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Dimensionality in Field Theory and in Spin Wave Theory

100%
Köbler U., Hoser A.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
356-358
EN
The different meaning of dimensionality and universality in field theory and in spin wave theory is illustrated on account of experimental examples. In spin wave theory it is distinguished between the dimensionality of the spin and the dimensionality of the exchange interactions. According to Renormalization Group (RG) theory, these atomistic characteristics are unimportant for the critical dynamics. Instead by inter-atomic interactions the dynamics of the ordered state is determined by the excitations of the continuous magnetic medium. These excitations are bosons. Consequently, the dimensionality of ordered magnets has to be assessed to the dimensionality of the relevant boson field. The most serious consequence of RG theory is that the magnetic ordering transition also is executed by the boson field. Typical for boson dynamics is a finite width of the critical range. In the atomistic models universality applies asymptotically at T_{c} only. It is evident that the critical power functions of the field dynamics are different from those of the atomistic dynamics.
2
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Boson Fields in Ordered Magnets

100%
Hoser A., Köbler U.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
350-352
EN
Spin wave theory of magnetism reveals two severe shortcomings. First, it considers non quantized classical spins and, second, the predicted temperature power functions for the thermal decrease of the magnetic order parameter hold asymptotically at T = 0 only. As experiments unambiguously show the dynamics is different for magnets with integer and half-integer spin and the "critical" power functions at T = 0 of type ΔM ≈ T^{ε} or at T = T_{c} of type ≈(T_{c}-T)^β hold over a finite temperature range, independent of spin structure. The finite critical range unequivocally indicates that the dynamics of the spins is controlled by a field of freely propagating bosons instead by exchange interactions. Consequently, field theories are necessary for description of the thermodynamics of ordered magnets. The experimental indications will be discussed that the field quanta are essentially magnetic dipole radiation emitted by the precessing magnetic moments. Since integer and half-integer spins precess differently the generated field quanta and the dynamics of the field are correspondingly different.
3
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Magnetic Interaction by Exchange of Field Bosons

100%
Köbler U., Hoser A.
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EN
It is shown that atomistic spin wave theory gives no correct account of the temperature dependence of the magnetic order parameter. The experimentally observed universal temperature dependence can be explained only by a field theory of magnetism. This means that instead by interacting spins (magnons) the dynamics is controlled by a boson field. The field quanta can be supposed to be magnetic density waves with dispersions that are simple power function of wave vector. This results in the observed universality. In three dimensions the field quanta have no mass and linear dispersion and cannot be observed using inelastic neutron scattering. Experiments on standing magnetic waves in thin ferromagnetic films provide direct information on the dispersion of the field quanta. A careful analysis of the available experimental data indicates that the dispersion of the field bosons is ım q, ım q^2, and ım q^{3/2} in three, two, and one dimensions.
4
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Evidence of the Non-Magnetic Ordering in TmRu₂Si₂ at Low Temperatures

81%
Szytuła A., Hoser A., Baran S., Penc B.
Acta Physica Polonica A
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2016
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vol. 130
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issue 6
1371-1372
EN
The neutron powder diffraction measurements of the TmRu₂Si₂ compound in the temperature range 0.47-2.5 K have been performed. The obtained results confirm that this compound in low temperature has a tetragonal ThCr₂Si₂-type crystal structure (space group I4/mmm). The long range magnetic ordering was not detected up to 0.47 K.
5
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Macroscopic and Microscopic Study of a CePdIn Compound

81%
Klicpera M., Javorský P., Puente-Orench I., Hoser A.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
970-972
EN
The magnetization and electrical resistivity measurements on a CePdIn single crystal as well as its preparation and structural characterization are presented. The negative paramagnetic Curie temperatures indicate antiferromagnetic ground state, the anisotropy of the paramagnetic Curie temperature amounts 22.7 K. No ferromagnetic correlations were indicated. Powder neutron diffraction experiment performed at temperatures down to 0.4 K did not lead to observation of any magnetic peak in diffraction patterns. We estimate the magnetic moment on Ce atoms to be significantly lower than 0.5 μ_{B}. The temperature development of lattice parameters documents the standard thermal expansion of the unit cell; no signs of structural phase transition were observed.
6
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Correlation between Magnetic Phases and Insulator-Metal Transition in La_{1/3}Nd_{1/3}Ca_{1/3}MnO_{3} Perovskite

81%
Baszyński J., Idzikowski B., Toliński T., Hoser A.
Acta Physica Polonica A
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2000
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vol. 97
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issue 5
779-782
EN
The La_{1/3}Nd_{1/3}Ca_{1/3}MnO_{3} ceramic perovskites are investigated using the neutron diffraction technique and resistance measurements in the temperature range from 260 K down to 5 K. We have found that the integrated intensity of the antiferromagnetic peaks was growing with decreasing temperature and reached the maximum at a temperature about 20 K lower than that of the semiconductor-metal transition and did not vanish at 5 K. The semiconductor-metal transition is correlated with the temperature of the maximum of the lattice c-parameter and the percolation of ferromagnetic domains. Our results suggest that although the ferromagnetic long-range order is established through the semiconductor-metal transition induced percolation network, locally the antiferromagnetic correlation can remain.
7
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Neutron Diffraction Studies of PrNi₅Sn

