Showing papers on "Metamagnetism published in 2017"

Giant Anisotropic Magnetocaloric Effect in Double-perovskite Gd 2 CoMnO 6 Single Crystals.

Abstract: The magnetocaloric effect (MCE) is described by the change in temperature of a material by magnetic field variation and is a crucial subject in magnetism; it is motivated by the desire to enhance energy-efficient magnetic refrigeration for clean technology. Despite the recent discovery of the giant cryogenic MCE in double perovskites, the role of magnetic anisotropy has not yet been clearly discussed, because of the averaging effect of polycrystalline samples. Here, we investigated the anisotropic MCE in the single-crystal double perovskite Gd2CoMnO6. In addition to the ferromagnetic order of the Co2+ and Mn4+ moments, the large Gd3+ moments align below T Gd = 21 K, exhibiting an isotropic nature. Because of the intricate temperature development of magnetically hysteretic behaviour and metamagnetism, the change in magnetic entropy along the c-axis appears to be relatively small. On the contrary, the smaller but almost reversible magnetization perpendicular to the c-axis leads to a large MCE with a maximum entropy change of 25.4 J/kg·K. The anisotropic MCE generates a giant rotational MCE, estimated as 16.6 J/kg·K. Our results demonstrate the importance of magnetic anisotropy for understanding the MCE and reveal essential clues for exploring suitable magnetic refrigerant compounds aiming at magnetic functional applications.

Two-dimensional frameworks formed by pentagonal bipyramidal cobalt(II) ions and hexacyanometallates: antiferromagnetic ordering, metamagnetism and slow magnetic relaxation

Abstract: We herein report the syntheses, structures, and magnetic properties of two isostructural two-dimensional (2D) coordination polymers based on a pentagonal bipyramidal CoII unit [Co(TODA)]2+ and two hexacyanometallates, namely [MIII(CN)6]2[CoII(TODA)]3·9H2O (M = Cr (1), Co (2), TODA = 1,4,10-trioxa-7,13-diazacyclopentadecane). Structure analyses show that both complexes have 2D honeycomb structures where the [Co(TODA)]2+ units are bridged by the [MIII(CN)6]3− groups through three cyano groups in the facial positions. Magnetic investigation reveals ferromagnetic coupling between the CrIII and CoII centres through cyanides in 1. Due to the antiferromagnetic interaction between the layers, compound 1 exhibits an antiferromagnetic ordering below 11.4 K, and shows a metamagnetic phase transition under an external dc field. Due to the disorder of the TODA ligands, compound 1 shows a spin glass behavior, which leads to slow magnetic relaxation in 1. A butterfly-shaped hysteresis loop at 1.8 K can be observed with a coercive field of 720 Oe, which is quite large for cyano-bridged Cr–Co molecular magnets. For compound 2 containing the diamagnetic [CoIII(CN)6]3− unit, field-induced slow magnetic relaxation was also verified, which makes compound 2 a rare example of an SIM assembled in a 2D network. An easy-plane magnetic anisotropy with a positive D value (29.9 cm−1 by PHI and 26.5 cm−1 by Anisofit2.0) was deduced for hepta-coordinated CoII centers. These results show the efficiency of the strategy of combining cyanometallates and pentagonal bipyramidal precursors for novel molecular magnetic materials.

Effect of epitaxial strain and lattice mismatch on magnetic and transport behaviors in metamagnetic FeRh thin films

Abstract: We grew 80 nm FeRh films on different single crystals with various lattice constants. FeRh films on SrTiO3 (STO) and MgO substrates exhibit an epitaxial growth of 45° in-plane structure rotation. In contrast, FeRh on LaAlO3 (LAO) displays a mixed epitaxial growth of both 45° in-plane structure rotation and cube-on-cube relationships. Due to the different epitaxial growth strains and lattice mismatch values, the critical temperature for the magnetic phase transition of FeRh can be changed between 405 and 360 K. In addition, the external magnetic field can shift this critical temperature to low temperature in different rates for FeRh films grown on different substrates. The magnetoresistance appears a maximum value at different temperatures between 320 and 380 K for FeRh films grown on different substrates.

