Showing papers on "Metamagnetism published in 1997"

Magnetic phase diagram of CexLa1-xB6 studied by static magnetization measurement at very low temperatures

Abstract: DC magnetization of single crystals of Ce x La 1- x B 6 , 0.5≤ x ≤1, have been measured at low temperatures ( T ) down to 40 mK in magnetic field H //[100], and the H - T - x phase diagrams were obtained. At zero field, the antiferro-quadrupolar (AFQ) transition temperature T Q rapidly decreases with decreasing x and vanishes abruptly between x =0.75 and 0.7. The Neel temperature T N , which is lower than T Q in CeB 6 , varies more slowly with x and exceeds T Q for \(x \gtrsim 0.8\). A clear peak observed in the susceptibility strongly suggests that a new antiferromagnetic (AF) state having no AFQ moment (phase IV) exists for \(0.8\gtrsim x\gtrsim 0.5\), in addition to the two ordered phases II (AFQ) and III (AF+AFQ). As H increases, a first-order phase IV-III transition is observed with a metamagnetic jump in the magnetization. Successive I (paramagnetic)-IV-III phase transitions are observable in a very narrow region of the H - T - x space.

Structure and magnetic properties of TbMn6−xAlxSn6 compounds

Abstract: In the present work, the influence of the substitution of Al for Mn on the structure and magnetic properties of TbMn6−xAlxSn6 compounds was investigated. With increasing Al concentration the lattice constants a, c, and the unit-cell volume V decrease monotonically. The TbMn6−xAlxSn6 compounds exhibit ferrimagnetic ordering. The magnetic ordering temperature first decreases with increasing Al content up to x=1.5, then increases with further increasing Al content. As for the unsubstituted material, it was found that this series of compounds exhibits a second magnetic transition at lower temperature that is attributed to spin reorientation. The spin-reorientation temperature and the magnetic anisotropy field first decrease with increasing Al content, go through a minimum at x=0.5, then increase with further increasing Al content. The saturation magnetization decreases monotonically with increasing Al content. Two metamagnetic transitions are found in TbMn6Sn6 compounds, one at 0.44 T, and the other at about ...

Single crystal growth and magnetic properties of CeRh2Si2

Abstract: We have grown single crystals of CeRh 2 Si 2 and LaRh 2 Si 2 by the Czochralski pulling method in a tetra-arc furnace. The electrical resistivity and magnetic susceptibility are highly anisotropic, reflecting the tetragonal crystal structure. A metamagnetic transition is found for the magnetic field along the [001] direction at 26 T.

Fermi Surface Properties and Metamagnetism in the Antiferroquadrupolar Compound PrPb3

Abstract: We have measured the de Haas-van Alphen effect of PrPb 3 whose antiferroquadrupolar ordering occurs at 0.4 K. Main Fermi surfaces consist of four closed ones, which are almost spherical. These Fermi surfaces are the same as those of a non- f reference compound LaPb 3 in topology, although the cyclotron effective masses are 2 to 6 times larger than those of LaPb 3 . The cyclotron effective masses are temperature-dependent, which starts gradually with decreasing the temperature below 1 K. A metamagnetic transition is also found to occur at about 70 kOe below 0.6 K through the magnetization, magnetostriction and AC susceptibility measurements. These phenomena are closely related to the antiferroquadrupolar ordering at 0.4 K.

Effects of external pressure on the 5f-band metamagnetism in UCoAl

Abstract: UCoAl exhibits below 16 K anisotropic 5f-band metamagnetism induced by magnetic fields as low as \ensuremath{\sim}1 T applied along the c axis of the hexagonal structure. No metamagnetic transition is observed in fields up to 40 T applied within the basal plane. The critical field of the metamagnetic transition ${\mathrm{B}}_{\mathrm{c}}$ is composition dependent within the homogeneity range. The metamagnetic transition is found to be very sensitive to external pressure. The value of ${\mathrm{B}}_{\mathrm{c}}$ increases with the rate ${\mathrm{dB}}_{\mathrm{c}}$ /dp=0.27 T/kbar, whereas the magnetization gained through the transition becomes reduced. The critical pressure of 24 kbar (corresponding to \ensuremath{\sim}2% volume contraction) for disappearance of metamagnetism in UCoAl has been estimated. Relations of UCoAl to 3d-band metamagnets are discussed.

