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The effect of hydrostatic pressure on antiferromagnetic ordering of Cr spins, magnetic compensation, and exotic spin switching in the single-crystal $\mathrm{GdCr}{\mathrm{O}}_{3}$ ferrimagnet is studied. The N\'eel temperature ${T}_{\mathrm{N}}=168\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ increases under pressure with the rate of 0.42 K/kbar, and the compensation temperature ${T}_{\mathrm{comp}}=144\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at which the canted ferromagnetic moment of Cr spins and antiparallel polarized moment of Gd spins cancel each other also increases by 0.3 K/kbar. It was found that the spin switching temperature ${T}_{\mathrm{sw}}$, at which the ferromagnetic moment is reversed, noticeably increases under pressure, and the spin switching energy required for magnetization reversal reduces significantly because of a decrease in magnetic anisotropy. Due to this mechanism, the spin switching line, described in the $T$\ensuremath{-}$H$ diagram by a certain ratio of switching energy to canted ferromagnetic moment, is shifted under pressure towards higher temperatures. Thus, switching between two opposite spin configurations in the $\mathrm{GdCr}{\mathrm{O}}_{3}$ ferrimagnet can be controlled by both applied magnetic field and external pressure.

Magnetic and structural properties of CaMn1– x Re x O3 (0.02 ≤ x ≤ 0.1) have been investigated. Substitution of Re5+ ion for the Mn4+ site of 3 generates Mn3+ ions according to the chemical formula CaMn1–2 x 4+Mn x 3+Re x 5+O3, accompanied by an increase of lattice parameters and unit-cell volume with increasing ${x}$ . With increasing doping level $x$ , the magnetic ground state evolves from an antiferromagnetic (AFM) with a weak ferromagnetic (FM) component, for $x = 0.02 - 0.06$ , to the charge ordered ${C}$ -type AFM state at $x = 0.1$ . Spontaneous magnetization at $T = 10$ K increases quickly with increasing $x$ , approaches the maximum value of 3.5 emu/g for $x = 0.04$ , and then decreases rapidly to 0.2 emu/g for $x = 0.1$ . Anomalous negative magnetization (NM) for $x = 0.02$ has been observed in the zero-field-cooled and field-cooled (FC) magnetization below the magnetic transition temperature. Exchange bias (EB) effect, manifested by horizontal shift in the hysteresis loops of FC samples, has also been observed. This effect is very small for $x = 0.02$ , almost zeroes for 0.04, and monotonously increases with increasing $x$ . The EB appears due to low-temperature phase separation into FM clusters and charge-ordered AFM phases. The effect of hydrostatic pressure for all samples revealed a significant increase of the FM phase volume under pressure, linked to both suppression of NM in $x = 0.02$ sample and reduction of the EB effect in all samples.

The effect of hydrostatic pressure on complex magnetic phase diagram of $\mathrm{LuF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$ has been investigated by various magnetic measurements in the range of 0--12 kbar. The temperature of the ferrimagnetic (fM) transition (${T}_{\mathrm{N}}\ensuremath{\approx}245\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) practically does not change with increasing pressure, while the temperature of the appearance of mixed fM and antiferromagnetic (AFM) state at $\ensuremath{\sim}\phantom{\rule{0.16em}{0ex}}200\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ increases with the rate $d{T}_{\mathrm{C}}/dP\ensuremath{\approx}0.8\phantom{\rule{0.16em}{0ex}}\mathrm{K}/\mathrm{kbar}$. Moreover, an applied pressure suppresses the magnetization, enhances the field of metamagnetic transition, and extends the range of existence of mixed fM and AFM state. Suppression of the ordered magnetic moment under pressure induces a transition from a counterclockwise (CCW) thermal hysteresis below $T\ensuremath{\approx}220\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ to a clockwise (CW) thermal hysteresis in a magnetic field $H=1\phantom{\rule{0.16em}{0ex}}\mathrm{kOe}$. Nevertheless, field induced metamagnetic transition from mixed fM and AFM state to fM state results in a narrowing of the temperature range of thermal hysteresis and in restoring of CCW type of thermal hysteresis. As a consequence of metamagnetic transition, the thermal hysteresis completed at $H=10\phantom{\rule{0.16em}{0ex}}\mathrm{kOe}$ remains one of the CCW type under applied pressure.

