Field-induced Magnetic Transition Research Articles

Magnetocaloric effect in Gd60Al25(NiCo)15 bulk metallic glass

Magnetic cooling technology is a very promising alternative to conventional vapor compression refrigeration systems. Searching for suitable magnetocaloric materials with improved properties is a key issue in this field. In this work, we report thermal, magnetic and magnetocaloric properties of the Gd60Al25(NiCo)15 bulk metallic glass. A completely amorphous sample of 3 mm in diameter is successfully fabricated by a vacuum suction casting method. The alloy demonstrates the distinct glass transition and near-eutectic melting. Magnetic measurements reveal ferromagnetic ordering in the BMG at about 91 K. We have found a field-induced magnetic transition in the glass, which provides a table-like behavior for the magnetic entropy changes. Due to this metamagnetic effect, the BMG demonstrates excellent magnetocaloric effect over a wide temperature range. The values of relative cooling power (RCP) and the full width of half maximum of magnetic entropy change (ΔTFWHM) under a magnetic field of 5 T are 890 J × kg−1 and 141 K, respectively. All that makes this glass a promising candidate for magnetic refrigeration applications working at liquid‑nitrogen temperatures.

Magnetic structure and high-field magnetization of the distorted kagome lattice antiferromagnet Cs2Cu3SnF12

High-resolution time-of-flight powder neutron diffraction and high-field magnetization were measured to investigate the magnetic structure and existence of a field-induced magnetic phase transition in the distorted kagome antiferromagnet Cs$_2$Cu$_3$SnF$_{12}$. Upon cooling from room temperature, the compound undergoes a structural phase transition at $T_\textrm{t}=185$ K from the rhombohedral space group $R\bar{3}m$ with the perfect kagome spin network to the monoclinic space group $P2_1/n$ with the distorted kagome planes. The distortion results in three inequivalent exchange interactions among the $S=1/2$ Cu$^{2+}$ spins that magnetically order below $T_\textrm{N}=20.2$ K. Magnetization measured with a magnetic field applied within the kagome plane reveals small in-plane ferromagnetism resulting from spin canting. On the other hand, the out-of-plane magnetization does not show a clear hysteresis loop of the ferromagnetic component nor a prominent anomaly up to 170 T, with the exception of the subtle knee-like bend around 90 T, which could indicate the 1/3 magnetization plateau. The combined analysis using the irreducible representations of the magnetic space groups and magnetic structure refinement on the neutron powder diffraction data suggests that the magnetic moments order in the magnetic space group $P2_1'/n'$ with the all-in-all-out spin structure, which by symmetry allows for the in-plane canting, consistent with the in-plane ferromagnetism observed in the magnetization.

Electronic, thermal and magneto-transport properties of the half-Heusler, DyPdBi

The electronic, thermal, and magneto-transport properties of the ternary half-Heusler, DyPdBi, crystallizing in a non-centrosymmetric face-centered cubic structure have been investigated. DyPdBi is known to exhibit antiferromagnetic (AFM) ordering and field-induced spin-flip transitions below the Néel temperature (TN = 4.0 K). Our heat capacity measurements revealed a λ-type anomaly near 4 K and a broad peak centering at ∼50 K corresponding to the AFM transition and the Schottky effect, respectively. Both the electrical resistivity (ρ) and thermal conductivity (κ) data showed anomalies at the onset temperature of antiferromagnetic ordering suggesting the presence of spin-charge-phonon coupling. The temperature-dependent magnetoresistance (MR) behaviour revealed a sign crossover from negative to positive at ∼20 K while the maximum positive MR of 20% was obtained at TN. The most interesting finding is the unusual field dependence of MR below TN with an enhancement of positive MR following the field-induced magnetic transition attributable to the interphase boundary scatterings. Hall effect studies show holes are the dominant charge carriers with the density of signifying the semimetallic nature of DyPdBi. Below TN, Hall resistivity is found to have additional contribution due to the anomalous Hall effect. The analyses of temperature-dependent Seebeck coefficient (S) and thermal conductivity behaviour suggest the presence of additional scattering mechanisms such as scattering between conduction electrons and narrow 4f derived Lorentzian shaped quasi-particle bands.

