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The effects of annealing process and chemical pressure on the structural and magnetocaloric properties of CoMn1-xVxGe (x=0.05 and 0.10) alloys have been studied. Rietveld refinement of XRD patterns revealed that all samples are single phase and they crystallize in hexagonal structure with a space group (P6(3)/mmc) at room temperature. The structural phase transition temperature T-struct decreases with increasing vanadium (V) content drastically in compare to CoMnGe alloy which exhibit a first order structural transition at around 450 K. The decrease in T-struct. by substituting fourth element in CoMnGebased alloys are discussed in frame of changing its valence electron concentration (e/a) values. We found that, alloys exhibiting a first order magneto-structural transition (FOMT) around room temperature, have an e/a value of 6.62-6.67. The e/a dependence of the magnetostructural transition temperature can be used as a guide to obtain an alloy with FOMT around room temperature. (C) 2019 Elsevier B.V. All rights reserved.

We have studied the magnetic properties and magnetocaloric effect of ball milled CoMn0.95V0.05Ge alloy by means of temperature and field dependence of magnetisation measurements. CoMn0.95V0.05Ge nano-powders with different particle size distribution were prepared by varying the milling time for 4, 6 and 8 h. The atomic force microscopy (AFM) images showed that the average size of the particles decreases with increased milling time as expected. The nature of the magnetic phase transition has been determined by using Arrott plots, rescaled magnetic entropy change and power exponents of Δ S M . We found that the nature of the magnetic transition for nano powders has a second order nature, although their bulk counterpart with same composition exhibits a first order magnetostructural phase transition. The observed maximum magnetic entropy change for nano powders is, therefore, slightly lower than that of their bulk counterparts. However a 50 % increasing of relative cooling power for nano-powders is achieved. These results suggest that CoMn0.95V0.05Ge nano-powders could be a suitable candidate as working substance for magnetic cooling technology around room temperature.

The structural, electronic, and magnetic features of Co2Mn1−xAlxTi (0 ≤ x ≤ 0.6) Heusler alloys (HAs) have been systematically investigated by experimental techniques (X-ray powder diffraction, scanning electron microscopy, and magnetization measurements) and ab initio theoretical calculations. Whole alloys have cubic structures at room temperature and exhibit ferromagnetic properties. The Curie temperature of Co2Mn1−xAlxTi (x = 0) is approximately 790 K, which is compatible with other studies. By increasing Al content, the temperature dependence of magnetization trials has proved a linear diminishment on Curie temperature and saturation magnetization.

The effect of heat treatment on the structural, magnetic and magnetocaloric properties of Ni43Mn46In11 melt-spun ribbons was systematically investigated using X-ray powder diffraction (XRD), scanni...

The effect of Cu substitution on the martensitic transition and magnetocaloric properties of arc-melted Ni 50−x Cu x Mn 39 Sn 11 (x = 6 and 7) Heusler alloys are investigated by differential scanning calorimetry, X-ray powder diffraction, scanning electron microscopy and magnetic measurements. According to XRD patterns, while Ni 44 Cu 6 Mn 39 Sn 11 alloy exhibit orthorhombic structure, Ni 43 Cu 7 Mn 39 Sn 11 alloy crystallize cubic L2 1 structure at room temperature. The substitution of Cu for Ni leads to decreasing on the martensitic transition temperatures to lower values. The magnetic entropy changes calculated from M(T) curves, for avoiding hysteresis losses in the vicinity of the martensitic transition region, by using Maxwell relation. The maximum magnetic entropy change, Δ S M is found 11.0 J kg −1 K −1 for Ni 43 Cu 7 Mn 39 Sn 11 alloy around the martensitic transition region, which is nearly twice as large as the Ni 44 Cu 6 Mn 39 Sn 11 alloy under the magnetic field changing from 0 to 2 T.

The effects of Ti substitution for Mn and heat treatment on structural, magnetic, and magnetocaloric properties of CoMnGe alloy have been investigated using electron microscopy, X-ray diffraction, calorimetric, and magnetic measurements. According to X-ray diffraction measurements, CoMn1−x Ti x Ge alloys are in a single phase hexagonal structure at room temperature. It is found that the as-cast CoMn0.95Ti0.05Ge alloy shows a magnetostructural phase transition close to room temperature. The transition shows a large magnetic entropy change and a small hysteresis in the isothermal magnetic field-dependent magnetization measurements. After annealing, the phase transition temperature decreases slightly and the magnetization is sharply decreasing at Curie temperature. The sharp change of magnetization at phase transition temperature is accompanied by a significant increase in the magnetic entropy change, i.e., magnetic entropy change value for the magnetic field change of 1 T was increased from −3.3 to −6.3 J kg−1 K−1. Moreover, after annealing, hysteresis losses reduced significantly for ∆H = 7 T. Accordingly, the heat treatment has a significant effect on magnetocaloric properties of the CoMn0.95Ti0.05Ge alloy.