Magnetization Process of the Kondo Insulator YbB12 in Ultrahigh Magnetic Fields

Abstract: The magnetization process of the Kondo insulator YbB12 has been unveiled in ultrahigh magnetic fields of up to 120 T at 4.2 K. We have found a novel metamagnetic transition at Bc2 = 102 T in addition to the previously known transition at Bc1 = 55 T. It has also been observed that the magnetization tends to saturate at around 112 T. Within the rigid band model, the two-energy-gap structure in the density of states (DOS) explains the successive two-step metamagnetism as a result of the Zeeman effect of the DOS. The metamagnetic transition at Bc1 occurs along with an insulator–metal transition and the field-induced phase is expected to be a heavy fermion metallic state. The Kondo effect can weaken at the second transition of Bc2, as theoretically found in the successive two-metamagnetic-transition process in the Kondo semimetal CeNiSn.

Large and reversible inverse magnetocaloric effect in Ni48.1Co2.9Mn35.0In14.0 metamagnetic shape memory microwire

Abstract: High-performance magnetocaloric materials should have a large reversible magnetocaloric effect and good heat exchange capability. Here, we developed a Ni48.1Co2.9Mn35.0In14.0 metamagnetic shape memory microwire with a large and reversible inverse magnetocaloric effect. As compared to the bulk counterpart, the microwire shows a better combination of magnetostructural transformation parameters (magnetization difference across transformation ΔM, transformation entropy change ΔStr, thermal hysteresis ΔThys, and transformation interval ΔTint) and thus greatly reduced critical field required for complete and reversible magnetic-field-induced transformation. A strong and reversible metamagnetic transition occurred in the microwire, which facilitates the achievement of large reversible magnetoresponsive effects. Consequently, a large and reversible magnetic-field-induced entropy change ΔSm of 12.8 J kg−1 K−1 under 5 T was achieved in the microwire, which is the highest value reported heretofore in Ni-Mn-based mag...

Towards an understanding of dynamic phase transitions

Abstract: We review the equivalencies and dissimilarities between ferromagnetic systems in thermodynamic equilibrium and those subjected to an external oscillating field. While the former undergo a thermodynamic phase transition at the Curie temperature, the latter show a dynamic phase transition at a critical period of the oscillating field. Over two decades of research have led to the conclusion that dynamic and thermodynamic phase transitions correspond to the same universality class and have analogous phase diagrams, among other similarities. Recently, the amplitude of the oscillating field driving the dynamic phase transition has emerged as a key variable, not only because it determines the value of the critical period directly and thus the speed of the critical dynamics, but also because it affects very substantially the degree of similarity in between thermodynamic and dynamic phase transitions. In particular, we discuss how low amplitudes of the oscillating field and corresponding slow critical dynamics lead to a suppression of the dynamic phase transition at surfaces and deviations from a Curie-Weiss type law at large periods. We also discuss the presence of metamagnetic anomalies in the paramagnetic dynamic phase and a severe shrinking of the critical region, which we have observed in magneto-optical Kerr effect experiments on in-plane uniaxial Co films and which we have analyzed in detail by means of mean-field calculations. At higher amplitudes of the oscillating field, and thus for faster critical dynamics, these phenomena are far less prominent and the equivalency picture between dynamic and thermodynamic phase transitions can be recovered.

Driving higher magnetic field sensitivity of the martensitic transformation in MnCoGe ferromagnet

Abstract: The sharp metamagnetic martensitic transformation (MMT) triggered by a low critical field plays a pivotal role in magnetoresponsive effects for ferromagnetic shape memory alloys (FSMAs). Here, a sharper magnetic-field-induced metamagnetic martensitic transformation (MFIMMT) is realized in Mn1−xCo1+xGe systems with a giant magnetocaloric effect around room temperature, which represents the lowest magnetic driving and completion fields as well as the largest magnetization difference around MFIMMT reported heretofore in MnCoGe-based FSMAs. More interestingly, a reversible MFIMMT with field cycling is observed in the Mn0.965Co0.035Ge compound. These results indicate that the consensus would be broken that the magnetic field is difficult to trigger the MMT for MnCoGe-based systems. The origin of a higher degree of sensitivity of martensitic transformation to the magnetic field is discussed based on the X-ray absorption spectroscopic results.