Impact of Mn3+ substitution on magnetization and electric polarization behavior in geometry frustrated CuFe1−xMnxO2

The Mn3+ doped single crystal samples CuFe1−xMnxO2 with x = 0.01, 0.03 and 0.05 were synthetic by floating zone method, and their magnetization and electric polarization were measured with static and pulsed high magnetic field up to 50 T in the temperature ranging from 2 to 300 K. A series of field-induced magnetic phase transitions and electric polarization, which show obviously anisotropy, were observed in all the doped samples, and their critical fields were directly related to the Mn3+ doping level. The pulsed high magnetic dielectric polarization measurements show that, in the ferroelectric incommensurate phase, the spontaneous electric polarization region is enhanced by the Mn3+ dopant. The impact of the Mn3+ substitution on magnetic and electric polarization behaviors may associate with the partial release of spin frustration in the CuFeO2. Based on the experimental results, the impact of Mn3+ doping on the magnetization and electric polarization behavior as well as their anisotropy are investigated and a detailed magnetic diagram are assumed.

Spin-charge-lattice coupling in quasi-one-dimensional Ising spin chain CoNb2O6

Magnetization, magnetostriction and dielectric constant measurements are performed on single crystals of quasi-one-dimensional Ising spin chain CoNb2O6 at temperatures below and above the antiferromagnetic phase transition. Field-induced magnetic transitions are clearly reflected in magnetodielectric and magnetostriction data. Sharp anomalies are observed around the critical fields of antiferromagnetic to ferrimagnetic and ferrimagnetic to saturated-paramagnetic transition in both magnetodielectric and magnetostriction experiments. Detailed analysis of temperature and field dependence of dielectric constant and magnetostriction suggests that spins are coupled with lattice as well as charges in CoNb2O6. Below the antiferromagnetic transition temperature, the overall resemblance in anomalies, observed in various physical parameters such as magnetization, dielectric constant, magnetostriction and magnetic entropy change gives a deeper insight about the influence of spin configuration on these parameters in CoNb2O6.

Critical phenomenon and phase diagram of Mn-intercalated layered MnNb3S6

The magnetization of Mn-intercalated layered MnNb3S6 single crystal has been systematically investigated. The angle-dependent magnetization (, , and ) displays that the magnetization of MnNb3S6 with is much stronger than that with H//c, but no magnetic anisotropy within the ab-plane. In addition, a field-induced magnetic phase transition is found when . The investigation of the critical behavior gives the critical exponents , , and with K, which belong to the universality class of three-dimensional Heisenberg model. The critical behavior and exponents indicate that the magnetic coupling in MnNb3S6 is of an isotropic short-range type. Based on universality scaling, the H − T phase diagram with is constructed. The magnetic behaviors and phase diagram of MnNb3S6 are analogous to those of CrNb3S6 which exhibits a chiral magnetic soliton lattice.

Spin dynamics and field-induced magnetic phase transition in the honeycomb Kitaev magnet α−Li2IrO3

The layered honeycomb iridate $\alpha$-Li$_2$IrO$_3$ displays an incommensurate magnetic structure with counterrotating moments on nearest-neighbor sites, proposed to be stabilized by strongly-frustrated anisotropic Kitaev interactions between spin-orbit entangled Ir$^{4+}$ magnetic moments. Here we report powder inelastic neutron scattering measurements that observe sharply dispersive low-energy magnetic excitations centered at the magnetic ordering wavevector, attributed to Goldstone excitations of the incommensurate order, as well as an additional intense mode above a gap $\Delta\simeq2.3$ meV. Zero-field muon-spin relaxation measurements show clear oscillations in the muon polarization below the N\'{e}el temperature $T_{\rm N}\simeq15$ K with a time-dependent profile consistent with bulk incommensurate long-range magnetism. Pulsed field magnetization measurements observe that only about half the saturation magnetization value is reached at the maximum field of 64 T. A clear anomaly near 25 T indicates a transition to a phase with reduced susceptibility. The transition field has a Zeeman energy comparable to the zero-field gapped mode, suggesting gap suppression as a possible mechanism for the field-induced transition.

