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A magnetic field-pressure-temperature (H-P-T) phase diagram for first-order antiferromagnetic (AFM) to ferromagnetic (FM) transitions in Fe(49)(Rh(0.93)Pd(0.07))(51) has been constructed using resistivity measurements under simultaneous application of magnetic field (up to 8 T) and pressure (up to 20 kbar). The temperature dependence of resistivity (ρ-T) shows that the width of the transition and the extent of hysteresis decreases with pressure and increases with magnetic field. By exploiting opposing trends of dT(N)/dP and dT(N)/dH (where T(N) is the first-order transition temperature), the relative effects of temperature, magnetic field and pressure on disorder-broadened first-order transitions has been studied. For this, a set of H and P values are chosen for which T(N)(H(1),P(1)) = T(N)(H(2),P(2)). Measurements for such combinations of H and P show that the temperature dependence of resistivity is similar, i.e. the broadening (in temperature) of transition as well as the extent of hysteresis remains independent of H and P. Isothermal magnetoresistance measurements under various constant pressures show that even though the critical field required for AFM-FM transition depends on applied pressure, the extent of hysteresis as well as transition width (in magnetic field) remains constant with varying pressure.

FeRh 0.8 Pd 0.2 is known to exhibit near room-temperature first-order antiferromagnetic (AF)–ferromagnetic (FM) transition, typical of chemically ordered FeRh system. In addition, it is also reported to show martensitic transition at a lower temperature. In this work, the effect of sample history on transition temperature (T t) and the magnetocaloric effect (MCE) have been studied. The experimentally determined MCE parameters across FM to AF transition induced either by isothermal magnetic field sweep or by temperature sweep showed a large isothermal change in entropy around room temperature, i.e., 14 J/kg K for 50 kOe magnetic field change, whereas MCE corresponding to AF–FM transition depends on cooling history. Our study shows that in the presence of martensite phase, the peak value of MCE is shifted to higher temperatures but with significantly reduced magnitude. [ABSTRACT FROM AUTHOR]

The effect of partial substitution of Ge for Sb on the first-order ferrimagnetic (FRI)–antiferromagnetic (AFM) transition in Mn 2 Sb has been studied. It shows that the transition temperature (T t) can be tuned between 119 K and 271 K by substituting 2.5%–10% Ge at Sb sites in Mn 2 Sb. The variation of density of state at the Fermi level N(E f) with Ge substitution shows that dN(E)/dE is positive at E f in the AFM state. With the application of a magnetic field, T t shifts to low temperature, which results in a giant negative magnetoresistance (MR) reaching a value of 70% for 2.5% substitution. Our results show that FRI to AFM transformation during cooling stops around 35 K, even though it remains incomplete. This, along with the nonmonotonic variation of lower critical field, open loop in isothermal MR, and increasing difference in zero field cooled warming and field cooled warming resistivity with increasing magnetic field, shows that the FRI to AFM transition is kinetically arrested in the case of 2.5% Ge substitution. [ABSTRACT FROM AUTHOR]

In this article, we provide an initial qualitative description of the basic magnetization reversal processes behind temperature and cooling field-dependent exchange bias effect at Co/CoO interface of Fe3O4/Alq3/Co/CoO/Au hybrid spin valve (SV) device structure. The exchange field at Co/CoO interface is observed to be inversely proportional to temperature, indicating enhanced magnetic field sensitivity of Co reverse domain nucleation at the high-temperature region. The exchange field, at constant temperature, is found to be insensitive to change in the cooling field, which may be due to efficient ferromagnetic coupling at the Co/CoO interface of the device. Sudden decrease of exchange field with training cycle number ($n$) has been observed at lower values of $n$ , which may be attributed to rearrangement of Co pinned layer spin configuration toward equilibrium. Interestingly, incorporation of antiferromagnetic CoO layer has not been observed to bring any change in magnetoresistance (MR) behavior of the exchange biased SV device, which shows a two-step switching pattern of MR at 100 K. [ABSTRACT FROM AUTHOR]

The magnetoresistance (MR) of Ni2+xMn1-xGa (-1≤x≤0.35) ferromagnetic shape memory alloy shows a large increase in magnitude at room temperature (RT) with increasing x. For Mn2NiGa (x=-1), MR at 8 T is -0.2%, while for Ni2.35Mn0.65Ga (x=0.35), it is -7.3%. Thus, MR of Ni2+xMn1-xGa can be varied over one order of magnitude by changing composition (x). Considering that the Curie temperature (TC) varies with x, the MR behavior in the austenitic phase is explained on the basis of the s-d scattering model. By fitting the MR at 8 T in the austenitic phase for different x and T, a (T/TC)6 power law dependence is obtained. In contrast to the monotonic MR variation with x, the magnetization at RT is highest for Ni2MnGa (x=0) and decreases for both Ni and Mn excess compositions. [ABSTRACT FROM AUTHOR]