Itinerant-electron metamagnetism and the onset of ferromagnetism in Laves phase compounds

Abstract: Detailed magnetization measurements have been carried out for Laves phase compounds which have a C15-type structure up to x = 0.220. A clear increase in the lattice constant occurs at room temperature in the vicinity of x = 0.095, corresponding to the critical concentration of the onset of ferromagnetism. A representative first-order metamagnetic transition was observed in the compounds with x = 0.090 and 0.093 in relatively low fields below 9 T. The critical temperature from the first- to second-order metamagnetic transition in both compounds and the susceptibility maximum temperature for several paramagnetic compounds were obtained. It should be noted that practically coincides with for x = 0.093, very close to the critical concentration of the onset of ferromagnetism. This result is well explained by the recent theory associated with spin fluctuations. The temperature shifts to lower temperatures with increasing x and disappears at x = 0.095 and above, correlated with the onset of ferromagnetism also. The spontaneous magnetization per Co atom exhibits a maximum value of at x = 0.110, whereas the Curie temperature does not show a maximum value at the same composition.

Metamagnetism in tetrachlorobis(N-phenylacetamidine)rhenium(IV)

Abstract: Single-crystal magnetisation and polarised neutron diffraction (PND) measurements have been made for the complex cis-[ReCl 4 (NHCMeNHPh) 2 ]. At higher temperatures the magnetic behaviour is typical of such a rhenium-(IV) complex, with three unpaired spins (µ = 3.6 µ B ), an almost isotropic g-tensor of 1.86(1) and a large zero-field splitting, 2D, of -20(2) cm -1 . At very low temperatures the magnetisation behaviour as a function of temperature and field strength and direction indicates two magnetically ordered structural phases when H||b, but only one for a and c, with T N = 9.7(1) K. A tricritical point at T = 5.8(2) K and H = 4.40(5) T was established on the transition line in H vs. T space between the two phases when H||b. This behaviour is metamagnetic. The two-dimensional form of the stronger magnetic exchange implied, with weaker interlayer interaction, can be correlated with the observed structural feature of ab planes of ReCl 4 units separated by layers of phenyl rings. The PND experiment showed that about half of the spin of the system is delocalised away from the Re by covalent bonding to the Cl atoms and the amidine ligand, accompanied by considerable effects resembling spin polarisation. The magnetic space groups are P2 1 /c at low magnetic fields and Pc2 1 n at high fields along b, compared with the nuclear structural space group of Pccn.

Magnetic ordering in perovskites containing manganese and cobalt

Abstract: The magnetization measurement of systems with the nominal formula (R = Eu, Gd, Tb, Y) has been made. It has been found that and are weak ferromagnets of Dzialoshinsky - Moriya type whereas is an antiferromagnet. The substitution of manganese ions by cobalt ones leads to the appearance of different magnetic states: cluster-spin-glass-like , inhomogeneous ferromagnets with well defined Curie temperatures and again a spin glass state . Spontaneous magnetizations and Curie temperatures reach maxima for compounds with x = 0.5. External magnetic field induces a metamagnetic transition in (R = Gd, Tb, Y). The transition becomes irreversible at low temperature in the Tb- and Y-based compounds. The annealing in vacuum of leads to the increase of the Curie temperature and to the appearance of a metamagnetic transition for the compound. The metamagnetic behaviour is interpreted taking into account the ionic ordering of and ions and possible 3d-orbital ordering in the sublattice.

The thermomagnetic irreversibility and metamagnetic behaviour of

Abstract: The results of magnetization measurements on , which orders antiferromagnetically , show interesting thermomagnetic irreversibility and metamagnetic behaviour. The possible origins of such effects are discussed.