Magnetic properties of Pr0.5Ca0.5Mn1−xCrxO3 (0.015⩽x⩽0.5) samples were investigated under pressures up to 11 kbar. For x=0.015 and 0.03 samples, an applied pressure enhances significantly the Curie temperature (dTC/dP∼2 K/kbar), enhances the ferromagnetic phase volume below TC, and narrows appreciably the hysteresis in the vicinity of TC. For x=0.2 and 0.5 samples, pressure does not affect practically the magnetic transition temperature, but reduces noticeably the magnetization in a wide temperature range. Observed phenomena for x=0.015 and 0.03 samples are related to the interfacial elastic energy at the interface of different magnetic phases and to the suppression of the Jahn–Teller distortions under pressure. For higher doped samples, pressure possibly increases antiferromagnetic interactions between Cr3+ and Mn4+ ions.

Magnetic properties of polycrystalline Sm0.1Ca0.9−ySryMnO3 (y = 0–0.3) samples have been investigated in the temperature range 5–250 K, magnetic fields up to 16 kOe and under hydrostatic pressures up to 11 kbar. The studies involved sequential measurements of zero field cooled (ZFC) magnetization and measurements of magnetization upon cooling in the same magnetic field (FCC). The low-doped group (y = 0–0.1) exhibits magnetic phase separation below TN≈TC≈100–110 K, consisting of ferromagnetic (FM) clusters embedded in an antiferromagnetic (AFM) G-type matrix. Magnetization and ac-susceptibility measurements of this group of materials indicate features reminiscent of a cluster glass-like state, below TC. It was found that the volume fraction of the FM phase at 10 K decreases with increasing y from 28% for Sm0.1Ca0.9MnO3 to 18% for Sm0.1Ca0.8Sr0.1MnO3. It was found that an applied pressure enhances TC with a pressure coefficient of dTC/dP≈0.4–0.5 K kbar−1. The low-temperature magnetization at this doping range (y = 0–0.1) depends on pressure only slightly, except for the case of Sm0.1Ca0.8Sr0.1MnO3, where an applied pressure enhances the FM phase volume considerably. Samples with y = 0.2 and 0.3 exhibit a heterogeneous spin configuration in their ground state, consisting of a C-AFM phase and a G-AFM phase with a very weak FM moment. The temperature of transition from the paramagnetic to the C-AFM state is almost insensitive to applied pressure, whereas the lower transition temperature to the G-AFM state increases slightly under pressure. It was found also that an applied pressure considerably reduces the FM correlations in the paramagnetic phase as well as the FM component of the G-AFM state.

The magnetic properties of La0.70Sr0.30MnO2.85 anion-deficient manganite are studied experimentally under hydrostatic pressure. The results show that, in the whole pressure range under investigation (0–1 GPa), the sample is a spin glass with a smeared phase transition to the paramagnetic state. It is found that the spin glass state arises from the frustration of the exchange coupling of the ferromagnetic clusters embedded in the antiferromagnetic matrix. The fraction of the sample volume occupied by the ferromagnetic phase is found to be V fer ∼ 13%. Under hydrostatic pressure, the freezing temperature T f of the magnetic moments of the ferromagnetic clusters increases at a rate of 4.30 K/GPa and the magnetic ordering temperature T MO increases at a rate of 12.90 K/GPa. In addition, the ferromagnetic part of the sample increases by ΔV fer ∼ 5%. The enhancement of the ferromagnetic properties of La0.70Sr0.30MnO2.85 anion-deficient manganite under hydrostatic pressure is explained by the redistribution of oxygen vacancies and a decrease in the unit-cell parameters.

Measurements of electrical resistance and magnetization of an La 0.8 Ca 0.2 MnO 3 single crystal were carried out at temperatures below and above the Curie temperature, T C =183.5±1 K. The effect of applied hydrostatic pressure P and magnetic field H on the magnetization and the resistive properties were also investigated. It was found that the pressure coefficient of the Curie temperature is rather small d T C /d P ≈0.3 K/kbar. At low temperatures a positive magnetoresistance was found. A nonlinear dependence of resistivity as a function of DC current was revealed. The results are interpreted in the frame of phase separation scenario.

