Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 20
Filtrar
Más filtros










Base de datos
Intervalo de año de publicación
1.
J Phys Condens Matter ; 36(31)2024 May 09.
Artículo en Inglés | MEDLINE | ID: mdl-38663416

RESUMEN

The effect of negative chemical pressure with the substitution of transition metal V in an itinerant helimagnetically ordered MnSi, Mn1-xVxSi withx= 0-0.1, is explored using dc and ac-susceptibilities. With increasingx, the manifestations are unaffected crystal structure with increasing unit cell volume, suppression of long-range magnetic order, weakening of itinerant character and reduced spin-cooperative phenomenon. The emergence of spin-glass behaviour forx⩾0.1intervenes in the occurrence of quantum phase transition. The constructed concentration-temperaturex-Tphase diagram illustrates the substitution-driven changes in the magnetism of MnSi. Further, the study suggests that the presence of a precursor state can favour the formation of spin-textures in magnetically ordered compositions0

2.
J Phys Condens Matter ; 36(20)2024 Feb 20.
Artículo en Inglés | MEDLINE | ID: mdl-38328924

RESUMEN

We report on the magnetic, electrical transport, caloric and electronic structure properties of TbFe4.4Al7.6polycrystalline alloy using experiment and theory. The alloy crystallizes in tetragonal structure with I4/mmm space group with lattice parametersa = b= 8.7234(5) Å andc= 5.0387(6) Å. It is ferrimagnetic with a compensation temperature ofTcmp∼151 K, Curie-Weiss temperatureθCW∼172.11 K and an effective magnetic momentµeff= (2.37±0.07)µB/f.u withZ= 2. At low temperatures, kinetic arrest-like first-order phase transition is realized through the thermal hysteresis between field-cooled cooling and field-cooled warming curves ofM(T) and virgin curves ofM(H) andρ(H)which are outside the hysteresis loops with metamagnetic transition. The high magnetic field suppression of multiple transitions and reduced coercive fieldHcoerand remnant magnetizationMremwith increasing temperature are reported.HcoerandMremcease to exist above the compensation temperatureTcmp. A correlation between the isothermal magnetization and resistivity is discussed. Specific heatC(T) analysis reveals a Sommerfeld parameter ofγ= 0.098 J⋅mol-1⋅K-2and a Debye temperature ofθD∼351.2 K. The sample is metallic as inferred from theρ(T)behavior and Sommerfeld parameter. The magnetoresistance of the alloy is low and negative which indicates the suppression of weak spin-fluctuations. This alloy avoids the tricritical point despite first-to-second order phase transition. The electronic and magnetic structure calculations, by making use of full potential linearized augmented plane wave method, suggest metallic ferrimagnetic ground state of TbFe4.4Al7.6with Tb atoms contributing ferromagnetically (5.87µB) and Fe atoms with antiferromagnetic contribution (2.67µB), in close agreement with the experimental observation.

3.
J Phys Condens Matter ; 36(13)2023 Dec 21.
Artículo en Inglés | MEDLINE | ID: mdl-38086084

RESUMEN

Ni-substituted Mn3Ga displays a weak ferromagnetism embedded in an antiferromagnetic (AF) phase. Upon field cooling, the alloy exhibits exchange bias and an open hysteresis loop, signifying kinetic arrest at room temperature. For the first time, a kinetic arrest is seen in a compound due to the first order transition of an embedded defect phase. A systematic study of crystal structure, local structure, and magnetic properties of Mn3-xNixGa (x= 0, 0.25) alloys reveal the origin of ferromagnetism in Mn2.75Ni0.25Ga is due to the segregation of a Heusler-type environment around Ni in the cubic Mn3Ga matrix. Upon temper annealing at 400∘C, these local structural defects around the Ni phase separate into a modulated ferromagnetic (FM) Ni-Mn-Ga Heusler phase. A strong interaction between the AF host and the FM defect phase gives rise to exchange bias. The first-order transition of the defect phase seems to be responsible for the observed kinetic arrest in Mn2.75Ni0.25Ga.

