) state above the AFM-to-FM spin-flop transition and a low-temperature spin-glass state. The complex (H,T) phase diagram is a result of competition between the periodic potential arising from the electronic band structure that favors periodic magnetic ordering, the substitutional-disorder-induced random local potential that favors spin-glass-type spin freezing in random directions, the Zeeman interaction with the external magnetic field that favors spin alignment along the field direction and the thermal agitation that opposes any spin ordering. The magnetoresistance reflects complexity of the (H,T) phase diagram. Its temperature dependence can be explained by a continuous weakening and final disappearance of the periodic potential upon cooling that leads to the destruction of long-range ordered periodic magnetic structures. The magnetoresistance is large only at temperatures, where the AFM and field-induced FM structures are present and exhibits a maximum at the critical field of the AFM-to-FM transition. Within the AFM phase, the magnetoresistance is positive with a quadratic field dependence, whereas it is negative with a logarithmic-like field dependence within the field-induced FM phase. At lower temperatures, the long-range periodic spin order "melts" and the magnetoresistance diminishes until it totally vanishes within the low-temperature spin glass phase. The magnetoresistance is asymmetric with respect to the field sweep direction, reflecting nonergodicity and frustration of the spin system.

Magnetic field effect on the chiral magnetism of noncentrosymmetric UPtGe: Experiment and theory

The effect of differently oriented magnetic field on chiral incommensurate helimagnet UPtGe is studied both experimentally and theoretically. The magnetization measurements up to the field above the saturation have revealed an isotropic magnetic response below 20 T and a remarkable nonmonotonic anisotropy in high fields. Moreover, the two principally different phase transitions from the noncollinear incommensurate to the field-induced ferromagnetic state have been observed. These properties are successfully explained by density-functional theory calculations taking into account the noncollinearity of the magnetic structures, arbitrary directed magnetic field, and relativistic effects. We also estimate the strength of different competing magnetic interactions and discuss possible scenarios of the field-induced phase transformations.

Element-specific observation of the ferromagnetic ordering process in UCoAl via soft x-ray magnetic circular dichroism

We have performed soft x-ray magnetic circular dichroism (XMCD) experiments on the itinerant-electron metamagnet UCoAl at the U $4d\ensuremath{-}5f({N}_{4,5})$ and Co $2p\ensuremath{-}3d({L}_{2,3})$ absorption edges in order to investigate the magnetic properties of the U $5f$ and Co $3d$ electrons separately. From the line shape of the XMCD spectrum, it is deduced that the orbital magnetic moment of the Co $3d$ electrons is unusually large. Through the systematic temperature $(T)$- and magnetic field $(H)$-dependent XMCD measurements, we have obtained two types of the magnetization curve as a function of $H$ and $T$ (M-H curve and M-T curve, respectively). The metamagnetic transition from a paramagnetic state to a field-induced ferromagnetic state was clearly observed under 15 K at ${H}_{\mathrm{M}}$. The value of the ${H}_{\mathrm{M}}$ and its $T$ dependence agree well between the U and Co sites, and the bulk magnetization. Whereas, we have discovered the remarkable differences in the M-H and M-T curves between the U and Co sites. The present findings clearly show that the role of the Co $3d$ electrons should be considered more carefully in order to understand the origin of the magnetic ordering in UCoAl.

Features of magnetization behavior in the rare-earth intermetallic compound (Nd0.5Ho0.5)2Fe14B

The crystal-electric field parameters are determined for the (Nd0.5Ho0.5)2Fe14B compound by analyzing experimental magnetization curves obtained in magnetic fields up to 60 T. The values of the crystal-field parameters B20, B40, B60, B44, B64 are 56.3, −73.2, −10.74, −8.9, 0 cm−1 for Nd3+ ion and 312.38, −176.78, 89.2, −88.43, 0 cm−1 for Ho3+ ion. The transition from the ferri-to the field-induced ferromagnetic state has been studied in detail.

Magnetic and Fermi Surface Properties of Antiferromagnet EuCd11

We succeeded in growing a high-quality single crystal of EuCd11 with the BaCd11-type tetragonal structure by the Cd self-flux method, and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization, and de Haas–van Alphen (dHvA) oscillations, together with the electrical resistivity under high pressures up to 8 GPa. The antiferromagnetic ordering was confirmed to occur at the Néel temperature TN = 2.7 K, and the antiferromagnetic state was found to change into the field-induced ferromagnetic state with 7 μB/Eu above a critical field Hc \( \simeq \) 15 kOe for both the magnetic fields H || [100] and [001], revealing a typical Eu-divalent antiferromagnet. Reflecting the large lattice parameters of a = 11.93 Å and c = 7.682 Å with the caged structure, where each Eu atom is surrounded by a polyhedron of 22 Cd atoms, the Brillouin zone and the corresponding Fermi surfaces are small in volume. The detected dHvA branches are well explained by the full potential linear augmented plane wave (FLAPW) energy band calculations for the non-4f reference compound SrCd11, revealing ellipsoidal Fermi surfaces with complicated concave and convex shapes. The present Eu-divalent electronic state is found to be robust against high pressures up to 8 GPa, and does not change into the Eu-trivalent state.