Investigations are performed of the crystal structure and magnetic and electromagnetic properties of single crystals (0.23 ≤x≤0.34) and polycrystals (0 ≤x ≤0.50) of an Nd1−x BaxMnO3−δ system of solid solutions. It is found that, for samples prepared in the air, the maximal Curie temperature (T C ) does not exceed 150 K, while, in the case of polycrystalline samples in the concentration range of 0.34 ≤x ≤0.50, prepared in a reducing medium (a gaseous mixture of argon and carbon monoxide), T C increases to 320 K. As a result of the reducing medium effect on the compositions, the type of the magnetic phase transition to the paramagnetic state changes from the first to second order. The electrical resistivity of reduced polycrystalline samples (0.34≤x ≤0.50) decreases in magnitude and correlates with the behavior of magnetization. Both series of samples, prepared both in the air and in a reducing medium, exhibit a transition from the metal to dielectric state at a temperature below T C . The temperature and field dependences of magnetization for the stoichiometric polycrystalline com-position of Nd0.50Ba0.50MnO3 are measured under conditions of hydrostatic pressure. It is demonstrated that the hydrostatic pressure induces in Nd0.50Ba0.50MnO3 the transition from the antiferromagnetic to ferromagnetic state. Based on the measurement results, hypothetical magnetic phase diagrams are constructed for the system of solid solutions being treated, depending on the concentration of barium and the method of preparation. It is found that no T TC increase is observed in single crystals (0.23≤x≤0.34) such as is observed in polycrystals. It is assumed that the abrupt increase in T C of polycrystalline samples prepared in a reducing medium is a result of the emergence of extended defects and microstresses in the crystal lattice.

Magnetization, electrical resistivity and magnetoresistance of Pr 0.50 Ba 0.50 MnO 3− δ manganites with perovskite structure have been investigated as a function of preparation conditions. It was found that the as-prepared samples (prepared in air) show T C =110 K (first order phase transition), whereas for those annealed in flowing argon the T C value increases up to 340 K without change of cubic symmetry (second order phase transition). Ferromagnet–paramagnet transition is accompanied by both a metal–insulator transition and a magnetoresistance peak. The X-ray study has revealed that the samples annealed in argon have broad peaks apparently due to microstrains and crystal structure defects. The argon-treated samples improve the magnetization after subsequent annealing in air at T ⩽1000°C. T C of argon-treated samples is stable with respect to annealing in air up to 1300°C where it becomes again 110 K. In contrast, a treatment in vacuum destroys the ferromagnetic order. Auger-spectroscopy has not revealed any additional ions except Pr, Ba, Mn and O for all the samples. External pressure enhances the Curie point of the sample prepared in air at a rate of 43 K/GPa. We have observed that the samples Pr 1− x Ba x MnO 3− δ , x⩾ 0.30, exhibited the above-mentioned effect of increasing T C after treatment in flowing argon without changes of the phase state, whereas the samples x T C after argon treatment is supposed to result from microstrains and crystal structure defects in the sample.

The pressure effect on exchange bias (EB) and coercive fields, ${H}_{\mathrm{E}}$ and ${H}_{\mathrm{C}}$, in phase-separated ferromagnetic/antiferromagnetic (FM/AFM) CaMn${}_{1\ensuremath{-}x}$Ru${}_{x}$O${}_{3}$ manganites with 0.06 \ensuremath{\le} $x$ \ensuremath{\le} 0.15 was studied by magnetization measurements performed in the temperature range 10--200 K and under hydrostatic pressure up to 11 kbar. Both ${H}_{\mathrm{E}}$ and ${H}_{\mathrm{C}}$ exhibit intriguing dependence on Ru doping and on applied pressure. It was found that ${H}_{\mathrm{E}}$ is apparent only at $x$ 0.1 and decreases progressively with increasing doping, while ${H}_{\mathrm{C}}$ depends nonmonotonically on Ru content, reaching a maximum at around $x$ \ensuremath{\sim} 0.09. The ${H}_{\mathrm{E}}$ was found to increase strongly under applied pressure within doping range 0.06 \ensuremath{\le} $x$ \ensuremath{\le} 0.1, while ${H}_{\mathrm{C}}$ exhibits irregular behavior, namely, increases with increasing pressure for $x$ $=$ 0.15, changes nonmonotonically for $x$ $=$ 0.1, decreases for $x$ $=$ 0.08, and is almost invariable for $x$ $=$ 0.06. Complex pressure and Ru-doping effects on ${H}_{\mathrm{E}}$ and ${H}_{\mathrm{C}}$ are explained within a model involving size-variable nanoscale FM regions (droplets) embedded in an AFM matrix. The enhancement of EB with increasing pressure is attributed to the reduction in the FM droplet size, evidenced by both pressure dependence of spontaneous FM moment and ${H}_{\mathrm{E}}$ dependence upon cooling field ${H}_{\mathrm{cool}}$. The impact of FM droplet size on the EB was further evidenced by the magnetic field effect, which, in contrast to the pressure effect, leads to a growth of the FM droplets. The intricate ${H}_{\mathrm{C}}$ dependencies on both pressure and Ru content are understandable in a view of the transition from the multidomain state to the single-domain one, induced by droplet size decrease with increasing pressure or with doping lowering. Concisely, owing to the unique mechanism of valence modification, the external pressure appears to be an effective tool for controlling the EB and the coercivity in Ru-doped CaMnO${}_{3}$ perovskites.