4.
Phys Chem Chem Phys ; 25(3): 2386-2400, 2023 Jan 18.
Artículo en Inglés | MEDLINE | ID: mdl-36597999

RESUMEN

In this study, manganese substituted strontium hexaferrite (SrFe12-xMnxO19; x = 0, 3, 5, and 7) prepared by the sol-gel auto-combustion method are studied. We observed that the substituted Mn preferentially goes to the 2a and 12k sites of Fe. Raman modes related to the 12k site suggest the stiffening of the lattice. The transformation of the grain's shape from hexagonal (x = 0 and 3) to rhombohedral (x = 7) was observed, as shown in the micrographs obtained from FESEM. The thermomagnetic curves show the shift of TC to lower temperatures with the increase in the Mn content. From x = 5 onwards, the growth of another magnetic phase (FiM2) of lower coercivity apart from the parent phase (FiM1) of higher coercivity is seen. The FiM2 phase was found to increase with the Mn content in the sample (16.4(3)% for x = 5 but 66.2(5)% for x = 7). Although the magnetization for both FiM1 and FiM2 decreases with the increase in temperature, both magnetic phases behave in contrast to each other for x = 5 and x = 7. The study suggests a transformation of the compound from high magnetic anisotropy (x = 0) to low magnetic anisotropy (x = 7). The x = 5 composition sample displays the highest value of the first-order ME coefficient (0.83(2) mV × cm-1 × Oe-1). The observed value for x = 5 composition is ∼2.5 times higher than that of the parent x = 0 composition sample (0.33(2) mV × cm-1 × Oe-1). The studies thus suggest that the x = 5 composition is one of the viable candidates for magnetoelectric applications.

5.
Phys Chem Chem Phys ; 24(48): 29539-29546, 2022 Dec 14.
Artículo en Inglés | MEDLINE | ID: mdl-36448471

RESUMEN

We have investigated the Mn2PtAl Heulser alloy to unravel its structural, magnetic, calorimetric and electronic structure properties. At room temperature, the alloy crystallizes in a hexagonal structure. Magnetization reveals a weak martensitic transition at 307 K, followed by a long range ferrimagnetic transition at 90 K. Griffiths phase-like signature and positive Weiss temperature in dc-magnetization, isothermal magnetic hysteresis loops and a frequency-independent peak confirm a nearly compensated ferrimagnetic order of Mn2PtAl. The theoretical electronic structure calculations also reveal the ferrimagnetic ground state of Mn2PtAl and Mn ions (occupying different sites) with a very small total magnetic moment. A giant exchange bias field of 2.73 kOe, at a temperature of 3 K and a cooling field of 70 kOe, has been estimated and is attributed to the unidirectional anisotropy associated with possible ferromagnetic clusters formed by the field cooling process in the ferrimagnetic matrix.

6.
Sci Rep ; 12(1): 16508, 2022 Oct 03.
Artículo en Inglés | MEDLINE | ID: mdl-36192489

RESUMEN

In this report, the effect of rare-earth (RE3+) ion substitution on structural, microstructural, and electrical properties in barium bismuth titanate (BaBi4Ti4O15) (BBTO) Aurivillius ceramics has been investigated. The Rietveld refinements on X-ray diffraction (XRD) patterns confirm that all the samples have an orthorhombic crystal system with A21am space group. Meanwhile, temperature dependent synchrotron XRD patterns reveal that the existence of dual phase in higher temperature region. The randomly oriented plate-like grains are experimentally strived to confirm the distinctive feature of bismuth layered Aurivillius ceramics. The broad band dielectric spectroscopic investigation signifies a shifting of ferroelectric phase transition (Tm) towards low temperature region with a decrease of the RE3+-ionic radii in BBTO ceramics. The origin of diffuse ferroelectric phase transitions followed by stabilization of the relaxor ferroelectric nature at high frequency region is explained using suitable standard models. The temperature dependent ac and dc conductivity results indicate the presence of double ionized oxygen vacancies in BBTO ceramics, whereas the dominance of single ionized oxygen vacancies is observed in RE-substituted BBTO ceramics. The room temperature polarization vs. electric field (P-E) hysteresis loops are shown to be well-shaped symmetric for BBTO ceramics, whereas slim asymmetric ferroelectric characteristics developed at RE-substituted BBTO ceramics.