81%
Penc B., Hoser A., Szytuła A.
Acta Physica Polonica A
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2016
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vol. 129
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issue 3
313-314
EN
Powder neutron diffraction measurements of PrNi₅Sn performed in the temperature range 1.5-76 K indicate that the compound crystallizes in a hexagonal CeNi₅Sn-type crystal structure (space group P6₃/mmc). The a lattice parameter and the unit cell volume V increase while the c lattice parameter does not change with increasing temperature. No long range magnetic ordering was detected down to 1.5 K, in contradiction to bulk magnetometric results.
8
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Neutron Diffraction Study of Ferromagnetic Ordering in La_{1/3}Nd_{1/3}Ca_{1/3}MnO_{3} Induced by Electric Field

81%
Baszyński J., Idzikowski B., Toliński T., Hoser A.
Acta Physica Polonica A
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2000
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vol. 97
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issue 5
831-834
EN
We used the neutron diffraction technique to study the ferromagnetic ordering process in La_{1/3}Nd_{1/3}Ca_{1/3}MnO_{3} induced by the short impulse of the external electric field E=4 V/cm at a magnetic field H=1.5 T. Our sample was prepared by the standard solid-state reaction. The diffraction measurements at 4 K, carried out for the neutron wavelength λ=0.2442 nm, have revealed the orthorhombic perovskite structure with the unit-cell parameters: a=0.5480 nm, b=0.5550 nm and c=0.7737 nm. We observed that a short impulse of the electric field develops the ferromagnetic ordering in a similar way as the magnetic field up to 4 T. We assume that the increased ferromagnetic ordering induced by the external electric field at a given magnetic field has the same physical origin as in the case of the Zener double exchange. The effect is confirmed by magnetic moment measurements using vibrating sample magnetometer.
9
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Size Effects in Antiferromagnetic NiO Nanoparticles

81%
Baran S., Hoser A., Penc B., Szytuła A.
Acta Physica Polonica A
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2016
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vol. 129
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issue 1
35-39
EN
X-ray and neutron diffraction as well as magnetometric methods were used in order to investigate crystal and magnetic structure together with magnetic properties of nickel oxide NiO obtained from thermal decomposition of Ni(OH)₂. It has been found that crystal unit cell volume and crystal unit cell deformation parameter decrease with increasing decomposition temperature T_{d} while grain size increases. The results of magnetization, magnetic susceptibility and neutron diffraction measurements reveal a formation of antiferromagnetic order with uncompensated magnetic moment below the Néel temperature. Magnetization together with coercive field decreases with increasing T_{d}. The neutron diffractogram of sample obtained at 240°C indicates broadening of both the peaks of nuclear and magnetic origin. The magnetic ordering may be described by a propagation vector k=[½,½,½].
10
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Neutron Diffraction Studies of Nanoparticle DyMnO_3 Compound

71%
Szytuła A., Penc B., Dyakonov V., Baran S., Hoser A.
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vol. 125
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issue 1
65-66
EN
The neutron powder diffraction (NPD) measurements of the nano-size DyMnO_3 manganite have been performed. The obtained results indicate that this compound crystallizes in the orthorhombic crystal structure described by the space group Pnma. The Mn and Dy moments order antiferromagnetically at different temperatures and form modulated magnetic structure described by the propagation vector k=(k_x, 0, 0) with the different values of k_x component for the Mn and Dy sublattices. The values of k_x component for Mn sublattice increase with decreasing of the temperature and are smaller that in bulk compound. The wide Bragg peaks related to the Dy sublattice suggest that the magnetic order in this sublattice has the cluster-like character.
11
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Neutron Diffraction Studies of NdNi_5Sn Compound

71%
Penc B., Baran S., Hoser A., Romaka L., Szytuła A.
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vol. 126
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issue 3
772-774
EN
The neutron powder diffraction measurements of the NdNi_5Sn compound have been performed. The obtained results indicate that this compound crystallizes in a hexagonal CeNi_5Sn-type crystal structure described by the space group P6_3/mmc. The parameters of the crystal structure at 1.55 and 14.8 K are determined. In contradiction to the magnetic data the long-range magnetic ordering was not detected up to 1.55 K.
12
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Crystal Structure and Magnetic Properties of Tb_{11}O_{20}

71%
Baran S., Duraj R., Hoser A., Penc B., Szytuła A.
Acta Physica Polonica A
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2013
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vol. 123
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issue 1
98-100
EN
Magnetic and neutron diffraction data for Tb_{11}O_{20} compound are reported. This compound crystallizes in a triclinic crystal structure described by the space group P1 and is antiferromagnetic with the Néel temperature 5.1 K.
13
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Neutron Diffraction Studies of Tb_2Ni_{2-x}In Intermetallic Compounds

