Metamagnetic Phase Transition Research Articles

Ab initio study of FeRh alloy properties

Abstract In this work the structural, energetic, thermodynamic, magnetic and thermoelectric properties of FeRh alloy have been studied using first-principles calculations. The structural and magnetic results obtained for the FM phase are in agreement with experimental and other theoretical calculated values (local magnetization of about 3 μB and 1 μB for Fe and Rh atoms respectively). The transition AFM to the FM state is accompanied by a 2.4% increase in the volume of the cell and by 9.6% in the Fe spin magnetic moment. The characterization of the AFM phase shows a distortion of the cubic and tetragonal cell to the orthorhombic solving the instabilities observed in the phonon band structures curves of the corresponding to cubic structure. The stability of the AFM configurations was corroborated with molecular dynamics (MD) simulations. The magnitude of the Seebeck coefficient increases with the temperature at a certain chemical potential. While the magnitude of the electrical conductivity does not present meaningful changes with the temperature in the selected values, the thermal conductivity increases with the temperature. Another consequence of the AFM to FM transition is the drop of the resistivity ρ in the FM phase as compared to the AFM state. Based on the results obtained using MD simulations from stable AFM configurations and the results of entropy changes, the configuration AFM-B (type I) could be identified as the most favorable in achieving the metamagnetic phase transition.

PNR study of the phase transition in FeRh thin films

The first order antiferromagnetic to ferromagnetic metamagnetic phase transition of equiatomic FeRh offers new opportunities for novel antiferromagnetic memories and spintronic devices with the caveat that it can be utilized in thin film structures (<50 nm). Here, we report a polarized neutron reflectivity (PNR) study for three representative film thicknesses (5, 20, and 50 nm) aimed at determining the physical and magnetic structure of FeRh at room temperature and partway through the transition. The PNR results are analyzed with reference to X-ray diffraction, X-ray reflectivity, and atomic force microscopy data which together provide a consistent description of the magnetic and physical state of the FeRh thin films. The data demonstrate that the nucleation of the ferromagnetic phase initiates at the MgO substrate, and results from structural and magnetic measurements demonstrate that the magnetic behavior and strain properties of FeRh correlate with the evolving topography of the three films investigated.

Crystal structure and magnetic properties of the Gd8Ag19.5Al45.2 and Ho8Ag21.2Al43.3 compounds

ABSTRACTThe crystal structures of the Gd8Ag19.5(2)Al45.2(2) (Gd4(Ag0.294Al0.706)32Ag0.340) and Ho8Ag21.2(2)Al43.3(2) (Ho4(Ag0.323Al0.677)32Ag0.252) compounds, which adopt the Yb8Cu17Al49-type structure with the space group I4/mmm, have been investigated by means of the X-ray powder diffraction. The structures of the compounds are characterized by the silver/aluminum mixing on several atomic positions and the partial occupancy of silver atoms on one atomic position. dc and ac magnetic data indicate antiferromagnetic properties below 46.5 K for Gd8Ag19.5Al45.2 and 15 K for Ho8Ag21.2Al43.3. In case of RE = Gd an anomaly observed in its magnetic susceptibility at 3.5 K suggests a magnetic transition of the order-order type. A metamagnetic phase transition is detected for RE = Ho.

Thermodynamic properties and rare-earth spectroscopy of Cu3Nd(SeO3)2O2X (X = Cl, Br)

The kagome lattice of copper ions in francisite-type compounds is quite sensitive to external stimuli, being easily affected by temperature and magnetic field. The rare-earth ions inserted between buckled layers of transition metal add new dimension to magnetism in these systems. Neodymium francisites, Cu3Nd(SeO3)2O2X (X = Cl, Br), experience long range magnetic order at TN = 34 K (Cl) or 35.2 K (Br) and spin reorientation transition at TR = 4 K (Cl) or 4.6 K (Br) marked by sharp anomalies in magnetization M, specific heat Cp, and optical spectra. The spin reorientation of Cu2+ ions is due to d-f interaction of transition and rare-earth magnetic subsystems. Under action of modest external field B < 2 T both compounds exhibit metamagnetic phase transition, largely hysteretic in case of Cl compound at T < TR.