7.
Phys Chem Chem Phys ; 24(8): 5083-5093, 2022 Feb 23.
Artículo en Inglés | MEDLINE | ID: mdl-35147154

RESUMEN

Green and sustainable energy production through renewable sources is an enormously exciting field of research. Herein, we report an A-site lanthanum doped oxygen excess ruthenate (predominantly Ru5+-ions) double perovskite system, CaLaScRuO6+δ (CLSR), as an excellent photocatalyst for water splitting. The well characterized polycrystalline compound shows canted antiferromagnetic (AFM) behavior due to the existence of disordered Ru-ions at the B-site. Based on density functional theory + U (Hubbard U) calculations, we have estimated various magnetic exchange interactions and found that the ground state is antiferromagnetic in nature which is in perfect agreement with our experimental results. Detailed analysis of the electronic structure further reveals that the present system belongs to the family of charge transfer semiconductors with an energy gap of ∼0.45 eV. Finally, the material is found to proficiently work for the oxygen evolution reaction (OER) via visible-light driven water splitting at neutral pH in an ecofriendly manner.

8.
J Phys Condens Matter ; 34(12)2022 Jan 05.
Artículo en Inglés | MEDLINE | ID: mdl-34933284

RESUMEN

Neutron diffraction andab initiostudies were carried out on Mn2V1-xCoxGa (x= 0, 0.25, 0.5, 0.75, 1) Heusler alloys which exhibits highTCfully compensated ferrimagnetic characteristics forx= 0.5. A combined analysis of neutron diffraction andab initiocalculations revealed the crystal structure and magnetic configuration which could not be determined from the x-ray diffraction and magnetic measurements. As reported earlier, Rietveld refinement of neutron diffraction data confirmedL21structure for Mn2VGa andXastructure for Mn2CoGa. The alloys withx= 0.25 and 0.5 possessL21structure with Mn(C)-Co disorder. As the Co concentration reaches 0.75, a structural transition has been observed from disorderedL21to disorderedXa. Detailedab initiostudies also confirmed this structural transition. The reason for the magnetic moment compensation in Mn2(V1-xCox)Ga was identified to be different from that of the earlier reported fully compensated ferrimagnet (MnCo)VGa. With the help of neutron diffraction andab initiostudies, it is identified that the disorderedL21structure with antiparallel coupling between the ferromagnetically aligned magnetic moments of (Mn(A)-Mn(C)) and (V-Co) atom pairs enables the compensation in Mn2V1-xCoxGa.

9.
J Phys Condens Matter ; 32(42): 425805, 2020 Jul 01.
Artículo en Inglés | MEDLINE | ID: mdl-32610306

RESUMEN

We report on the structure, spin-lattice and magneto-electric coupling in (1-x)Pb(Fe2/3W1/3)O3-(x)BiFeO3(where x = 0.1 and 0.4) (PBFW) solid solution synthesized through two-step solid-state reaction method. The room temperature (RT) crystallographic studies were carried out using x-ray diffraction and neutron diffraction measurements which show a single-phase Pseudocubic crystal system with Pm-3m space group. Rietveld refinement was carried out to obtain the structural parameters using Fullprof software and the observed structural parameters are in good agreement with the previous reports. Temperature-dependent neutron diffraction measurements reveal the presence of commensurate G-type antiferromagnetic structure. The magnetic structure was analyzed using the propagation wave vector k ∼ (½ ½ ½) for both the solid solutions. The obtained lattice constants increase linearly and the magnetic moment decrease with temperature, which shows a remarkable anomaly around the magnetic (T N ∼ 405 K for x = 0.1 and 531 K for x = 0.4) transition temperatures. This anomaly clearly indicates the existence of spin-lattice and magnetoelectric coupling. The magnetic susceptibility (ZFC and FC at 500 Oe) and M-H hysteresis loop measurements show spontaneous magnetic moment due to the Fe3+-O2--Fe3+ superexchange interaction coexisting with the weak ferromagnetism. Bifurcation of ZFC and FC curve reveals the strong anisotropic nature. Astonishingly, magnetic measurements show the non-zero magnetic moment above T N and broadening of the magnetic transition indicates the presence of short-range uncompensated sublattice weak ferromagnetic clusters in the paramagnetic region. The Mossbauer spectroscopy and electron paramagnetic resonance studies exhibit the RT magnetically ordered system and confirm the +3 state of Fe along with the fraction of Fe2+ ions.

