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Polycrystalline Ni-Co-Mn-Sn based ferromagnetic shape memory alloys (FSMAs) show promise as actuator materials, but their practical application involving magnetic field induced strain (MFIS) is often limited by three factors: the requirement for high magnetic fields (> 5 T), martensitic transition temperature away from room temperature, and limited recovery of pre-strain applied to the martensite phase. Current work investigates the martensitic transition (MT) and shape memory effect under the application of magnetic field for bulk polycrystalline Ni37Co11Mn43Sn9 alloy. The outcome of the study reveals a metamagnetic transition from the martensitic phase to the austenitic phase at a low field of 2.8 T at 300 K which results 0.25% spontaneous MFIS. Interestingly, 1.3% pre-strained specimen registers a 100% recovery with the application of magnetic field of 4.5 T. Furthermore, the pre-strained specimen exhibited a two-way shape memory effect between a strain value of 1.0% to 1.55% during the field loading and unloading sequences. Notably, this study also demonstrates, to the best of our knowledge , for the first time, that the spontaneous strain and pre-strain add together. This finding paves the way for achieving a giant MFIS by pre-straining a Ni-Mn-Sn/In class of FSMAs which shows large spontaneous MFIS., Comment: 39 pages,9 figures

We investigate the magnetic behavior and critical exponents of quaternary CoFeV$_{0.8}$Mn$_{0.2}$Si Heusler alloy to understand the interactions across the Curie temperature ($T_{\rm C}$). The Rietveld refinement of the x-ray diffraction pattern with the space group F$\bar{4}$3m confirms a single-phase cubic Y-type crystal structure. The magnetic susceptibility $\chi (T)$ data show a ferromagnetic nature with a second-order phase transition from paramagnetic to ferromagnetic at $446\pm1$~K. The saturation magnetization at 5~K is determined to be 2.2~$\mu_B$/f.u., which found to be close to the Slater--Pauling rule and indicates its half-metallic nature. The values of asymptotic critical exponents ($\beta$, $\gamma$, and $\delta$) and the $T_{\rm C}$ are extracted through detailed analytical analysis including the Modified Arrott plot, the Kouvel-Fisher (K--F) method, and the Widom scaling relation. Interestingly, the estimated values of $\beta$ = 0.369 and $\gamma$ = 1.445 closely approximate the theoretical values of the 3D Heisenberg model and second-order thermodynamic phase transition across the $T_{\rm C}$. The obtained exponents lead to the collapse of renormalized isotherms, represented by the relationship between the magnetization (m) and the applied magnetic field (h), into two distinct branches above and below the $T_{\rm C}$, which validates the reliability of the analysis. Furthermore, these exponents suggest that the spin interaction follows a decay pattern of $J(r) \sim r^{-4.99}$, indicating a short-range magnetic ordering, akin to the itinerant-electron 3D Heisenberg model., Comment: submitted

Based on our experimental and theoretical studies, we report the identification of the quaternary Heusler alloy, CoRuVSi as a new member of the recently discovered spin semimetals class. Spin polarised semimetals possess a unique band structure in which one of the spin bands shows semimetallic nature, while the other shows semiconducting/insulating nature. Our findings show that CoRuVSi possesses interesting spintronic and thermoelectric properties. Magnetization data reveal a weak ferri-/antiferro magnetic ordering at low temperatures, with only a very small moment $\sim$ 0.13 $\mu_B$/f.u., attributed to the disorder. Transport results provide strong evidence of semimetallicity dominated by two-band conduction, while magnetoresistance data show a non-saturating, linear, positive, magnetoresistance. Spin polarization measurements using point-contact Andreev reflection spectra reveal a reasonably high spin polarization of $\sim$ 50\%, which matches fairly well with the simulated result. Furthermore, CoRuVSi shows a high thermopower value of $0.7$ $m Watt/ m-K^{2}$ at room temperature with the dominant contribution from the semimetallic bands, rendering it as a promising thermoelectric material as well. Our ab-initio simulation not only confirms a unique semimetallic feature, but also reveals that the band structure hosts a linear band crossing at $\sim$ -0.4 eV below the Fermi level incorporated by a band-inversion. In addition, the observed topological non-trivial features of the band structure is corroborated with the simulated Berry curvature, intrinsic anomalous Hall conductivity and the Fermi surface. The coexistence of many interesting properties relevant for spintronic, topological and thermoelectric applications in a single material is extremely rare and hence this study could promote a similar strategy to identify other potential materials belonging to same class.