Static and dynamic magnetic properties of two synthetic francisites Cu3La(SeO3)2O2X (X = Br and Cl)

Abstract: The formation of long-range magnetic order at low temperatures was established in francisite—type compounds Cu3La(SeO3)2O2X (X = Br and Cl) through measurements of magnetic susceptibility, magnetization, specific heat and X-band electron spin resonance. The significantly enhanced critical index p = 1.0 ± 0.1 in Cu3La(SeO3)2Br and p = 0.8 ± 0.1 in Cu3La(SeO3)2Cl in the temperature dependence of the width of ESR signal evidence the reduced dimensionality of the kagome-type francisite’s magnetic subsystem. Under action of external magnetic field, the presumably non-collinear six-sublattices antiferromagnetic structure of these compounds experiences the first-order metamagnetic transformation. The B–T magnetic phase diagrams were established from the positions of singularities in temperature and field dependences of thermodynamic properties. Contrary to pristine mineral Cu3Bi(SeO3)2Cl, no signature of structural phase transition was detected.

An Ising iron(ii) chain exhibits a large finite-size energy barrier and "hard" magnetic behaviour.

Abstract: One-dimensional spin chains featuring strong axial anisotropic magnetism are promising candidates for isolatable and miniatured information storage materials, the so-called single-chain magnets (SCMs). Here we show a mixed azido/carboxylato bridged metamagnetic iron(II) chain [Fe(N3)2(4-mpc)]n (4-mpc = N-methylpyridinium-4-carboxylate) with a large energy barrier of 150 K, a large remnant magnetization (1.55Nβ) and coercivity (1.7 T at 2 K) for homo-spin SCMs. Heat capacity and Mossbauer spectroscopy studies corroborate the intrinsic nature of SCM behavior regardless of weak interchain magnetic interactions, which lead to the coexistence of metamagnetism but not long-range magnetic ordering. Moreover, detailed magnetic investigations indicate that the system is not only within the “Ising limit” but also in the “finite-size” regime.

Missing magnetism in Sr 4 Ru 3 O 10 : Indication for Antisymmetric Exchange Interaction

Abstract: Metamagnetism occuring inside a ferromagnetic phase is peculiar. Therefore, Sr4Ru3O10, a T C = 105 K ferromagnet, has attracted much attention in recent years, because it develops a pronounced metamagnetic anomaly below T C for magnetic fields applied in the crystallographic ab-plane. The metamagnetic transition moves to higher fields for lower temperatures and splits into a double anomaly at critical fields H c1 = 2.3 T and H c2 = 2.8 T, respectively. Here, we report a detailed study of the different components of the magnetization vector as a function of temperature, applied magnetic field, and varying angle in Sr4Ru3O10. We discover for the first time a reduction of the magnetic moment in the plane of rotation at the metamagnetic transition. The anomaly shifts to higher fields by rotating the field from H ⊥ c to H || c. We compare our experimental findings with numerical simulations based on spin reorientation models taking into account magnetocrystalline anisotropy, Zeeman effect and antisymmetric exchange interactions. While Magnetocrystalline anisotropy combined with a Zeeman term are sufficient to explain a metamagnetic transition in Sr4Ru3O10, a Dzyaloshinskii-Moriya term is crucial to account for the reduction of the magnetic moment as observed in the experiments.