Magnetism in GdCo2B2Studied on a Single Crystal

We have prepared a high quality single crystal of GdCo2B2 and studied complicated magnetism by measuring the magnetization, AC susceptibility and heat capacity. The results can be conceived in terms of low-temperature antiferromagnetism (below TN = 22 K) undergoing three order to order magnetic phase transitions at T1 = 18.5, T2 = 13, and T3 = 7 K, respectively. Measurements on the single crystal allowed us determining the weak magnetocrystalline anisotropy when the a-axis appears to be direction of the easy magnetization. In addition spin-flop transitions have been detected on magnetization loops. We have constructed complex H–T magnetic phase diagrams and calculated magnetocaloric effect (MCE). The large magnetic entropy change of \(\Delta S_{\text{mag}}^{(9\text{T})} = 24\) J kg−1 K−1 is attributed to the instability of antiferromagnetic ordering which can be easily changed to field-induced ferromagnetic state. The interpretation of experimental results is corroborated by ab initio electronic structure calculations.

Ferromagnetic Quantum Criticality Studied by Hall Effect Measurements in UCoAl

Hall effect measurements were performed under pressure and magnetic field up to 2.2 GPa and 16 T on a single crystal of UCoAl. At ambient pressure, the system undergoes a first order metamagnetic transition at the critical field B_m = 0.7 T from a paramagnetic ground state to a field-induced ferromagnetic state. The Hall signal is linear at low field and shows a step-like anomaly at the transition, with only little change of the Hall coefficient. The anomaly is sharpest at the temperature of the critical end point T_0 = 12 K above which the first order metamagnetic transition becomes a crossover. Under pressure B_m increases and T_0 decreases. The step-like anomaly in the Hall effect disappears at P_M ~= 1.3 GPa and the metamagnetic transition is not detected above the quantum critical end point (QCEP) at P_Delta ~= 1.7 GPa, B_m ~= 7 T. Using magnetization data, we analyse our Hall resistivity data at ambient pressure in order to quantitatively account for both ordinary and anomalous contributions to the Hall effect. Under pressure, a drastic change in the field dependence of the Hall coefficient is found on crossing the QCEP. A possible Fermi surface change at B_m remains an open question.

Separation of magnetic properties at uranium and cobalt sites in UCoAl using soft x-ray magnetic circular dichroism

Temperature ($T$) and magnetic field ($H$) dependence of the magnetic properties in metamagnetic UCoAl have been investigated using a soft x-ray magnetic circular dichroism (XMCD). In order to extract element-specific magnetic properties at the U and Co sites, the XMCD experiment has been performed at the U 4$d$-5$f$ (${N}_{4},5$) and Co 2$p$-3$d$ (${L}_{2},3$) absorption edges, respectively. Directions of magnetic moments at the U and Co sites have been determined from shapes of the XMCD spectra. The directions of the total magnetic moments at the U and Co sites are parallel to the $H$ direction ($c$ axis), but the direction of the spin magnetic moment at the U site is opposite to that at the Co site. The XMCD intensities at both the U and Co sites at $T=5.5$ K increase steeply at $H=0.77$ T (${H}_{\mathrm{m}}$), corresponding to the metamagnetic transition. The XMCD intensities do not saturate, even in the field-induced ferromagnetic state above ${H}_{\mathrm{m}}$. In addition, the ratio of the increase of the XMCD intensity at the Co site is smaller than that at the U site. From comparison of the $H$ dependence of the XMCD intensities at $T=25$ and 5.5 K, we found that the magnetic behavior of the Co atom has a stronger $T$ dependence than that of the U atom.

Weak ferromagnetic polar phase in the BiFe1−xTixO3 multiferroics

Neutron powder diffraction and magnetization measurements of selected samples of the BiFe1−xTixO3 series were performed. Ti4+ substitution was shown to induce the appearance of weak ferromagnetism in the initial polar R3c phase stable at x ≤ 0.1. In the concentration range 0 ≤ x ≤ 0.1, room-temperature residual magnetization increases from 0 to 0.25 emu/g (the latter is characteristic of the field-induced weak ferromagnetic state in pure BiFeO3). The calculated ferroelectric polarization decreases from ~70 μC/cm2 (x = 0) to ~60 μC/cm2 (x = 0.1) at room temperature. Magnetic ordering coexists with the large spontaneous polarization in a broad temperature range to make the BiFe1−xTixO3 (x → 0.1) perovskites promising for multiferroic applications.