We report a combined theoretical and experimental study of a new topological semimetal CrFeVGa with an emphasis on the role of atomic disorder on the magnetoelectronic properties and its applications.CrFeVGa belongs to the quaternary Heusler alloy family and crystallizes in the cubic structure. Synchrotron XRD measurement confirms B2 disorder, which plays a crucial role in dictating the electronic and magnetic properties of the system.

Spin semimetals are a recently discovered new class of spintronic materials, which exhibit a band gap in one spin channel while a semimetallic feature in the other and thus allows for tunable spin transport. Here, we present experimental verification of spin semimetallic behavior in FeRhCrSi, a quaternary Heusler alloy with saturation moment 2 $\mu_B$ and Curie temperature $>$ 400 K. It crystallises in the L2$_1$ structure with 50$\%$ antisite disorder between Fe and Rh. Below 300 K, it shows a weakly temperature dependent electrical resistivity with negative temperature coefficient, indicating the normal semimetal or spin semimetal behavior. Anomalous magnetoresistance data reveals dominant contribution from asymmetric part, a clear signature of spin-valve nature, which is retained even at room temperature. \textcolor{black}{The asymmetric part of magneto-resistance shows an unusual increase with increasing temperature.} Hall measurements confirm the anomalous nature of conductivity originating from the intrinsic Berry curvature, with holes being the majority carriers. Ab-initio simulation confirms a unique long-range ferrimagnetic ordering to be the ground state, explaining the origin behind the unexpected low saturation moment. The ferrimagnetic disordered structure confirms the spin semimetallic feature of FeRhCrSi, as observed experimentally., Comment: FeRhCrSi, Quaternary Heusler Alloys, Spin semimetal, Spin valve, Heusler alloys, Half metal, High T_C Heusler alloys, Fleur, FLAPW, unfolded band structure

We report a combined theoretical and experimental study of a novel quaternary Heusler system CoFeVSb from the view point of room temperature spintronics and thermoelectric applications. It crystallizes in cubic structure with small DO$_3$-type disorder. The presence of disorder is confirmed by room temperature synchrotron X-ray diffraction(XRD) and extended X-ray absorption fine structure (EXAFS) measurements. Magnetization data reveal high ordering temperature with a saturation magnetization of 2.2 $\mu_B$/f.u. Resistivity measurements reflect half-metallic nature. Double hysteresis loop along with asymmetry in the magnetoresistance(MR) data reveals room temperature spin-valve feature, which remains stable even at 300 K. Hall measurements show anomalous behavior with significant contribution from intrinsic Berry phase. This compound also large room temperature power factor ($\sim0.62$ mWatt/m/K$^{2}$) and ultra low lattice thermal conductivity ($\sim0.4$ W/m/K), making it a promising candidate for thermoelectric application. Ab-initio calculations suggest weak half-metallic behavior and reduced magnetization (in agreement with experiment) in presence of DO$_3$ disorder. We have also found an energetically competing ferromagnetic FM)/antiferromagnetic (AFM) interface structure within an otherwise FM matrix: one of the prerequisites for spin valve behavior. Coexistence of so many promising features in a single system is rare, and hence CoFeVSb gives a fertile platform to explore numerous applications in future.

We report the results of experimental investigations on structural, magnetic, resistivity, caloric properties of Fe$_2$RhZ (Z=Si,Ge) along with \textit{ab-initio} band structure calculations using first principle simulations. Both these alloys are found to crystallize in inverse Heusler structure but with disorder in tetrahedral sites between Fe and Rh. Fe$_2$RhSi has saturation moment of 5.00 $\mu_B$ and while its counterpart has 5.19 $\mu_B$. Resistivity measurement reveals metallic nature in both of them. Theoretical simulations using generalized gradient approximation(GGA) predict inverse Heusler structure with ferromagnetic ordering as ground state for both the alloys. However it underestimates the experimentally observed moments. GGA+$U$ approach, with Hubbard $U$ values estimated from density functional perturbation theory helps to improve the comparison of the experimental results. Fe$_2$RhSi is found to be half metallic ferromagnet while Fe$_2$RhGe is not. Varying $U$ values on Fe and Rh sites does not change the net moment much in Fe$_2$RhSi, unlike in Fe$_2$RhGe. Relatively small exchange splitting of orbitals in Fe$_2$RhGe compared to that of Fe$_2$RhSi is the reason for not opening the band gap in the minority spin channel in the former. High ordering temperature and moment make Fe$_2$RhSi useful for spintronics applications., Comment: Full Heusler alloys, inverse Heusler alloys, Fe2RhSi, Fe2RhGe, half metals, high T_C ferromagnets, spintronics, 9 figures, 2 tables, Rh- based Heusler alloys