Field-induced phases in a heavy-fermion U(Ru0.92Rh0.08)2Si2 single crystal

We report the high-field induced magnetic phases and phase diagram of a high quality \urxrs~single crystal prepared using a modified Czochralski method. Our study, that combines high-field magnetization and electrical resistivity measurements, shows for fields applied along the $c$-axis direction three field-induced magnetic phase transitions at $\mu_{0} H_{c1}$ = 21.60 T, $\mu_{0} H_{c2}$ = 37.90 T and $\mu_{0} H_{c3}$ = 38.25 T, respectively. In agreement with a microscopic up-up-down arrangement of the U magnetic moments the phase above $H_{c1}$ has a magnetization of about one third of the saturated value. In contrast the phase between $H_{c2}$ and $H_{c3}$ has a magnetization that is a factor of two lower than above the $H_{c3}$, where a polarized Fermi-liquid state with a saturated moment $M_{s}$ $\approx$ 2.1 $\mu_{B}$/U is realized. Most of the respective transitions are reflected in the electrical resistivity as sudden drastic changes. Most notably, the phase between $H_{c1}$ and $H_{c2}$ exhibits substantially larger values. As the temperature increases, transitions smear out and disappear above $\approx$ 15 K. However, a substantial magnetoresistance is observed even at temperatures as high as 80 K. Due to a strong uniaxial magnetocrystalline anisotropy a very small field effect is observed for fields apllied perpendicular to the $c$-axis direction.

Molecular structures of nickel adducts in zeolites – Interpretation of experimental EPR g-tensors guided by DFT calculations

Computational electron paramagnetic resonance (EPR) spectroscopy is a combination of robust simulation techniques of complex spectra with density functional theory (DFT) calculations of spin-Hamiltonian parameters for the adopted models of the investigated paramagnetic species. This approach was used for guiding interpretation of the experimental EPR data of selected adducts of nickel(I) and nickel (II) centers in high-silica zeolites with gas-phase small molecules of environmental significance (CO, NO, C2H2, NH3, O2). As a result, a quantitative connection between the spectroscopic fingerprints, in particular g-tensors, and structure of the molecular clusters mimicking the real intrazeolitic species was obtained. Possible calculation schemes for assessing g-tensor values were explored. Various levels of relativistic effects (including relativistic corrections to the composition of electronic ground state and spin-orbit approximations) were studied. Selection of a proper exchange-correlation functional was also discussed underlying its influence for the systems for which spin density is delocalized over a metal core and a ligand. The conformation analysis of g-tensor anisotropy for amine adducts in assessing its structure was shown. Finally, molecular interpretation of electronic g-tensor in terms of the magnetic field-induced transitions between involved orbitals was shown taking as an example a diamine Ni(I) adduct.

Magnetic and magnetotransport properties of single-crystalline R2PdGe6 (R = Pr, Gd and Tb)

Single crystals of R2PdGe6 (R = Pr, Gd and Tb) compounds were grown by the Bi-flux method. Pr2PdGe6 is an antiferromagnetic compound with Néel temperature TN = 15 K, in which a field-induced magnetic transition (spin flip) occurs when a magnetic field is applied along either a or b axis; a small magnetization and hysteresis loop were observed when a field is applied along c axis. Gd2PdGe6 is a collinear antiferromagnetic compound with TN = 37 K along b axis. Tb2PdGe6 is an antiferromagnetic compound with TN = 48 K and its hard magnetization direction is along b axis. The temperature dependences of the resistance of the entire three compounds present inflection points at the respective TN. A large resistance (as well as magnetoresistance) change can be found at the spin flip transition of Pr2PdGe6, but the change is not obvious at the spin flop transition of Gd2PdGe6.