10.
J Phys Condens Matter ; 32(36): 365803, 2020 May 06.
Artículo en Inglés | MEDLINE | ID: mdl-32375138

RESUMEN

The magnetocaloric effect of intermetallic compounds of Tb3Co and Ho3Co is studied under high pressures up to ∼1 GPa using pressure dependent dc magnetisation and specific heat measurements at ambient conditions. The magnetic entropy change (-ΔS M) obtained from magnetisation data and adiabatic change in temperature (ΔT ad) determined from zero-field specific heat and magnetisation data are found to be nearly identical within error limits with those deduced from purely field dependent specific heat experiments. With increasing hydrostatic pressure to ∼1 GPa, the -ΔS M and ΔT ad, both show a significant enhancement of about 37% and 13%, respectively for 9 T field change in case of Tb3Co. On the other hand, Ho3Co exhibits a decrease of about 8% in both -ΔS M and ΔT ad with increasing pressure. The refrigerant capacity (RC) also increases from 650 J kg-1 to 847 J kg-1 in the case of Tb3Co and it goes down from 665 J kg-1 to 615 J kg-1 for Ho3Co for an increase of pressure to 1 GPa. With increasing pressure, the peak widths of both -ΔS M and ΔT ad increase in case of Tb3Co, although the increase is more in -ΔS M. However, such noticeable changes in peak widths with pressure were not observed in Ho3Co. At ambient pressure, peak of -ΔS M ([Formula: see text]) scales with [Formula: see text] for both the compounds, consistent with the prediction of mean field theory (MFT) for second order magnetic transition. However, deviation from MFT was noticed at high pressures as [Formula: see text] was found to scale with [Formula: see text] instead of [Formula: see text] for both the alloys. Further, normalised -ΔS M curves for different ΔH and pressures collapse on a single universal curve in both the compounds thereby indicating that the second order magnetic transition persists even up to ∼1 GPa pressure.

11.
Phys Chem Chem Phys ; 22(13): 6906-6918, 2020 Apr 07.
Artículo en Inglés | MEDLINE | ID: mdl-32181452

RESUMEN

The intriguing coupling phenomena among spin, phonon, and charge degrees of freedom in materials having magnetic, ferroelectric and/or ferroelastic order have been of research interest for the fundamental understanding and technological relevance. We report a detailed study on structure and phonons of Al0.5Ga0.5FeO3 (ALGF), a lead-free magnetoelectric material, carried out using variable temperature dependent powder neutron diffraction and Raman spectroscopy. Neutron diffraction studies suggest that Al3+ ions are distributed in one tetrahedrally (BO4) and three octahedrally (BO6) coordinated sites of the orthorhombic (Pc21n) structure and there is no structural transition in the temperature range of 7-800 K. Temperature dependent field-cooled and zero-field-cooled magnetization studies indicate ferrimagnetic ordering below 225 K (TN), and that is reflected in the low temperature powder neutron diffraction data. An antiferromagnetic type arrangement of Fe3+ ions with net magnetic moment of 0.13 µB/Fe3+ was observed from powder neutron diffraction analysis and it corroborates the findings from magnetization studies. At the magnetic transition temperature, no drastic change in lattice strain was observed, while significant changes in phonons were observed in the Raman spectra. The deviation of several mode frequencies from the standard anharmonicity model in the ferrimagnetic phase (below 240 K) is attributed to coupling effect between spin and phonon. Spin-phonon coupling effect is discernable from Raman bands located at 270, 425, 582, 695, 738, and 841 cm-1. Their coupling strengths (λ) have been estimated using our phonon spectra and magnetization results. BOn (n = 4, 6) libration (restricted rotation) mode at 270 cm-1 has the largest coupling constant (λ∼ 2.3), while the stretching vibrations located at 695 and 738 cm-1 have the lowest coupling constant (λ∼ 0.5). In addition to the libration mode, several internal stretching and bending modes of polyhedral units are strongly affected by spin ordering.