We report the theoretical prediction of a new class of spintronic materials, namely bipolar magnetic semiconductor (BMS), which is also supported by our experimental data. BMS acquires a unique band structure with unequal band gaps for spin up and down channels, and thus are useful for tunable spin transport based applications such as spin filters. The valence band (VB) and conduction band (CB) in BMS approach the Fermi level through opposite spin channels, and hence facilitate to achieve reversible spin polarization which are controllable via applied gate voltage. We report the quaternary Heusler alloy VNbRuAl to exactly possess the band structure of BMS. The alloy is found to crystallize in LiMgPdSn prototype structure (space group $F\bar{4}3m$) with B$2$ disorder and lattice parameter 6.15 \AA . The resistivity and Hall measurements show a two channel semiconducting behavior and a quasi linear dependence of negative magneto resistance (MR) indicating the possible semiconducting nature. Interestingly, VNbRuAl also shows a fully compensated ferrimagnetic (FCF) behavior with vanishing net magnetization (m$_s$$\sim$ $10^{-3}$ $\mu_B/f.u.$) and significantly high ordering temperature ($> 900$ K). Unlike conventional FCF, vanishing moment in this case appears to be the result of a combination of long range antiferromagnetic (AFM) ordering and the inherent B2 disorder of the crystal. This study opens up the possibility of finding a class of materials for AFM spintronics, with great significance both from fundamental and applied fronts., Comment: 9 pages, 9 figures

We report high temperature synchrotron X-ray diffraction (SXRD), dc magnetization and current-voltage (I-V) characteristics for the samples of Co$_{2.75}$Fe$_{0.25}$O$_4$ ferrite. The material was prepared by chemical reaction of the Fe and Co nitrate solutions at pH = 11 and subsequent annealing at temperatures 200 0C, 500 0C and 900 0C. The measurements were performed by cycling the temperature from 300 K to high temperature (warming mode) and return back to 300 K (cooling mode). The SXRD patterns indicated a fine bi-phased cubic spinel structure in the highly Co rich spinel oxide. Magnetization curves showed intrinsic ferrimagnetic features and defect induced additional ferromagnetic phase at higher temperatures. Electrical conductivity showed thermal hysteresis loop between warming and cooling modes of temperature variation. The samples exhibited new information on the irreversibility phenomena of lattice structure, magnetization and electrical conductivity on cycling the measurement temperatures.

Neutron diffraction and ab initio studies were carried out on Mn2V1-xCoxGa (x=0, 0.25, 0.5, 0.75, 1) Heusler alloys which exhibits high TC fully compensated ferrimagnetic characteristic for x=0.5. A combined analysis of neutron diffraction and ab initio calculations 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 confirmed L21 structure for Mn2VGa and Xa structure for Mn2CoGa. The alloys with x=0.25 and 0.5 possess L21 structure with Mn(C)-Co disorder. As the Co concentration reaches 0.75, a structural transition has been observed from disordered L21 to disordered Xa. Detailed ab initio studies 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 and ab initio studies, it is identified that the disordered L21 structure 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.

We report the experimental evidence in support of room temperature ferromagnetism in Ni doped 3C-SiC. Curie temperature is found to be > 350 K. Temperature dependent Electron paramagnetic resonance (EPR) study reveals that the valence state of Ni is 2+ and its environmental symmetry. A clear shift in both XRD and Raman peak confirms the incorporation of Ni in the host lattice. The variation in number of vacancies $V_{\mathrm{Si}}$, $V_{\mathrm{C}}$ and the number of free electron due to doping is consistent with the change in magnetization of the system. A direct correlation of ferromagnetic order (FM) with F+ centers exchange mechanism is established. The temperature variation of the anisotropic constant was determined using Law of Approach to Saturation (LAS). It was found that effective magnetic anisotropic constant decreases with increase in temperature. The EPR line width of the annealed sample increases with decrease in temperature, whereas the integrated intensity decreases with decrease in temperature. This could be due to incomplete quenching of orbital angular momentum in Si$_{x}$Ni$_{1-x}$C. In addition to this, the orbital degeneracy of fast relaxing impurity such as Ni in the cubic crystal field is not completely removed. This results in the line width decrease with increase in temperature., Comment: We wish to improve upon it and then want to resubmit

