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We report here the electrical transport and magnetic properties of the newly synthesized quaternary Heusler compounds CoFeTiSn and CoFeVGa. Our study indicates a striking change in the electronic transport properties of CoFeTiSn as the system undergoes the paramagnetic to ferromagnetic transition. While the sample shows an activated semiconducting behaviour in the paramagnetic phase, it turns abruptly to a metallic phase with the onset of ferromagnetic transition. We have compared the system with other Heusler compounds showing similar anomaly in transport, and it appears that CoFeTiSn has much similarities with the Fe 2 VAl compound having pseudogap in the paramagnetic phase. On the other hand, CoFeVGa shows a semiconducting behaviour from high temperature to 90 K. On cooling below 90 K, a broad hump like feature is observed. Both the compositions show negative Seebeck coefficient varying linearly with temperature. The value of the Seebeck coefficient of CoFeTiSn is comparable to that of many Heusler alloys identified as potential thermoelectric materials.

The rare-earth intermetallic compound Ho$_5$Sn$_3$ demonstrates fascinating magnetic properties which include temperature-driven multiple magnetic transitions and field driven metamagnetism. We address the magnetic character of this exciting compound through a combined experimental and theoretical studies. Ho$_5$Sn$_3$ orders antiferromagnetically below $~28$ K, and shows further spin reorientation transitions at 15 K and 12 K. We observe a sizable amount of low-temperature magnetocaloric effect in Ho$_5$Sn$_3$ with a maximum value of entropy change $\Delta S$ = -9.5 JKg$^{-1}$K$^{-1}$ for an applied field of $H$ = 50 kOe at around 30 K. The field hysteresis is almost zero above 15 K where magneto-caloric effect is important. Interestingly, $\Delta S$ is found to change its sign from positive to negative as the temperature is increased above about 8 K, which can be linked to the multiple spin reorientation transitions. The signature of the metamagnetism is visible in the $\Delta S$ versus $H$ plot. The magnetic ground-state, obtained from the density functional theory based calculation, is susceptible to the effective Coulomb interaction ($U_{\rm eff}$) between electrons. Depending upon the value of $U_{\rm eff}$, the ground-state can be ferromagnetic or antiferromagnetic. The compound shows large relaxation (14\% change in magnetization in 60 min) in the field cooled state with a logarithmic time variation, which may be connected to the competing magnetic ground-states observed in our theoretical calculations. The competing magnetic ground-states is also evident from the small value of the paramagnetic Curie-Weiss temperature., Comment: 10 pages, 6 figures

Magnetic transition element doping in topological insulators, which breaks the time-reversal symmetry, gives rise to the diverse range of exotic consequences, though proper understanding of the magnetic order has rarely been attempted by using any microscopic experiments. We report the occurrence of the magnetic order in (${\mathrm{Sb}}_{0.95}{\mathrm{Cr}}_{0.05}{)}_{2}{\mathrm{Te}}_{3}$ using the muon spin relaxation studies. The asymmetry curve at low temperature ($T$) shows an evidence of a damped oscillation, providing a clue about the internal magnetic field (${H}_{\mathrm{int}}$), which follows ${H}_{\mathrm{int}}(T)={H}_{\mathrm{int}}(0){[1\ensuremath{-}T/{T}_{C}]}^{\ensuremath{\beta}}$ with ordering temperature ${T}_{C}\ensuremath{\approx}6.1$ K and critical exponent $\ensuremath{\beta}\ensuremath{\approx}0.22$. The critical exponent is close to the two-dimensional XY-type interaction. The magnetization curves at low $T$ exhibit a ferromagnetic behavior at low field ($H$) and the de Haas--van Alphen (dHvA) effect at high $H$. The analysis of the dHvA oscillation proposes the charge carrier that acts like a massive Dirac fermion. The Berry phase, as obtained from the Landau-level fan diagram, suggests a surface state gap at the Dirac point. The complex electronic structure is discussed by correlating the magnetic order attributed to the Cr doping in ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$.

The magnetic behavior of cobalt pyrovanadate compound Co 2 V 2 O 7 with dichromate structure is reported. The compound undergoes long range magnetic ordering below T C =8 K and our study identifies the ground state to be a canted antiferromagnetic type with a weak ferromagnetic component. The transition at T C is found to be first-order in nature as evident from the presence of distinct thermal hysteresis in the temperature dependent magnetization data. Below T C , a significantly large value of magnetic relaxation is observed which is possibly due to the metastability associated with the first order phase transition. Interestingly, the sample exhibits a sizable magneto-caloric effect around T C (∼4.1 J kg −1 . K −1 for 50 kOe of field change) which is reasonably high among antiferromagnetic transition metal oxides with weak ferromagnetism.