This paper presents the role of the conventional and Soliton wave model deposition at low substrate temperature (300–100 K) on the structural, electric and magnetic properties of Co35Fe65 thin films deposited by thermal evaporation using bulk polycrystalline Co35Fe65 alloy. On account of obtaining superior quality magnetic thin films without any high temperature growth processes or heat treatment, the Soliton wave growth model at suitable low temperature range is used. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques are employed to investigate the various structural properties. Morphological and structural analyses of entire 30 nm Co35Fe65 thin films deposited on Si (100) substrate reveal that the stoichiometry is preserved over the whole temperature deposition and BCC crystalline formed with (110) texture. To attain the electrical and magnetic properties, resistivity and vibrating-sample magnetometer (VSM) measurements are evaluated. Soliton wave model deposition significantly increased magnetic anisotropy constant K1 = 0.105 Merg/cm3, MR/MS = 0.83 and coercivity HC = 272 Oe at 300 K when the compared to conventional deposition range in this work (K1 = 0.014 Merg/cm3, MR/MS = 0.6 and HC = 50 Oe). Growth with novel approach of Co35Fe65 thin films highlights the reasonable low coercivity, the high saturation magnetization, the high magnetic anisotropy and the low electrical resistivity values, with tailored grain size, make them feasible to use in magnetic sensor technology in the near future.

In this work, we have studied on double-layered perovskite (Ruddlesden–Popper) manganite structure in Pr1.75Sr1.25Mn2O7 synthesised by sol–gel method. The crystal structure of the double-layered perovskite is found as tetragonal from the X-ray diffraction analysis with I4/mmm space group. A high Curie temperature, TC= 305 K is observed from the temperature dependence of magnetisation measurement. The isothermal magnetisation curves showed that magnetic phase transition is second order due to the positive slope of the Arrott plots. Maximum magnetic entropy change (?SM) and adiabatic temperature change (?Tad) values are calculated as 3.99 J kg-1 K-1 and 2.1 K under external magnetic field of 70 kOe, respectively. Since our double-layered perovskite manganite sample has desired TC value and relatively high ?SM, it can be a potential candidate as a magnetocaloric material for room temperature magnetic cooling systems. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

The magnetic and magnetocaloric properties of CoMn 0.9 Fe 0.1 Ge alloy has been investigated by using of electron microscopy, X-ray diffraction, calorimetric, heat capacity and magnetic measurements. The substitution of Fe atoms for Mn atoms in the CoMnGe system leads to a decrease in the martensitic transition temperature from 650 K to room temperature (RT) and presents the magnetostructural properties in vicinity of RT. In order to assess MCE, temperature dependent of magnetization measurements have performed under applying variable magnetic fields. The largest entropy change values are −34.9 J kg−1 K−1 (magnetization) and −33.6 J kg−1 K −1 (demagnetization) for Δ H = 5 T . The adiabatic temperature change value of CoMn 0.9 Fe 0.1 Ge is calculated 8.5 K for 2 T from magnetic and heat capacity measurements. The density of states of electrons at Fermi level and the Debye temperature values of this alloy are found 1.19 states eV−1 atom−1 and 353 K from low temperature heat capacity measurements. This giant magnetocaloric effect makes this material a very promising candidate for future RT cooling applications.

The effect of number of arachidic acid (AA) Langmuir layers and pH values on morphology and local electrical properties of polycrystalline cadmium sulphide (CdS) film was investigated by atomic force microscopy, electric force microscopy (EFM) and scanning Kelvin probe microscopy (SKPM). Atomic force microscopy (AFM) surface analysis showed the polycrystalline relief of CdS surface with the roughness value about 8.5 +/- 0.3 nm and the drastic increases up to 25 +/- 0.9 nm for semiconductor surface modified by 1, 3 and 5 AA Langmuir layers at both pH value (pH 3.6 and 8.6). Surface potential (SP) values were estimated by EFM method and showed the same sequence of changes and were equal to -1 V for CdS film and to 2.4 V and 3.5 V for 3 AA layers at pH 3.6 and 8.6, respectively. SP of 1 and 5 AA Langmuir layers was about 2 V at both pH values. Furthermore, the electrical characteristics and parameters of samples calculated by EFM quantitative method were compared with SKPM method. EFM analysis showed more pronounced SP value changes than SKPM measuring, due to mathematical value processing of the established Coulomb interaction between the probe and the sample surface.

In this study, magnetic and electromagnetic energy conversion of magnetocaloric materials (MCMs) and magnetic refrigeration, which is based on magnetocaloric effect (MCE), is presented in detail and made apprehensible. The MCE is defined as cooling or warming occurring in the magnetic material under adiabatic conditions when the external magnetic field is applied or removed from the magnetic material and vice versa. This result has been known as “adiabatic demagnetization” for years, though this phenomenon is a practical use of the MCE in magnetic materials. The magnetic materials demonstrate the MCE in the vicinity of their critical temperature. The magnetocaloric system is environmentally friendly and more efficient than conventional refrigeration cycle system based on vapor compression. Magnetic refrigeration is a cooling technology based on the MCE. This technique can be used to attain low temperatures, as well as the ranges used in common refrigerators. In magnetic and electromagnetic energy conversion, the coefficient of the performance (COP) for the system reaches 30–60% theoretical efficiency of the Carnot cycle. Magnetic refrigeration is being pursued using low magnetic fields near room temperature in hopes of enabling commercial devices using permanent magnets as the field source.