The influence of hydrostatic pressure up to 1 GPa on the transition temperature to the superconducting state in orthorhombic samples of GdBa1.5Sr0.5Cu3Ox with the oxygen content x=6.63, 6.73 and 6.93 has been studied. The observations of Tc changes were done by means of DC magnetic-susceptibility measurements. A monotonical strong increase of the pressure effect, dTc/dP, with decreasing x value has been found. This behavior differs from the complex character of the dependence of dTc/dP on the oxygen content in YBa2Cu3Ox. In the case of GdBa1.5Sr0.5Cu3O6.63 a pressure effect dTc/dP as high as 13.7 K/GPa was obtained, higher than that reported for YBa2Cu3O6.71 (11.5 K/GPa) in the region of the ortho(I)-to-ortho(II) transition.

Magnetic properties of self-doped LaMn1−xO3 manganites (0⩽x⩽0.06) under hydrostatic pressure up to 12 kbar have been investigated. Samples with x=0 and 0.02 are antiferromagnetic insulators with a Neel temperature TN=138 K and 124 K, respectively. Materials with x=0.04 and 0.06 are ferromagnetic with a Curie temperature TC close to 110 K. With increasing self-doping, the ferromagnetic moment at T=5 K increases significantly while the pressure coefficient of TN decreases significantly. Pressure dependences of TC and of spontaneous magnetization are markedly different. For x=0.04, both quantities increase under increasing pressure. However, for x=0.06 transition temperature becomes pressure independent while magnetization markedly decreases with increasing pressure. Suppression of the ferromagnetism under pressure is tentatively attributed to the development of antiferromagnetic domains capable of competing with the ferromagnetic order under pressure.

Pressure effect on magnetic properties of polycrystalline La${}_{1\ensuremath{-}x}$Ba${}_{x}$CoO${}_{3}$ (0.1 \ensuremath{\leqslant} $x$ \ensuremath{\leqslant} 0.5) was studied by magnetization measurements in the temperature range 5--240 K, magnetic field up to 16 kOe, and under hydrostatic pressure up to 10.5 kbar. For low-doped cobaltites ($x$$=$0.1,0.15), it was found that applied pressure enhances the ferromagnetic (FM) cluster phase, resulting in an increase of both spontaneous FM moment and transition temperature of clusters ${T}_{C}^{\mathrm{cl}}$, while the freezing temperature ${T}_{f}$ lowers under pressure appreciably (${\mathit{dT}}_{f}/\mathit{dP}$ \ensuremath{\approx} \ensuremath{-}1.4 K/kbar), suggesting the weakening of interaction between clusters. For higher-doped La${}_{1\ensuremath{-}x}$Ba${}_{x}$CoO${}_{3}$ (0.2 \ensuremath{\leqslant} $x$ \ensuremath{\leqslant} 0.5), having developed long-range FM order, the systematic increase of ${T}_{C}$ under pressure was observed with coefficient ${\mathit{dT}}_{C}/\mathit{dP}$ linearly increasing with doping up to 1.8 K/kbar at $x$$=$0.5, the highest value reported for cobaltites. The positive value of the ${\mathit{dT}}_{C}/\mathit{dP}$ coefficient found for the Ba compound in a whole range of studied doping is in strong contrast to that found in Ca and Sr cobaltites, where the ${\mathit{dT}}_{C}/\mathit{dP}$ was found to change a sign from a negative to a positive one with increasing doping. It is shown that the sign reversal of the ${\mathit{dT}}_{C}/\mathit{dP}$ coefficient for La${}_{1\ensuremath{-}x}{M}_{x}$CoO${}_{3}$ ($m$$=$Ca,Sr,Ba) cobaltites can be caused by the hole doping and also, independently, by the lattice expansion only induced by an increase of the dopant ion size. The complex pressure effect on ferromagnetic transition ${T}_{C}$ in cobaltites is well described in terms of competing ${e}_{g}$-electron bandwidth $\mathit{W}$ and crystal-field splitting energy, basing on the known pressure variations of the steric factors. For La${}_{1\ensuremath{-}x}$Ba${}_{x}$CoO${}_{3}$ with $x$$=$0.3,0.5, having a high enough concentration of intermediate spin Co states, we observed a Jahn-Teller-like magnetic transition signified by a distinct hysteresis in field-cooled magnetization below ${T}_{C}$. This transition was found to disappear under moderate applied pressure, evidenced for La${}_{0.7}$Ba${}_{0.3}$CoO${}_{3}$ by abrupt changes in the spontaneous magnetization and coercive field at 5 K.

