We report on the fabrication, and the magnetic and structural properties of novel glass-coated Ni
50.95Mn
25.45Ga
23.6 microwires with a metallic core diameter of 44
μm and a total diameter of 82
μm ...prepared by the Taylor–Ulitovsky method. These annealed microwires showed ferromagnetic behaviour with a well-defined easy axis that corresponds to the axis of the wire. X-ray diffraction confirmed a tetragonal
martensitic structure with a lattice parameters a
=
3.75
Å and c
=
6.78
Å. The Curie temperature was estimated to be ∼315
K. The maximum entropy change at the magnetic transition was −0.7
J
kg
−1
K
−1.
•Production of Ni2FeGa Heusler micro-wire with high shape memory effect is reported.•The microwires show 2% reversible strain in the axis of microwire.•The 2% strain is accompanied by a 1600% ...variation of initial permeability.•Therefore they are ideal material for SMART actuators.
We report on the production and characterization of Heusler-based Ni2FeGa microwires exhibiting two – way shape memory effect. The microwires are characterized by a monocrystalline structure with a strong preferred crystallographic orientation that shows 1 1 1 axis parallel to the wire’s axis for high-temperature L21 austenite phase, while the 0 1 7 axis is preferred for low-temperature monoclinic phase. Variation of crystallographic axis (and corresponding easy magnetization axis) leads to 1600% variation of magnetic permeability due to a 2% strain in axial direction. Such straining is reversible immediately after production without the necessity of further thermal treatment. These properties give the microwire function of very sensitive SMART actuators that can be easily produced in a large amount.
The structural, magnetic and magnetocaloric properties of glass-coated magnetic microwires, composed of Ni2MnGa and produced with the Taylor-Ulitovski technique, have been investigated with XRD, ...EBSD, SEM and magnetization measurements. At room temperature, the microwires exhibit a monocrystalline phase with a Cu2MnAl-type crystal structure (space group Fm-3m; cell parameter a = 5.832 Å). The microwires in this study show a magnetocaloric effect with a sharp martensitic transformation in the range of 185–195 K, as well as a magnetocaloric effect owing to the magnetic phase transition at the Curie temperature. Due to the different strength of anisotropy and easy magnetization axis, the magnetocaloric effect during the martensitic transformation exhibit a maximum at low fields (0.5 T), and high efficiency (defined as a ratio between refrigerant capacity and applied magnetic field) at 0.2 T.
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•Large scale production of monocrystalline Heusler micro-wire is reported.•Such a wire is characterized by well oriented anisotropy.•Half-metallic behaviour is observed in the low temperature range.
•Large scale production of monocrystalline Heusler micro-wire is reported.•Such a wire is characterized by well oriented anisotropy.•Half-metallic behaviour is observed in the low temperature range.
...Large scale production of single crystalline phase of Heusler Co2FeSi alloy microwire is reported. The long microwire (∼1 km) with the metallic nucleus diameter of about 2 µm is characterized by well oriented monocrystalline structure (B2 phase, with the lattice parameter a = 5.615 Å). Moreover, the crystallographic direction 101 is parallel to the wire’s axis along the entire length. Additionally, the wire is characterized by exhibiting a high Curie temperature (Tc > 800 K) and well-defined magnetic anisotropy mainly governed by shape. Electrical resistivity measurement reveals the exponential suppression of the electron-magnon scattering which provides strong evidence on the half-metallic behaviour of this material in the low temperature range.
In the given contribution, the production of shape-memory glass-coated microwires based on Ni2FeZ (Z = Ga, Sn, Sb) and Co2Cr(GaSi) alloys is shown, focusing to their repeatable production. Such wires ...are characterized by monocrystalline structure along entire length. This leads to 1.5% reversible temperature shape memory effect for Ni2FeGa microwire in the as-cast state without necessity of additional thermal treatment. Moreover, well defined anisotropy results in the variation of permeability up to 550% during the phase transition. On the other hand, Co2Cr(GaSi) microwires show reversible superelastic straining up to 1.1% with a very small irreversible strain (<0.1%).
•Ni2FeZ and Co2Cr(GaSi) glass-coated magnetic microwires were produced.•They are characterized by monocrystalline structure along entire length.•Ni2FeGa microwire exhibit 1.5% reversible temperature shape memory effect without necessity of thermal treatments.•Co2Cr(GaSi) microwire shows reversible superelastic straining up to 1.1%.
We are dealing with the influence of Hopkinson effect on magnetocaloric effect in glass-coated Ni-Mn-In-Co microwires in the given contribution. We have shown that although the entropy change is ...smaller in low fields, the refrigerant capacity per unit of applied field is three times higher for low field (300 Oe) comparing to that of 30 kOe. This points to the fact that Hopkinson effect can be employed to increase the efficiency of magnetocaloric effect.