It was shown that the complex research of iron nanoparticles properties by different methods, supplemented each other, permit to receive the data about the interior sizes of nanoparticles, a number of physical properties of particles, their dependence on frequency and changes produced by various influences. It was found that the conductivity of nanoparticles changed under the square depen-dence σ = σoω2

The influence of Cu substitution for Mn on magnetic and magnetocaloric properties has been investigated in Ni 50 Mn 34− x Cu x In 16 ( x =1.3 and 1.6) Heusler alloys by using calorimetric and magnetic measurements. The temperature dependent magnetization measurements and calorimetric studies indicate that martensitic transition temperatures shift to higher temperatures with increasing valence electron concentrations, e / a . The isothermal magnetization curves around the martensitic transition temperatures show a typical metamagnetic behavior. Associated with that, large positive values of magnetic entropy changes around structural transition region were determined by using the Maxwell and Clausius–Clapeyron relations. The maximum magnetic entropy change values were found to be 25.2 and 5.7 J kg −1 K −1 for Ni 50 Mn 34− x Cu x In 16 ( x =1.3 and 1.6) alloys by Maxwell relation in a magnetic field change of 2 T. In order to understand the limit can be reached for, the magnetic entropy change values recalculated by Clausius–Clapeyron relation. Obtained maximum entropy change values are 22.8 and 16.3 J kg −1 K −1 for Ni 50 Mn 34− x Cu x In 16 ( x =1.3 and 1.6) alloys by Clausius–Clapeyron relation.

The magnetic and magnetocaloric properties of CoMnGe1−xGax (0.02 ⩽ x ⩽ 0.063) alloys have been investigated by using calorimetric, X-ray diffraction and magnetic measurements. Our results show that the structural and magnetic phase transitions in CoMnGe1−xGax alloys are tailored by the substitution of Ga for Ge. The CoMnGe1−xGax (x = 0.05, 0.055 and 0.06) alloys exhibit a giant magnetocaloric effect due to coexistence of magnetic and Martensitic phase transitions at the same temperatures. The entropy change values range from −3.2 to −38.4 J kg−1 K−1 for Δ H = 7 T and are proportional to the volume differences of the phases involved in the transition. The adiabatic temperature change value of CoMnGe0.945Ga0.055 is calculated as 6.5 K for the magnetic field change of 2 T from magnetic and heat capacity measurements. The density of states of electrons at Fermi level and the Debye temperature values of this alloy are found 1.37 states eV−1 atom−1 and 337 K from low temperature heat capacity measurements.

The magnetostructural and magnetocaloric properties of CoMnGe 1 − x Ga x B 0.015 ( x =0.05 and 0.06 are named Alloy-1 and Alloy-2, respectively) alloys have been investigated by X-ray powder diffraction, calorimetric and magnetization measurements. Both alloys have hexagonal structures at room temperature and show first order phase transition below room temperature. The entropy change- Δ S of these alloys are calculated as −22.1 J kg −1 K −1 (for Alloy-1 alloy) and −27.1 J kg −1 K −1 (for Alloy-2 alloy) under Δ H = 7 T . Magnetic hysteresis losses of these alloys are very small when compared with the undoped alloy. Considering the high magnetocaloric effect and low magnetic hysteresis features, boron doping on CoMnGe family alloys provides an alternative method to tailor magnetic and magnetocaloric properties.

The magnetic properties of La1-xNdxMn2Si2 (x = 0.30-0.45) compounds are studied over the temperature range 5 K

We report the preparation and characterization of spherical core-shell structured Fe3O4-Au magnetic nanoparticles, modified with two component self-assembled monolayers (SAMs) consisting of 3-mercaptophenylboronic acid (3-MBA) and 1-decanethiol (1-DT). The rapid and room temperature synthesis of magnetic nanoparticles was achieved using the hydroxylamine reduction of HAuCl4 on the surface of ethylenediaminetetraacetic acid (EDTA)-immobilized iron (magnetite Fe3O4) nanoparticles in the presence of an aqueous solution of hexadecyltrimetylammonium bromide (CTAB) as a dispersant. The reduction of gold on the surface of Fe3O4 nanoparticles exhibits a uniform, highly stable, and narrow particle size distribution of Fe3O4-Au nanoparticles with an average diameter of 9 +/- 2 nm. The saturation magnetization value for the resulting nanoparticles was found to be 15 emu/g at 298 K. Subsequent surface modification with SAMs against glucoside moieties on the surface of bacteria provided effective magnetic separation. Comparison of the bacteria capturing efficiency, by means of different molecular recognition agents 3-MBA, 1-DT and the mixed monolayer of 3-MBA and 1-DT was presented. The best capturing efficiency of E. coli was achieved with the mixed monolayer of 3-MBA and 1-DT-modified nanoparticles. Molecular specificity and selectivity were also demonstrated by comparing the surface-enhanced Raman scattering (SERS) spectrum of E. coli-nanoparticle conjugates with bacterial growth media.