Bound Magnetic Polarons (BMP) have been proposed to play an important role in doped wide band gap semiconductors. We report the experimental evidence supporting polaronic magnetism and the role of defects on it. Temperature variation of electron paramagnetic resonance study reveals that the valence state of cobalt is 2+ and its nearest environment in the system is distorted tetrahedral in nature. Room temperature ferromagnetism have been found in all the doped [Co (1, 3, 5) % doped 3C-SiC] samples. The Curie temperature, TC of the samples have been found to be above 800 K. The isothermal magnetization plots, to determine the strength of domain wall pinning were analyzed using the Jiles-Atherton Model. The temperature variation of the anisotropic constant was determined using Law of Approach to saturation (LAS), which decreases with increase in temperature. Quantitative analysis of magnetic interaction has been carried out and the result is explained by using BMP Model, which probably arises out of the exchange interaction of Co2+ ions with related (Si, C) defects., Comment: We wish to improve upon and then resubmit

We report the structural, magnetic, and magnetocaloric properties of Co$_2$Cr$_{1-x}$Ti$_x$Al ($x=$ 0--0.5) Heusler alloys for spintronic and magnetic refrigerator applications. Room temperature X-ray diffraction and neutron diffraction patterns along with Rietveld refinements confirm that the samples are of single phase and possess a cubic structure. Interestingly, magnetic susceptibly measurements indicate a second order phase transition from paramagnetic to ferromagnetic where the Curie temperature (T$_{\rm C}$) of Co$_2$CrAl increases from 330~K to 445~K with Ti substitution. Neutron powder diffraction data of the $x=$ 0 sample across the magnetic phase transition taken in a large temperature range confirm the structural stability and exclude the possibility of antiferromagnetic ordering. The saturation magnetization of the $x=$ 0 sample is found to be 8000~emu/mol (1.45~$\mu_{\rm B}$/{\it f.u.}) at 5~K, which is in good agreement with the value (1.35$\pm$0.05~$\mu_{\rm B}$/{\it f.u.}) obtained from the Rietveld analysis of the neutron powder diffraction pattern measured at temperature of 4~K. By analysing the temperature dependence of the neutron data of the $x=$ 0 sample, we find that the change in the intensity of the most intense Bragg peak (220) is consistent with the magnetization behavior with temperature. Furthermore, an enhancement of change in the magnetic entropy and relative cooling power values has been observed for the $x=$ 0.25 sample. Interestingly, the critical behavior analysis across the second order magnetic phase transition and extracted exponents ($\beta\approx$ 0.496, $\gamma\approx$ 1.348, and $\delta\approx$ 3.71 for the $x=$ 0.25 sample) suggest the presence of long-range ordering, which deviates towards 3D Heisenberg type interactions above T$_{\rm C}$, consistent with the interaction range value $\sigma$., Comment: submitted

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 a clear evidence for AF order in martensitic phase of Ni45Co5Mn38Sn12 alloy and rule out SPM and SG orders. Identical studies on another alloy of close composition of Ni44Co6Mn40Sn10 point to presence of SG order in martensitic phase and absence of SPM behavior, contrary to earlier report. SANS results do show 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., Comment: 33 pages, 13 figures

In this letter, we report the discovery of a new class of spintronic materials, namely spin semi-metals (SSM), employing both theoretical and experimental tools. The band structure of this class of materials is such that one of the spin bands resembles that of a semi-metal, while the other is similar to that of an insulator/semiconductor. This report is the experimental verification of the first SSM, FeRhCrGe, a quaternary Heusler alloy with a magnetic moment 3 $\mu_B$ and a Curie temperature of 550 K. The measurement below 300 K shows nearly temperature independent conductivity and a relatively moderate Hall effect. SSM behavior for FeRhCrGe is also confirmed by rigorous first principles calculations. Band structure calculations also reveal that the spin up (semi metallic) band has combined features of type II Weyl and nodal line semimetal. As such, this study opens up the possibility of a new class of material with combined spintronic and topological properties, which is important both from fundamental and applied point of view., Comment: 7 figures, quaternary Heusler alloys, ferromagnetic materials, spintronics, spin semi-metals, Weyl semimetal, nodal line semimetal