62%
Szytuła A., Baran S., Hoser A., Kalychak Y. M., Penc B., Tyvanchuk Y.
Acta Physica Polonica A
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2013
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vol. 124
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issue 6
994-997
EN
The magnetic ordering of the Tb_2Ni_{1.78}In and Tb_2Ni_2In have been studied by neutron diffraction measurements. Tb_2Ni_{1.78}In with the tetragonal Mo_2FeB_2-type (space group P4/mbm, tP10) is antiferromagnet with the Néel temperature equal to 20 K. Below this temperature Tb moments form collinear magnetic structure commensurate with the crystal, described by the propagation vectors equal to (1/4, 1/4, 1/2). Magnetic moment equal to 7.60(6) μ_{B} is parallel to c-axis. The Tb_2Ni_2In in the orthorhombic Mn_2 lB_2-type (space group Cmmm, oC10) was detected as an impurity in the studied sample. It orders antiferromagnetically below ≈ 100 K with collinear moment arrangement described by the propagation vector (1/2, 1/2, 1/2). t 1.6 K μ_{Tb} = 6.33(14) μ_{B} and is parallel to the c-axis.
14
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From Heavy Fermion and Spin-Glass Behavior to Magnetic Order in CeT_4M Compounds

62%
Toliński T., Kowalczyk A., Falkowski M., Synoradzki K., Chełkowska G., Hoser A., Rols S.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1014-1018
EN
We report on the transitions between the ferromagnetic order, spin-glass behavior, heavy fermion and fluctuating valence state in a series of isostructural compounds CeT_4M (T = Ni, Cu; M = Al, Ga, Mn). The dilution of Ce or the T and M elements allowed us to follow the physical properties evolution employing the measurements of the heat capacity, dc magnetic susceptibility, frequency dependent ac magnetic susceptibility, magnetization relaxation, inelastic neutron scattering and also the X-ray photoemission spectroscopy. It is shown that the Mn rich compounds lean towards the spin glass behavior. For the compounds governed by the close to localization Ce 4f states the effect of the crystal electric field has been studied. It has been shown that the spin glass-like behavior can significantly influence the physics of the CeT_4M compounds.
15
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Influence of the Grain Size on the Magnetic Properties of TbMnO_{3}

42%
Bażela W., Dul M., Dyakonov V., Gondek Ł., Hoser A., Hoffmann J., Penc B., Szytuła A., Kravchenko Z., Nosalev I., Zarzycki A.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
785-788
EN
The magnetic properties including magnetic structure of poly and nano samples of TbMnO_{3} are determined. All the samples investigated are antiferromagnets. In these samples the Mn ad Tb moments order antiferromagnetically at different temperatures and form modulated magnetic structure described by the propagation vector k=(k_{x},0,0) with different value of k_{x} for the Mn and Tb sublattices. Comparison of the data for poly and nano samples indicates the decrease of the moment and increase of the k_{x} component of propagation vector in the nano specimens. The wide Bragg peak related to the Tb sublattice suggests that the magnetic order has the claster-like character. The magnetic moments value in both sublattices is smaller, whereas the k_{x} values are larger for nano samples.
16
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Magnetic and Neutron Diffraction Studies of the Polycrystalline and Nanoparticle TbMnO_3

42%
Bażela W., Dul M., Dyakonov V., Gondek Ł., Hoser A., Hoffmann J., Penc B., Szytuła A., Kravchenko Z., Nosalev I., Zarzycki A.
Acta Physica Polonica A
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2012
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vol. 122
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issue 2
384-390
EN
This paper reports on investigations of magnetic properties, crystal and magnetic structures on TbMnO_3 prepared in various ways, namely, as conventional polycrystalline sample and two nano particle specimens (synthesized with a sol-gel method at temperatures of 800 and 850°C). The X-ray and neutron diffraction data confirm the orthorhombic crystal structure (space group Pbnm, No. 62) without noticeable differences of the lattice parameters for poly- and nanocompounds. For the polycrystalline sample, a subsequent ordering of the Mn and Tb sublattices with decreasing temperature was observed. Namely, the Mn sublattice exhibits a modulated magnetic structure with the propagation vector k = (0, k_{x}, 0) in between 41-5 K. Below T = 21 K, a change from a collinear (A_{y} mode) into non-collinear (A_{y}G_{z} mode) structure was evidenced. Further decreasing of temperature below 10 K results in magnetic ordering of the Tb sublattice (modulated G_{x}A_{y}F_{z} mode). For nanoparticle compounds, magnetic ordering in the Mn and Tb sublattices is described by propagation vector k = (0, k_{y}, 0), with k_{y} components higher than observed for polycrystalline sample. The magnetic ordering in the Mn sublattice is described by a collinear A_{y} mode down to 1.6 K where the Tb moment becomes ordered (G_{x}A_{y} mode). The observed broadening of the Bragg peaks connected to the Tb sublattice suggests the cluster-like character of its magnetic structure.
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