A comparative study of the magnetic and transport properties of three Dy-In intermetallic compounds, namely DyIn3, Dy5In3 and Dy3In, is reported. DyIn3 has cubic crystal structure; on the other hand, Dy5In3 and Dy3In crystallize in tetragonal structure, albeit with different space groups. DyIn3 orders antiferromagnetically below T N = 23 K, while Dy5In3 and Dy3In show ferromagnetic-like ground state with much higher ordering temperatures (119 and 125 K respectively). The ferromagnetic compounds show significant magneto-caloric effect around their respective Curie temperatures. On the other hand, the magneto-caloric effect in DyIn3 is low but associated with the change in sign around T N . All the samples show small magneto-resistance, and it is found to be positive in case of DyIn3 at 5 K. The signature of metamagnetic transition in DyIn3 is visible in the magneto-caloric and magneto-resistance data. Efforts have been made to account the observed magnetic phenomena based on Dy concentration and Dy-Dy bond distance in these three compositions.

DyMn 2 O 5 is an intriguing multiferroic material showing multiple magnetic, electric and structural transitions. We present here the systematic study on the effect of Sr doping at the Dy site of DyMn 2 O 5 through magnetic and dielectric measurements. Doping of divalent Sr at the Dy site is expected to enhance the Mn 4 + : Mn 3 + ratio and it will also dilute the Dy site. Our study indicates large enhancement in the magnetic anomaly observed close to 43 K, which we believe to be related to the increased ferromagnetic correlations on Sr doping. Gradual increase in coercive field at 3 K with the Sr doping and decrease in bond length of adjacent Mn 4 + ions further support the enhancement of ferromagnetic correlations in the system. The parent sample shows a large magnetocaloric effect around 12 K, the magnitude of which found to decrease with increasing Sr concentration. The doping also enhances the anomaly at around 28 K observed in the dielectric permittivity versus temperature data, and this anomaly was earlier claimed to be associated with the spin reorientation as well as a simultaneous transition from one ferroelectric state to other. The electric orderings observed below 25 K are found to be susceptible to the applied magnetic field, and supports the view of Ratcliff II et al. (Phys. Rev. B 72, 060407(R) (2005)) of concomitant changes in the magnetic structure associated with the multiple electric transitions.

A series of Ni-doped Ni 50+x Mn 35−x Sn 15 samples for x = −1, 0, 1, 2, 3 and 4 have been investigated by transport and dc magnetization measurements. The parent sample ( x = 0) undergoes martensitic phase transition around 180 K during cooling along with ferromagnetic Curie point ( T C ) to be 340 K. Interestingly, Ni doping at the Mn site leads to rather unusual non-monotonous variation of martensitic transition temperature ( T MS ) which is precisely corroborated by the similar non-monotonous variation of lattice volume ( V 300 K ). Between −1 ≤ x ≤ 2, the variation of various physical parameters in the studies alloys is conventional and can be explained on the basis of e / a ratio of the samples. However, for x > 2, parameters such as T C , T MS , V 300 K etc. show sudden change in the nature of their variation which is anomalous and cannot be accounted by the e / a ratio formalism. Present study reveals that possible reason behind this non-monotonous variation is closely connected with a self-sustained mechanism originating from the change in the strength of hybridization between Ni 3 d e g state and the excess Mn at the Sn site on Ni substitution. The samples also show large negative magnetoresistance near T MS with its magnitude showing similar non-monotonous variation with Ni doping.

We report intrinsic memory effect in magnetization for zircon-type DyCrO4, pointing the cooperative glassy response below ∼ 7 K. Intriguingly, the memory effect is observed well below the ferromagnetic and antiferromagnetic ordering temperatures, indicate re-entrant spin-glass state in DyCrO4. Above the magnetic order ferroelectricity emerges with a ferroelectric T C at 97 K, which is associated with a signature of magnetoelectric coupling. Thus DyCrO4 attracts the community for multiple interesting properties with a high temperature ferroelectricity and low temperature re-entrant spin-glass-like behavior.

Significant exchange bias effect has been identified in the granular Nickel oxide (NiO) film prepared by sol-gel dip-coating technique on a silicon wafer substrate. Atomic force microscopy displays grain sizes in the range 15–25 nm. Thermal variation of zero field cooled magnetization (ZFC) measured in 500 Oe shows a broad peak around 156 K. Below 25 K, both field cooled (FC) and ZFC magnetization display a significant rise indicating existence of a ferromagnetic (FM) component, which is suggested due to the uncompensated (UC) spins residing at the grain boundaries. The systematic shift in the magnetic hysteresis loops are observed when the sample is field cooled. The shift is the manifestation of exchange bias effect (EB). Training effect is observed at 6 K which could be analyzed by a recursive formula in the framework of spin configurational relaxation model. We propose that pinning mechanism at the interface between antiferromagnetic core and shell consisting of uncompensated spins leads to the EB effect in the granular NiO film.

High conductivity and the absence of ferromagnetism in pristine graphene fail to satisfy primary criteria for possible technological application in spintronics. Opening of the bandgap in graphene is primarily desirable for such applications. We report a simplified and novel approach of controlled grafting of a magnetic alloy on reduced graphene oxide. This eventually leads to ferromagnetism of the stable hybrid material at room temperature, with a large moment (∼1.2 μB) and a remarkable decrease in conductivity (∼10 times) compared to highly ordered pyrolytic graphite. Our model band-structure calculation indicates that the combined effect of controlled vacancies and impurities attributed to the nanocrystalline alloy grafting leads to a promising step toward band gap engineering.