Structural, magnetic and magnetocaloric properties of arc-melted polycrystalline Ni43Mn46 xAlxIn11 (x = 0, 0.5 and 1.0) alloys have been investigated by X-ray powder diffraction, scanning electron microscope and magnetic measurements. It is found that all investigated alloys undergo a first-order structural phase transition from austenite (cubic) to martensite (tetragonal) structure on cooling. According to temperature dependent magnetization measurements, the martensitic and magnetic phase transition temperatures decrease by substituting small amounts of Al for Mn in Ni43Mn46In11 alloy. Inverse magnetic entropy changes and relative cooling power (RCP) values are found 5.10, 9.63, 11.42 J kg (1) K (1) and 57.4, 60.67, 65.04 J kg (1) for x = 0, 0.5 and 1.0 alloys for a magnetic field change of 2 T, respectively. (C) 2017 Elsevier B.V. All rights reserved.

The effect of Cu alloying on the structural, magnetic, and magnetocaloric properties of the Mn-rich Ni43Mn46−x Cu x In11 (x = 0, 0.9, 1.3 and 2.3) alloys was investigated with scanning electron microscopy, X-ray powder diffraction (XRD), and magnetization measurements. The substitution of Cu for Mn efficiently reduces the structural and magnetic transition temperatures of the Ni43Mn46In11 alloy. As a result, while the XRD pattern of the Ni43Mn46In11 alloy shows only tetragonal structure, the structures of Cu-doped alloys consist of both cubic and tetragonal phases at room temperature. The positive magnetic entropy changes (ΔS M) in the alloys were determined from the magnetic field-dependent magnetization measurements-M(H) using the Maxwell relation. Around the structural transition region, a maximum ΔS M was found 21.08 J kg−1 K−1 for the Ni43Mn46−x Cu x In11 (x = 2.3) alloy in a magnetic field change of 18 kOe.

Magnetocaloric and magnetoresistance properties of SmMn2−xFexGe2 (x=0.05 and 0.10) and SmMn2−xCoxGe2 (x=0.05 and 0.15) compounds have been studied by magnetic and resistance measurements in the temperature range between 30 and 350 K. All compounds exhibit metamagnetic transition from antiferromagnetism to ferromagnetism around the Sm moments ferromagnetic ordering temperature-TSm and Mn moments antiferromagnetic ordering temperature-TN1. The magnetic entropy changes of these compounds are estimated from the Maxwell equation, Maxwell Clausius Clapeyron equation, Landau theory and mean-field theory. The maximum magnetic entropy change values of SmMn1.90Fe0.10Ge2 and SmMn1.85Co0.15Ge2 compounds are −8.1 J kg−1 K−1 and −5.1 J kg−1 K−1 in a magnetic field change of 5 T, respectively. These compounds show negative magnetoresistance around the magnetic phase transition temperatures. The magnetoresistance value of SmMn1.95Fe0.05Ge2 is −23% at TSm which is bigger than the magnetoresistance value of SmMn2Ge2 (−15%).

We study magnetothermal properties of the La0.775Gd0.225Mn2Si2 compound. The magnetic contribution to the heat capacity is estimated by zero-field and 0.5 T magnetic field data. According to Arrott plot, the La0.775Gd0.225Mn2Si2 has a second order transition at a Curie temperature (TC) and a first order transition at a lower temperature. The λ-type peak in the heat capacity data also confirms the second order transition at the Curie temperature. We determined the electronic, magnetic and lattice contributions to the heat capacity. In addition, Debye temperature and N(EF) are estimated by heat capacity data as a function of temperature under zero and 0.5 T magnetic field.

Evolution of magnetocaloric effect (MCE) of nanostructured CoMnGe0.95Ga0.05 powders has been investigated by electron microscopy (SEM), X-ray powder diffraction (XRD), thermal (DSC) and magnetization measurements. The nanostructured powders are composed of very fine grains (7 +/- 2 and 35 +/- 2 nm) obtained from Rietveld refinements. The nanostructured powders show the unique ferromagnetic martensite-paramagnetic austenite transition around the room temperature like the bulk alloy. Furthermore, while the martensitic transition occurs in narrow temperature for bulk alloy, it occurs in broad temperature range for the nanostructured powders. The isothermal magnetic entropy change values -Delta S-M are estimated from the isothermal magnetization curves. The maximum Delta S-M values of 5 h milled nanopowders are -7.2 and -21.5 J kg(-1) K-1 for a magnetic field change of 2 and 7 T, respectively. The magnitudes of the MCE, magnetic and thermal hysteresis values of nanostructured powders are smaller than those of bulk alloy. Our findings offer the nanostructured CoMnGe0.95Ga0.05 powders for the promising applications in magnetic refrigeration. (C) 2012 Elsevier B. V. All rights reserved.

The structure,magnetic and magnetocaloric properties of the Ge-rich Gd5Ge2.05-xSi1.95-xMn2x (x=0.01 and 0.03) alloys were investigated by scanning electron microscopy,X-ray powder diffraction,differential scanning calorimeter (DSC) and magnetization measurements.The results of energy dispersive X-ray analysis (EDX) and X-ray diffraction analyses showed that the composition and crystal structure of the alloys were desired.DSC measurements were performed to determine the transformation temperatures for each alloy.Both alloys exhibited the first order phase transition around room temperature.The alloys showed an anti-ferromagnetic transition around 60 K.The isothermal magnetic entropy changes of the alloys were determined from the isothermal magnetization measurements by using the Maxwell relation.The maximum values of isothermal magnetic entropy change of the Gd5Ge2.05-xSi1.95-xMn2x alloy with x=0.01 was found to be -12.1 and -19.8 J/(kg·K) using Maxwell equation around 268 K in applied fields of 2 and 5 T,respectively.

