Metamagnetic Phase Transition Research Articles

Effect of the magnetic prehistory on the low-temperature heat capacity of the La(Fe0.88Al0.12-xSix)13 compounds

The measured heat capacity C of solids is thought in general to involve the change of the internal energy which is a state property. Therefore the electron density of states at the Fermi level is derived from the low-temperature data C=γ T + β T3. The La(Fe0.88Al0.12-xSix)13 compounds are the antiferromagnets (AFM) TN=200 K with 0<x<0.03 and the ferromagnets (FM) with 0.03<x<0.12 TC=194 K. For x=0.024 and x=0.027 a metamagnetic phase transition from AFM to the field-induced FM (FIFM) occurs in low external magnetic field. The FIFM state of the sample remains if the magnetic field turns off. The measurements of the low-temperature heat capacity in this FIFM state have shown an increase of coefficient γ in comparison with the value both the AFM and the FM. The measured heat capacity depends on a thermodynamic path and thus is not a state property. The change of the work of the magnetostrictive strain of the sample as a part of the low-temperature heat capacity is discussed.

Lattice Instabilities in the Frustrated Magnet CdCr2O4: An Ultrasonic Study

We report results on ultrasound studies of the frustrated magnet CdCr2O4. This compound demonstrates an antiferromagnetic ordering at T N =7.8 K and a metamagnetic phase transition at 28 T followed by a wide magnetization plateau with one half of the full moment of S=3/2 of Cr3+ ions. A longitudinal acoustic mode in the [111] crystallographic direction exhibits pronounced effects both in the temperature and magnetic-field dependencies. Pulsed-field measurements show a drastic change in the sound velocity just below and above the 1/2 magnetization plateau. Our results suggest a large spin-strain coupling and give evidence for a pronounced interplay between spin and lattice degrees of freedom in CdCr2O4.

Thermodynamic properties and neutron diffraction studies of silver ferriteAgFeO2

We present thermodynamic and neutron scattering data on silver ferriteAgFeO2. The data imply that strong magnetic frustrationΘ/TN∼10 and magnetic ordering arise via two successive phase transitions atT2 = 7 K andT1 = 16 K. AtT<T2, two metamagneticphase transitions at B1∼14 T and B2∼30 T can be identified through the change of slope in the magnetization curvemeasured up to 53 T. These transitions roughly correspond to an eighth and aquarter of the saturation magnetizations. Unlike for the ‘classical’ delafossiteCuFeO2, the wavevector of the magnetic structure is independent of temperature both atT<T2 andat T2<T<T1.

Competition between the Quadrupole Interaction and Crystalline Electric Field Effect in the Antiferromagnetic Ordered Phase of NdB6

We have studied the thermal and transport properties of NdB 6 focused on the anisotropic behaviors depending on the applied magnetic field direction. The magnetic field dependence of the physical properties in the type-I antiferromagnetic phase is small for H ∥[001] or [110] but is large for H ∥[111]. These anisotropic behaviors are associated with the different domain distribution depending on the applied magnetic field direction. For H ∥[001] or [110], the domain with only the χ ⊥ component is realized, and for H ∥[111], that with both the χ ⊥ and χ || components is realized, where the competition among the crystalline electric field effect leading to the three-fold easy axis and the O 2 0 -type ferro-quadrupole interaction leading to the four-fold easy axis and also the antiferromagnetic interaction plays an important role. This competition might be important for the appearance of the successive metamagnetic phase transitions for H ∥[111]. The anisotropic behaviors of the magnetization, the specific he...

Magnetocaloric effect in UNiGa compound with the multiple magnetic phase transitions

The magnetocaloric effect (MCE) in the UNiGa compound has been studied using the dc magnetization measurement technique. This system shows normal and inverse MCEs at low field around the paramagnetic to ferrimagnetic transition temperature (38.4 K), and the ferrimagnetic to antiferromagnetic transition temperature (34.5 K), respectively. At higher fields, the inverse MCE becomes very weak, which could be explained due to the presence of a field-induced metamagnetic phase transition. The maximum value of the magnetic entropy change - Δ S M , for Δ μ 0 H = 5 T , has been found to be 3.56 J kg - 1 K - 1 at ∼ 37.2 K with a relative cooling power of 22.5 J kg - 1 .