Missing magnetism in Sr$_{4}$Ru$_{3}$O$_{10}$: Indication for Antisymmetric Exchange Interaction

Abstract: We report a detailed study of the magnetization modulus as a function of temperature and applied magnetic field under varying angle in Sr$_{4}$Ru$_{3}$O$_{10}$ close to the metamagnetic transition at $H_{c}\backsimeq 2.5\,$T for $H \perp c$. We confirm that the double-feature at $H_{c}$ is robust without further splitting for temperatures below 1.8 K down to 0.48 K. The metamagnetism in Sr$_{4}$Ru$_{3}$O$_{10}$ is accompanied by a reduction of the magnetic moment in the plane of rotation and large field-hysteretic behavior. The double anomaly shifts to higher fields by rotating the field from $H\,\perp \,c$ to $H\,\parallel\,c$. We compare our experimental findings with numerical simulations based on spin reorientation models caused by intrinsic magnetocrystalline anisotropy and Zeeman effect. Crystal anisotropy is able to explain a metamagnetic transition in the ferromagnetic ordered system Sr$_{4}$Ru$_{3}$O$_{10}$, but a Dzyaloshinskii-Moriya term is crucial to account for a reduction of the magnetic moment as discovered in the experiments.

Atomistic modelling of metamagnetic transition in FeRh with four-spin exchange

Abstract: The metamagnetic transformation of FeRh from antiferromagnetic (AFM) to ferromagnetic (FM) ordering makes it suitable for a wide scope of applications, ranging from magnetic recording media to antiferromagnetic spintronics and magnetic refrigeration Exchange spring systems of FeRh coupled with a hard magnetic layer (FePt) are a promising approach for heat-assisted magnetic recording technologies that assure high density of stored information It has been shown that different temperature scalings of the exchange interactions can lead to a first-order phase transition in FeRh systems (Barker, J, & Chantrell, R W (2015) Higher-order exchange interactions leading to metamagnetism in FeRh Physical Review B, 92(9), 094402) This model assumes the presence of a higher-order exchange term in the form of four-spin exchange, that arises from four consecutive hops of electrons from one spin configuration to the spin-flipped one, the higher order four-spin interaction being mediated in FeRh by the Rh atoms At small temperatures the four-spin exchange is responsible for the AFM ordering, while, at higher temperatures the FM ordering is given by the bilinear exchange since the four-spin term decreases more rapidly with temperature than the bilinear term In this work, the first-order phase transition that appears in FeRh is systematically studied via the four-spin parametric model that was previously given in literature A degeneracy in the ground-state of the four-spin exchange system is found The effect of the parameters entering into the spin Hamiltonian was systematically analysed The model has been implemented for FeRh and then developed in order to consider other materials with different crystal structures As nanoscale applications of the FeRh systems are more practical due to the high cost of Rh, the finite size effects of FeRh grains and thin films are systematically investigated As a further test of the model, ultrafast simulations have been performed In accordance to the literature, it is found that, by laser-heating the FeRh system, the ferromagnetic ordering is generated in picosecond time-scales Additionally the dynamical and equilibrium properties of FePt/FeRh bilayers have been systematically investigated, as this system is of particular interest for recording media applications

Observation of ultrasharp metamagnetic jumps in polycrystalline Er2Cu2O5.

Abstract: The observation of ultrasharp metamagnetic jumps in the field variation of magnetization (M versus H) data for the highly insulating metal oxide Er2Cu2O5 is investigated. The compound orders antiferromagnetically below about T N1 = 28 K and shows conventional 'not-so-sharp' metamagnetism around 13 kOe on the field-increasing leg in the polycrystalline sample. The uniqueness of the ultrasharp jumps in Er2Cu2O5 resides in the fact that they are only observed in the field-decreasing segment of the magnetization curve. We observe that the jumps are affected by the sweep rate of the magnetic field, similarly to several other systems that show such ultrasharp jumps. Er2Cu2O5 shows a considerable amount of thermo-remanent magnetization when it is cooled in a field that is higher than the critical field of 13 kOe. Our analysis indicates that above 13 kOe the system remains phase separated, with the coexistence of antiferromagnetic and field-induced ferromagnetic-like phases. The jumps in the return leg occur because of the shear-dominated martensitic-like phase transition of the ferromagnetic-like phase to an antiferromagnetic phase, and interfacial strain plays a major role in the observed jumps.