We report a novel approach of designing ordered arrangement of disorder on the extended structures of graphene. We prepared single phase nanoparticles of Co80Ni20 alloy embedded in Reduced Graphene Oxide (RGO). Co80Ni20 shows a large moment and a soft ferromagnetic character like permalloy at room temperature. Temperature dependence of permittivity shows a behavior quite contrary to usual ceramic materials showing an increase with decreasing temperature, exhibiting a maximum. A very large magnitude of permittivity ~ 5000 is observed, which is possibly related to an interesting Maxwell-Wagner type effect arising from the charge localization in the graphene sheets. For a deeper insight of the mechanism, correlations with other phenomena are studied through magnetization, dc resistivity, I-V etc. investigations. Temperature dependent magnetization indicates toward strong ferromagnetic interaction and MH loop shows low coercivity ferromagnetic interaction at 4 K and even at room temperature.

We report here the results of transport and dc magnetization studies of Ga-doped Ni2Mn1.32In0.68 (Ni2Mn1.32In0.68−xGax, x = 0, 0.04, 0.08, 0.16, 0.20, and 0.28) alloys. The parent sample (x = 0) does not show any structural instability, however small Ga substitution at the In site (x = 0.08) suddenly induces martensitic transition in it. The studied alloys are all found to be ferromagnetic below about room temperature and the martensitic transition temperatures are found to be in the range between 175 K and 240 K depending upon x. Samples showing thermally driven maretnsitic transition ( x ≥ 0.08) are also found to be susceptible to the applied magnetic field, and both magnetization and magnetoresistance indicate the signature of field-induced transition. Upon cooling under a magnetic field, we observe kinetically arrested state which is particularly prominent in low Ga containing samples (x = 0.08, 0.16). It clearly demonstrate that these Ga doped samples posses all the properties of metamagnetic shape memory alloys. We argue that the magnetically arrested state in the alloys is closely connected to the competition between chemical and magnetic free energies associated with the martensitic and austenitic phases.

The transport and magnetic properties of ferromagnetic shape memory alloy of nominal composition Ni46Mn41In13 are reported. The alloy undergoes martensitic phase transition (MPT) around 240 K. The region around this structural transition is found to be highly metastable and susceptible to the applied magnetic field. Giant negative magnetoresistance (∼ −64% at 70 kOe) is observed in the vicinity of the thermally driven MPT. The existence of large inverse magnetocaloric effect around the MPT is also confirmed by the direct measurement using modulated ac field technique. The sample shows large exchange bias at low temperature. The role of Mn–Mn intersite antiferromagnetic correlation is discussed for the above magneto-functional behaviors.

The effect of Sn doping at the Ga site of Ni2MnGa is investigated through magnetic and magneto-transport measurements. Clear signatures of martensitic and premartensitic transitions are observed in the pure as well as in 5% Sn doped alloy. For 10% Sn doping, the martensitic transition vanishes, while the premartensitic transition remains visible at low temperature. All the samples are found to have a ferromagnetic ground state with saturation moment decreasing with increasing Sn concentration. The magnetocaloric effect near the martensitic transition in the pure and 5% Sn doped samples is found to be positive. However, the entropy change is found to decrease with increasing magnetic field, which is particularly prominent in the undoped sample. The samples also show negative magnetoresistance with anomalies at the martensitic and premartensitic transition points.

Magnetization, magnetoresistance, and magnetodielectric measurements have been carried out on oxygen deficient charge ordered manganite, Pr 0.5 Ca 0.5 MnO 3 − δ . The low temperature state shows characteristics which are strongly dependent on the oxygen stoichiometry. A disorder driven phase separation in low temperature state is noticed in the magnetization curve, magnetoresistance, and dielectric measurements which are attributed to oxygen deficiency in the compound. Magnetization and magnetoresistance curves at low temperature display melting of charge ordering and appearance of ferromagnetic metallic state above a critical field, ≈ 35 kOe . This melting of charge ordered state is not observed even up to 50 kOe for the specimen which is annealed in oxygen atmosphere. A considerable magnetodielectric (MD) effect is noticed close to room temperature at 280 K which may be useful for technological applications. Strongest MD effect observed in the range 180–200 K, around TN, is found to be uncorrelated with magnetoresistance. The strong MD effect seems to emerge from the high sensitivity of incommensurate state to the external perturbation such as external magnetic field.

Nanocrystalline Cr 2 O 3 and NiO are prepared using high-energy ball milling. Average sizes of the particles obtained from Scanning Electron Microscopy and crystallite sizes obtained from X-ray diffraction are larger for Cr 2 O 3 than NiO particles. At low temperature, large high-field magnetization and small coercivity lead to a weak exchange bias for Cr 2 O 3 , whereas small high-field magnetization and large coercivity lead to a considerable exchange bias for NiO. The training effect is observed for NiO at 4 K which could be described with a recursive formula constructed in the framework of the spin configurational relaxation model. The results suggest that the pinning mechanism at the interface between the antiferromagnetic and the weak ferromagnetic component ascribed to uncompensated spins leads to the exchange bias effect.