Magnetic field driven complex phase diagram of antiferromagnetic heavy-fermion superconductor Ce3PtIn11

We present the results of our comprehensive investigation on the antiferromagnetic heavy-fermion superconductor Ce3PtIn11 carried out by means of electrical transport, heat capacity and ac magnetic susceptibility measurements, performed on single-crystalline specimens down to 50 mK in external magnetic fields up to 9 T. Our experimental results elucidate a complex magnetic field – temperature phase diagram which contains both first- and second-order field-induced magnetic transitions and highlights the emergence of field stabilized phases. Remarkably, a prominent metamagnetic transition was found to occur at low temperatures and strong magnetic fields. In turn, the results obtained in the superconducting phase of Ce3PtIn11 corroborate an unconventional nature of Cooper pairs formed by heavy quasiparticles. The compound is an almost unique example of a heavy fermion system in which superconductivity may coexist microscopically with magnetically ordered state.

Multiple magnetic transitions in single crystals of Ce12Fe57.5As41 and La12Fe57.5As41

Measurements of magnetic and transport properties were performed on needle-shaped single crystals of Ce12Fe57.5As41 and La12Fe57.5As41. The availability of a complete set of data enabled a side-by-side comparison between these two rare earth compounds. Both compounds exhibited multiple magnetic orders within 2-300 K and metamagnetic transitions at various fields. Ferromagnetic transitions with Curie temperatures of 100 and 125 K were found for Ce12Fe57.5As41 and La12Fe57.5As41, respectively, followed by antiferromagnetic type spin reorientations near Curie temperatures. The magnetic properties underwent complex evolution in the magnetic field for both compounds. An antiferromagnetic phase transition at about 60 K and 0.2 T was observed merely for Ce12Fe57.5As41. The field-induced magnetic phase transition occurred from antiferromagnetic to ferromagnetic structure. A strong magnetocrystalline anisotropy was evident from magnetization measurements of Ce12Fe57.5As41. A temperature-field phase diagram was present for these two rare earth systems. In addition, a logarithmic temperature dependence of electrical resistivity was observed in the two compounds within a large temperature range of 150-300 K, which is rarely found in 3D-based compounds. It may be related to Kondo scattering described by independent localized Fe 3d moments interacting with conduction electrons.

Influence of Ferromagnetic Carbon Nanotubes on Magnetic Transitions in Liquid Crystals

Magnetic field-induced orientational transitions in suspensions of carbon nanotubes (CNTs) in nematic liquid crystals have been studied in the framework of a continuum theory. Ferromagnetic CNTs are considered that possess, in addition to a large anisotropy of diamagnetic susceptibility, an additional magnetic moment due to ferromagnetic particles either situated on the CNT surface or encapsulated inside. It is established that, depending on the energy of coupling between disperse CNTs and liquid-crystalline matrix, the external magnetic field induces various sequences of orientational transitions. A threshold value of the coupling energy is determined, above which a transition from the initial homogeneous planar phase to inhomogeneous state (angular phase) becomes possible. At coupling energies below the threshold, the increasing magnetic field induces the following sequence of orientational transitions: homogeneous planar phase–inhomogeneous (angular) phase–homogeneous homeotropic phase–inhomogeneous angular phase. It is established that, depending on the intensity of segregation phenomena, these transitions can be of the first or second order. Analytical expressions for the fields of second-order transitions between phases are found. On an example of the optical phase difference between the ordinary and extraordinary rays of light passing through the cell of CNT suspension, it is shown that the suspension can exhibit optical bistability during the first-order orientational transition.