Magnetism in PrPdSn and NdPdSn studied on single crystals

Abstract We present the results of specific heat, magnetization and susceptibility measurements performed on single crystals of PrPdSn and NdPdSn intermetallic compounds. Both compounds crystallize in the orthorhombic TiNiSi-type crystal structure and order antiferromagnetically at TN = 4.2(1) K (PrPdSn) and TN = 3.5(1) K (NdPdSn). NdPdSn also undergoes an order-to-order phase transition at T1 = 1.95(3) K. Both compounds exhibit high magnetocrystalline anisotropy at low temperatures and a complicated magnetic structure, which is underlined by the metamagnetic phase transitions of both compounds.

Martensitic transformation and magnetic field-induced strain in Fe–Mn–Ga shape memory alloy

Martensitic and magnetic properties of Fe–Mn–Ga single and polycrystalline alloys were investigated. It was found that Fe–Mn–Ga alloys exhibit martensitic transformation from the paramagnetic L21 Heusler parent phase to the ferromagnetic L10 martensite phase. The martensitic transformation temperatures increased by about 20 K by the application of a magnetic field of 7 T, and a metamagnetic phase transition was observed. In addition, a magnetic field-induced strain of 0.6% associated with magnetic field-induced forward transformation was confirmed in an Fe43Mn28Ga29 single crystal.

Magnetic-field-induced gapless state in multiband superconductors

We investigate theoretically the properties of $s$-wave multiband superconductors in the weak-coupling (BCS) limit in the presence of pair-breaking effects of magnetic field. It is shown that a gapless superconducting state must appear in quasi-two-dimensional superconductors in magnetic fields parallel to the plane, corresponding to a Sarma state induced on one of the Fermi surfaces. The emergence of the state in $s$-wave multiband superconductors in the absence of anisotropy or spin-orbit interaction is usually accompanied by a zero-temperature first-order metamagnetic phase transition. For anisotropic or non-$s$-wave multiband superconductors the order of the zero-temperature metamagnetic transition depends on model parameters, and it may take the form of a smooth crossover. The details of the temperature--magnetic-field phase diagram for multiband superconductors are investigated analytically at zero temperature and numerically at a finite temperature. It is shown the zero-temperatures first-order phase transition gives rise to a critical region on the $B\text{\ensuremath{-}}T$ phase diagram. We suggest possible experiments to detect the gapless state.

Anisotropic magnetic phase diagrams of HoB4 single crystal

We have investigated the magnetic and electronic properties of a single-crystal HoB4. Antiferromagneticlike transitions were revealed by the temperature-dependent magnetization exhibiting two transition temperatures at TN1=7.1 K and TN2=5.7 K for an applied magnetic field along the c-axis, and showed only one transition at T=5.7 K for an applied magnetic field perpendicular to the c-axis. The isothermal magnetization with an applied magnetic field along the c-axis exhibited three distinct metamagnetic phase transitions at Hc1=2 T, Hc2=3.5 T, and Hc3=3.9 T at T=2 K. On the other hand, the isothermal magnetization with an applied magnetic field perpendicular to the c-axis showed two metamagneticlike transitions. A rapid change in the temperature and the field-dependent resistivity was found to be intimately correlated with magnetic transitions. Based on the isothermal magnetization and field-dependent resistivity for both magnetic field directions (H∥c and H⊥c), anisotropic phase diagrams of HoB4 were constructed. From the comparison of the phase diagram of HoB4 with that of DyB4, it was deduced that HoB4 has a geometrical quadrupolar frustration of Ho3+ moment.