The granular CuO films are deposited on n-Si (1 0 0) and sapphire substrates using sol–gel route. Small microstrain leads to ∼5 times larger grain sizes (200–300 nm) and ∼2.5 times larger film thickness (∼0.57 μm) for sapphire than n-Si substrate, which are confirmed by X-ray diffraction and Atomic Force Microscopy. A diode-like current–voltage characteristics are observed for film deposited on n-Si substrate, which is absent for sapphire substrate. Typical manifestation of ferromagnetic character is observed for CuO films, which are strongly influenced by the substrates. Magnetic anisotropy is larger for sapphire substrate than n-Si substrate. At room temperature considerably large magnetoconductance ∼21% and soft ferromagnetic character of CuO film on n-Si substrate are attractive for functional applications.

Magnetic properties of rare-earth intermetallics RE 2 Ni 7 (RE=Dy, Ho) are reported. Both the samples undergo two successive magnetic transitions at T h (paramagnetic to ferromagnetic) and T l (spin reorientation) below 100 K. The transitions are found to be second order in nature as evident from the Arrot plot analysis. Large reversible magnetocaloric effect (MCE) was observed at low temperature in the studied samples. The maximum value of the magnetic entropy change in Ho 2 Ni 7 is found to be −12.5 J/kg K (for 0 to 50 kOe of field change) around 25 K with a high relative cooling power (RCP) of 534 J/kg. The Dy counterpart also shows moderately large values of MCE (−7.3 J/kg K) and RCP (475 J/kg) around the magnetic transition region for similar change in the magnetic field. RE 2 Ni 7 compounds can be promising materials for magnetic refrigeration in the temperature range of helium and hydrogen liquefaction.

We have investigated the magnetocaloric effect in Pr 0.5 Sr 0.5 Mn 1 − x Cr x O 3 nanoparticles with x=0, 0.02, and 0.035. Average grain sizes of the nanoparticles are found to be ≃ 80 nm . Magnitude of magnetocaloric effect (MCE) increases for x=0.02 and then decreases for x=0.035. A bulk compound with x=0.02 with average grain size ≃ 0.5 μ m has also been investigated and we note that size effect significantly tunes the MCE for this material, in which interplay between ferromagnetic and antiferromagnetic interactions leads to the observed results.

The magnetic properties of the cubic Heusler alloys with nominal compositions Ni 2 + x Mn 1 - x In have been investigated experimentally as well as theoretically using first principles electronic structure calculations. Magnetization measurements indicate that all the alloys considered in this work have ferromagnetic ground state. The Curie temperature and the saturation moment of the samples are found to decrease systematically with increasing Ni concentration. No indication of structural transition was evident from our experimental data recorded down to 5 K. Electronic structure calculation indicates that localized magnetic moments are predominantly contributed by the Mn atoms and the calculated magnetic moment as a function of excess Ni concentration agrees well with the experimental data.

We investigate the nonlinear electrical transport as a function of temperature in Co/CoO nanoparticles having core-shell nanostructure. Nanoparticle was synthesized by sol-gel citrate precursor technique where core-shell nanostructure is confirmed by the high resolution Transmission Electron Microscopy. Current–voltage ( I – V ) characteristics are measured over the temperature range 20–295 K. I – V curve exhibits ohmic behaviour at 295 K. Nonlinear electrical transport is observed at low temperature (T) for T ⩽ 275 K . Electrical transport properties have been interpreted in terms of tunneling mechanism where tunneling between ferromagnetic Co nanoparticles takes place through the antiferromagnetic CoO layer. Analysis of dynamic conductance ( G = d I / d V ) indicates that the inelastic tunneling via localized states of antiferromagnetic CoO layers is dominant in the transport mechanism at low temperature.

The magnetotransport and magnetic properties of the binary intermetallic compound Ho2In have been investigated. Clear signature of long range ferromagnetic order in the resistivity and the magne- tization data at TC = 85 K is observed. A further spin reorientation type transition is also apparent in our measured data at around Tt = 32 K. The sample exhibits negative magnetoresistance (peak value of -14% at 5 T) over a wide temperature range that extends well above TC. Substantially large magneto-caloric effect is also observed in the sample (maximum value of -8.5 J kg �1 K �1 for 0 → 5 T), which peaks around the TC of the sample. The observed magnetoresistance and magnetocaloric effect are related to the sup- pression of spin disorder by an external magnetic field. Ho2In can be an interesting addition to the list of rare-earth based magnetic refrigerant materials showing magneto-caloric effect across a second order phase transition. PACS. 75.30.sg Magnetocaloric effect, magnetic cooling - 75.47.-m Magnetotransport phenomena; mate- rials for magnetotransport

Nanoparticles of Ni/NiO structure were prepared by sol–gel route followed by the annealing in presence of controlled oxygen and argon gas mixture. When the sample was cooled down to 5 K from room temperature in a static magnetic field, a systematic shift of the magnetic hysteresis loop was observed. The shift was absent when the sample was cooled in zero field. For cooling the sample in field-cooled mode a small horizontal shift was noticed along with a moderate vertical shift of the hysteresis loop at the saturation of magnetization, which indicates the typical manifestation of exchange bias effect. The horizontal shift increases with decreasing particle size retaining almost unchanged relative vertical shift, where vertical shift is found to be uncorrelated with the horizontal shift. The exchange bias like effect in the Ni/NiO nanostructure is suggested at the Ni/NiO interface, where Ni is ferromagnetic and NiO is in the disordered magnetic state.