The magnetic structures of the La 0.65 Nd 0.35 Mn 2 Si 2 have been investigated by powder neutron diffraction between 5 and 350 K. According to magnetic measurements this compound shows multiple magnetic phase transitions. Neutron diffraction indicates a canted ferromagnetic structure above 220 and below 46 K. Between 50 ≤ T ≤ 70 K there is a mixed phase where canted ferromagnetic and antiferromagnetic structure coexist. Moreover, La 0.65 Nd 0.35 Mn 2 Si 2 has a two-step magnetic transition from an antiferromagnetic to ferromagnetic state between 65 and 22 K. This two-step transition had not been observed so far and in this study it is studied in depth.

The thermal and magnetothermal properties of La0.5Pr0.5Mn2Si2 and isostructural LaFe2Si2 intermetallic compounds in the temperature range 4.5–303 K are reported with and without applied magnetic field. The electronic, lattice, and magnetic contributions to the heat capacity of La0.5Pr0.5Mn2Si2 are determined and analyzed. We have determined T C i n t e r and T N i n t e r from heat capacity experiments; the values are in line with those from the magnetization measurements. We conclude that in order to observe the anomaly in the heat capacity data around T N i n t e r in the R 1 − x R x ′ Mn 2 Si 2 system, the transition around T N i n t e r should occur in a narrow temperature interval.

The preparation and application of rod-shaped core-shell structured Fe(3)O(4)-Au nanoparticles for immunomagnetic separation and sensing were described for the first time with this study. To synthesize magnetic gold nanorod particles, the seed-mediated synthetic method was carried out and the resulting nanoparticles were characterized with transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV-Vis), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD). Magnetic properties of the nanoparticles were also examined. Characterization of the magnetic gold nanorod particles has proven that the resulting nanoparticles were composed of Fe(3)O(4) core and the gold shell. The rod-shaped gold-coated iron nanoparticles have an average diameter of 16 +/- A 2 nm and an average length of about 50 +/- A 5 nm (corresponding aspect ratio of 3). The saturation magnetization value for the magnetic gold nanorod particles was found to be 37 emu/g at 300 K. Rapid and room temperature reaction synthesis of magnetic gold nanorod particles and subsequent surface modification with E. coli antibodies provide immunomagnetic separation and SERS application. The analytical performance of the SERS-based homogenous sandwich immunoassay system with respect to linear range, detection limit, and response time is also presented.

The effect of the substitution of Cu for Ni on the magnetoresistance behaviour and the magnetocaloric properties of the Ni 50 Mn 34 In 16 alloy has been investigated. The (Ni–Cu) 50 Mn 34 In 16 alloys crystallize in the cubic L2 1 structure in austenite phase. While the M s temperature is about 160 K for the Ni 47.5 Cu 2.6 Mn 34.0 In 15.9 alloy, the martensitic transition is not observed for Ni 45.5 Cu 4.6 Mn 33.8 In 16.1 alloy. To estimate the magnetic entropy change of the Ni 47.5 Cu 2.6 Mn 34.0 In 15.9 alloy, the magnetization measurements as function of magnetic field are performed by continuous and noncontinuous heating methods. The Ni 47.5 Cu 2.6 Mn 34.0 In 15.9 alloy shows the magnetostructural transition whose irreversible ratio is about 50% at 160 K. The magnetocaloric effect strongly depends on the sample history due to the occurrence of the irreversible magnetostructural transition. For the magnetic field change of 2 T, giant magnetoresistance value is about −68% that is rather big among the similar bulk alloys.

The influence of the manganese-alloying on the structure and magnetocaloric properties of the Gd5Si2.05Ge1.95 compound was studied by X-ray powder diffraction and magnetization measurements. The Gd5Si2.05–xGe1.95–xMn2x (2x=0, 0.03 and 0.08) compounds crystallized in the Gd5Si2Ge2-type monoclinic structure. In all X-ray powder diffraction patterns, a minor hexagonal Gd5Si3 phase was observed as a second phase. With increasing Mn content, the unit cell volume increased. For the compounds with x=0, 0.03 and 0.08, the first order phase transition was observed. The maximum isothermal magnetic entropy change of the Gd5Si2.05–xGe1.95–xMn2x compound with 2x=0.03 at 275 K was found to be −11.6 J/(kg·K) in an applied field of 5 T.

Nanocrystalline LaMn 2 Si 2 powders have been obtained by high-energy ball milling for 30 min from bulk alloys. After milling a high coercivity about 6 kOe is observed at 10 K in contrast to neglectable coercivity for the bulk LaMn 2 Si 2 at 5 K. The average grain size of the optimum particles which is obtained from X-ray diffraction pattern and HRTEM picture is about 20 nm. The magnetic hardening is observed for the nanocrystalline LaMn 2 Si 2, reflected in the coercivity field strength of 6 kOe at 10 K.