Metamagnetism emergence and spectroscopic elucidation of SmFeO3 nanoceramics

Temperature- and field-dependence of magnetization measurements on SmFeO3 nanoceramics have been carried out, and a first order type metamagnetic phase transition has been observed below 280 K. The Arrott plot on M(H) measurements confirms the emergence of such a first order transition, this could be argued by the creation of a ferromagnetic cluster between the antiferromagnetic Sm3+–O–Fe3+ and Fe3+–O–Fe3+ chains by Sm3+ ions around the respective transition. Additionally, a quasi-paramagnetic ordering of Sm3+ spins is observed below 20 K due to canted moment from Sm3+–O–Sm3+. Electron paramagnetic resonance and Raman measurements at various temperatures exhibit an analogue to the instantaneous first order metamagnetic transition, confirming the predominance of Sm3+–O–Fe3+ and Fe3+–O–Fe3+ interactions above and below 273 K, respectively. The present study brings an important aspect of the presence of the magnetic property in SmFeO3 pertaining to active and non-active interaction of Sm–O–Fe at the nanoscale regime.

Magnetization and Giant Magnetoresistance of Polycrystalline TbSb at Low Temperatures

Dependences of the magnetization M and the resistance R on the temperature T in the range from 2 to 300 K and on the magnetic field H up to 14 T were investigated in polycrystalline samples of terbium antimonide TbSb. A peculiarity (bending) was observed on the M(H) dependences at each temperature below the transition point of TbSb into the antiferromagnetic phase (TN = 14.8 K), which is due to a metamagnetic phase transition. Positive giant magnetoresistance was found in TbSb near the antiferromagnetic phase region.

Large magnetocaloric effect in ErCoSn driven by metamagnetic phase transition and short-range ferromagnetic correlations

Abstract Here, we report the results of structural, magnetic, thermal and magnetocaloric properties of ErCoSn compound. The compound undergoes an antiferromagnetic (AFM) ordering around TN = 4.6 K and magnetic correlation is observed above TN, up to T = 11 K. Below TN, a spin-glass state was observed for ErCoSn due to an apparent coexistence of ferromagnetic (FM) interaction with long-range AFM order. External applied magnetic field induces a first-order-like metamagnetic phase transition from AFM to FM state that is responsible for the large values of the maximum isothermal entropy change (− Δ M max = 16.5 J/kgK@50 kOe) and adiabatic temperature change (ΔTad = 8.2 K). Furthermore, short-range ferromagnetic correlation above TN contributes to the widening of −ΔSM and ΔTad peaks as well as the increase of the ErCoSn compound refrigerant capacity. The results indicate attractive properties of this compound for magnetic refrigeration at cryogenic temperatures.

Magnetic field-induced magnetostructural transition and huge tensile superelasticity in an oligocrystalline Ni-Cu-Co-Mn-In microwire.

Meta-magnetic shape-memory alloys combine ferroelastic order with ferromagnetic order and exhibit attractive multifunctional properties, but they are extremely brittle, showing hardly any tensile deformability, which impedes their practical application. Here, for the first time, an Ni-Cu-Co-Mn-In microwire has been developed that simultaneously exhibits a magnetic field-induced first-order meta-magnetic phase transition and huge tensile superelasticity. A temperature-dependent in situ synchrotron high-energy X-ray diffraction investigation reveals that the martensite of this Ni43.7Cu1.5Co5.1Mn36.7In13 microwire shows a monoclinic six-layered modulated structure and the austenite shows a cubic structure. This microwire exhibits an oligocrystalline structure with bamboo grains, which remarkably reduces the strain incompatibility during deformation and martensitic transformation. As a result, huge tensile superelasticity with a recoverable strain of 13% is achieved in the microwire. This huge tensile superelasticity is in agreement with our theoretical calculations based on the crystal structure and lattice correspondence of austenite and martensite and the crystallographic orientation of the grains. Owing to the large magnetization difference between austenite and martensite, a pronounced magnetic field-induced magnetostructural transition is achieved in the microwire, which could give rise to a variety of magnetically driven functional properties. For example, a large magnetocaloric effect with an isothermal entropy change of 12.7 J kg-1 K-1 (under 5 T) is obtained. The realization of magnetic-field- and tensile-stress-induced structural transformations in the microwire may pave the way for exploiting the multifunctional properties under the coupling of magnetic field and stress for applications in miniature multifunctional devices.