Magnetic hyperfine interactions in the Zintl phase EuZnSn

Abstract: Magnetic susceptibility, 119 Sn and 151 Eu Mossbauer effect measurements are reported for the Zintl phase EuZnSn which crystallizes with the TiNiSi-type structure. The stannide shows Curie–Weiss behaviour above 40 K with an experimental magnetic moment of µ exp =7.88(5) µ B /Eu, close to that of the free Eu 2+ ion of µ eff =7.94 µ B . At 20.5(2) K a magnetic phase transition to the antiferromagnetic state is observed in the temperature dependence of the inverse susceptibility at a magnetic flux density of 0.01 T. Magnetization measurements at 5 K indicate metamagnetism with a saturation magnetic moment of 6.80(5) µ B /Eu and a critical field of 0.7(1) T. 151 Eu Mossbauer measurements show an isomer shift δ=-10.9 mm s -1 against EuF 3 , as is typically observed for divalent europium. While onset of magnetic ordering is evident at T 0 =26.5(5) K, full magnetic order is detected near 15 K. 119 Sn Mossbauer spectra show a large transferred magnetic field of 12.8 T at 4.2 K. The temperature dependence of this field is closely correlated with the internal magnetic field measured at the 151 Eu site (23.4 T at 4.2 K).

Magnetization in Heavy-Fermion Compounds

Abstract: We calculate the magnetization as a function of magnetic field in the mean-field approximation for the periodic Coqblin-Schrieffer model. Prior to a metamagnetic second-order transition from heavy-fermion to local-moment state, a rapid increase in the magnetization, which resembles the metamagnetic-like behavior in CeRu 2 Si 2 , appears if the anisotropy of the hybridization matrix element is taken into account.

Collapse of the itenerant Co moment in Er1−xLuxCo2 by the application of high magnetic fields

Abstract: The collapse of the Co moment in the ferrimagnetic Er1−xLuxCo2 compounds has been studied by means of magnetization, magnetostriction and 59Co spin echo measurements. The collapse of the Co moment is observed at the critical concentration around x = 0.3 in zero magnetic field. The application of a high magnetic field also induces the moment collapse in the compounds below the critical concentration, which is observed as a metamagnetic transition. From the metamagnetic transition field of ErCo2 observed at 52 T, the exchange constant between Er and Co can be estimated to be JErCo = − 1.3 × 10−22 J.

Anomalous magnetoresistance near the metamagnetic transition in

Abstract: , a layered intermetallic compound, displays two magnetic phase transitions below room temperature, the lower one being a metamagnetic transition occurring near 100 K. We have completed measurements of both zero-field resistivity for and the magnetoresistance in fields of up to 8 T for temperatures between 1.5 and 120 K; in addition the magnetization has been studied in fields up to 5.5 T in the temperature range . As the spin configuration in the ordered phases remains uncertain, these measurements concentrate on the behaviour near the `ferromagnetic-to-antiferromagnetic' transition, and as such they can be compared and contrasted with those reported recently for Ru-doped in which the spin configurations are better known. Plots of the metamagnetic field as a function of temperature yield metamagnetic transition temperatures of between 94 and 96 K (in zero field), in good agreement with earlier estimates. Additional features are observed below 100 K in this system, suggesting differences between and the doped system, originating possibly from fundamental differences in spin structure.

Metamagnetism in tetrachlorobis (N - phenylacetamidine) - rhenium(IV)

Abstract: Single-crystal magnetisation and polarised neutron diffraction (PND) measurements have been made for the complex cis-[ReCl 4 (NHCMeNHPh) 2 ]. At higher temperatures the magnetic behaviour is typical of such a rhenium-(IV) complex, with three unpaired spins (µ = 3.6 µ B ), an almost isotropic g-tensor of 1.86(1) and a large zero-field splitting, 2D, of -20(2) cm -1 . At very low temperatures the magnetisation behaviour as a function of temperature and field strength and direction indicates two magnetically ordered structural phases when H||b, but only one for a and c, with T N = 9.7(1) K. A tricritical point at T = 5.8(2) K and H = 4.40(5) T was established on the transition line in H vs. T space between the two phases when H||b. This behaviour is metamagnetic. The two-dimensional form of the stronger magnetic exchange implied, with weaker interlayer interaction, can be correlated with the observed structural feature of ab planes of ReCl 4 units separated by layers of phenyl rings. The PND experiment showed that about half of the spin of the system is delocalised away from the Re by covalent bonding to the Cl atoms and the amidine ligand, accompanied by considerable effects resembling spin polarisation. The magnetic space groups are P2 1 /c at low magnetic fields and Pc2 1 n at high fields along b, compared with the nuclear structural space group of Pccn.

