The Hopkinson effect has been experimentally observed and theoretically investigated in a disorde... more The Hopkinson effect has been experimentally observed and theoretically investigated in a disordered system of fine (single domain) BaFe,,O,, particles. An explanation based on the Stoner-Wohlfarth model which accounts for thermal activation is proposed.
We explore the thermal activation contribution to the initial thermomagnetic curves with a Hopkin... more We explore the thermal activation contribution to the initial thermomagnetic curves with a Hopkinson maximum. The thermal activation is incorporated into the Stoner-Wohlfarth model of magnetization of noninteracting uniaxial single-domain particles of random orientation.
The bulk amorphous alloys Sm,Co,, Gd,Co,, and Er,Co, are investigated. Their magnetic peculiariti... more The bulk amorphous alloys Sm,Co,, Gd,Co,, and Er,Co, are investigated. Their magnetic peculiarities are determined in the temperature range from 4.2 to 300 K. Paramagnetic Curie temperatures 110, 212, and 22 K are measured for Srn,Co,, Gd,Co,, and Er,Co,, respectively. The magnetic moments and the anisotropy energies are also derived.
ABSTRACT Single-phase polycrystalline Ni0.85-x-yCu0.15Znx Coy Fe2O4 (x = 0.2, 0.4, 0.6; y = 0, 0,... more ABSTRACT Single-phase polycrystalline Ni0.85-x-yCu0.15Znx Coy Fe2O4 (x = 0.2, 0.4, 0.6; y = 0, 0,02, 004, 006) were synthesized by a standard ceramic technology. The mean particle sizes range between 2 and 30 mum. The main magnetic parameters such as saturation magnetization, remanence and coercivity were obtained from the entire hysteresis loops plotted in AC (2 kHz) magnetic field at room temperature. Saturation magnetization decreases slightly with increasing Co-concentration for x = 0.2, 0.4 only. The remanence decreases with increasing Co-concentration for all the compounds, but the coercivity is practically constant for most of the samples. Hysteresis losses were evaluated from the hysteresis loops by using the Fourier decomposition. The initial permeabilities were obtained from the minor hysteresis loops in low enough fields. It was found that: only for x = 0.4 and y = 0.04, the initial permeability increases, hysteresis losses decrease and the changes of other magnetic parameters are negligible.
Here we present some new results on the srtucture and properties of the High Temperature Supercon... more Here we present some new results on the srtucture and properties of the High Temperature Superconductor YBa 2 Cu 3 O 7−y synthesed at different technological conditions.
... 5, Blvd. Anton Ivanov, 1126 Sofia, Bulgaria. Page 2. ... This value corresponds to a magtic: ... more ... 5, Blvd. Anton Ivanov, 1126 Sofia, Bulgaria. Page 2. ... This value corresponds to a magtic: ill rr~~rneiit of ll).F)un 'dysprositi Lii atom. The magnetization curves of Dyo,lYo,o do t 3 t <:xhiIrti2 :I ;iiii:p kiiil, haw :t c.li:iiige of the ciirvature at H = H,. . Above H,, the in; p-iii:liza~~iori ciirvl? ...
A method for the estimation of reversible and irreversible susceptibilities of initial magnetizat... more A method for the estimation of reversible and irreversible susceptibilities of initial magnetization curves has been developed. It deals with the energy necessary for magnetizing and demagnetizing the sample, but neither with the nature of the magnetization processes nor with a specific type of anisotropy, so it could be applied for a wide variety of real materials. A set of minor hysteresis loops of an initially demagnetized sample, plotted with progressively increasing maximum magnetic field, has been used. The obtained results showed excellent agreement with those calculated by the remanence curve method for a Stoner–Wohlfarth model system.
Amorphous alloys with non-S state rare earth ions (Gd4Fe 3 and Y4Fe3) are prepared as ribbons. Th... more Amorphous alloys with non-S state rare earth ions (Gd4Fe 3 and Y4Fe3) are prepared as ribbons. The amorphism is proved by X-ray diffraction and differential scanning calorimetry. The crystallization of the alloys was studied using a variable heating rate and the results were analysed by Kissinger's method. The phases formed during the crystallization process were identiffed by means of X-ray diffraction and thermomagnetic measurements. The magnetic properties were investigated from 4.2 to 400 K in steady fields of up to 140 kOe. A spin-glass-like behaviour was observed for the amorphous Y4Fe3 alloy and this was due to the presence of both positive and negative exchange interactions. The observed reduction in the iron magnetic moment was discussed in terms of the environmental model of Jaccarino and Walker. The magnetic properties of the alloys investigated were compared with those of similar rare earth alloys containing cobalt instead of iron.
