Mn
5
Ge
3
is a ferromagnetic hexagonal crystal promising for spintronics and magnetocalorics. A systematic study and analysis of the magnetic properties of the Mn
5
Ge
3
thin film grown on Si(111) ...were performed. The magnetic anisotropy of the film is determined by the shape anisotropy and the easy magnetization axis aligned along the
c
axis of the crystal. The uniaxial anisotropy constant
K
u
fully corresponds to that for a bulk single crystal, which indicates that
c
axis coincides with film normal. Mn
5
Ge
3
film demonstrates high saturation magnetization
M
S
= 900 emu/cm
3
(900 kA/m) at
T
= 100 K and magnetocaloric effect Δ
S
= 3.16 ± 0.22 J kg
−1
K
−1
at 300 K and
B
= 1.5 T. Δ
S
is comparable to that for multicomponent or Gd rare earth films. Furthermore, a different anisotropy of the magnetocaloric effect compared to bulk Mn
5
Ge
3
was found, which may be related to the anisotropy of the film shape and, possibly, to the domain structure. The results obtained are promising for the design and development of magnetocaloric, spintronic, and spin-caloritronic devices on a silicon platform.
Nanoparticles of Co
1 –
x
Mg
x
Fe
2
O
4
with
x
equal to 0, 0.2, 0.4, 0.6, 0.8, and 1.0 have been synthesized. For all values of
x
, they are nanocrystals with a cobalt ferrite structure and an ...average linear size (
nm. Based on the analysis of the Mössbauer effect spectra, the Co
2+
ions were shown to occupy only octahedral positions at all values of
x
. The experimentally obtained dependence of the nanoparticles magnetization on
x
corresponds to the dependence calculated using the Mössbauer effect data, except for the sample with
. The effective magnetic anisotropy constant estimated for 0 K from the analysis of the coercive force temperature dependences decreases from
at
to
erg/cm
3
at
and drops sharply to
erg/cm
3
at
.
Polarized absorption spectra of crystal Ho0.75Nd0.25Fe3(BO3)4 in the region of the 5I8→5F5 absorption band of Ho ions were investigated depending on temperature in the range of 5–20 K. Absorption ...spectra are decomposed into components of the Lorentz form. The spin-reorientation phase transition was detected at 6.9 K. The observed line position shifts during the reorientation transition were different for different lines, which indicated different local magnetic anisotropy of the Ho ion in its excited states. Significant changes in absorption line intensities as a function of temperature were observed during the reorientation transition and above. These were explained as a consequence of the change in even components of the local crystal field in excited states. These components mix the closely spaced 4f states. Distortion of local symmetry in the ground state was detected at one of the electron transitions.
•Absorption spectra of 5.•I8→5F5 transition in the range of 5 – 20 K.•Magnetic reorientation phase transition was revealed at TR=6.9 K.•Different local magnetic anisotropy of Ho ion in excited states.•Even local distortions in the excited states in the region of TR.
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•Fe3O4-Ag nanoparticles were synthesized by solvothermal method using different duration of the thermolysis process.•The nanoparticles morphology depends on the thermolysis ...duration.•Correlations between morphology and adsorption properties have been found.•Nanoparticles demonstrate high catalytic activity for degradation of organic dyes.
The morphology and magnetic properties as well as adsorption capacity and catalytic activity of Fe3O4-Ag nanoparticles synthesized by the solvothermal method were studied in dependence on the duration of the thermolysis process (3, 6, and 8 h). X-ray diffraction, transmission electron microscopy, and energy-dispersive spectroscopy measurements showed that the morphology of nanoparticles changed strongly as the duration of thermolysis increased. At 6 and 8 h duration, Fe3O4 nanocrystals grow and assemble into porous spherical globules with an Ag core (samples 2 and 3). These samples demonstrate high magnetization value and very low coercivity. The adsorption capacity of nanoparticles was studied with respect to two organic dyes: cationic methylene blue (MB) and anionic Congo red (CR). The particles showed preferential adsorption of the cationic dye. High catalytic activity towards four dyes: MB, methyl orange (MO), CR, and Rhodamine C (RhC) at the presence of NaBH4 is the remarkable property of these samples. The rate constant of the catalytic reaction was 1.4 min−1. Simultaneous exposure of CR and MO dyes to nanoparticles and NaBH4 caused their irreversible 100 % degradation while in the case of MB and RhC, a transition to their leuco form occurred.