Our systematic path dependent resistivity study in H – T space shows that paramagnetic (PM)–ferromagnetic (FM) transition in CoS 1.76 Se 0.24 is kinetically arrested. The resistivity at low temperature depends on the path followed in H – T space and the critical field required for PM to FM transition varies non-monotonically with temperature. Measurements under CHUF (cooling and heating in unequal magnetic field) protocol show reentrant transition on warming under higher magnetic field (than that applied during cooling), which indicate that PM state is the non-equilibrium state. Among the growing list of diverse system showing glass like arrested magnetic states, the present system is the first example where, kinetic arrest is observed for a disordered (here PM) to ordered (here FM) magnetic transition. [ABSTRACT FROM AUTHOR]

The pinch performance of a plasma focus (PF) device is sensitive to the physical conditions of the breakdown phase. It is therefore essential to model and study the initial phase in order to optimize device performance. An external circuit is self consistently coupled to the electromagnetic particle in cell code to model the breakdown and initial lift phase of the United Nations University/International Centre for Theoretical Physics (UNU-ICTP) plasma focus device. Gas breakdown during the breakdown phase is simulated successfully, following a drop in the applied voltage across the device and a concurrent substantial rise in the circuit current. As a result, the plasma becomes magnetized, with the growing value of the magnetic field over time leading to the gradual lift off of the well formed current sheath into the axial acceleration phase. This lifting off, with simultaneous outward sheath motion along the anode and vertical cathode, and the strong magnetic fields in the current sheath region, was demonstrated in this work, and hence validates our method of coupling the external circuit to PF devices. Our method produces voltage waveforms that are qualitatively similar to the observed experimental voltage profiles of the UNU-ICTP device. Values of the mean electron energy before and after voltage breakdown turned out to be different, with the values after breakdown being much lower. In both cases, the electron energy density function turned out to be non-Maxwellian. [ABSTRACT FROM AUTHOR]

We report room temperature giant baroresistance (≈128%) in Fe49(Rh0.93Pd0.07)51. With the application of external pressure (P) and magnetic field (H), the temperature range of giant baroresistance (≈600% at 5K, 19.9 kilobars and 8 T) and magnetoresistance (≈ ~85% at 5K and 8 T) can be tuned from 5 K to well above room temperature. It is shown that under external pressure, antiferromagnetic state is stabilized at room temperature and shows giant magnetoresistance (≈~55%). Due to coupled magnetic and lattice changes, the isothermal change in resistivity at room temperature under pressure (at constant H) as well as magnetic field (at constant P) can be scaled together to a single curve, when plotted as a function of X = T + 12.8 x H -- 7.3 x P. [ABSTRACT FROM AUTHOR]

We have achieved giant enhancement of magnetoresistance (MR) by the formation of La0.67Sr0.33MnO3 (LSMO)-Pr0.67Ca0.33MnO3 (PCMO) core-shell nanostructure. Astonishingly, 1143% enhancement of MR in the core-shell nanostructure has been observed with respect to the parent PCMO nanoparticles at 100 K and 2 T magnetic field. The observed giant enhancement is the result of significantly weaken the charge ordered state in the created ferromagnetic-charge ordered core-shell nano structure. Our study clearly indicates a method to achieve huge enhancement of magnetoresistance that can eventually give rise artificially created superior materials important for magnetic field sensor technology. [ABSTRACT FROM AUTHOR]

Using the tridimensional magnetic probe, the current sheath velocity at 0.25 Torr is studied in Sahand, a Filippov-type plasma focus facility. The current sheath velocity in argon-filled plasma focus with different percentages of helium impurity at different operating voltages was studied. The highest average current sheath velocity of 12.26 ± 1.51 cm μs−1 at the top of the anode in the axial phase was achieved at 17 kV. Minimum average current sheath velocity is 5.24 ± 1.18 cm μs−1 at 12 kV with 80% argon + 20% helium as a working gas. The full width at half-maximum of peaks of the magnetic probe was found to be inversely related to the current sheath velocity, i.e. smaller at higher voltages for different impurity and decreased with increasing of impurity. [ABSTRACT FROM AUTHOR]