The ferromagnetic shape memory alloys Ni71−xCoxAl29( x = 35 – 39 ) were studied through transport and magnetic investigations. The structural instability and the magnetic behaviour of the alloys were found to be extremely sensitive to the composition. All the compositions are ferromagnetic below room temperature and undergo martensitic transition in the temperature range between 100 and 270 K. The saturation moment, magneto-crystalline anisotropy constant, and the martensitic transition temperatures show a very interesting linear dependence on the cobalt concentration. The observed behaviour can be understood on the basis of increasing valence electron concentration when Ni is replaced by Co.

We observe the exchange bias effect in the low hole doped cobaltite Nd0.88Sr0.12CoO3. Training effect as well as systematic horizontal and vertical shifts of the hysteresis loops as a function of temperature and cooling field indicate the exchange bias effect. Temperature dependence of magnetization exhibits a peak at 28 K and an anomaly around ∼ 297 K below which zero-field cooled and field-cooled magnetizations deviate from each other. Strong frequency dependence in the ac susceptibility measurements indicates the spin freezing process at the low temperature peak which behaves like a spin-glass transition. The signature of exchange bias suggests the spontaneous separation between ferromagnetic (FM) and spin-glass like phases in the compound where FM domains or clusters have a single domain structure.

Ferromagnetic shape memory alloy with nominal composition Co37Ni34Al29 is investigated by transport and magnetic measurements. The anomaly due to the martensitic transition is observed around 130–210 K. The thermal hysteresis, observed due to martensitic transition in the dc magnetization versus temperature data, gets suppressed at higher applied field. Below 50 K, magnetization varies with temperature perfectly as T 3 / 2 , which signifies that spin wave excitations are largely responsible for thermal demagnetization. The sample shows small negative magneto-resistance, which varies non-monotonically with temperature showing largest value at around 200 K.

Ferromagnetic shape memory alloy of nominal composition Ni50Mn35Sn15 has been investigated by magnetic and transport measurements. Clear signature of first order martensitic transition is observed over a region around 180 K in resistivity, dc magnetization and ac susceptibility data. Field-cooled and zero-field-cooled magnetizations diverge below the martensitic transition, signifying magneto-thermal irreversibility originating from pinning by variants. The sample shows large negative magneto-resistance (-25% at 90 kOe) in the region of martensitic transition, which was found to be highly irreversible. A clear correspondence between magnetoresistance and dc magnetization is observed above the field of technical saturation.

The transport, magnetic and structural properties of the ferromagnetic shape memory alloy with nominal composition Co 1.28 Ni 1.17 Al have been investigated. The alloy shows long range ferromagnetic order below 269 K. The anomaly due to the martensitic transition is observed in the resistivity and magnetization data in the temperature range around 175 K, which is associated with clear thermal hysteresis. A significant magneto-thermal irreversibility between the zero-field-cooled and the field-cooled data is observed below the martensitic start temperature. The structural change is confirmed by temperature dependent X-ray diffraction, and our analysis indicate that both martensite and austenite phases mutually coexist in the region of hysteresis. Existence of distinct minor hysteresis loops in the resistivity data is also in accordance with a metastable region of phase coexistence across the martensitic transition.

The ferromagnetic Heusler-type alloy Ni 50 Mn 35 Sb 15 exhibits well defined shape memory behaviour. We have investigated the transport and magnetic properties of this alloy across the martensitic transformation. Pronounced thermo-magnetic irreversibility between zero-field-cooled and field-cooled susceptibility data was observed below the martensitic transition temperature. We observe significant magnetic after-effect in magnetisation in both austenite and martensitic phases. However, a clear change in the nature of relaxation is observed as the sample is cooled across the martensitic transition temperature. These observations can be explained on the basis of complex domain dynamics in presence of rich micro-structure formation in the martensite.

The static and dynamic features of magnetization are investigated using dc magnetization and ac susceptibility measurements on La1−δMn0.7Fe0.3O3 for δ = 0 and 0.13. The results indicate that short range ferromagnetic clusters coexist with the glassy magnetic state. The analysis on the frequency dependence of spin freezing temperature (Tf) using the Vogel–Fulcher law and the dynamical scaling behaviour near Tf indicates that the spin freezing temperature behaves like a spin-glass transition temperature for both the compounds. The cluster-glass states of both the compounds exhibit similar characteristic features.