CeMn2Ge2 nanopowders have been obtained by high-energy ball milling for 5 and 10 hours from bulk compound to investigate the effect of milling time on magnetic and magnetocaloric properties. CeMn2Ge2 nanopowders have been characterized by X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy, transmission electron microscopy, and magnetization measurements. The average grain size of the nanoparticles from XRD measurements is about 12.2 and 8 nm for 5-hour and 10-hour ball-milled samples, respectively. The investigations reveal that magnetic entropy change (∆S m) can be altered by changing the particle size of the compound. Maximum ∆S m is −2.45 and −1.30 J kg−1 K−1 for the 5- and 10-hour ball-milled nanopowders, respectively.

We have studied the effects of Co substitution for Mn on the structure and magnetic properties of the HoMn 6− x Co x Sn 6 compounds (0⩽ x ⩽0.25) with HfFe 6 Ge 6 -type structure (space group P6/mmm) by X-ray powder diffraction and magnetization measurements. A monotonic decrease of the lattice parameters a and c is observed with increasing Co content. While the compounds with x =0 and 0.05 exhibit ferrimagnetism in the whole temperature range, the compounds with 0.1⩽ x ⩽0.15 show ferrimagnetism, helimagnetism and re-entrant ferrimagnetism with decreasing temperature. For the compounds with x =0 and 0.05, the spin reorientation temperature is observed. A metamagnetic transition from helimagnetic magnetic ordering to ferrimagnetism is observed for the compounds with x =0.1 and 0.2. The results are summarized in the HoMn 6− x Co x Sn 6 magnetic phase diagram.

The magnetic structures of the La 1 - x Pr x Mn 2 Si 2 ( x = 0.4 , 0.7 and 1) have been investigated by powder neutron diffraction between 2 and 308 K. According to magnetic measurements, the x = 0.4 sample shows a typical SmMn 2 Ge 2 -like magnetic behavior. Neutron diffraction indicates a canted antiferromagnetic structure below 130 K and a canted ferromagnetic structure above 240 K. Between 130 and 240 K, the canted ferromagnetic and antiferromagnetic structures coexist. Since the magnetic moments of Mn atoms, the unit cell parameters and the scale parameters of the canted antiferromagnetism and canted ferromagnetism are highly correlated between 130 and 240 K, a special refinement procedure was introduced. The critical Mn–Mn value was determined as 2.87 A ˚ , and the spontaneous volume change and linear magnetostriction are derived. Neutron diffraction revealed a canted antiferromagnetic structure for La 0.3 Pr 0.7 Mn 2 Si 2 . A canted antiferromagnetic structure was also detected for PrMn 2 Si 2 by neutron diffraction in contrast to previous reports of a collinear arrangement. The present results are compiled together with previous ones on RMn 2 Ge 2 and RMn 2 Si 2 (R: Y, La and rare-earth) compounds in two magnetic phase diagrams. These two graphics summarize the general magnetic behavior of Mn in the RMn 2 Ge 2 and RMn 2 Si 2 compounds.

We have investigated the magnetic properties of R x R 1 - x ′ Mn 2 X 2 (X: Si, Ge) for various combinations of rare-earth elements R and R ′ by examining the evolution of the features in the temperature dependence of the low-field magnetization. By making use of the known magnetic structure of the parent compositions x = 0 and 1, the results of low-field magnetization measurements are interpreted for intermediate compositions to give information on their magnetic structure. We find antiferromagnetic–ferromagnetic (AF–FM) transitions, whereby the transition can be sharp or evolve over a considerable temperature range. We examine the magnetic transition temperatures as a function of the tetragonal unit cell parameter a and find that the critical spacings associated with interlayer AF–FM transitions are different in the silicides and germanides.

In the ongoing search for magnetocaloric materials, Heusler compound based ferromagnetic shape memory alloys (FSMA) of the system Ni-Mn-Z (Z=Sb, Ga, In, Sn) turned out to be very promising due to low cost of the containing elements and sizable magnetocaloric effects (MCE).[1] Substitution of Ni against Co in Ni-Mn-Z is known to improve the metamagnetic behavior of the martensitic transition, and thus the magnetocaloric properties as it increases the austenite Curie temperature T C A and leads to a transition from weak magnetic martensite to ferromagnetic austenite. Off-stoi-chiometric Ni-Mn-Al also shows a martensitic transition but accompanied by only small changes in the magnetization and hence neglectable MCE.[2] Substitution of up to 10at.% Co for Ni strongly promotes the ferromagnetism in the austenite phase and leads to a metamagnetic martensitic transition.[3] The magnetization difference between austenite and martensite enables magnetic field induced reverse transition together with an inverse magnetocaloric effect.[4,5]

The magnetic properties of Ce 1−xTbxMn2Ge2 ( 0 ⩽ x ⩽ 1 ) were investigated by means of field-cooled and zero-field-cooled magnetization measurements in the temperature range 5 K ⩽ T ⩽ 600 K . Earlier neutron diffraction experiments showed that Tb orders below 100 K while Ce does not order at any temperature. The substitution of Tb for Ce leads to a linear decrease in the lattice constants, and the magnetic interactions in the Mn sublattice cross over from a ferromagnetic character to an antiferromagnetic one. At low temperatures, the Tb sublattice also orders and reconfigures the ordering in the Mn sublattice. The results are collected in a phase diagram.