First-order antiferromagnetic insulating (AFI)-ferromagnetic metallic (FMM) transition as a function of temperature and magnetic field has been imaged using magnetic force microscopy (MFM) in La5/8-yPryCa3/8MnO3 (y = 0.45) thin film grown on NdGaO3 substrate. These images, showing AFI to FMM transformation during in-field cooling and reverse transformation during warming of the same region, cannot be described solely in terms of the broad first-order transition due to quench disorder. Growth morphology of the FMM phase is observed to be path dependent as larger size FMM regions (but with smaller net fraction) are observed for isothermal field induced transition when compared to isofield thermal transition. This is shown to be a consequence of the glasslike arrested AFI state even at ≈100 K. Apparent variable range hopping like transport near TMi during cooling is shown to be a consequence of growth of the FMM phase in an AFI matrix. [ABSTRACT FROM AUTHOR]

Abstract: The origin of anomalous thermomagnetic irreversibility in rare earth germanide has been addressed. Open hysteresis observed in magnetoresistance (MR) at low temperature is shown to decrease with increasing temperature which correlates with the corresponding isothermal magnetostriction (MS) measurements. These thermomagnetic irreversibilities are interpreted in terms of kinetic arrest of magnetic field induced first order transition. The minor loop study of isothermal MS suggests that open loop in MS and MR is associated with large magnetostriction across metamagnetic transitions. The magnetoresistance associated with the second metamagnetic transition at higher field is reversible where magnetostriction variation with field is negligible. [Copyright &y& Elsevier]

• Relaxation in polycrystalline FeRh 0.46 Pd 0.54 depends on the path followed in H-T space. • Resistivity relaxation follows logarithmic time dependence. • For kinetically arrested state, relaxation rate (Z) increase with temperature. • For supercooled/superheated states Z depends on the available phase fraction for transformation. • Z is one order higher in supercooled state than superheated state. Path dependent resistivity (ρ) relaxation behavior of FeRh 0.46 Pd 0.54 is studied in magnetic field (H) – temperature (T) parameter space. It shows that within the hysteresis region of zero field ρ – T curve, relaxation rate for AFM to FM forward transition during cooling is one order higher than the reverse transition during warming. However, below the hysteresis region, kinetics of the transition dominates and relaxation behavior depends on the path followed in H-T space to reach the measurement point. These measurements show that at low temperatures relaxation rate for AFM to FM transformation decreases irrespective of metastable phase fraction and it is maximum around 75 K. This is in contrast to relaxation behavior of supercooled/superheated metastable sate where relaxation rate depends on the available phase fraction for the transformation. [ABSTRACT FROM AUTHOR]

In the present work, we have studied the effect of Fe composition on the superconducting properties, such as transition temperature (Tc), upper critical field (Hc2), and irreversibility field (Hirr) of FeSe1/2Te1/2. The polycrystalline samples have been prepared via solid state reaction route with nominal compositions FexSe1/2Te1/2 (x = 0.95, 1.00, 1.05 and 1.10). The x-ray diffraction results show the presence of tetragonal α-FeSe phase with the p4/nmm space group symmetry in all the samples. The zero resistance temperatures, Tczero, measured in zero magnetic field, have been found to be 10.0, 12.4, 12.3, and 11.7 K for x = 0.95, 1.00, 1.05, and 1.10, respectively. The temperature dependence of Hc2(T) and Hirr(T) have been calculated from the magnetoresistance data using the criteria of 90% and 10% of normal state resistivity (ρn) values, respectively. The values of Hc2(0) are 121.3 T, 142.8 T, 82.7 T, and 79.3 T for x = 0.95, 1.00, 1.05, and 1.10, respectively. The possible reasons for the variation of superconducting properties with Fe composition (x) have been described and discussed in this paper. [ABSTRACT FROM AUTHOR]