Nature of unusual spontaneous and field-induced phase transitions in multiferroics RMn 2O 5

Complex magnetic, magnetoelectric and magnetoelastic studies of spontaneous and field-induced phase transitions in TmMn 2O 5 were carried out. In the vicinity of spontaneous phase transition temperatures (35 and 25 K) the magnetoelectric and magnetoelastic dependences demonstrated the jumps of polarization and magnetostriction induced by the field ∼150 kOe. These anomalies can be attributed to the influence of magnetic field on the conditions of incommensurate–commensurate phase transition at 35 K and the reverse one at 25 K. In b-axis dependences the magnetic field-induced spin-reorientation phase transition was also observed below 20 K. Finally the magnetoelectric anomaly associated with metamagnetic transition is observed below the temperature of rare-earth subsystem ordering at relatively small critical fields of 5 kOe. This variety of spontaneous and induced phase transitions in RMn 2O 5 stems from the interplay of three magnetic subsystems: Mn 3+, Mn 4+, R 3+. The comparison with YMn 2O 5 highlights the role of rare earth in low-temperature region (metamagnetic and spin-reorientation phase transitions), while the phase transition at higher temperatures between incommensurate and commensurate phases should be ascribed to the different temperature dependences of Mn 3+ and Mn 4+ ions. The strong correlation of magnetoelastic and magnetoelectric properties observed in the whole class of RMn 2O 5 highlights their multiferroic nature.

Measurement of the magnetocaloric properties ofCoMn0.95Fe0.05Si: Large change with Fe substitution

CoMnSi and ${\text{CoMnSi}}_{1\ensuremath{-}x}{\text{Ge}}_{x}$ have recently been shown to exhibit negative magnetocaloric properties at a first-order magnetic-field-driven metamagnetic phase transition between a low-temperature antiferromagnetic phase and a high-temperature ferromagnetic phase. We find that doping with Fe changes the magnetocaloric properties drastically by (a) lowering the metamagnetic transition temperature and field, (b) yielding a higher magnetocaloric effect at lower fields than in CoMnSi, and (c) producing an unusual downturn in the entropy change in the highest fields measured. We also find that fragmentation of the sample lowers the transition field reflecting the role of strain in these samples but makes no significant change to the hysteresis loss or the entropy change.

Martensitic Transformation in NiCoMnSn Metamagnetic Shape Memory Alloy Powders

Martensitic and magnetic properties of NiCoMnSn metamagnetic shape memory alloy powders obtained by a gas atomization method were investigated. The as-atomized powders showed a dendritic structure which changed to a single-phase one by annealing at 1173 K for 2 h. Although the martensitic transformation behavior was almost the same as that in bulk samples, the transformation thermal interval, namely, M s - M f , of the as-annealed powders decreased with increasing annealing time. In the powders annealed at 1173 K for 144 h, a reversible metamagnetic phase transition was confirmed by the application of a magnetic field of 7 T.

Thermodynamic model of the stabilization of an intermediate state in the region of the metamagnetic phase transition in erbium orthoferrite

The possible mechanisms of the thermodynamic stabilization of an intermediate state in the first-order metamagnetic phase transition in a magnetic field parallel to the Ising c axis of the Er3+ ions in erbium orthoferrite at T = 1.6 K have been analyzed. The model is chosen using the magneto-optical experimental data on the features of this state.

Correlations of the electrical and magnetic phase transitions in the Sm1− x Sr x MnO3 ( x = 0.33, 0.45) and RE0.55Sr0.45MnO3 (RE0.55 = Eu0.397Nd0.153, Tb0.25Nd0.30) manganites at the high magnetic stationary fields

Motto The first address of Satan to the human race began most modestly with the word: why? Adam Mickiewicz (1798–1855) The resistance, magnetoresistance and magnetization measurements have been performed in the temperature range of 4.2–300 K and in the external magnetic inductions up to 14 T for the Sm1− x Sr x MnO3 (x = 0.33, 0.45) and RE0.55Sr0.45MnO3 (RE0.55 = Eu0.397Nd0.153, Tb0.25Nd0.30) manganites. In these samples the metal–semiconductor phase transitions as well as two kinds of the magnetic phase transitions the ferromagnetic–paramagnetic and metamagnetic (both spin-flip and spin-flop) have been observed. It was found that correlations between the magnetic and electrical phase transitions appear at high values of the external magnetic inductions. These correlations consist, simultaneously, of the large negative magnetoresistance and metamagnetic phase transitions. The existence and reconstruction of the ferromagnetic and antiferromagnetic clusters under the influence of the external magnetic induction is considered as a driving force of those correlations.

