CrI3 is a promising candidate for van der Waals bonded ferromagnetic devices since its ferromagnetism can be maintained upon exfoliating bulk crystals down to a single layer. In this work we studied ...critical properties of bulk CrI3 single crystals around the paramagnetic to ferromagnetic phase transition. Critical exponents β = 0.260(4) with a critical temperature Tc = 60.05(13) K and γ = 1.136(6) with Tc = 60.43(4) K are obtained by the Kouvel-Fisher method, whereas δ = 5.32(2) is obtained by a critical isotherm analysis at Tc = 60 K. The critical exponents determined in bulk CrI3 single crystals suggest a three-dimensional long-range magnetic coupling with the exchange distance decaying as J(r)≈r−4.69.
The critical properties of the single-crystalline semiconducting ferromagnet Cr2Ge2Te6 were investigated by bulk dc magnetization around the paramagnetic to ferromagnetic phase transition. Critical ...exponents β=0.200±0.003 with a critical temperature Tc=62.65±0.07 K and γ=1.28±0.03 with Tc=62.75±0.06 K are obtained by the Kouvel-Fisher method whereas δ=7.96±0.01 is obtained by a critical isotherm analysis at Tc=62.7 K. These critical exponents obey the Widom scaling relation δ=1+γ/β, indicating self-consistency of the obtained values. With these critical exponents the isotherm M(H) curves below and above the critical temperatures collapse into two independent universal branches, obeying the single scaling equation m=f±(h), where m and h are renormalized magnetization and field, respectively. The determined exponents match well with those calculated from the results of the renormalization group approach for a two-dimensional Ising system coupled with a long-range interaction between spins decaying as J(r)≈r−(d+σ) with σ=1.52.
The magnetic field response of the transport properties of novel materials and then the large magnetoresistance effects are of broad importance in both science and application. We report large ...transverse magnetoreistance (the magnetoresistant ratio ~ 1.3 × 10(5)% in 2 K and 9 T field, and 4.3 × 10(6)% in 0.4 K and 32 T field, without saturation) and field-induced metal-semiconductor-like transition, in NbSb2 single crystal. Magnetoresistance is significantly suppressed but the metal-semiconductor-like transition persists when the current is along the ac-plane. The sign reversal of the Hall resistivity and Seebeck coefficient in the field, plus the electronic structure reveal the coexistence of a small number of holes with very high mobility and a large number of electrons with low mobility. The large MR is attributed to the change of the Fermi surface induced by the magnetic field which is related to the Dirac-like point, in addition to orbital MR expected for high mobility metals.
Van der Waals (vdW) ferromagnets are an important class of materials for spintronics applications. The recent discovery of atomically vdW magnets CrI3 and Cr2 Ge2 Te6 has triggered a renaissance in ...the area of two-dimensional (2D) magnetism. Herein we systematically studied 2H-Mn0.28 TaS2 single crystal, a 2D vdW ferromagnet with Tc ∼ 82.3K, and a large in-plane magnetic anisotropy. MnK-edge x-ray absorption spectroscopy was measured to provide information on its electronic state and local atomic environment. The detailed magnetic isotherms measured in the vicinity of Tc indicates that the spin coupling inside 2H-Mn0.28 TaS2 is of a 3D Heisenberg type coupled with the attractive long-range interaction between spins that decay as J(r) ≈ r−4.85. Both resistivity ρ(T) and thermopower S(T) exhibit anomalies near Tc, confirming that the hole-type transport carriers strongly interact with local moments. An unusual angle-dependent magnetoresistance is further observed, suggesting a possible field-induced novel magnetic structure.
Abstract
Two-dimensional (2D) materials with intrinsic ferromagnetism provide unique opportunity to engineer new functionalities in nano-spintronics. One such material is CrI
3
, showing long-range ...magnetic order in monolayer with the Curie temperature (
T
c
) of 45 K. Here we study detailed evolution of magnetic transition and magnetic critical properties in response to systematic reduction in crystal thickness down to 50 nm. Bulk
T
c
of 61 K is gradually suppressed to 57 K, however, the satellite transition at
T
*
= 45 K is observed layer-independent at fixed magnetic field of 1 kOe. The origin of
T
*
is proposed to be a crossover from pinning to depinning of magnetic domain walls. The reduction of thickness facilitates a field-driven metamagnetic transition around 20 kOe with out-of-plane field, in contrast to the continuous changes with in-plane field. The critical analysis around
T
c
elucidates the mean-field type interactions in microscale-thick CrI
3
.