The enhanced magnetocaloric effect in Dy2In1−xAlx by a non-hysteresis metamagnetic phase transition

To enhance the magnetocaloric effect of the second-order magnetic phase transition is eagerly sought in the development of practical magnetic refrigeration technology. Here, demonstrated by Dy2In1−xAlx (0 ≤ x ≤ 0.5) system, the max magnetic entropy change is significantly enhanced to 13.4 Jkg−1 K−1 in Dy2In0.7Al0.3 and 10.8 Jkg−1 K−1 in Dy2In0.6Al0.4 alloys compared with 8.8 Jkg−1 K−1 in Dy2In through a field-induced metamagnetic phase transition, which is unconventionally of nonhysteresis confirmed by magnetic measurements. Considering that nonhysteresis metamagnetic transition occurs at the critical composition where hexagonal structure is formed for x ≤ 0.3 while orthorhombic structure for x ≥ 0.4, the origin is ascribed to the lattice distortion.

The effects of Ge occupation and hydrostatic pressure on the metamagnetic phase transition and magnetocaloric effect in Mn2Sb alloy

The effects of Ge occupations at Sb and Mn sites in Mn2Sb system had been re-examined along with the influence of hydrostatic pressure. The metamagnetic phase transition from ferrimagnetic (FRI) to antiferromagnetic (AFM) state was observed in Mn2Sb1-xGex (x = 0.05, 0.1) and (Mn1-yGey)2Sb (y = 0.025, 0.04) alloys. The phase transition temperature, Tt, was gradually increased with increased Ge substitution for both Sb and Mn, but slightly decreased under increased hydrostatic pressure in Mn2Sb0.95Ge0.05 alloy. Meanwhile, the slope of critical field as the function of temperature was reduced with increased hydrostatic pressure and Ge substitution amount in (Mn1-yGey)2Sb (y = 0.025, 0.04) alloys. For a field change of 7 T, the maxima of magnetic entropy changes of 6 Jkg-1K-1 and 7.1 Jkg-1K-1 have been achieved in Mn2Sb0.95Ge0.05 and Mn1.95Ge0.05Sb alloys, which are gradually decreased by more Ge substitution and increased hydrostatic pressure.

Difference in magnetic and ferroelectric properties between rhombohedral and hexagonal polytypes of AgFeO2 : A single-crystal study

We have investigated magnetic and dielectric properties of rhombohedral $3R\ensuremath{-}{\mathrm{AgFeO}}_{2}$ and hexagonal $2\mathrm{H}\ensuremath{-}{\mathrm{AgFeO}}_{2}$ by using magnetic and dielectric bulk measurements and a neutron diffraction experiment with single crystals grown by hydrothermal synthesis. Magnetic phase transitions occur at $T=14.0$ K and $T=6.0$ K in $3R\ensuremath{-}{\mathrm{AgFeO}}_{2}$ and $T=17.0$ K and $T=9.5$ K in $2H\ensuremath{-}{\mathrm{AgFeO}}_{2}$ under zero magnetic field. Multistep metamagnetic phase transitions were observed in $3R\ensuremath{-}{\mathrm{AgFeO}}_{2}$ in magnetization measurements up to 60 T, while a single phase transition occurs in $2H\ensuremath{-}{\mathrm{AgFeO}}_{2}$. The ferroelectric polarization parallel and perpendicular to the triangular lattice plane appears below $T=6.0\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ in $3R\ensuremath{-}{\mathrm{AgFeO}}_{2}$, which is concomitant with the onset of the cycloid magnetic ordering with the propagation vector $\mathbit{k}=(\ensuremath{-}\frac{1}{2},q,\frac{1}{2};q\ensuremath{\simeq}0.2)$ and the magnetic point group polar $m{1}^{\ensuremath{'}}$. On the other hand, the ferroelectric polarization is absent even below the lower phase transition temperature in $2H\ensuremath{-}{\mathrm{AgFeO}}_{2}$, which can be explained by the proper screw magnetic structure with $\mathbit{k}=(0,q,0;q\ensuremath{\simeq}0.4)$ and the nonpolar ${2221}^{\ensuremath{'}}$ point group. Although the two-dimensional triangular lattice layers of ${\mathrm{Fe}}^{3+}$ are common in the two polytypes, the magnetic and ferroelectric properties are significantly different. The emergence of ferroelectric polarization which is not confined to be within the plane of the cycloid for $3R\ensuremath{-}{\mathrm{AgFeO}}_{2}$ can be explained by the extended inverse Dzyaloshinskii-Moriya effect with two orthogonal components, ${\mathbit{p}}_{1}\ensuremath{\propto}{\mathbit{r}}_{ij}\ifmmode\times\else\texttimes\fi{}[{\mathbit{S}}_{i}\ifmmode\times\else\texttimes\fi{}{\mathbit{S}}_{j}]$ and ${\mathbit{p}}_{2}\ensuremath{\propto}{\mathbit{S}}_{i}\ifmmode\times\else\texttimes\fi{}{\mathbit{S}}_{j}$. Unlike other delafossite compounds, the ${\mathbit{p}}_{2}$ component is not allowed in the proper screw phase of $2H\ensuremath{-}{\mathrm{AgFeO}}_{2}$ due to the symmetry restriction of the parent space group.