Magnetic properties of compacted La0.8Ca0.2MnO3 manganite nanoparticles with average particle size of 18 and 70 nm and Curie temperatures TC 231 K and TC 261 K, respectively, have been investigated. The relative volume of the ferromagnetic phase has been estimated to be 52% for ensembles of 18 nm particles and 92% for 70 nm particles. It was found that applied hydrostatic pressure enhances TC of La0.8Ca0.2MnO3 nanoparticles at a rate dTC /dP 1.8– 1.9 K / kbar, independently on the average particle size. Pronounced irreversibility of magnetization below Tirr 208 K and strong frequency dependent ac susceptibility below TC for smaller 18 nm particles have been observed. 18 nm particles have also shown aging and memory effects in zero-field-cooled ZFC and field-cooled magnetization. These features indicate the appearance of spin-glasslike state, partially reminiscent the behavior of La1�xCaxMnO3 crystals, doped below the percolation threshold xxC = 0.225. In contrast, ensembles of larger 70 nm particles have shown insignificant irreversibility of magnetization only and no frequency dependence of ac susceptibility, similarly to the behavior of La1�xCaxMnO3 crystals with xxC. The temperature of the ZFC magnetization maximum for 18 nm particles decreases with increasing magnetic field and forms a critical line with an exponent 1.89 0.56. The results suggest that superspin-glass features in ensembles of interacting 18 nm particles appear along with superferromagnetic-like features.

Magnetic properties of polycrystalline ${\mathrm{Pr}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{O}}_{3}\phantom{\rule{0.3em}{0ex}}(x=0.015,0.03)$ samples have been investigated in the temperature range $1.5--300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, magnetic field up to $16\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$ and under hydrostatic pressures up to $11\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$. The studies involved sequential zero field cooled (ZFC) magnetization $(M)$ measurements followed by measurements during cooling in the same magnetic field $(H)$. Additional measurements of magnetization vs $H$ were carried out at ambient and applied pressure. The volume of the ferromagnetic phase for $x=0.015$ sample exhibits a considerable decrease upon thermal cycling even after many cycles. On the other hand, both the Curie temperature $({T}_{\mathrm{C}})$ and the width of thermal hysteresis remain practically unchanged during the thermal cycling. In contrary to the effect of thermal cycling, applied pressure enhances ${T}_{\mathrm{C}}$ and the volume of the ferromagnetic phase below ${T}_{\mathrm{C}}$ and reduces considerably the width of thermal hysteresis. A ferromagnetic contribution to magnetization due to short range ferromagnetic coupling was observed in the vicinity of the charge order transition temperature ${T}_{\mathrm{CO}}\ensuremath{\approx}220\phantom{\rule{0.3em}{0ex}}\mathrm{K}$; it appears to enhance under pressure. In the case of ${\mathrm{Pr}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{Mn}}_{0.97}{\mathrm{Cr}}_{0.03}{\mathrm{O}}_{3}$ an applied pressure also increases the magnetization and ${T}_{\mathrm{C}}$ with a pressure coefficient of $d{T}_{\mathrm{C}}∕dP\ensuremath{\approx}1.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}∕\mathrm{kbar}$, at the same time the hysteresis in the vicinity of ${T}_{\mathrm{C}}$ narrows. The results observed are related to the interfacial elastic energy at the phase boundaries of the phase separated Cr doped manganites. The effect of the suppression of the Jahn-Teller distortions and of the electron-phonon coupling in interfacial regions and in ferromagnetic domains under an applied hydrostatic pressure is also discussed.