Tuning the metamagnetism in a metallic helical antiferromagnet

Abstract: The antiferromagnetic (AFM)-ferromagnetic (FM) conversion in martensite was observed in Mn/Ni-substitution upon FM elements, such as Fe or Co, in MnNiGe helical antiferromagnets. Here, we report an AFM-FM conversion and consequently a sharp magnetic-field-driven metamagnetic martensitic transformation from paramagnetic (PM) austenite to FM martensite in the Ni- and Mn-substituted MnNiGe alloys with indium, a non-magnetic and large-sized main group element. Accordingly, a giant magnetocaloric effect such that a twofold increase of the magnetic entropy change in MnNi0.92GeIn0.08 and even a nearly threefold increase in the Mn0.92NiGeIn0.08 alloy is obtained with respect to the MnNiGe0.95In0.05 alloy. The origin of AFM-FM conversion and resultantly sharp magnetic-field-induced PM-FM metamagnetic transformation is discussed based on the first-principles calculations and X-ray absorption spectroscopic results.

Flux synthesis, crystal structures, and physical properties of new lanthanum vanadium oxyselenides

Abstract: The new lanthanum vanadium oxyselenides LaVSe2O, La5V3Se6O7, La5V3Se7O5, La7VSe5O7, and La13V7Se16O15 were synthesized in eutectic NaI/KI fluxes, and their crystal structures were determined using single-crystal and powder X-ray diffraction experiments. LaVSe2O and La5V3Se6O7 adopt known structure types, whereas La5V3Se7O5, La7VSe5O7, and La13V7Se16O15 crystallize in hitherto unknown structure types. The main building blocks of these compounds are chains of edge-sharing VSe6, VSe5O, and/or VSe4O2 octahedra, linked together by edge-sharing OLa4 and/or OLa3V tetrahedra forming fluorite-like ribbons. LaVSe2O, La5V3Se7O5, and La7VSe5O7 contain only V(III) ions, whereby La5V3Se6O7 and La13V7Se16O15 contain mixtures of either V(III)/V(IV) or V(III)/V(V) cations. Magnetic measurements indicate Curie–Weiss paramagnetism and magnetic ordering of the vanadium moments at low temperatures. More precisely, we observe antiferromagnetism for La5V3Se6O7, metamagnetism for La5V3Se7O5, ferromagnetism for La7VSe5O7 and a complex magnetic structure for La13V7Se16O15.

Temperature Dependence of Nonlinear Susceptibilities in an Infinite Range Interaction Model

Abstract: We present a model to probe metamagnetic properties in systems with an arbitrary number of interacting spins. Thermodynamic properties such as the magnetization per particle $m(B,T,N)$, linear susceptibility $\chi_1(T)$, nonlinear susceptibilities $\chi_3(T)$ and $\chi_5(T)$, specific heat $C(B,T,N)$, and pressure $P(B,T,N)$ were calculated. The model produces a different magnetic response for $N$ particles when comparing to $N - 1$ particles for small $N \sim 1$. For an even number of particles, the susceptibilities show maxima in their temperature dependence. An odd number produces an additional free spin response that dominates at low temperatures. This free spin response for odd $N$ also produces a step in the magnetization per particle at $B = 0$. The magnetization shows $N/2$ steps at $\gamma B_c/J = n$ with integer $n$ for even $N$ and $(N-1)/2$ additional steps at half-integer $n$ starting at 3/2 for odd $N$. Small clusters respond with metamagnetism in an otherwise isotropic spin space, while the large clusters show no metamagnetism.

Neutron diffraction study of antiferromagnetic ErNi3Ga9 in magnetic fields

Abstract: We report specific heat, magnetization, magnetoresistance, and neutron diffraction measurements of single crystals of ErNi3Ga9. This compound crystalizes in a chiral structure with space group R 32 . The erbium ions form a two–dimensional honeycomb structure. ErNi3Ga9 displays antiferromagnetic order below 6.4 K. We determined that the magnetic structure is slightly amplitude–modulated as well as antiferromagnetic with q = ( 0 , 0 , 0.5 ) . The magnetic properties are described by an Ising–like model in which the magnetic moment is always along the c–axis owing to the large uniaxial anisotropy caused by the crystalline electric field effect in the low temperature region. When the magnetic field is applied along the c–axis, a metamagnetic transition is observed around 12 kOe at 2 K. ErNi3Ga9 possesses crystal chirality, but the antisymmetric magnetic interaction, the so-called Dzyaloshinskii–Moriya (DM) interaction, does not contribute to the magnetic structure, because the magnetic moments are parallel to the DM–vector.