Absorption and magnetic circular dichroism (MCD) spectra of HoFe3(BO3)4 and HoAl3(BO3)4 single crystals were measured as a function of temperature in the range of 90–293 K. Based on integrals of f-f ...absorption and МСD bands, temperature dependences of the paramagnetic magneto-optical activity (MOA) of f-f transitions were obtained for the first time. It was revealed that MOA of the same f-f transitions in the studied crystals were substantially different and their temperature dependences did not follow the Curie-Weiss law in contrast to the properties of allowed transitions. The observed phenomena were accounted for as a consequence of the nature of f-f transitions allowance. In temperature dependences of the MOA of two transitions the singularities were revealed, which indicated to some local structural distortions in the corresponding excited states.
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•Temperature dependences of magnetic circular dichroism spectra of HoFe3(BO3)4 and HoAl3(BO3)4.•Magneto-optical activity of f-f transitions does not follow the Curie-Weiss law.•Magneto-optical activity of f-f transitions consists of several contributions of different sign.•Local structural distortions in some excited states were found.
Planar and vertical hybrid structures, which combine ferromagnetic and semiconductor layers are essential for implementation and study of spin transport phenomena in semiconductors, which is crucial ...for the advancement and development of spintronics. We have developed approaches for the synthesis of Fe
3 +
x
Si
1 –
x
epitaxial thin films and demonstrated the spin accumulation effect in multiterminal devices based on Fe
3 +
x
Si
1 –
x
/Si. Fe
3 +
x
Si
1 –
x
/Ge/Fe
3
Si and Fe
3 +
x
Si
1 –
x
/Ge/Mn
5
Ge
3
multilayer hybrid structures were synthesized on a Si(111) substrate, study of their structural, magnetic and transport properties were performed. The effect of synthesis conditions on the growth of epitaxial structures and on their magnetic and transport properties was discussed. The results obtained may prove valuable in the development and fabrication of spintronic devices.
The polarized optical absorption spectra in the region of a series of the
f
–
f
transitions of Nd
3+
ions in the Ho
0.75
Nd
0.25
Fe
3
(BO
3
)
4
, Nd
0.5
Gd
0.5
Fe
3
(BO
3
)
4
, and NdFe
3
(BO
3
)
4
...crystals at 90 K have been compared. The spectral features related to the difference in the local environment of Nd
3+
ions in these crystals have been established. In the region of the transition
4
I
9/2
→
4
G
5/2
+
2
G
7/2
of Nd
3+
ions in the Ho
0.75
Nd
0.25
Fe
3
(BO
3
)
4
crystal, the appearance of some absorption lines at the structural transition
R
32 →
P
3
1
21 around ~200 K due to the local symmetry variation has been found. The intensity of these lines smoothly increases with a decrease in temperature from the transition point. The temperature dependence of the lattice parameters of the Ho
0.75
Nd
0.25
Fe
3
(BO
3
)
4
crystal has been measured. It has been found that, at the transition temperature, the lattice parameter
a
changes stepwise, which is indicative of the occurrence of a first-order phase transition. The lattice parameter
c
changes smoothly.
By the example of α-Fe
2
O
3
hematite, 5Fe
2
O
3
⋅9H
2
O ferrihydrite, and γ-Fe
2
O
3
maghemite powders, a microwave-radiation-induced powder system temperature growth Δ
T
max
of several degrees has ...been measured in the ferromagnetic resonance mode at a frequency of 8.9 GHz. The powders heat up the most in the external field
H
coinciding with the ferromagnetic resonance field. The value of the Δ
T
max
effect depends on the magnetization of a powder material. The results obtained allow us to propose a new magnetic hyperthermia method for biomedical applications.
Fe
3
O
4
@C, Fe
3
O
4
@C@C, and Fe
3
O
4
@SiO
2
core–shell nanoparticles are synthesized via thermal decomposition and coprecipitation. Samples are characterized via X-ray spectroscopy, transmission ...electron microscopy, and magnetometry. It is shown that the magnetic core of all nanoparticles is nanocrystalline and has crystal parameters corresponding to only one phase of Fe
3
O
4
, covered with a uniform shell of amorphous carbon or silicon oxide around 8 nm thick. Special attention is given to adsorption properties of the nanoparticles with respect to four dyes: Methylene blue, Congo Red, Eosin Y, and Rhodamine C. The high selectivity of Fe
3
O
4
@C nanoparticles to various dyes is revealed.
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