Structural and magnetic characterization of Y-type hexaferrite powders prepared by sol-gel auto-combustion and sonochemistry

We present results from a study on the influence of the preparation technique on the structural and magnetic properties of Ba0.5Sr1.5Zn2Fe12O22 powders synthesized by citric-acid sol-gel auto-combustion and sonochemistry and characterized by X-ray diffraction, scanning electron microscopy and magnetic measurements. Two magnetic intermediate phases were observed at room temperature in magnetic fields of moderate strength. Metamagnetic phase transitions were observed in an ac magnetic field. Their temperature increased with the magnetic field amplitude.

Намагниченность и гигантское магнетосопротивление поликристаллов TbSb при низких температурах

On the terbium antimonide TbSb polycrystals, the dependences of the magnetization M and the resistance R on the temperature T in the range of 2 ÷ 300 K and on the magnetic field H up to H = 14 T have been studied. On the dependences M (H) at each temperature, a feature (kink) was observed associated with the metamagnetic phase transition. Giant positive magnetoresistance of TbSb in the region of the antiferromagnetic phase has been found.

Temperature-Dependent Studies of Coupled Fe55Pt45 / Fe49Rh51 Thin Films

Fe${}_{50}$Rh${}_{50}$ is an unusual alloy with a first-order metamagnetic phase transition above room temperature. Thin-film structures of FeRh with engineered interfacial exchange interactions are multifunctional, responding to temperature, magnetic field, and strain. The authors use experiments and simulations to study reduced switching fields in both macroscale Fe-Pt/FeRh thin films and mesoscale islands, allowing the exchange constants between layers to be determined. This will promote the development of nanoscale, multifunctional magnetic materials for applications including heat-assisted magnetic recording, spintronics, antiferromagnetic memory, and medical hyperthermia treatments.

Correlated excited states in the narrow band gap semiconductor FeSi and antiferromagnetic screening of local spin moments

The physical properties of the semiconductor FeSi with very narrow band gap, anomalous behavior of the magnetic susceptibility and metal-insulator transition at elevated temperatures attract gross interest due to the still controversial theoretical understanding of their origin. On one side the purely band like mechanism of the gap formation in FeSi at low temperature is well established, on other side a number of experiments and their theoretical interpretation suggest a rich physics of strong correlations at finite temperature. In this work we use an ab-initio scheme based on the Random Phase Approximation and Local Spin Density Approximation (RPA@LSDA) to reveal the role of the electron correlation effects in FeSi extending it by applying a fixed spin moment constraint. In the parameter free framework we show that correlation effects essentially alter the one-electron LSDA results leading to the formation of an additional state with finite magnetic moment on Fe, whose energy is almost degenerate with the non-magnetic ground state. This explains the results of high field experiments, which found a first-order meta-magnetic phase transition into a metallic ferromagnetic state. Our results suggest a strongly correlated nature of the low-energy excitations in FeSi. From our super-cells calculations we reveal that these excitations are local and exhibit a Kondo-like behavior since a strong antiferromagnetic screening is present.