The structure and magnetic properties of Nd 1− x Er x Mn 2 Ge 2 (0.0⩽ x ⩽1) were studied by X-ray powder diffraction and magnetization measurements. All compounds crystallize in the ThCr 2 Si 2 -type structure with space group I 4/ mmm . Substitution of Er for Nd led to a linear decrease in the lattice constants and the unit cell volume. Increasing substitution of Er for Nd in NdMn 2 Ge 2 shows a depression of ferromagnetic ordering and the gradual development of antiferromagnetic ordering. A typical SmMn 2 Ge 2 -like behaviour is observed for the x =0.4 sample. The results are summarized in α preliminary magnetic phase diagram.

Two series of epitaxial Ni-Mn-Sn thin films of different thickness are investigated for the thickness and composition dependence of the martensitic transformation. Thin films ranging in thickness from 20 to 200 nm (series A) and 10 to 100 nm (series B) were prepared by magnetron co-sputtering and deposited on heated MgO(001) substrates. The structural characterization was done by temperature-dependent X-ray diffraction measurements. Magnetization and resistivity measurements were performed to investigate the transformation characteristics. We find a strong influence of the film thickness on the relative amount of material undergoing the martensitic transformation, the temperature range of the transformation, and the transformation temperatures. The main contribution originates from the rigid substrate which delays the transformation of the Ni-Mn-Sn near the interface and even leads to a layer of residual austenite at low temperatures. Another issue are size effects which presumably broaden the martensitic transformation and decrease the transformation temperatures. By variation of the thin film composition we find changes of the substrate influence due to a different mismatch between the lattice of MgO and austenite. A better phase compatibility between martensite and austenite, denoted by lambda(2), not only results in a smaller hysteresis but is also beneficial for the transformation of material close to the substrate. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

We have systemically studied the effects of annealing temperature and alloy composition on the structural and magnetic properties of bulk Ni$_{2}$MnGe and Ni$_{2.1}$Mn$_{0.9}$Ge Heusler alloys. We have observed that both annealing temperature and the alloy composition drastically alter the phases found in the samples due to the presence of competing ternary phases. Annealing at 900 and 950 $^{\circ}$C for both alloy compositions facilitate the formation of L2$_{1}$ Heusler phase. Nevertheless, formation of Ni$_{5}$Mn$_{4}$Ge$_{3}$ and Ni$_{16}$Mn$_{6}$Ge$_{7}$ phases cannot be prevented for Ni$_{2}$MnGe and Ni$_{2.1}$Mn$_{0.9}$Ge alloys, respectively. In order to estimate the magnetic contribution of the Ni$_{5}$Mn$_{4}$Ge$_{3}$ impurity phase to that of the parent Ni$_{2}$MnGe, we have also synthesized pure Ni$_{5}$Mn$_{4}$Ge$_{3}$ alloy. Antiferromagnetic nature of Ni$_{5}$Mn$_{4}$Ge$_{3}$ with low magnetization response allows us to reveal the magnetic response of the stoichiometric bulk Ni$_{2}$MnGe. Bulk Ni$_{2}$MnGe shows simple ferromagnetic behavior with a Curie temperature of 300 K, in agreement with the previous results on thin films. Despite the divergence of magnetization curves between field cooled (FC) and field heated (FH) modes, stoichiometric Ni$_{2}$MnGe alloy does not undergo a martensitic phase transition based on our variable temperature x-ray diffraction experiments., Comment: 6 pages, 9 figures; to appear in Journal of Alloys and compounds

The structural and magnetic properties of PrMn 2− x Cr x Ge 2 (0⩽ x ⩽1.0) were studied by X-ray diffraction and magnetization measurements. The powder samples crystallize in the ThCr 2 Si 2 -type structure, and the lattice constants at room temperature show almost no variation as Cr substitutes Mn. The observed phase transitions are summarized in a proposed magnetic x − T phase diagram and compared with previous Moessbauer spectroscopy and neutron diffraction results for x =0.

The structural, magnetic, and magnetocaloric properties of epitaxial Ni-Co-Mn-Al thin films with different compositions have been studied. The films were deposited on MgO(001) substrates by co-sputtering on heated substrates. All films show a martensitic transformation, where the transformation temperatures are strongly dependent on the composition. The structure of the martensite phase is shown to be 14M. The metamagnetic martensitic transformation occurs from strongly ferromagnetic austenite to weakly magnetic martensite. The structural properties of the films were investigated by atomic force microscopy and temperature dependent X-ray diffraction. Magnetic and magnetocaloric properties were analyzed using temperature dependent and isothermal magnetization measurements. We find that Ni$_{41}$Co$_{10.4}$Mn$_{34.8}$Al$_{13.8}$ films show giant inverse magnetocaloric effects with magnetic entropy change of 17.5\,J\,kg$^{-1}$K$^{-1}$ for $\mu_0 \Delta H=5\,\text{T}$., Comment: 8 pages, 8 figures

Magnetic properties of La 1− x Nd x Mn 2 Si 2 ( x =0.35 and 0.40), crystallizing with the tetragonal ThCr 2 Si 2 -type crystal structure, are investigated by means of magnetic and calorimetric measurements. La 1− x Nd x Mn 2 Si 2 ( x =0.35 and 0.40) compounds have complex magnetic states. Anomalies are observed in the heat capacity data which refer to different magnetic states. In addition, the electronic, magnetic and lattice contributions to the heat capacity of the compound are determined. Moreover, the characteristic Debye ( Θ D ) temperatures of both compounds are estimated. We present the comparative results of magnetothermal properties of several compounds in the R 1− x R′ x Mn 2 Si 2 family which show reentrant ferromagnetism at low temperatures due to rare-earth elements.