Ferromagnetic Quantum Critical Endpoint in UCoAl

Resistivity and magnetostriction measurements were performed at high magnetic fields and under pressure on UCoAl. At ambient pressure, the 1st order metamagnetic transition at H m ∼0.7 T from the paramagnetic ground state to the field-induced ferromagnetic state changes to a crossover at finite temperature T 0 ∼11 K. With increasing pressure, H m linearly increases, while T 0 decreases and is suppressed at the quantum critical endpoint (QCEP, P QCEP ∼1.5 GPa, H m ∼7 T). At higher pressure, the value of H m identified as a crossover continuously increases, while a new anomaly appears above P QCEP at higher field H * in resistivity measurements. The field dependence of the effective mass ( m * ) obtained by resistivity and specific heat measurements exhibits a step-like drop at H m at ambient pressure. With increasing pressure, it gradually changes into a peak structure and a sharp enhancement of m * is observed near the QCEP. Above P QCEP , the enhancement of m * is reduced, and a broad plateau is found between H m and H * . We compare our results on UCoAl with those of the ferromagnetic superconductor UGe 2 and the itinerant metamagnetic ruthenate Sr 3 Ru 2 O 7 .

The first semiquinone-bridged bisdithiazolyl radical conductor: a canted antiferromagnet displaying a spin-flop transition

The alternating ABABAB π-stacked bis-1,2,3-dithiazolyl radical 2a (2, R(2)=Ph) has a conductivity σ of 3×10(-5) S cm(-1) at 300 K, and orders as a spin-canted antiferromagnet (T(N)=4.5 K) which undergoes a spin-flop transition to a field-induced ferromagnetic state saturating (at 2 K) at H ∼20 kOe.

Magnetic properties of the field-induced ferromagnetic state in MnSi

We present results of dc magnetization measurements focusing on the magnetic propertiesof the field-induced ferromagnetic state in MnSi. The temperature dependence ofsaturation magnetization in this ferromagnetic state exhibits the signatures of both spinwave excitations and itinerant electron ferromagnetism. The Arrott plots obtained from theisothermal field dependence of magnetization, however, are found to be distinctly nonlinearand hence cannot be explained within a simple framework of itinerant electron magnetism.

強磁場下における強磁性体MnBiの相転移

X-ray powder diffraction, magnetization measurements, and differential thermal analysis (DTA) of polycrystalline MnBi were carried out in zero magnetic field as will as in magnetic fields of up to 14 T and in the temperatures range of 300-773 K, in order to investigate magnetic phase transition. In zero magnetic field, a magnetic phase transition from ferromagnetic to paramagnetic state is exhibited at temperature (Tt) of 628 K, accompanied by decomposition. With increasing magnetic field up to 14 T, Tt increases linearly with the rate of 2 KT-1. A metamagnetic transition between the paramagnetic and field-induced ferromagnetic states was observed just above Tt. The exothermic and endothermic peaks were detected in the magnetic field dependence of DTA signals in the interval of 626-623 K, which relates to the metamagnetic transition. The obtained results are discussed on the basis of a mean field theory.

Elastic and magnetic properties of the bilayer manganese oxide(Pr0.6La0.4)1.2Sr1.8Mn2O7

The elastic and magnetic properties of a single crystal of the bilayer manganese oxide ${({\mathrm{Pr}}_{0.6}{\mathrm{La}}_{0.4})}_{1.2}{\mathrm{Sr}}_{1.8}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ have been investigated by means of ultrasonic and high-field magnetization measurements. Remarkable changes in the elastic constants ${C}_{11}$, ${C}_{33}$, ${C}_{44}$, and ${C}_{66}$ as a function of temperature and magnetic field have been observed. In particular, a distinct elastic anomaly was observed at low temperatures and in magnetic fields when crossing the phase boundary between the paramagnetic insulating and the field-induced ferromagnetic metallic state. A pronounced elastic softening as a function of magnetic field $(H)$ appears across the boundary of the low-temperature magnetic phase below around $40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, accompanied by a distinct hysteresis. In the high-field region, however, these elastic constants exhibit a monotonic increase upon increasing the magnetic field. The high-field magnetization measurements characterizing the magnetic state point out a strong coupling between the elastic strain and the magnetic moment. The data can be described reasonably well considering a strong coupling between elastic strain and magnetic susceptibility ${\ensuremath{\chi}}_{m}=\ensuremath{\partial}M∕\ensuremath{\partial}H$.