12.
RSC Adv ; 10(35): 21019-21027, 2020 May 27.
Artículo en Inglés | MEDLINE | ID: mdl-35517732

RESUMEN

Polycrystalline samples of Ba0.96Ca0.04Ti0.91Fe0.09O3 were prepared using a conventional solid state reaction route with different Fe starting precursors (Fe2O3, Fe3O4). The Rietveld refined XRD data confirmed the phase purity and tetragonal crystal structure of both the samples. The average grain size measured using SEM was ≈0.40 µm in both the samples. XPS analysis confirmed the presence of only Fe2+ and both Fe2+/Fe3+ in Fe2O3 and Fe3O4 doped BCT samples. The P r and M r values have been measured to be 1.34 µC cm-2, 2.88 µC cm-2 and 0.0015 emu g-1 and 0.135 emu g-1 in Fe2O3 and Fe3O4 doped BCT samples, respectively. The Fe3O4 doped samples exhibit much better M-E coupling (≈22%) as compared to Fe2O3 (≈7%) doped BCT samples. The results obtained hence suggest that Fe3O4 doping in BCT is better suited for multiferroic applications.

13.
J Phys Condens Matter ; 32(11): 115801, 2020 Mar 13.
Artículo en Inglés | MEDLINE | ID: mdl-31739303

RESUMEN

The magnetic state of low temperature martensite phase in Co-substituted Ni-Mn-Sn-based ferromagnetic shape memory alloys (FSMAs) has been investigated, in view of numerous conflicting reports of occurrences of spin glass (SG), superparamagnetism (SPM) or long range anti-ferromagnetic (AF) ordering. Combination of DC magnetization, AC susceptibility and small angle neutron scattering (SANS) studies provide clear evidence for AF order in the martensitic phase of Ni45Co5Mn38Sn12 alloy and rule out SPM and SG orders. Identical studies on another alloy of close composition, Ni44Co6Mn40Sn10, point to the presence of SG order in the martensitic phase and the absence of SPM behavior, contrary to earlier reports. SANS results do show the presence of nanometre-sized clusters but they are found to grow in size from 3 nm at 30 K to 11 nm at 300 K, and do not correlate with magnetism in these alloys.

14.
J Phys Condens Matter ; 31(50): 505802, 2019 12 18.
Artículo en Inglés | MEDLINE | ID: mdl-31480022

RESUMEN

The magnetic properties of rare earth rich intermetallic compound, Tb3Co, were studied under external pressures up to ∼1.21 GPa. The application of external pressure results in a decrease of the transition temperatures, [Formula: see text] (paramagnetic to modulated antiferromagnetic) by about 6 K, and the order to order transition that coincides with a glass transition at 72 K by about 15 K, respectively. The low temperature drop in the zero-field cooled magnetisation signifying the strengthening of spin-orbit coupling remains more or less unaffected (shifts only by 3 K) by the external pressures but significant changes in the magnetic behaviour were observed above 40 K. The overall long range non-collinear magnetic order coexisting with glassy behaviour (below 72 K) is sustained even at ∼1.07 GPa pressure. The rate of decay of [Formula: see text] (d[Formula: see text]) is found to be linear with -7.2 K GPa-1 up to ∼0.9 GPa and then it deviates from linearity. The magnetic relaxations and memory effects studied under different measurement protocols confirm the presence of glassiness right up to the highest pressure, although the glassy behaviour is weakened to some extent with increasing pressure as reflected by faster relaxations.