Epitaxial Ni-Mn-Sn thin films of 200 nm thickness were prepared by magnetron sputtering and deposited onto MgO(100) substrate. They reveal an inverse magnetocaloric effect with a martensitic phase transition around 260 K. The resulting magnetocaloric properties of these films have been determined performing magnetization measurements in the temperature range between 10 and 330K applying different magnetic fields. The maximum values of entropy change and relative cooling power are 1.6 J kg(-1) K-1 and 36.5 J kg(-1) for cooling and 1.5 J kg(-1) K-1 and 33.9 J kg(-1) for heating in mu(0)Delta DH = 1 T, respectively. These data are comparable with bulk values of Ni-Mn-Sn Heusler alloys. (C) 2013 AIP Publishing LLC.

Electrodynamic properties' investigation of chemisorption materials ≪POLYCON K≫ with introduced iron and nickel nanoparticles are discussed.

Arc plasma synthesis of iron nanoparticles: morphological, dielectric and magnetic characterization are discussed.

The structural, magnetic and magnetocaloric properties of CoMnGe0.95Ga0.05 have been investigated by using electron microscopy, calorimetric, synchrotron and magnetic measurements. The substitution of Ga for Ge leads to decreasing on the martensitic transition temperature from 650 K to 315 K. CoMnGe0.95Ga0.05 has hexagonal structure (space group P63/mmc) above the martensitic transition temperature and orthorhombic structure (space group Pnma) below this temperature. The magnetic field dependence of magnetization measurements are performed in the heating and cooling processes around the martensitic transition temperature to determine magnetocaloric effect. It is observed that the magnetic entropy change associated with the martensitic transition temperature can be as high as −5.2 J kg−1 K−1 in field of 1 T. Highlights ► CoMnGe0.95Ga0.05 alloy shows a structural phase transformation from hexagonal to orthorhombic. ► In CoMnGe0.95Ga0.05, the giant magnetocaloric effect is observed around room temperature. ► The maximum magnetic entropy change is −5.2 J kg−1 K−1 in magnetic field change of 1 T.

Aqueous colloidal suspension of iron oxide nanoparticles has been synthesized. Z-potential of iron oxide nanoparticles stabilized by citric acid was - 35 +/- 3 mV. Iron oxide nanoparticles have been characterized by the light scattering method and transmission electron microscopy. The polyelectrolyte/iron oxide nanoparticle thin films with different numbers of iron oxide nanoparticle layers have been prepared on the surface of silicon substrates via the layer-by-layer assembly technique. The physical properties and chemical composition of nanocomposite thin films have been studied by atomic force microscopy, magnetic force microscopy, magnetization measurements, Raman spectroscopy. Using the analysis of experimental data it was established, that the magnetic properties of nanocomposite films depended on the number of iron oxide nanoparticle layers, the size of iron oxide nanoparticle aggregates, the distance between aggregates, and the chemical composition of iron oxide nanoparticles embedded into the nanocomposite films. The magnetic permeability of nanocomposite coatings has been calculated. The magnetic permeability values depend on the number of iron oxide nanoparticle layers in nanocomposite film. (C) 2012 Elsevier B.V. All rights reserved.

We investigate the influence of the film thickness on the martensitic transformation for the example of Ni-Mn-Sn thin films. Epitaxial films with thicknesses ranging from 100 nm down to 10 nm were deposited on MgO by co-sputtering on heated substrates. The martensitic transformation is investigated using temperature dependent x-ray diffraction, magnetization and resistivity measurements. X-ray diffraction and transmission electron microscopy is used to study the growth and the martensitic structure of the films. We find that the martensitic transformation temperatures reduce and the transformation range increases with decreasing film thickness. We show that the transformation is still possible down to a film thickness of 10 nm. A systematic study on the resistance change caused by the martensitic transformation implies that the transformation is suppressed close to the interfaces to the MgO.

We aim to reveal the influence of pH values of the working solution on spatial arrangement of metal-containing inclusions in the monolayer coatings prepared by Langmuir–Blodgett (LB) technology and transferred to solid substrates with consequent modification of surface electrical properties. Consequently, films with inclusions in the form of dendrites and cluster shapes have been obtained. Submicron and micron lead-containing formations in Langmuir–Blodgett films have been characterized by using the atomic force microscopy, Kelvin probe microscopy, and scanning electron microscopy methods. The results show that increasing pH value of the subphase has caused the significant changes in the shape and composition of the inclusions in Langmuir–Blodgett films. The synthesized inclusions on the solid substrate surface resulted in formation of the regions with the local electric fields and, as consequence, to significant modification of the structure and electrical properties. The location and length of the regions with surface potential disturbance depend on the shape of inclusions, and consequently, on pH value of the subphase used in LB technology.