Magnetic properties of polycrystalline ${\mathrm{CaMn}}_{1\ensuremath{-}x}{\mathrm{Ru}}_{x}{\mathrm{O}}_{3}(x=0--0.5)$ samples were investigated in the temperature range $4.2--250\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, under external magnetic field up to $15\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$ and under hydrostatic pressure up to $12\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$. Transport properties of the samples with $x=0.1$, 0.2, 0.4, 0.5 were also investigated under pressure up to $10\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$. For $x$ up to 0.4, the pressure was found to suppress ferromagnetic correlations and to increase the resistivity, while for $x=0.5$ to act in the opposite way. While long ferromagnetic order is completely suppressed, in small clusters ferromagnetic correlations probably survive under pressure, as was revealed for ${\mathrm{CaMn}}_{0.9}{\mathrm{Ru}}_{0.1}{\mathrm{O}}_{3}$. The pressure effect on the magnetic interactions and on the volume of ferromagnetic phase was found to depend strongly on the Ru content, and absolute value of the pressure coefficient of spontaneous magnetization was found to decrease practically linearly with increasing $x$ in the range $0.1lxl0.5$. The experimental data are discussed in the frame of proposed energy-level diagram, which includes magnetoimpurity states at low and moderate Ru content and mixed-valence states of Ru presented by a strongly correlated ${t}_{2g}$-like band at heavy Ru doping. An impact of disorder introduced by Ru doping on the energy diagram and on derived magnetic interactions is discussed. Predictions of the model regarding the pressure effects on conductivity and temperature scales characteristic for magnetic interactions are in reasonable agreement with experiment.

Pressure effect on magnetic order and anisotropy of low-doped ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Co}{\mathrm{O}}_{3}$ $(0.1\ensuremath{\leqslant}x\ensuremath{\leqslant}0.2)$ and ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Co}{\mathrm{O}}_{3}$ $(0.1\ensuremath{\leqslant}x\ensuremath{\leqslant}0.3)$ single crystals and ceramics was studied by magnetization measurements. It was found that applied hydrostatic pressure leads to a quite different effect on ferromagnetic (FM) interactions in materials doped with ions of different size. For ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Co}{\mathrm{O}}_{3}$, a remarkable suppression of FM interactions leading to a contraction of FM phase fraction was observed under pressure, in good agreement with reduction of effective paramagnetic moment ${\ensuremath{\mu}}_{\mathrm{eff}}$ and already reported pressure-induced increase of electrical resistivity. The behavior may be explained by recently proposed mechanism of pressure-induced suppression of double exchange FM interactions in cobaltites, due to an increase of the energy of the crystal-field splitting $({t}_{2g}\ensuremath{-}{e}_{g})$, leading to a suppression of ${e}_{g}$-electron hopping. In strong contrast, an opposite pressure effect on ferromagnetism was found in ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Co}{\mathrm{O}}_{3}$. It appears that pressure enhances visibly the FM interactions in the spin- or cluster-glass state as well as in the long-range FM state for $x=0.3$ but surprisingly the pressure coefficient $d{T}_{C}∕dP$ changes sign at the percolation threshold. The intricate behavior indicates on a competition of at least two different mechanisms on overall pressure effect in ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Co}{\mathrm{O}}_{3}$ with an expanded unit cell caused by doping with a large size ion. In addition, in Sr-doped single crystals with developed long-range FM order, a drastic changes in magnetic anisotropy with pressure were observed at around $9\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$, leading in the case of ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Co}{\mathrm{O}}_{3}$ to nearly isotropic magnetization within the $ac$ plane at $Pg9\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$. The radical changes in the magnetic anisotropy suggest some kind of pressure-induced phase transition.

Measurements of electrical resistance, magnetization, ac magnetic susceptibility, and ferromagnetic resonance of ${\mathrm{La}}_{0.82}{\mathrm{Ca}}_{0.18}{\mathrm{MnO}}_{3}$ single crystal were carried out at temperatures below and above the Curie temperature, ${T}_{C}=180\ifmmode\pm\else\textpm\fi{}1\mathrm{K}.$ A state of mixed ferromagnetic phases, metallic and insulating, is clearly evident from the measurements of magnetization, ac susceptibility, and electron magnetic resonance, below ${T}_{C}.$ The effect of applied hydrostatic pressure P and magnetic field H on the magnetic and the resistive properties were also investigated. It was found that the pressure enhances the magnetization, ${T}_{C},$ and stabilizes the ferromagnetic metal-like phase. It is concluded that phase separation plays an important role in most magnetic and transport effects observed in ${\mathrm{La}}_{0.82}{\mathrm{Ca}}_{0.18}{\mathrm{MnO}}_{3}$ below and above ${T}_{C}.$