Complex magneto structural behaviour of rare rich intermetallic Tb$_3$Co is reported in this study. Below the 84K (T$_N$), it undergoes a first order magnetic transition 72K confirmed from specific heat and magnetization measurements. Detailed study using magnetization, specific heat, neuron diffraction and ac-susceptibility measurements suggests that the compound in the question possesses canted magnetic structure. Neutron diffraction reveals that Tb moments are aligned antiferromagnetically (AFM) in ab plane and ferromagnetically (FM) along c direction. This study focusses on the temperature evolution of magnetic order at low temperatures. Neutron Diffraction clearly shows that magnetic structure remains more or less same up to 70K although low field magnetization exhibits a transition like feature around 30K. Field dependent neutron diffraction suggests that a strong spin-lattice coupling is present at lower temperature region (below 20K) compared to that for T above 40K. This is responsible for the observed drop in ZFC magnetization around 30K and is not due to any change in magnetic structure. Another important but surprising result that observed is the signature of magnetic glass below 72K in frequency dependent ac susceptibility measurements. Real part of ac-susceptibility data shows dispersion with frequency which on detailed analysis provides evidence for spin glass behaviour in the compound riding on top of non-collinear AFM order. Higher order harmonics in ac non-linear) susceptibilities, which are expected to show a well-defined behaviour for pure FM or AFM or spin glass or cluster glass systems, were also measured. However, the non-linear susceptibilities do not exhibit any well-known variation but show complex behaviour thus indicating Tb$_3$Co is neither a pure AFM or FM or spin glass system but provides another evidence for non-collinear magnetic structure., Comment: 10 pages, 15 figures being submited as regular paper

Novel thermal effects across the first order antiferromagnetic (AFM) - ferromagnetic (FM) transition in an intermetallic alloy are reported. They show instances of warming when heat is extracted from the sample, and cooling when heat is provided to the sample across AFM-FM transition in Ta doped $HfFe_2$, thus providing indisputable evidence of metastable supercooled AFM and superheated FM states, respectively. Such thermal effects in a magnetic solid prepared from commercially available materials has been reported for the first time. The transition proceeds in multiple steps which is interpreted in the framework of quenched disorder broadening of AFM-FM transition and classical nucleation theory. Measurements in the presence of magnetic field conform to above frame work., Comment: 5 pages, 3 figures and 1 Table

In an effort to produce Giant Magnetocaloric effect (GMCE) near room temperature, in a first ever such study, the austenite transformation temperature (As) was fine tuned to ferromagnetic Curie temperature (TC) in Ferromagnetic Shape Memory Alloys (FSMA) and a large GMCE of delta-SM = - 81.75 J/Kg-K was achieved in Ni50Mn18.5Cu6.5Ga25 alloy during reverse martensitic transformation (heating cycle) for a magnetic field change of 9 T at 302.5 K. Fine tuning of As with TC was achieved by Cu substitution in Ni50Mn25-xCuxGa25 (0< x < 7.0)-based FSMAs. Characterizations of these alloys were carried out using Optical and Scanning Electron Microscopy, X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC) and DC magnetization measurements. Addition of Cu to stoichiometric Heusler type Ni2MnGa increases the martensitic transformation temperatures and decreases TC. Concurrently, DSM increases with Cu addition and peaks at 6.5 at. % Cu for which there is a virtual overlap between TC and As. Maximum Refrigerant Capacity (RCP) of 327.01 J/Kg was also achieved in the heating cycle for 9 T field change at 302.5 K. Corresponding values for the cooling cycle measurements (measured during forward transformation) were 30.4 J/Kg-K and 123.52 J/Kg respectively for the same 6.5 at. % Cu sample and same thermo-magnetic conditions., Comment: 32 pages, 10 figures, 4 tables, submitted to Journal of Alloys and Compounds