The correlation of the infrared spectra of zinc(II) carboxylates with their structures was investigated in the paper. The complexes with different modes of the carboxylate binding, from chelating, ...through bridging (
syn–syn,
syn–anti,
monatomic), ionic to monodentate were used for the study, namely Zn(C
6H
5CHCHCOO)
2(H
2O)
2 (
I) with chelating carboxylate group (C
6H
5CHCHCOO
=
cinnamate), Zn
2(C
6H
5COO)
4(pap)
2 (
II) with
syn–syn bridging carboxylate (C
6H
5COO
=
benzoate; pap
=
papaverine), Zn(C
6H
5CHCHCOO)
2(mpcm)
n
(
III) with
syn–anti carboxylate bridge (mpcm
=
methyl-3-pyridylcarbamate), Zn(C
5H
4NCOO)
2(H
2O)
4 (
IV) with ionic carboxylate group (C
5H
4NCOO
=
nicotinate), Zn(C
6H
5COO)
2(pcb)
2
n
(
V) with monodentate carboxylate coordination (pcb
=
3-pyridylcarbinol) and Zn
3(C
6H
5COO)
6(nia)
2 (
VI) with
syn–syn and
monatomic carboxylate bridges (nia
=
nicotinamide). First, the mode of the carboxylate binding was assigned from the infrared spectra using the magnitude of the separation between the carboxylate stretches,
Δ
exp
=
ν
as(COO
−)
−
ν
s(COO
−). Then the values
Δ
exp were compared with those calculated from structural data of the carboxylate anion (
Δ
calc). The conclusions about the carboxylate binding which resulted from the
Δ values, were confronted with the crystal structure of the complexes. The limitations and recommendations were formulated to assign the mode of the carboxylate binding from the infrared spectra. The dependence of the
Δ
exp values on the magnitudes of Zn–O–C angles in bidentate carboxylate coordination was observed.
The ligand, 4-chloro-2,6-dipicolinic acid (H
2
PDA-Cl), and its two heavy metal complexes, Ag(HDPA-Cl)(H
2
DPA-Cl)·2H
2
O (1) and {Cd(μ
2
-H
2
O)(H
2
O)(PDA-Cl)}
n
(2), were prepared and then ...characterized by single-crystal X-ray diffraction. In addition, spectral and thermal correlations with structural results complete their solid-state description and facilitate complex 3 (Pb(DPA-Cl)) composition determinations. Complex 1 crystallizes in a monoclinic space group C2/c and each DPA-Cl ligand is tridentate to Ag(I) through the pyridine N and two monodentate carboxyl O atoms. The carboxy group with carbonyl C1 is semideprotonated and forms a symmetric hydrogen bond with a carboxy group of a neighboring complex. Complex 2 crystallizes in a triclinic lattice with space group P
The Cd(II) ions are seven-coordinate and the coordination polyhedra can be described as a distorted pentagonal bipyramid. IR data are consistent with monodentate coordination of the carboxylate to Ag(I), Cd(II), and Pb(II) and observed wavenumber shifts confirm PDA-Cl ligand coordination to Pb(II) in 3. Thermal stability of anhydrous complexes indicates the metal-ligand interactions. The thermal stability of prepared compounds is reflected by the strength of interaction between metal-ligand and hydrogen bonds.
Trinuclear Ag(I) (1) and dinuclear and mononuclear Zn(II) isonicotinate (2 and 3) complexes were prepared and characterized by X-ray crystallography, elemental analysis, IR spectroscopy, and thermal ...analysis. Single-crystal analysis of the Ag(I) complex reveals two different monodentate carboxylate coordination modes, protonated and deprotonated, respectively. IR spectra showed correlations between isonicotinate coordination modes and Δ(ν
as
− ν
s
)
IR
values. In addition, the hydrogen bonds significantly influence a position of carboxylate absorption bands. Moreover, IC
50
and MIC data for bacteria, yeasts, and filamentous fungi were determined and the binding of Ag(I) and Zn(II) complexes to calf thymus DNA was investigated using electronic absorption, fluorescence, and CD measurements. Biological tests showed that the Ag(I) complex is more active than commercially used Ag(I) sulfadiazine against Escherichia coli. The fluorescence spectral results indicate that the complexes can bind to DNA through an intercalative mode. The Stern-Volmer quenching constants for investigated complexes obtained from the linear quenching plot are in the range of 1.67 × 10
4
-3.42 × 10
4
M
−1
.
Toxic metal (Cd
2+
, Hg
2+
, Pb
2+
, and Ag
+
) complexes with the tetradentate macrocyclic ligand - cyclen (1,4,7,10-tetraazacyclododecane, 12aneN
4
, L) were prepared and studied in the solid state ...by IR, X-ray diffraction, elemental and thermal analysis. Diffraction results have yielded three molecular structures, Cd(12ane-κ
4
N
1,4,7,10
)(NO
3
)
2
) (1), Hg(12ane-κ
4
N
1,4,7,10
)(NO
3
-κ
2
O,O`)NO
3
(2), Pb
2
(12ane-κ
4
N
1,4,7,10
)
2
Pb(NO
3
)
6
(3) and one polymeric structure {Ag
2
(12ane-κ
3
N
1,4,7
)(μ
2
-12aneN
10
)(NO
3
)
2
∙2H
2
O)}
n
(4) featuring a unique coordination mode not observed before with cyclen as a ligand. The monodentate (1) and chelate (with small bite angle 50.3(3)°, (2) coordination modes of nitrate ligands were confirmed. Stereochemically active 6s
2
lone pair was suggested in 3 and DFT results confirmed no significant metal-metal covalent bond. The stability constants of the complexes with Cd
2+
and Pb
2+
ions were determined by potentiometric methods in aqueous solutions. Additionally, the structures of complexes in solution were observed by
1
H NMR. Both methods confirm similar cyclen complexing properties toward Zn
2+
biometal and Cd
2+
, Pb
2+
toxic metals.
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