Tricritical phenomenon and H−T phase diagram in a single crystal of the double-perovskite iridate La2ZnIrO6

We report a detailed study of magnetic properties in double perovskite iridate ${\mathrm{La}}_{2}{\mathrm{ZnIrO}}_{6}$ single crystal, which exhibits an antiferromagnetic (AFM) ground state. The field- and angle-dependent magnetizations $[M(H)$ and $M(\ensuremath{\varphi})]$ suggest strong magnetic anisotropy in this system. The magnetization of ${\mathrm{La}}_{2}{\mathrm{ZnIrO}}_{6}$ is isotropic in the $ab$ plane, while it is much stronger than that along the $c$ axis. A field-induced magnetic transition from AFM to ferromagnetic (FM) state is found, which is of a first-order type. The critical behavior is investigated, where critical exponents $\ensuremath{\beta}=0.2317(1),\phantom{\rule{0.28em}{0ex}}\ensuremath{\gamma}=0.9783(2)$, and $\ensuremath{\delta}=5.0071(5)$ are obtained. The critical exponents belong to the universality class of the tricritical mean-field model, which indicates a field-induced tricritical phenomenon. Based on the scaling equations, we construct the $H\text{\ensuremath{-}}T$ phase diagram for ${\mathrm{La}}_{2}{\mathrm{ZnIrO}}_{6}$ single crystal with $H//b$. A tricritical point is revealed at the intersection point between the AFM, FM, and paramagnetic phases (${T}_{tr}\ensuremath{\approx}8$ K; ${H}_{tr}\ensuremath{\approx}170$ Oe).

Effects of external magnetic field and hydrostatic pressure on magnetic and structural phase transitions in Pr0.6Sr0.4MnO3

We investigate the effect of hydrostatic pressure on the temperature dependence of magnetization and also the influence of magnetic field on the linear thermal expansion in polycrystalline Pr0.6Sr0.4MnO3, which is ferromagnetic at room temperature (TC = 305 K) but its magnetization undergoes an abrupt decrease at TS = 89 K within the ferromagnetic state. Normal and inverse magnetocaloric effects around TC and TS, respectively, were reported earlier in this single phase compound [Repaka et al., J. Appl. Phys. 112, 123915 (2012)]. The thermal expansion shows an abrupt decrease at TS in zero magnetic field but transforms into an abrupt increase at the same temperature under 7 T, which we interpret as a consequence of magnetic field-induced structural transition from the low-temperature monoclinic (I2/a symmetry) to high-temperature orthorhombic (Pnma symmetry) phase in corroboration with a published neutron diffraction study in zero magnetic field. While the external magnetic field does not change TS, the application of a hydrostatic pressure of P = 1.16 GPa shifts the magnetic anomaly at TS towards high temperature. The pressure induced shift of the low-temperature magneto-structural anomaly (ΔTS = 27 K) is nine-times higher than that of the ferromagnetic Curie temperature (ΔTC = 3 K). Our results suggest that while the hydrostatic pressure stabilizes the low temperature monoclinic phase at the expense of the orthorhombic phase, the applied magnetic field does not affect the structural transition temperature.

Change in the entropy during a first-order phase transition induced by a magnetic field in an isotropic non-Heisenberg ferromagnet

We describe a first-order phase transition in an isotropic non-Heisenberg ferromagnet induced by a magnetic field with a fourth-order spin exchange interaction at temperatures above the Curie point. The field behavior of the magnetization is analyzed and the temperature dependences of the critical fields of the stability of the paramagnetic and ferromagnetic phases as well as the critical field of the phase transition between them are determined. It is shown that this first-order phase transition has a finite amplitude of the magnetization jump and can occur in small magnetic fields. An H–T phase diagram is presented. It is found that the amplitude of the phase jump during the magnetic field-induced transition from the paramagnetic to the ferromagnetic phase can exceed the magnitude of the entropy change of an isotropic Heisenberg ferromagnet by two orders of magnitude when it is magnetized at the Curie point. It is shown that the expansion of the free energy model up to the 6th power in magnetization can only qualitatively describe the entropy behavior in the phase transition between the paramagnetic and ferromagnetic phases.