Band metamagnetism and related phenomena in Er(Co1-xSix)2

Abstract: We report on magnetic, transport, and cohesive properties of Er(Co1−xSix)2 compounds in varying external conditions (T,H,p). The localized Er 4f magnetic moments in ErCo2 order ferromagnetically below TC=33 K. The Co 3d band states form no moment above TC, but below TC the majority and minority 3d sub-bands split due to strong 4f−3d exchange interaction. Consequently, Co moments of ∼1 μB appear coupled antiparallel to the Er moments. This is accompanied by a ∼50% resistivity drop and an abrupt lattice expansion. The sharp magnetization, resistivity, and volume anomalies in the critical temperature region indicate a first order magnetic phase transition. Detailed comparative studies reveal that the onset of Co magnetizm appears at T0∼(TC−1) K. Si substitution for Co enhances both, TC (up to 66 K for x=0.1) and ΔT=TC−T0, but the lattice parameter remains unchanged. In opposite, both the magnetovolume and resistivity anomaly at T0 become reduced. Pressure effect on TC(T0) is large and negative, ∂ ln TC/∂p∼−2...

Anomalous magnetoresistance in antiferromagnetic polycrystalline materials R2Ni3Si5 (R=rare earth)

Abstract: Magnetoresistance (MR) studies on polycrystalline R2Ni3Si5, (R=Y, rare earth) which order antiferromagnetically at low temperatures, are reported here. MR of the Nd, Sm, and Tb members of the series exhibit positive giant magnetoresistance, largest among polycrystalline materials (85%, 75%, and 58% for Tb2Ni3Si5, Sm2Ni3Si5, and Nd2Ni3Si5, respectively, at 4.4 K in a field of 45 kG). These materials have, to the best of our knowledge, the largest positive GMR reported ever for any bulk polycrystalline compounds. The magnitude of MR does not correlate with the rare earth magnetic moments. We believe that the structure of these materials, which can be considered as a naturally occurring multilayer of wavy planes of rare earth atoms separated by Ni–Si network, plays a role. The isothermal MR of other members of this series (R=Pr,Dy,Ho) exhibits a maximum and a minimum, below their respective TN’s. We interpret these in terms of a metamagnetic transition and short-range ferromagnetic correlations. The short-range ferromagnetic correlations seem to be dominant in the temperature region just above TN.

Metamagnetism in perovskites RMnO3+x (R=Gd, Tb, Dy)

Abstract: A magnetic study of perovskites RMnO3+x (R = Nd, Eu, Gd, Tb, Dy) is reported. The compounds NdMnO2.99 and EuMnO2.99 are weak ferromagnets with TN=88 and 49 K respectively. It is shown that GdMnO3 undergoes a transition from antiferromagnetic to weak ferromagnetic state upon cooling. The antiferromagnetic ordering of the magnetic moments in the Gd sublattice is observed below 6 K. The magnetic moments of TbMnO3.01 and DyMnO3.01 are ordered below 7 K. The external field induces an antiferromagnet–ferromagnet transition in the rare-earth sublattice. The critical fields for GdMnO3,TbMnO3.01, and DyMnO3.01 are 5, 10, and 7 kOe, respectively.

Single-Site and Inter-Site Effects in Heavy Fermion Compound CeRu 2 Si 2 Studied by Constant Volume Dilution

Abstract: In order to study the single-site and inter-site effects in CeRu 2 Si 2 , a systematic diluting experiment has been performed with the single crystals of pseudo-ternary alloys Ce 1- x (La 0.63 Y 0.37 ) x Ru 2 Si 2 [0≤ x ≤1], where the unit cell volume is kept unchanged to avoid the chemical pressure effect. Magnetization process in fields H ≤200 kOe and at applied pressures P ≤5 kbar, specific heat C ( T ), electrical resistivity ρ( T ) and thermal expansion have been measured at temperatures above 1.5 K, with a special attention being paid to the metamagnetic behavior inherent in CeRu 2 Si 2 . In a whole Ce concentration range, the system remains in a non-magnetic state. Sharp metamagnetism shows a rapid broadening with x , and disappears at x ∼0.2 where incoherent Kondo scattering becomes significant in ρ( T ). By careful analysis of single-site contributions, a peak structure is revealed in C ( T ) which is not explained by the “Kondo peak” alone. The result can be interpreted by a pseudo-gap in the qu...