The influence of the application of a magnetic field (H) on the temperature (T) dependence of heat capacity and isothermal magnetization has been investigated in Gd[sub 2]PdSi[sub 3], a compound ordering antiferromagnetically below (T[sub N]=)21 K in zero H. Among other findings, the one to be emphasized is the observation of significant magnetocaloric effect (MCE) over about a 30 K range with a peak in the vicinity of T[sub N]. This finding suggests that this material could be useful for magnetic refrigeration below 50 K. The results also establish that either of the two experimental methods--heat capacity or magnetization--can be applied to identify materials with large MCE. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic field induced first order antiferromagnetic (AFM) to ferrimagnetic (FRI) transition in polycrystalline Mn1.85Co0.15Sb has been studied using magnetic force microscopy (MFM) at 60K and up to 8T magnetic fields. Our MFM studies provide real space visualization of AFM to FRI transition. It shows growth (decay) of FRI phase with increasing (decreasing) magnetic field. The hysteretic behavior and co-existing FRI and AFM phases across the critical field required for FRI–AFM transition in Mn1.85Co0.15Sb are highlighted. This study demonstrates the potential of MFM for studying phase co-existence at high field and low temperatures. [Copyright &y& Elsevier]

Co 4 Nb 2 O 9 (CNO) having Co chains along c-direction shows gigantic magnetoelelctric coupling below antiferromagnetic ordering temperature of 27.3 K but above a spin flop field of 1.6 T. We have investigated the effect of substitution of 20% of isovalent magnetic Fe 2+ on magnetic and magnetoelectric properties. With Fe substitution, magnetization with temperature has shown a weak ferromagnetic behavior at low magnetic fields and antiferromagnetic like behavior at higher fields. Interestingly, linear magnetoelelctric and ferroelectric behaviors are evidenced in the Fe substituted samples but for an electric field as small as 5 kV/m and the magnetoelelctric coupling is ensured for magnetic fields as low as 0.25 T, which is far below the spin flop field. The reduction in single ion anisotropy of Co and modified Dzyaloshinkii-Moriya interactions with Fe appear to be important in inducing low field ME effect. [ABSTRACT FROM AUTHOR]

[Display omitted] • TS500 CFAS film has the highest B2 structural order and lowest residual resistivity. • Diffuson and WL effects (e-m and e-p scattering) dominate for T < T min (T > T min) • Phonon-induced non-spin-flip two-band (s↑↓- d↑↓) scattering accounts for. ρ e - p • Thermal renormalization of spin-wave stiffness significantly contributes to. ρ e - m (T) • Suppression of WL an d e – m scattering by magnetic field results in negative MR. An exhaustive study of the effect of anti-site disorder on the 'zero-field', ρ(T , H = 0), and 'in-field', ρ(T , H = 80 kOe), electrical resistivity in 50 nm thick Co 2 FeAl 0.5 Si 0.5 (CFAS) Heusler alloy thin films (deposited on the Si(1 0 0) or SiO 2 /Si(1 0 0) substrates at fixed substrate temperatures in the range 27 ° C ≤ T S ≤ 550 ° C), has been carried out. Irrespective of the strength of disorder, resistivity goes through a minimum as a function of temperature at T = T min. With increasing substrate temperature, the crystalline order of the CFAS thin films improves so much so that the films deposited at 500 °C have the lowest anti-site disorder within the B2 structure and the least residual resistivity. A quantitative comparison of our results with the predictions of the existing theoretical models permits us to unambiguously identify the diffusive and ballistic transport mechanisms, responsible for ρ(T , H = 0) and ρ(T , H = 80 kOe) in different temperature ranges and accurately determine their relative magnitudes. The electron-diffuson (e – d) scattering and weak localization (WL) mechanisms, responsible for negative temperature coefficient of resistivity (TCR) for T < T min , compete with the positive TCR mechanisms, electron-magnon (e – m) and electron–phonon (e – p) scattering, to produce the resistivity minimum at T min. The e – d and WL contributions to ρ, ρ e - d and ρ wl , dominate over the e – m and e – p contributions, ρ e - m and ρ e - p , for T < T min whereas the reverse is true for T > T min . At any given temperature, ρ e - d , ρ wl and ρ e - m decrease while ρ e - p increases as the atomic order improves with increasing substrate temperature, T S. ρ e - p and ρ e - m originate from the phonon-induced non-spin-flip two-band (s↑↓- d↑↓) scattering and magnon - induced spin-flip s - d interband (s↑↓- d↓↑) transitions, respectively. In all the CFAS films, except for the one deposited at T S = 27 ° C , the thermal renormalization of the spin-wave stiffness, due to the electron - magnon interaction, contributes significantly to ρ e - m (T). Furthermore, we demonstrate that the negative magnetoresistance (MR) is a consequence of a progressive suppression of the WL effect and e – m scattering by external magnetic field. However, the WL contribution to MR turns out to be negligibly small as the e – m contribution almost entirely accounts for MR over the temperature range 5 K ≤ T ≤ 300 K. [ABSTRACT FROM AUTHOR]