Two New Three-Dimensional Pillared-Layer Co(II) and Cu(II) Frameworks Involving a [M₂(EO-N₃)₂] Motif from a Semi-Flexible N-Donor Ligand, 5,5'-Bipyrimidin: Syntheses, Structures and Magnetic Properties.

Two new three-dimensional (3D) Co(II)- and Cu(II)-azido frameworks, [Co2(N3)4(bpym)2]n (1) and [Cu2(N3)4(bpym)]n (2), were successfully synthesized by introducing a semi-flexible N-donor ligand, 5,5′-bipyrimidin (bpym), with different bridging modes and orientations. Compounds 1 and 2 were structurally characterized by X-ray crystallography, IR spectroscopy, thermogravimetry and elemental analysis. Compounds 1 and 2 are 3D pillared-layer frameworks with double end-on (EO) azido bridged dinuclear motifs, [M2(EO-N3)2]. In Compound 1, the bpym ligands show trans μ2-bridging mode and the role as pillars to connect the Co(II)-azido layers, composed of [Co2(EO-N3)2] motifs and single end-to-end (EE) azido bridges, to a 3D network with BN topology. In contrast, in 2, the bpym ligand adopts a twisted μ4-bridging mode, which not only connects the adjacent [Cu2(EO-N3)2] units to a layer, but also functions as a pillar for the layers of the 3D structure. The structural diversities between the two types of architectures can be attributed to the coordination geometry preference of the metal ions (octahedral for Co2+ and square pyramidal for Cu2+). Magnetic investigations revealed that Compound 1 exhibits ferromagnetic-like magnetic ordering due to spin canting with a critical temperature, TC = 33.0 K, and furthers the field-induced magnetic transitions of metamagnetism at temperatures below TC. Compound 2 shows an antiferromagnetic ordering with TN = 3.05 K and a field-induced magnetic transition of spin-flop at temperatures below the TN.

A one-dimensional cobalt phosphonate showing field-induced magnetic transition

A one-dimensional cobalt phosphonate showing field-induced magnetic transition

Field-induced magnetic phase transitions and memory effect in bilayer ruthenate Ca3Ru2O7 with Fe substitution

Bilayer ruthenate Ca3(Ru1−xFex)2O7 (x = 0.05) exhibits an incommensurate magnetic soliton lattice driven by the Dzyaloshinskii–Moriya interaction. Here we report complex field-induced magnetic phase transitions and memory effect in this system via single-crystal neutron diffraction and magnetotransport measurements. We observe first-order incommensurate-to-commensurate magnetic transitions upon applying the magnetic field both along and perpendicular to the propagation axis of the incommensurate spin structure. Furthermore, we find that the metastable states formed upon decreasing the magnetic field depend on the temperature and the applied field orientation. We suggest that the observed field-induced metastability may be ascribable to the quenched kinetics at low temperature.

Magnetization, ESR and large magnetocaloric effect in zigzag chain SrGd2O4

We performed the magnetization and electron spin resonance (ESR) measurements in the zigzag chain antiferromagnet SrGd2O4. First, the temperature-dependent ESR spectra suggest the presence of spin–spin correlations well above the ordering temperature due to geometric frustration. Second, the ESR data reveal the field-induced magnetic transition from an ordered state to a paramagnetic state, in accordance with the magnetization data. Third, the magnetization process exhibits a large magnetocaloric effect, which is associated with the alignment of paramagnetic spins along the direction of magnetic field. The maximum magnetic entropy change (−ΔSM) near 3 K and refrigerant capacity (RCP) are 27 J · Kg−1 · K−1 and 325 J · Kg−1, respectively, for a field change of 0–7 T. With negligible thermal and field hysteresis, SrGd2O4 can be considered as a cryogenic refrigerant material.