15.
J Phys Condens Matter ; 31(44): 445801, 2019 Nov 06.
Artículo en Inglés | MEDLINE | ID: mdl-31295732

RESUMEN

Detailed and systematic study of rare earth rich intermetallic compound Tb3Co, using dc magnetisation, neutron powder diffraction, and linear and non-linear ac-susceptibilities, shows the presence of an unexpected magnetic glassy state along with complex non-collinear or modulated antiferromagnetic (AFM) order. Our neutron diffraction study shows that the magnetic structure remains more or less the same except for a decrease in moment values in the temperature range of 2 K-70 K and rules out any phase transition around 30 K. However, it reveals sharp changes in structural parameters around 30 K, which indicates strong spin-lattice coupling and change in strength. It appears to be mainly responsible for the observed increase in ZFC magnetisation on warming around 30 K. Another important unexpected result of this study is the strong frequency dispersion in linear and non-linear (higher order harmonics) ac-susceptibilities below [Formula: see text] K. The analysis in terms of various spin glass theoretical formulisms and even stronger frequency dispersion in non-linear susceptibilities provides evidence for the presence of a spin glass like state in Tb3Co. The final picture that emerges out of this study is that a spin glass like state coexists with the long range modulated AFM order below 72 K.

16.
ACS Appl Mater Interfaces ; 8(50): 34387-34395, 2016 Dec 21.
Artículo en Inglés | MEDLINE | ID: mdl-27998122

RESUMEN

Oxygen reduction reaction (ORR) is increasingly being studied in oxide systems due to advantages ranging from cost effectiveness to desirable kinetics. Oxygen-deficient oxides like brownmillerites are known to enhance ORR activity by providing oxygen adsorption sites. In parallel, nitrogen and iron doping in carbon materials, and consequent presence of catalytically active complex species like C-Fe-N, is also suggested to be good strategies for designing ORR-active catalysts. A combination of these features in N-doped Fe containing brownmillerite can be envisaged to present synergistic effects to improve the activity. This is conceptualized in this report through enhanced activity of N-doped Ca2Fe2O5 brownmillerite when compared to its oxide parents. N doping is demonstrated by neutron diffraction, UV-vis spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Electrical conductivity is also found to be enhanced by N doping, which influences the activity. Electrochemical characterization by cyclic voltammetry, rotating disc electrode, and rotating ring disk electrode (RRDE) indicates an improved oxygen reduction activity in N-doped brownmillerite, with a 10 mV positive shift in the onset potential. RRDE measurements show that the compound exhibits 4-electron reduction pathways with lower H2O2 production in the N-doped system; also, the N-doped sample exhibited better stability. The observations will enable better design of ORR catalysts that are stable and cost-effective.

17.
Dalton Trans ; 44(33): 14686-96, 2015 Sep 07.
Artículo en Inglés | MEDLINE | ID: mdl-26215789

RESUMEN

Magnetic luminescent hybrid nanostructures (MLHN) have received a great deal of attention due to their potential biomedical applications such as thermal therapy, magnetic resonance imaging, drug delivery and intracellular imaging. We report the development of bifunctional Fe3O4 decorated YPO4:Eu hybrid nanostructures by covalent bridging of carboxyl PEGylated Fe3O4 and amine functionalized YPO4:Eu particles. The surface functionalization of individual nanoparticulates as well as their successful conjugation was evident from Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), zeta-potential and transmission electron microscopy (TEM) studies. X-ray diffraction (XRD) analysis reveals the formation of highly crystalline hybrid nanostructures. TEM micrographs clearly show the binding/anchoring of 10 nm Fe3O4 nanoparticles onto the surface of 100-150 nm rice grain shaped YPO4:Eu nanostructures. These MLHN show good colloidal stability, magnetic field responsivity and self-heating capacity under an external AC magnetic field. The induction heating studies confirmed localized heating of MLHN under an AC magnetic field with a high specific absorption rate. Photoluminescence spectroscopy and fluorescence microscopy results show optical imaging capability of MLHN. Furthermore, successful internalization of these MLHN in the cells and their cellular imaging ability are confirmed from confocal microscopy imaging. Specifically, the hybrid nanostructure provides an excellent platform to integrate luminescent and magnetic materials into one single entity that can be used as a potential tool for hyperthermia treatment of cancer and cellular imaging.