We report a systematic investigation of dc magnetization and ac susceptibility, as well as anisotropic magnetocaloric effect in bulk CrI3 single crystals. A second-stage magnetic transition was ...observed just below the Curie temperature Tc, indicating a two-step magnetic ordering. The low temperature thermal demagnetization could be well fitted by the spin-wave model rather than the single-particle model, confirming its localized magnetism. The maximum magnetic entropy change −ΔSMmax∼5.65 J kg−1K−1 and the corresponding adiabatic temperature change ΔTad∼2.34 K are achieved from heat capacity analysis with the magnetic field up to 9 T. Anisotropy of ΔSM(T,H) was further investigated by isothermal magnetization, showing that the difference of −ΔSMmax between the ab plane and the c axis reaches a maximum value ∼1.56 J kg−1K−1 with the field change of 5 T. With the scaling analysis of ΔSM, the rescaled ΔSM(T,H) curves collapse onto a universal curve, indicating a second-order type of the magnetic transition. Furthermore, the −ΔSMmax follows the power law of Hn with n=0.64(1), and the relative cooling power depends on Hm with m=1.12(1).
The critical properties of flux-grown single-crystalline quasi-two-dimensional weak itinerant ferromagnet Cr0.62Te were investigated by bulk dc magnetization around the paramagnetic to ferromagnetic ...phase transition. Critical exponents β=0.315(7) with a critical temperature Tc=230.6(3) K and γ=1.81(2) with Tc=229.1(1) K are obtained by the Kouvel-Fisher method whereas δ=6.35(4) is obtained by a critical isotherm analysis at Tc=230 K. With these obtained exponents, the magnetization-field-temperature curves collapse into two independent curves following a single scaling equation M|T−TcTc|−β=f±(H|T−TcTc|−βδ) around Tc, suggesting the reliability of the obtained exponents. Additionally, the determined exponents of Cr0.62Te exhibit an Ising-like behavior with a change from short-range order to long-range order in the nature of magnetic interaction and with an extension from two to three dimensions on cooling through Tc.
The Cooper pairing mechanism of heavy fermionsuperconductors, long thought to be due to spin fluctuations, has not yet been determined. It is the momentum space (k-space) structure of the ...superconducting energy gap Δ(k) that encodes specifics of this pairing mechanism. However, because the energy scales are so low, it has not been possible to directly measure Δ(k) for any heavy fermion superconductor. Bogoliubov quasiparticle interference imaging, a proven technique for measuring the energy gaps of superconductors with high critical temperatures, has recently been proposed as a new method to measure Δ(k) in heavy fermion superconductors, specifically CeCoIn 5 (ref. ). By implementing this method, we detect a superconducting energy gap whose nodes are oriented along k||(±1,±1)π/a 0 directions. Moreover, for the first time in any heavy fermion superconductor, we determine the detailed structure of its multiband energy gaps Δ i (k). For CeCoIn 5 , this information includes: the complex band structure and Fermi surface of the hybridized heavy bands, the fact that largest magnitude Δ(k) opens on a high- k band so that the primary gap nodes occur at unforeseen k-space locations, and that the Bogoliubov quasiparticle interference patterns are most consistent with d x2-y2 gap symmetry. Such quantitative knowledge of both the heavy band-structure and superconducting gap-structure will be critical in identifying the microscopic pairing mechanism of heavy fermion superconductivity. PUBLICATION ABSTRACT
The critical properties and magnetocaloric effect of semiconducting ferrimagnet Mn3Si2Te6 single crystals have been investigated by bulk magnetization and heat capacity around Tc. Critical exponents ...β=0.41±0.01 with a critical temperature Tc=74.18±0.08K and γ=1.21±0.02 with Tc=74.35±0.05K are deduced by the Kouvel-Fisher plot, whereas δ=4.29±0.05(3.40±0.02) is obtained by a critical isotherm analysis at T=74(75)K. The magnetic exchange distance is found to decay as J(r)≈r−4.79, which lies between the mean-field and 3D Heisenberg models. Moreover, the magnetic entropy change −ΔSM features a maximum at Tc, i.e., −ΔSMmax∼2.53(1.67)Jkg−1K−1 with in-plane (out-of-plane) field change of 5 T, confirming large magnetic anisotropy. The heat capacity measurement further gives −ΔSMmax∼2.94Jkg−1K−1 and the corresponding adiabatic temperature change ΔTad∼1.14K with out-of-plane field change of 9 T.
Fundamental electronic principles underlying all transition metal compounds are the symmetry and filling of the d-electron orbitals and the influence of this filling on structural configurations and ...responses. Here we use a sensitive local structural technique, x-ray atomic pair distribution function analysis, to reveal the presence of fluctuating local-structural distortions at high temperature in one such compound, CuIr
S
. We show that this hitherto overlooked fluctuating symmetry-lowering is electronic in origin and will modify the energy-level spectrum and electronic and magnetic properties. The explanation is a local, fluctuating, orbital-degeneracy-lifted state. The natural extension of our result would be that this phenomenon is likely to be widespread amongst diverse classes of partially filled nominally degenerate d-electron systems, with potentially broad implications for our understanding of their properties.
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