Magnetic and electrical properties of the compounds

Abstract: The magnetization, a.c. susceptibility, resistivity and magnetoresistance have been measured for the invariable-unit-cell-parameter compounds. The Si substitution for Co in yields a dramatic initial increase of , whereas the 3d magnetic moment is reduced. These findings may be attributed to the strong involvement of Si p states in the hierarchy of exchange interactions. The magnetic phase transition at is of first order for the compounds with x < 0.075. For these compounds, the coexistence of metamagnetism and the quenching of spin fluctuations at are provided.

5f-band metamagnetism in UCoAl

Abstract: UCoAl is a 5f-band metamagnet characterized by a very low critical field Bc ≈ 0.8 T, which induces magnetization of 0.3 μB/f.u. by a distinct transition. Bc increases with increasing temperature with the rate consistent with the reduced γ-coefficient in the high-field state. Bc-values are also sensitive to stoichiometry and external pressure.

Field-Induced Itinerant Metamagnetism in Iron Monosilicide

Abstract: Influence of high magnetic fields and pressure on band structure of FeSi has been studied by the full-potential LMTO–ASA method. It is found that the semiconducting ground state of FeSi is stable in the wide volume range of ±15% of V / V exp . At the same time, as follows from the LSDA calculations, the applied external magnetic fields induce the metallic magnetic state. At low fields our results agree with the measured magnetization. There is steep increase of calculated magnetization at high critical field H cr = 170 T (itinerant metamagnetic transition).

Metamagnetism and magnetostriction of the Ising antiferromagnet DyCrO3

Abstract: The magnetostriction of the Ising antiferromagnet DyCrO3 during metamagnetic transitions induced by a magnetic field applied along the a and b axes of the crystal is investigated experimentally and theoretically. The magnetostriction measurements performed in the temperature range 1.5–4.2 K in magnetic fields up to 3 T clearly reveal the two-step character of the transition from the original antiferromagnetic structure to the ferromagnetic structure with the intermediate formation of a low-symmetry structure (when H is parallel to the a axis). The unusual behavior of the magnetostriction discovered during the magnetizing process provides information on the nature of magnetostriction in rare-earth Ising metamagnets.

Field Dependence of the Magnetic Quantum Phase Transition in {{MnSi}}

Abstract: We report on precision measurements of the AC susceptibility in high-purity samples of MnSi as a function of pressure up to 16 kbar, field up to 7 T and temperature down to 30 mK. In zero field it has previously been shown, that the weakly spin polarised (ordered) phase collapses above a critical pressure P c = 14.6 kbar. The normal metallic state at this quantum phase transition was thereby reported to be consistent with the presence of a highly dispersive spectrum of magnetic fluctuations. Our new results reveal that a field polarised state is restored above P c by application of a magnetic field, which can be considered as a further sensitive control parameter to tune a quantum critical regime. The crossover between the non-polarised and polarised regimes is characterised by a strongly field and pressure dependent maximum in χ characteristic of itinerant electron metamagnetism.

Magnetic properties of NbFe2 single crystal

Abstract: Magnetization measurements on nearly stoichiometric NbFe 2 single crystals have revealed the metamagnetic transition along the c -axis, which is consistent in supporting the previous NMR deduction that the magnetic ground state is antiferromagnetic. Anomalous and anisotropic temperature dependence of magnetic susceptibility has been observed: a remarkably difference in χ c -axis ( T ) and χ c -plane ( T ) below 200 K; the strong downward deviation from the Curie-Weiss law and the loss of anisotropy above 200 K.

First-order metamagnetic transition in iron monosilicide

Abstract: The influence of a high magnetic field on the band structure and optical conductivity of FeSi has been studied by the ab initio full-potential LMTO-PW and relativistic LMTO-ASA methods with an applied field included. It is found that the applied external magnetic field induces a metallic magnetic state through a first-order metamagnetic transition, i.e. at a critical magnetic field of about there is a large steplike increase in the calculated magnetization, with a magnetic moment of . The magnetized state persists while the field is gradually reduced from above the metamagnetic transition (a hysteresis effect). The calculated optical conductivity (OC) at the critical field differs substantially from the zero-field OC in the infrared region.