The pressure effect on magnetic order and anisotropy of low-doped ${\mathrm{LaMnO}}_{3.05}$ single crystals with two competing ferromagnetic and antiferromagnetic insulating phases was studied by magnetization measurements. It was found that applied hydrostatic pressure leads to an increase of both Curie and N\'eel temperatures, with different rates: ${\mathrm{dT}}_{C}/dP=0.8\mathrm{K}/\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r}$ and ${\mathrm{dT}}_{N}/dP=0.16\mathrm{K}/\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r}.$ External pressure strongly suppresses the magnetic anisotropy, resulting in a decrease of the coercive field ${H}_{C}$ with ${\mathrm{dH}}_{C}/dP=\ensuremath{-}0.1\mathrm{k}\mathrm{O}\mathrm{e}/\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r}.$ The results obtained indicate that the applied pressure both enhances ferromagnetic interactions and enlarges the volume fraction of the ferromagnetic phase. The evolution of the ferromagnetic phase was explained taking into account the reduction of the Jahn-Teller distortion with increasing pressure. Changes in ferromagnetic characteristics ${T}_{C},$ ${H}_{C},$ and spontaneous magnetization ${M}_{0}$ result mainly from the shortening of the long Mn-O distance in the ${\mathrm{MnO}}_{6}$ octahedron. Moreover, we found a similarity in dependences of those parameters on the degree of the ${\mathrm{MnO}}_{6}$ distortion for two different effects: hydrostatic pressure and the level of self-doping \ensuremath{\delta}. Such a similarity strongly suggests that pressure-induced suppression of the Jahn-Teller distortion is responsible for the observed enhancement of ferromagnetism in the ${\mathrm{LaMnO}}_{3.05}$ crystals.

Ferromagnetic and transport properties of ${\mathrm{La}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{MnO}}_{3}$ and ${\mathrm{La}}_{0.78}{\mathrm{Ca}}_{0.22}{\mathrm{MnO}}_{3}$ single crystals were studied in temperature range $4.2\mathrm{K}lTl300\mathrm{K}$ and under hydrostatic pressure up to 12 kbar. It was found that the above compounds exhibit different shifts of Curie temperatures ${T}_{C}$ under pressure. For ${\mathrm{La}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{MnO}}_{3}$ ${\mathrm{dT}}_{C}/dP\ensuremath{\approx}0.3\mathrm{K}/\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r},$ whereas for ${\mathrm{La}}_{0.78}{\mathrm{Ca}}_{0.22}{\mathrm{MnO}}_{3}$ a stronger nonlinear increase ${T}_{C}(P)$ was observed. A significant change of the easy axis magnetization with temperature was found for ${\mathrm{La}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{MnO}}_{3},$ in the (110) plane. The above effect is almost entirely suppressed by an external pressure of 6 kbar. The ac susceptibility of ${\mathrm{La}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{MnO}}_{3}$ shows a sharp frequency dependent increase at $T=80\mathrm{K},$ upon heating indicating a transition to cluster spin-glass formation. The results observed are discussed regarding a coexistence of ferromagnetic metallic and ferromagnetic insulating phases.

Magnetic properties of ${\mathrm{Sm}}_{0.2}{\mathrm{Ca}}_{0.8}{\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Ru}}_{x}{\mathrm{O}}_{3}$ $(x=0,$ 0.04, and 0.08) are investigated in the temperature range 4.2--240 K, external magnetic fields up to 15 kOe and hydrostatic pressure up to 12 kbar. Transport properties of ${\mathrm{Sm}}_{0.2}{\mathrm{Ca}}_{0.8}{\mathrm{Mn}}_{0.92}{\mathrm{Ru}}_{0.08}{\mathrm{O}}_{3}$ are also investigated in the temperature range 77--280 K and under pressure up to 10 kbar. It is found that for a pristine phase $(x=0),$ hydrostatic pressure increases the ferromagnetic domains embedded in an antiferromagnetic matrix, and slightly decreases the N\'eel temperature. The effect of pressure on the magnetic interactions depends upon Ru doping. For ${\mathrm{Sm}}_{0.2}{\mathrm{Ca}}_{0.8}{\mathrm{Mn}}_{0.96}{\mathrm{Ru}}_{0.04}{\mathrm{O}}_{3}$ an applied pressure decreases both Curie and N\'eel temperatures, but enhances the ferromagnetic fraction. In the case of ${\mathrm{Sm}}_{0.2}{\mathrm{Ca}}_{0.8}{\mathrm{Mn}}_{0.92}{\mathrm{Ru}}_{0.08}{\mathrm{O}}_{3}$ an applied pressure suppresses the ferromagnetic interactions and surprisingly increases the resistivity. To the best of our knowledge this is the first time that such an effect was observed in perovskites. All of the above observations are discussed in the context of phase separation.