Двойной метамагнитный фазовый переход в изинговском антиферромагнетике с легкоплоскостной одноионной анизотропией и со спином ионов S = 1

Двойной метамагнитный фазовый переход в изинговском антиферромагнетике с легкоплоскостной одноионной анизотропией и со спином ионов <i>S</i> = 1

Pressure-enhanced magnetocaloric effects in Mn2Sb1-xSnx system with uniaxial magnetocrystalline anisotropy

The magnetocaloric effects in Sn-substituted Mn2Sb1-xSnx system (x = 0.1, 0.2, 0.3) have been studied. With more Sn content, metamagnetic phase transition temperature (Tt) is increased with gradually reduced Curie temperature, thermal hysteresis and the maximum of magnetic entropy change (ΔSmax). By hydrostatic pressure of 2.5 kbar, Tt is lowered but ΔSmax is enhanced from 4.2 JKg−1K−1 to ∼5.5 Jkg−1K−1 in Mn2Sb1-xSnx (x = 0.1, 0.2) ingots. The uniaxial magnetocrystalline anisotropy is found in all Mn2Sb1-xSnx ingots and abnormally increased with elevated temperature, leading to the abnormal coercivity-temperature dependence in the corresponding ribbons. The microstructure of the ribbons is sensitively dependent on Sn composition. Our work demonstrates that high ΔSmax tuned by hydrostatic pressure and high magnetocrystalline anisotropy can be realized together in Mn2Sb1-xSnx system, which may help the development of such bifunctional alloy exhibiting refrigerating capability as well as the hard magnetic properties simultaneously.

Synthesis, structure and magnetic properties of Pr0.65Ca0.3M0.05MnO3 (M = Na, K and Ag): A perovskite manganites with metamagnetic phase transitions

The synthesis, structural characterization, and magnetic properties of Pr0.65Ca0.3M0.05MnO3 (M = Na, K and Ag) perovskite manganites are reported. Our samples were synthesized using the solid state reaction method at high temperature. Rietveld refinements of the X-ray diffraction patterns show that all our samples are single phase and crystallize in the distorted orthorhombic system with Pbnm space group. The surface morphology and infrared absorption of the samples were systematically investigated. Magnetization measurements versus temperature in a magnetic applied field of 50 mT showed that the antiferromagnetic ordering temperature TAFM occurring below the charge-ordering transition temperature TCO in these narrow band manganites are slightly dependent with monovalent element. The critical magnetic field (Hc) required for metamagnetism is found to reduce drastically from 7 T for Pr0.65Ca0.35MnO3 to 2.9 T for Pr0.65Ca0.3Na0.05MnO3.

Causes of the Metamagnetism in a Disordered EuMn0.5Co0.5O3 Perovskite

The magnetic properties of the EuMn0.5Co0.5O3 perovskite synthesized under various conditions are studied in fields up to 140 kOe. The sample synthesized at T = 1500°C is shown to exhibit a metamagnetic phase transition, which is irreversible below T = 40 K, and the sample synthesized at T = 1200°C demonstrates the field dependence of magnetization that is typical of a ferromagnet. Both samples have TC = 123 K and approximately the same magnetization in high magnetic fields. The metamagnetism is assumed to be related to a transition from a noncollinear ferromagnetic phase to a collinear phase, and the presence of clusters with ordered Co2+ and Mn4+ ions leads to ferromagnetism. The noncollinear phase is formed due to the competition between positive Co2+–Mn4+ and negative Mn4+–Mn4+ and Co2+–Co2+ interactions, which make almost the same contributions, and to the existence of a high magnetic anisotropy.

Kondo behavior and metamagnetic phase transition in the heavy-fermion compound CeBi2

Heavy fermions represent an archetypal example of strongly correlated electron systems which, due to entanglement among different interactions, often exhibit exotic and fascinating physics involving Kondo screening, magnetism and unconventional superconductivity. Here we report a comprehensive study on the transport and thermodynamic properties of a cerium-based heavy fermion compound CeBi$_2$ which undergoes an anti-ferromagnetic transition at $T_N$ $\sim$ 3.3 K. Its high temperature paramagnetic state is characterized by an enhanced heat capacity with Sommerfeld coefficient $\gamma$ over 200 mJ/molK$^2$. The magnetization in the magnetically ordered state features a metamagnetic transition. Remarkably, a large negative magnetoresistance associated with the magnetism was observed in a wide temperature and field-angle range. Collectively, CeBi$_2$ may serve as an intriguing system to study the interplay between $f$ electrons and the itinerant Fermi sea.