We report on the effect of Fe substitution in the self doped manganite, La0.87Mn1−xFexO3 in the composition range 0 ≤ x ≤ 0.15. The electrical resistivity (ρ) and dc magnetization were measured as a function of temperature, field and time. The metal to semiconducting transition is clearly observed for x ≤ 0.02, while a semiconducting temperature dependence of resistivity is noticed for x ≥ 0.08. The compound with x = 0.05 shows interesting features of ρ in field-cooled (FC) condition such as bifurcation in the zero-field cooled and FC temperature dependence, weak thermal hysteresis and memory effect. We observe the enhancement of colossal magnetoresistance by the Fe substitution in the low substitution range. The paramagnetic to ferromagnetic transition (Tc) is found to decrease with increasing x. The large thermal hysteresis in magnetization under FC condition is noticed for x ≤ 0.02, which is different in character for the composition range 0.05 ≤ x ≤ 0.15. The relaxation of magnetization indicates the ferromagnetic (FM) character for x = 0, while the coexistence of FM and glassy components is observed for x ≥ 0.02. The glassy magnetic phase increases with the increase in Fe substitution. The inhomogeneous phase separation between FM and glassy magnetic phases has been proposed to explain the magnetic and electrical transport properties of La0.87Mn1−xFexO3.

Present work reports on the observation of multiple magnetic transitions in a Ni-excess ferromagnetic shape memory alloy with nominal composition Ni$_{2.048}$Mn$_{1.312}$In$_{0.64}$. The magnetization data reveal two distinct thermal hystereses associated with two different phase transitions at different temperature regions. The high temperature magnetic hysteresis is due to the martensitic phase transition whereas the low temperature hysteresis occurs around the magnetic anomaly signifying the transition from a paramagnetic-like state to the ferromagetic ground state within the martensite. Clear thermal hysteresis along with the sign of the curvatures of Arrott plot curves confirm the {\it first order nature of both the transitions}. In addition, the studied alloy is found to be functionally rich with the observation of large magnetoresistance (-45\% and -4\% at 80 kOe) and magnetocaloric effect (+16.7 J.kg$^{-1}$.K$^{-1}$ and -2.25 J.kg$^{-1}$.K$^{-1}$ at 50 kOe) around these two hysteresis regions (300 K and 195 K respectively)., 5 pages, 3 figs

The electron correlation in the 3d heavy-electron compound with linear spin chains, LaMn 4 Al 8 , has been investigated. Like a similar compound, YMn 4 Al 8 , we found a broad maximum in the temperature dependence of the susceptibility. This is interpreted by assuming the presence of a narrow pseudogap with the width Δ≃280 K in the spin excitation spectrum, which leads to the quenching of spin at low temperatures. Anomalies in susceptibility, resistivity and thermal expansion data, observed below approximately 50 K in spite of the absence of any phase transition, suggest the recovery of spin and the development of short-range magnetic correlation in this low-temperature range. This is in contrast to the case of YMn 4 Al 8 . No apparent long-range ordering in spite of the markedly developed magnetic correlation is probably due to the one-dimensional nature of the Mn spin arrangement.

Single phases of LaMn 1 - x Fe x O 3 ( 0 ⩽ x ⩽ 0.60 ) have been prepared by using chemical route to study the effect of Fe substitution on magnetic and transport properties of LaMnO 3 . Slightly non-stoichiometric oxygen concentration is expected for these samples. Mossbauer study indicates that Fe in these compounds is in the trivalent high-spin state. The absolute value of the resistivity decreases initially at x = 0.15 and then increases rapidly with the further increase of x. The temperature dependence, ρ ( T ) , is semiconducting for all the compounds and explained well by the variable range hopping rather than the adiabatic small polaron hopping. The compounds with x ⩽ 0.15 show ferromagnetic characters while those for x = 0.30 and ⩾ 0.50 exhibit typical cluster glass-like and complicated glassy features, respectively.

Experimental results of the susceptibility, the Knight shift and the nuclear spin–lattice relaxation rate suggest that the tetragonal intemetallic compound with linear chains of Mn atoms, YMn 4 Al ...

Magnetic and transport properties of ferromagnetic BaVSe 3 (the Curie temperature T C ≃43 K) were investigated. The resistivity shows metallic behavior. The saturation magnetization in the ferromagnetic state is homogeneously reduced to 0.34 µ B /f.u. in contrast to the large paramagnetic moment 1.42 µ B /f.u.; the nearly full moment value for a local spin 1/2. NMR experiments revealed a single magnetic V site below T C . Although the macroscopic magnetic properties of BaVSe 3 is similar to those of sulfur-deficient BaVS 3-δ , BaVSe 3 is characterized by the itinerant electron magnetism in contrast to more ionic characters of the BaVS 3 system.