Magnetic and transport properties of Pr 0.8 Ca 0.2 MnO 3 crystal have been studied. It was found that the magnetic anisotropy in (1 0 0) plane increases with decreasing temperature and increasing pressure. The resistivity for T >140 K obeys Arrhenius law with an activation energy E a =130 meV, while at T E a =62 meV. The magnetoresistance maximizes near the Curie temperature of Mn moments T C1 =130 K. The dynamic resistivity shows a marked dependence on a bias current I at T T C1 . The results are discussed in the frame of magnetic phase separation and spin-density wave scenario.

Magnetic and structural properties of nanocrystalline low-doped La0.8Ca0.2CoO3 cobaltites with particle size of 8, 13, 23, and 50 nm, prepared by the glycine-nitrate method, were investigated in temperature range 5–320 K, magnetic field up to 50 kOe and under hydrostatic pressure up to 10 kbar. With particle downsizing, a noticeable expansion of unit cell, with concomitant changes in the rhombohedral structure toward the cubic one was observed. It was found that the increased surface-disorder effect strongly suppresses the ferromagnetic state in La0.8Ca0.2CoO3 nanoparticles leading to a decrease, by factor of about 2, both in spontaneous magnetization, MS, and Curie temperature, TC, when particle’s size decreases from 23 to 8 nm. The effective magnetic moment μeff was found also to decrease distinctly due to the strong interdependence between Co–O–Co interactions and Co spin state. The size-induced magnetic disorder drives the La0.8Ca0.2CoO3 nanoparticles to a dominant glassy behavior for 8 nm particles. This is evidenced by the fact that the freezing temperature varies with magnetic field in a strict conformity with the de Almeida–Thouless law for spin glasses and also by the observation of characteristic slowing down in the spin dynamics. The applied pressure suppresses TC, MS, and coercive field HC, like it is observed for bulk La0.8Ca0.2CoO3. Nevertheless, in nanoparticles the pressure effect on TC is noticeably stronger, while HC diminishes with pressure much slower then in bulk material.

Structural, magnetic, and transport properties in Pr0.5Ca0.5Mn1−xNixO3 (x=0, 0.04, 0.07, 0.1) were investigated. It is remarkable that low Ni-doping levels at Mn sites induce drastic changes in the physical properties of Pr0.5Ca0.5MnO3 due to melting of the charge ordered state and the consequent capability of Ni ions to create ferromagnetic (FM) clusters. It was found that oxygen deficient samples (3−δ=2.84±0.03) exhibit resistivities higher by four to five orders than that of their stoichiometric counterparts and do not exhibit metal-insulator transition. Only a stoichiometric x=0.04 sample with higher content of the FM phase shows metal-insulator transition at T≈80 K. A change in slope in the zero field cooling magnetization curve observed for x=0.04 and 0.07 (may be slightly oxygen deficient samples) are indicative of spin-glass-like state. Applied hydrostatic pressure of about 10 kbars reduces the temperature of charge ordering in x=0 sample by about 10 K indicating on pressure induced suppression of...

The magnetic properties of nanocrystalline manganites La1?xMnO3+? with particle size of 20 (LMO20), 25 (LMO25), and 30 nm (LMO30), prepared by the citrate method, have been investigated in the temperature range 5?320?K, magnetic field up to 90?kOe and under quasi-hydrostatic pressures up to 14.5?kbar. The studies involve sequential zero-field-cooled magnetization (M) measurements followed by magnetization measurements during cooling in the same magnetic field (H) and complementary measurements of ac susceptibility. Additional measurements of M versus H were carried out at ambient and applied pressures. All nanoparticles exhibit a paramagnetic to ferromagnetic transition (PFT) at a Curie temperature TC>200?K. It was found that the relative volume of the ferromagnetic phase increases for larger particle size and approaches a value of about 93% for LMO30. The real part of the ac susceptibility of sample LMO20 exhibits strong frequency dependence in a wide temperature range below TC, whereas for sample LMO30 only relatively weak frequency dependence was observed. The magnetization of sample LMO30 exhibits a PFT of second order; the type of transition could not be established for the smaller particles. It was found that an applied pressure enhances the TC of La1?xMnO3+? nanoparticles with a pressure coefficient of dTC/dP?1.9?K?kbar?1 for LMO20 and dTC/dP?1.4?K?kbar?1 for LMO25 and LMO30 samples. Peculiar magnetic memory effects observed for sample LMO20 are discussed.