Specific heat of dipolar glasses does not obey Debye law. It is of interest to know if the non-Debye specific heat can be accounted for in terms of Schottky-type specific heat arising from rotational tunneling states of the dipoles. This paper deals with rotational tunneling spectra of NH$_{4}^{+}$ ions and the non-Debye specific heat of mixed salts (e.g. (NH$_{4})_{x}$Rb$_{1-x}$Br) of ammonium and alkali halides which are known to exhibit dipolar glass phase. We have measured specific heat of above mixed salts at low temperatures (1.5 K $< T <$ 15 K). It is seen that while the specific heat of pure salts obeys Debye law, the specific heat of mixed salts does not obey Debye law. We have studied the effect of the NH$_{4}^{+}$ ion concentration, first neighbor environment of NH$_{4}^{+}$ ion and the lattice strain field on the non-Debye specific heat by carrying out measurements on suitably chosen mixed salts. Independent of above, we have measured the rotational tunneling spectra, $f(\omega $), of the NH$_{4}^{+}$ ions in above salts using technique of neutron incoherent inelastic scattering. The above studies show that both the non-Debye specific heat and the tunneling spectra of the NH$_{4}^{+}$ ions depend on the NH$_{4}^{+}$ ion concentration, first neighbor environment of NH$_{4}^{+}$ ions and the lattice strain field. We have further shown that the temperature dependence of the measured specific heat can be explained for all the samples in terms of a model that takes account of contributions to the specific heat from the Debye phonons and the rotational tunneling states of the NH$_{4}^{+}$ ions. To the best of our knowledge, this is a first study where it is shown that measured specific heat of (NH$_{4})_{x}$Rb$_{1-x}$Br can be quantitatively explained in terms of an experimentally measured rotational tunneling spectra $f(\omega $) of the NH$_{4}^{+}$ ions., Comment: 10 pages, 7 figures

Neutron diffraction measurements, performed in 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 a glass-like arrested state (GLAS). The CHUF (cooling and heating under unequal fields) protocol has been used to establish phase coexistence of metastable and equilibrium states of GLAS and also to demonstrate the devitrification of the arrested metastable states in the neutron diffraction patterns. We also explore the field-temperature (H,T) phase diagram for the two compounds, which depicts the kinetic arrest line TK(H). TK is seen to increase as H increases., Comment: This submission adds considerable amount of data on a new material to arXiv:1211.0238, and has been accepted as a regular paper in Journal of Physics: Condensed Matter

The structural properties of the CaFe2As2 have been investigated by x-ray and neutron powder diffraction techniques as a function of temperature. Unambiguous experimental evidence is shown for coexistence of tetragonal and orthorhombic phases below 170 K in contrast to existing literature. Detailed Rietveld analyses of thermo-diffractograms show that the sample does not transform completely in to the orthorhombic phase at the lowest temperature even though it is the majority phase. We have found that the unit cell volume of the orthorhombic phase is higher compared to that of the tetragonal phase for all the temperatures. X-ray data on CaFe2As2 shows anomalous (at) lattice parameter contraction with increasing temperature and phase co-existence behavior below 170 K unlike other members of the 122 family of compounds like SrFe2As2 and EuFe2As2. Temperature dependent magnetization of polycrystalline CaFe2As2 sample show weak anomalies below 170 K. This behavior of the polycrystalline sample is in contrast to that of a single crystal reported earlier., Comment: 15 pages, 8 figures

Neutron diffraction measurements, performed in presence of an external magnetic field, have been used to show structural evidence for the kinetic arrest of the first-order phase transition from the high temperature austenite phase to the low temperature martensite phase in the magnetic shape memory alloy Ni37Co11Mn42.5Sn9.5 and the formation of a glass-like arrested state (GLAS). The CHUF (cooling and heating under unequal fields) protocol has been used to establish phase coexistence of metastable and equilibrium states of GLAS in the neutron diffraction patterns. We also explore the field-temperature (H,T) phase diagram for this composition which depicts the kinetic arrest line TK(H). TK is seen to increase as H increases., Comment: 17 pages, 10 figures, Synopsis of MI-1 Seminar at Helmholtz Zentrum Berlin, November 7, 2012

Magnetic behavior of the pseudo-binary alloy $Hf_{1-x}Ta_xFe_2$ has been studied, for which the zero field ferromagnetic (FM) to antiferromagnetic (AFM) transition temperature is tuned near to T=0 K. These alloys show anomalous thermomagnetic irreversibility at low temperature due to kinetic arrest of the first order AFM-FM transition. All the three studied compositions show re-entrant transition in zero field cooled warming curve and anomalous non-monotonic variation of upper critical field in isothermal magnetization. The region in H-T space, where these features of kinetic arrest manifest themselves, increases with increasing Ta concentration., Comment: Data is relevant to coupling of latent heat to thermal conduction criterion for Glass formation (arXiv:1004.3116)