The mixed-valent multiferroic compound CaMn7O12 is studied for its magnetic and electric properties. The compound undergoes magnetic ordering below 90 K with a helimagnetic structure followed by a low temperature magnetic anomaly observed around 43 K. The present study shows that the magnetic anomaly at 43 K is associated with thermal hysteresis indicating first order nature of the transition. The compound also shows field-cooled magnetic memory and relaxation below 43 K, although no zero-field-cooled memory is present. Clear magnetic hysteresis loop is present in the magnetization versus field measurements signifying the presence of some ferromagnetic clusters in the system. We doped trivalent La at the cite of divalent Ca expecting to enhance the fraction of Mn$^{3+}$ ions. The La doped samples show reduced magnetization, although the temperatures associated with the magnetic anomalies remain almost unaltered. Interestingly, the spontaneous electrical polarization below 90 K increases drastically on La substitution. We propose that the ground state of the pure as well as the La doped compositions contain isolated superparamagnetic like clusters, which can give rise to metastability in the form of field-cooled memory and relaxation. The ground state is not certainly spin glass type as it is evident from the absence of zero-field-cooled memory and frequency shift in the ac suceptibility measurements.

We report an unusual high-temperature ferromagnetic transition in bulk single-phase nanocrystalline La0.95Sr0.05MnO3þd, achieved through localized strain and inhomogeneous Sr-doping. Magnetization measurements show a well defined transition at 290 K and a broad one at 150 K. HRTEM imaging reveals the strain on the highly crystalline nanometer sized grains and Sr-doping gradients, while oxygen homogeneity at the grain interfaces is confirmed by EELS-spectra. The magnetic behavior, far from the expected bulk phase diagram, shows how local doping and strain can strongly tune the macroscopic properties of a bulk material., Fundação para a Ciência e a Tecnologia (FCT)

The magnetic ground state of the ferromagnetic shape memory alloy of nominal composition Cu$_{2.84}$Mn$_{0.44}$Al$_{0.72}$ was investigated. The sample shows reentry of a glassy magnetic phase below the martensitic transition temperature, which is found to have complex character with two distinct anomalies in the temperature dependent ac susceptibility data. The sample retains its glassy phase even below the second transition as evident from the magnetic memory measurements in different protocols. Existence of two transitions along with their observed nature suggest that the system can be described by the mean field Heisenberg model of reentrant spin glass as proposed by Gabay and Toulous. \cite{rsg-GT1} The sample provides a fascinating example where a Gabay-Toulous type spin glass state is triggered by a first order magneto-structural transition.

The manganite Nd(0.25)Sm(0.25)Sr(0.5)MnO(3) (NSSMO) shows a first-order metal to insulator transition on cooling, which is concomitant with a magnetic transition from the ferromagnetic to antiferromagnetic state. In some respect the sample shows a striking similarity with Ni-Mn-Sn based ferromagnetic shape memory alloys (FSMAs) undergoing a first-order magneto-structural transition, and efforts have been made to highlight the similarities and dissimilarities of the studied manganite with one such FSMA of composition Ni(2)Mn(1.36)Sn(0.64). From our transport and magnetic investigations, the region of transition in the NSSMO is found to be highly metastable, with a clear indication of a magnetically arrested state which persists even when the sample is cooled down to the lowest temperature of measurement. Interestingly, the studied manganite shows an inverse magnetocaloric effect similar to the FSMA. However, a striking difference between the two compositions is evident in the low-temperature magneto-transport behavior: while a clear signature of tunneling magnetoresistance is present in NSSMO due to the coexisting metallic and insulating clusters of nanometer dimension, the studied FSMA do not show such behavior due to the absence of any insulating phase in the intermetallic alloy.

We investigate magnetic properties of nanocrystalline Fe0.5Ni0.5 alloy embedded in the amorphous SiO2 host with volume fractions φ ≈ 10%. The static and dynamic aspects of the magnetic properties are investigated by investigating thermal and time dependence of low-field dc magnetization. Signature of strong interparticle interaction is noted in the magnetization results. The relaxation process at low temperature is fitted with stretched exponential function, displaying coexistence of ferromagnetic and glassy magnetic components.

The weak itinerant ferromagnetic behavior of Y${}_{2}$Ni${}_{7}$ is investigated through magnetic, transport, and calorimetric measurements. The low value of the saturation moment, large Rhodes-Wohlfarth ratio, large value of the linear term in heat capacity, and Fermi-liquid-like resistivity behavior with enhanced electron-electron scattering contribution establish firmly the weak itinerant ferromagetic nature of the sample. The critical exponents associated with the paramagnetic-to-ferromagnetic transition are also investigated from magnetization isotherms using modified Arrott plot, Kouvel-Fisher plot, and critical isotherm technique. The more accurate Kouvel-Fisher plot provides the critical exponents to be $\ensuremath{\beta}=0.306$ ($\ifmmode\pm\else\textpm\fi{}$0.002), $\ensuremath{\gamma}=1.401$ ($\ifmmode\pm\else\textpm\fi{}$0.02), and $\ensuremath{\delta}=5.578$. These values differ markedly from the mean-field values and correspond closely to the two-dimensional Ising spin system with long-range spin-spin interactions.