Metamagnetic phase transition in Nd1−x TbxCo2 compounds

Metamagnetic phase transition in Nd1−x TbxCo2 compounds

Metamagnetic phase transitions in perovskite manganites

A detailed study of step-like metamagnetic transitions in polycrystalline Pr 0.75Na 0.25Mn 1 − x Fe x O 3 (0 ≤ x ≤ 0.30) is reported. It shows that the charge-orbit ordering antiferromagnetic (COOAF) phase in the phase-separated materials is responsible for the step-like metamagnetic transition with extremely sharp steps (width <0.01 T). The fraction of antiferromagnet II (AFII) with larger antiferromagnetic exchange interaction than COOAF is proved to be the effective factor of critical fields ( H c). A model of anisotropy barrier for up/down thermal blocking spins has been proposed to explain the sharp step-like transitions in polycrystalline manganites for the first time. The metamagnetic transitions at 2 K (below the spin blocking temperature T B) and high temperatures are compared. Both sorts of metamagnetic transitions originate from COOAF phase. And the temperature is responsible for the difference between them.

Gapless Fermi Surfaces of Anisotropic Multiband Superconductors in a Magnetic Field

We propose that a new state with a fully gapless Fermi surface appears in quasi-2D multiband superconductors in magnetic field applied parallel to the plane. It is characterized by a paramagnetic moment caused by a finite density of states on the open Fermi surface. We calculate thermodynamic and magnetic properties of the gapless state for both s-wave and d-wave cases, and discuss the details of the first order metamagnetic phase transition that accompanies the appearance of the new phase in s-wave superconductors. We suggest possible experiments to detect this state both in the s-wave (2-H NbSe2) and d-wave (CeCoIn5) superconductors.

Competing magnetic fluctuations inSr3Ru2O7probed by Ti doping

We report the effect of nonmagnetic Ti4+ impurities on the electronic and magnetic properties of Sr3Ru2O7. Small amounts of Ti suppress the characteristic peak in magnetic susceptibility near 16 K and result in a sharp upturn in specific heat. The metamagnetic quantum phase transition and related anomalous features are quickly smeared out by small amounts of Ti. These results provide strong evidence for the existence of competing magnetic fluctuations in the ground state of Sr3Ru2O7. Ti doping suppresses the low temperature antiferromagnetic interactions that arise from Fermi surface nesting, leaving the system in a state dominated by ferromagnetic fluctuations.

Specific features of an intermediate state in the magnetic field range of the metamagnetic phase transition in ErFeO3

An intermediate state revealed upon a first-order metamagnetic phase transition in a magnetic field aligned parallel to the Ising c axis of Er3+ ions in crystals of erbium ferrite ErFeO3 at a temperature of 1.6 K is visualized for the first time. The region of existence of the intermediate state and the parameters of the domain structure are determined, and the possible conditions providing for visualization of the intermediate state and its specific features are analyzed. A thermodynamic model is proposed for the stabilization of the intermediate state. It is shown that theoretical results are in good agreement with experimental data.

Mössbauer study of partially ordered cobaltitesNd2CoMnO6+δ with perovskite structure

The properties of Nd2CoMnO6+δ (δ = 0, 0.12) samples were investigated by Mössbauer,μSR and magnetization measurements. Our experimental data were interpreted in thefollowing model. The samples consist mainly of clusters of cobalt and manganese ionswith different degrees of order. The valence state of these ions is predominantlyCo2+/Mn4+. Increasing the oxygen content leads to an enhancement of the disordered fraction of thesample which contains mainly three-valent ions. The highly ordered stoichiometric(δ = 0) compound exhibits both pronounced ferromagnetic and weak spin-glass-likecomponents. Ionic disordering leads to a partial destruction of the ferromagneticcomponent and to strong enhancement of the spin-glass-like one in non-stoichiometric(δ = 0.12) samples. The spin-glass-like component transforms into the ferromagnetic one as afirst-order metamagnetic phase transition in an external magnetic field.