Asunto(s)
Europio/química , Óxido Ferrosoférrico/química , Sustancias Luminiscentes/química , Nanoestructuras/química , Fosfatos/química , Itrio/química , Línea Celular Tumoral , Europio/uso terapéutico , Óxido Ferrosoférrico/uso terapéutico , Humanos , Hipertermia Inducida , Sustancias Luminiscentes/uso terapéutico , Campos Magnéticos , Magnetismo , Nanopartículas de Magnetita/química , Nanopartículas de Magnetita/uso terapéutico , Nanoestructuras/uso terapéutico , Nanoestructuras/ultraestructura , Neoplasias/diagnóstico , Neoplasias/terapia , Imagen Óptica , Itrio/uso terapéutico
18.
J Phys Condens Matter ; 25(49): 496011, 2013 Dec 11.
Artículo en Inglés | MEDLINE | ID: mdl-24222379

RESUMEN

Neutron diffraction measurements, performed in the presence of an external magnetic field, have been used to show structural evidence for the kinetic arrest of the first order phase transition from (i) the high temperature austenite phase to the low temperature martensite phase in the magnetic shape memory alloy Ni37Co11Mn42.5Sn9.5, (ii) the higher temperature ferromagnetic phase to the lower temperature antiferromagnetic phase in the half-doped charge ordered compound La0.5Ca0.5MnO3 and (iii) the formation of glass-like arrested states in both compounds. The cooling and heating under unequal fields protocol has been used to establish phase coexistence of metastable and equilibrium states, and also to demonstrate the devitrification of the arrested metastable states in the neutron diffraction patterns. We also explore the field­temperature dependent kinetic arrest line TK(H), through the transformation of the arrested phase to the equilibrium phase. This transformation has been observed isothermally in reducing H, as also on warming in constant H. TK is seen to increase as H increases in both cases, consistent with the low-T equilibrium phase having lower magnetization.

19.
J Phys Condens Matter ; 25(6): 066011, 2013 Feb 13.
Artículo en Inglés | MEDLINE | ID: mdl-23315512

RESUMEN

Magnetic behavior of the pseudo-binary alloy Hf(1-x)Ta(x)Fe(2) has been studied, for which the zero-field ferromagnetic (FM) to antiferromagnetic (AFM) transition temperature is tuned near to T = 0 K. Our studies show that such composition lies around x = 0.230. Detailed magnetization studies on x = 0.225, 0.230 and 0.235 show thermomagnetic irreversibility at low temperature due to kinetic arrest of the first-order AFM-FM transition. All three compositions studied show a reentrant transition in the zero-field-cooled warming curve and non-monotonic variation of the upper critical field. The region in H-T space where these features of kinetic arrest manifest themselves increases with increasing Ta concentration.


Asunto(s)
Aleaciones/química , Hafnio/química , Hierro/química , Magnetismo , Imanes/química , Modelos Químicos , Tantalio/química , Simulación por Computador , Cinética , Temperatura
20.
J Phys Condens Matter ; 24(33): 336007, 2012 Aug 22.
Artículo en Inglés | MEDLINE | ID: mdl-22836484

RESUMEN

The band structure calculation for the compound Mn(2)VGa carried out using the plane wave self-consistent field package with generalized gradient approximation shows that the compound is nearly half-metallic at the equilibrium lattice parameter. However, theoretical investigations have shown that a certain percentage of atomic anti-site disorder can destroy the half-metallic nature of the sample. Hence it is important to quantify the site disorder in these systems. We have deduced the percentage of atomic anti-site disorder from the refinement of the higher angle room temperature (300 K) neutron diffraction (ND) pattern and it was observed to be roughly 8% in our sample. The field variation of resistance recorded at different temperatures shows a positive slope at low temperatures and a negative slope at higher temperatures, indicating the half-metallic character at low temperatures. The ab initio calculations predict a ferrimagnetic ground state for this system. The analysis of the magnetic structure from ND data measured at 6 K yields magnetic moment values of 1.28 µ(B) and -0.7 µ(B) for Mn and V, respectively, confirming the ferrimagnetic ordering.

SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA
...