We study the effect of Ga doping at the Ge site of the metamagnetic compound Gd(5)Ge(4). For 5% Ga doping, the resulting alloy (Gd(5)Ge(3.8)Ga(0.2)) shows antiferromagnetic ordering around 130 K, and a thermally driven first order magneto-structural transition at low temperature leading to the ferromagnetic ground state. The alloy shows a noticeable amount of training effect in resistivity when thermally cycled through this first order phase transition (FOPT). The training effect is present in the case of isothermal field cycling. The FOPT region is found to be metastable and extremely sensitive to the applied magnetic field with a clear signature of a metamagnetic transition in the magnetization and resistivity. The metastability is further supported by the large relaxation observed in the resistivity. The giant magnetoresistance observed in the sample is found to be positive near the FOPT, while below the transition it is negative. The resistivity shows irreversibility due to field cycling, which is related to both a field-induced arrested state and some permanent micro-structural changes in the sample.

In reply to the comment by Geshev we emphasize that loop shift in the compounds is not a simplified phenomenon of minor loop effect of a ferromagnet rather, it is a genuine signature of exchange bias effect. The estimate of anisotropy field and the plot of exchange bias field at 5 K with the maximum field used for the measurement of hysteresis loop, in addition to the previously reported results such as temperature dependence of exchange bias field, training effect, etc, confirm the exchange bias effect.

The phenomenology of exchange bias effects observed in structurally single-phase alloys and compounds but composed of a variety of coexisting magnetic phases such as ferromagnetic, antiferromagnetic, ferrimagnetic, spin-glass, cluster-glass and disordered magnetic states are reviewed. The investigations on exchange bias effects are discussed in diverse types of alloys and compounds where qualitative and quantitative aspects of magnetism are focused based on macroscopic experimental tools such as magnetization and magnetoresistance measurements. Here, we focus on improvement of fundamental issues of the exchange bias effects rather than on their technological importance.

The phenomenology of exchange bias effects observed in structurally single-phase alloys and compounds but composed of a variety of coexisting magnetic phases such as ferromagnetic, antiferromagnetic, ferrimagnetic, spin-glass, cluster-glass and disordered magnetic states are reviewed. The investigations on exchange bias effects are discussed in diverse types of alloys and compounds where qualitative and quantitative aspects of magnetism are focused based on macroscopic experimental tools such as magnetization and magnetoresistance measurements. Here, we focus on improvement of fundamental issues of the exchange bias effects rather than on their technological importance.

We report the observation of giant magneto-caloric effect (MCE) in ferromagnetic shape memory alloys (FSMAs) of nominal compositions Ni$_2$Mn$_{1.36}$Sn$_{0.64-x}$Ga$_{x}$ ($x$ =0.24, 0.28 and 0.32). Irrespective of the Ga doping, all the samples undergo long range ferromagnetic ordering below around 330 K. However, the martensitic transition temperature ($T_{MS}$) of the samples varies strongly with Ga concentration. Clear signature of field induced transition around $T_{MS}$ is visible for all the samples. The observed MCE ($\Delta S$ = 13.6 J/kg K for field changing from 0 to 50 kOe) is found to be highest for $x$ = 0.28 with peak near 249 K, while $x$ = 0.32 shows $\Delta S$ = 12.8 J/kg K at 274 K. This series of Ga-doped alloys are found to be interesting materials with high value of $\Delta S$ over a varied range of temperature, Comment: 8 pages, 4 figures

We report the magnetocaloric effect (MCE) in a Pr0.52Sr0.48MnO3 single crystal. A peak in the temperature dependence of magnetic entropy change (Delta S-M) with a fairly large negative value (approximate to 3.8 J/ kg K) is observed at 275 K close to Curie temperature. MCE is spread over a wide temperature range resulting in a considerable refrigerant capacity (approximate to 293 J/kg). At low temperature the sign of Delta S-M changes, below which anomalous field dependence of Delta S-M is observed indicating the coexistence of ferromagnetic and antiferromagnetic interactions. Interplay between the interactions is strongly influenced by direction and magnitude of applied magnetic field in the ordered state. (C) 2010 American Institute of Physics. [doi:10.1063/1.3340524]

We report the exchange bias (EB) effect along with tunneling magnetoresistance (MR) in polycrystalline La_{0.88}Sr_{0.12}CoO_3. Analogous to the shift in the magnetic hysteresis loop along the field (H)-axis a shift is clearly observed in the MR-H curve when the sample is cooled in a static magnetic field. Training effect (TE) is a significant manifestation of EB effect which describes the decrease of EB effect when sample is successively field-cycled at a particular temperature. We observe TE in the shift of the MR-H curve which could be interpreted by the spin configurational relaxation model. A strong field-cooled (FC) effect in the temperature as well as time dependence of resistivity is observed below spin freezing temperature. The unusual MR results measured in FC mode are interpreted in terms of intragranular interface effect between short range ferromagnetic clusters and spin-glass matrix giving rise to the EB effect. EB effect in MR has been observed in bilayer or multilayer films which has not yet seen in a polycrystalline compound. EB effect involved with tunneling MR and semiconducting transport property attributed to the intragranular intrinsic nanostructure is promising for the spintronic applications., Accepted in Europhysics Letters