The Hopkinson effect has been experimentally observed and theoretically investigated in a disorde... more The Hopkinson effect has been experimentally observed and theoretically investigated in a disordered system of fine (single domain) BaFe,,O,, particles. An explanation based on the Stoner-Wohlfarth model which accounts for thermal activation is proposed.
We explore the thermal activation contribution to the initial thermomagnetic curves with a Hopkin... more We explore the thermal activation contribution to the initial thermomagnetic curves with a Hopkinson maximum. The thermal activation is incorporated into the Stoner-Wohlfarth model of magnetization of noninteracting uniaxial single-domain particles of random orientation.
The bulk amorphous alloys Sm,Co,, Gd,Co,, and Er,Co, are investigated. Their magnetic peculiariti... more The bulk amorphous alloys Sm,Co,, Gd,Co,, and Er,Co, are investigated. Their magnetic peculiarities are determined in the temperature range from 4.2 to 300 K. Paramagnetic Curie temperatures 110, 212, and 22 K are measured for Srn,Co,, Gd,Co,, and Er,Co,, respectively. The magnetic moments and the anisotropy energies are also derived.
ABSTRACT Single-phase polycrystalline Ni0.85-x-yCu0.15Znx Coy Fe2O4 (x = 0.2, 0.4, 0.6; y = 0, 0,... more ABSTRACT Single-phase polycrystalline Ni0.85-x-yCu0.15Znx Coy Fe2O4 (x = 0.2, 0.4, 0.6; y = 0, 0,02, 004, 006) were synthesized by a standard ceramic technology. The mean particle sizes range between 2 and 30 mum. The main magnetic parameters such as saturation magnetization, remanence and coercivity were obtained from the entire hysteresis loops plotted in AC (2 kHz) magnetic field at room temperature. Saturation magnetization decreases slightly with increasing Co-concentration for x = 0.2, 0.4 only. The remanence decreases with increasing Co-concentration for all the compounds, but the coercivity is practically constant for most of the samples. Hysteresis losses were evaluated from the hysteresis loops by using the Fourier decomposition. The initial permeabilities were obtained from the minor hysteresis loops in low enough fields. It was found that: only for x = 0.4 and y = 0.04, the initial permeability increases, hysteresis losses decrease and the changes of other magnetic parameters are negligible.
Here we present some new results on the srtucture and properties of the High Temperature Supercon... more Here we present some new results on the srtucture and properties of the High Temperature Superconductor YBa 2 Cu 3 O 7−y synthesed at different technological conditions.
... 5, Blvd. Anton Ivanov, 1126 Sofia, Bulgaria. Page 2. ... This value corresponds to a magtic: ... more ... 5, Blvd. Anton Ivanov, 1126 Sofia, Bulgaria. Page 2. ... This value corresponds to a magtic: ill rr~~rneiit of ll).F)un 'dysprositi Lii atom. The magnetization curves of Dyo,lYo,o do t 3 t <:xhiIrti2 :I ;iiii:p kiiil, haw :t c.li:iiige of the ciirvature at H = H,. . Above H,, the in; p-iii:liza~~iori ciirvl? ...
A method for the estimation of reversible and irreversible susceptibilities of initial magnetizat... more A method for the estimation of reversible and irreversible susceptibilities of initial magnetization curves has been developed. It deals with the energy necessary for magnetizing and demagnetizing the sample, but neither with the nature of the magnetization processes nor with a specific type of anisotropy, so it could be applied for a wide variety of real materials. A set of minor hysteresis loops of an initially demagnetized sample, plotted with progressively increasing maximum magnetic field, has been used. The obtained results showed excellent agreement with those calculated by the remanence curve method for a Stoner–Wohlfarth model system.
Amorphous alloys with non-S state rare earth ions (Gd4Fe 3 and Y4Fe3) are prepared as ribbons. Th... more Amorphous alloys with non-S state rare earth ions (Gd4Fe 3 and Y4Fe3) are prepared as ribbons. The amorphism is proved by X-ray diffraction and differential scanning calorimetry. The crystallization of the alloys was studied using a variable heating rate and the results were analysed by Kissinger's method. The phases formed during the crystallization process were identiffed by means of X-ray diffraction and thermomagnetic measurements. The magnetic properties were investigated from 4.2 to 400 K in steady fields of up to 140 kOe. A spin-glass-like behaviour was observed for the amorphous Y4Fe3 alloy and this was due to the presence of both positive and negative exchange interactions. The observed reduction in the iron magnetic moment was discussed in terms of the environmental model of Jaccarino and Walker. The magnetic properties of the alloys investigated were compared with those of similar rare earth alloys containing cobalt instead of iron.
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Papers by M. Mikhov