Magnetic characteristics of polymorphic single crystal compounds DyIr 2 Si 2

Abstract: We have confirmed that the tetragonal ternary compound DyIr2Si2 shows polymorphism; the ThCr2Si2-type structure as a low temperature phase (I-phase) and the CaBe2Ge2-type one as a high temperature phase (P-phase) exist. A comparative study on magnetic characteristics of the morphs was performed on the I- and P-phase single crystals in order to elucidate how magnetic properties are influenced by crystallographic symmetry. The magnetic behavior changes drastically depending on the structure. The DyIr2Si2(I) shows an antiferromagnetic ordering below TN = 30 K, additional magnetic transitions of T1 = 17 K and T2 = 10 K, and a strong uniaxial magnetic anisotropy with the easy [001] direction. The [001] magnetization shows four metamagnetic transitions at low temperatures. On the other hand, the DyIr2Si2(P) has comparatively low ordering temperature of TN1 = 9.4 K and an additional transition temperature of TN2 = 3.0 K, and exhibits an easy-plane magnetic anisotropy with the easy [110] direction. Two metamagnetic transitions appear in the basal plane magnetization processes. In both the morphs, the χ-T behavior suggests the existence of component-separated magnetic transitions. The ab-component of magnetic moments orders at the higher transition temperature TN1 for the P-phase compound, which is contrast to the I-phase behavior; the c-component orders firstly at TN. The crystalline electric field (CEF) analysis was made, and the difference in magnetic behaviors between both the morphs is explained by the CEF effects.

Mathematical-Physics Investigation on the Behaviour of a Metamagnetic System

Abstract: Abstract In order to exemplify, we consider a finite itinerant-electron metamagnetic gas at sufficiently low absolute temperature so that relevant new results are obtained. In fact, we study key aspects related to derive the electronic energy of the abovementioned metamagnetic gas in relation to the Fermi levels of the spin-up and spin-down electron bands and in relation to the exchange energy and magnetic susceptibility. Within an unprecedented mathematical–physics approach, the abovementioned electronic energy is reinterpreted by defining it as an averaged quantity from the corresponding nonrelativistic, time-independent, Schrödinger equation with two-band energy-eigenvalue spectrum. In parallel, a matrix formulation is presented.

In-field neutron diffraction investigation of metamagnetism in Nd 7 Rh 3

Abstract: The binary intermetallic compound, Nd7Rh3 shows exotic magnetic properties which are rare among the R7X3 type compounds. Previous magnetic measurements on Nd7Rh3 revealed two antiferromagnetic transitions in Nd7Rh3 (TN1 = 32 K and TN2 = 16 K). This compound exhibits metamagnetic transition at 2 K, as in isostructural counterparts Nd7Ni3 or Tb7Rh3. But there are ample differences in the metamagnetic transition features. Further investigations on Nd7Rh3 gave evidence for phase-coexistence, which is rarely observed in stoichiometric compounds. Electronic phase separation is observed due to the first order transition brought out by a change in temperature or magnetic field (H). This compound was also shown to exhibit features attributable to devitrification of the arrested metastable state, after travelling across metamagnetic transition. In the present work, neutron diffraction studies on Nd7Rh3 were carried out in external magnetic fields to have an in-depth knowledge of kinetic arrest due to field-induced first order phase transition, phase coexistence and devitrification of the arrested metastable state, using the CHUF (cooling and heating in unequal fields) protocol. The sample was cooled in a field of 3 T (T) and was warmed in different fields (0–0.8 T). On the basis of these experiments, a field (H)-Temperature (T) phase diagram could be inferred which shows the critical field (HK) and temperature (TK) curve across which the devitrification of the arrested metastable state begins. Above the (HK, TK) curve, the system is in the arrested (high field) state, whereas below the curve the system has returned partially to its magnetic de-arrested state.