Multiple Magnetic Phase Transitions Research Articles

Multiple magnetic transitions in Ag-substituted DyPt2

We show that the partial substitution of Ag in place of Pt in the cubic Laves phase ferromagnetic (below 9.2 K) compound DyPt2 leads to multiple temperature and field induced magnetic phase transitions. We study these phase transitions in details in a Dy(Pt0.94Ag0.06)2 alloy with the help of magnetization and specific heat measurements. One of the magnetic transitions produces an unusually sharp peak in the temperature dependence of heat capacity of Dy(Pt0.94Ag0.06)2, which is not observed in either of the parent compounds DyPt2 or DyAg2. The shape of this peak resembles those observed in the temperature dependence of heat capacity of the rare earth elements and some rare-earth based alloys and compounds across first order magnetic transitions accompanied by magneto-elastic effects and structural changes. The magnetic properties of Dy(Pt0.94Ag0.06)2 are analyzed in terms of the enhancement of crystal field effect and quadrupolar interactions. Large magneto-elastic coupling resulting from these interactions and changes in the electronic density of states near Fermi level because of the chemical substitution seem to introduce into the system the temperature and field induced multiple magnetic phase transitions mentioned above.

Investigation of the nature of the unusual magnetic behavior of La0.65Nd0.35Mn2Si2 compound by neutron diffraction study

The magnetic structures of the La0.65Nd0.35Mn2Si2 have been investigated by powder neutron diffraction between 5 and 350K. According to magnetic measurements this compound shows multiple magnetic phase transitions. Neutron diffraction indicates a canted ferromagnetic structure above 220 and below 46K. Between 50≤T≤70K there is a mixed phase where canted ferromagnetic and antiferromagnetic structure coexist. Moreover, La0.65Nd0.35Mn2Si2 has a two-step magnetic transition from an antiferromagnetic to ferromagnetic state between 65 and 22K. This two-step transition had not been observed so far and in this study it is studied in depth.

Surface effect in antiferromagnetic Ba6Mn24O48 nanoribbons

The magnetic properties of Ba6Mn24O48 nanoribbons and bulk are studied by zero-field-cooled and field-cooled magnetization, and ac susceptibility. Upon cooling, we find that both nanoribbons and bulk experience multiple magnetic phase transitions, i.e. paramagnetic, antiferromagnetic and re-entrant spin glass (RSG) phases at a low temperature. The main focus of this work is to understand the origin of RSG behaviour and to investigate the surface effect on magnetism in Ba6Mn24O48 nanoribbons. The dc susceptibility measurement shows that the paramagnetism in these nanoribbons involves the Curie–Weiss paramagnetism and temperature-independent contributions to magnetic susceptibility due to Pauli and Van Vleck paramagnetism. The Pauli paramagnetic contribution to susceptibility might give rise to uncompensated spins due to the breaking of sublattice pairing on the surface of nanoribbons. An exchange bias phenomenon is found in both Ba6Mn24O48 nanoribbons and bulk. The exchange field (HE) in the nanoribbons is larger than that of the corresponding bulk, which may also be induced by the uncompensated surface spins. The resistivity of Ba6Mn24O48 bulk presents the relation ln(ρ) ∝ T−1/2, and the possible conduction mechanism is suggested.

Temperature and magnetic field induced multiple magnetic transitions inDyAg2

The magnetic properties of the rare-earth intermetallic compoundDyAg2 are studied in detail with the help of magnetization and heat capacity measurements.It is shown that the multiple magnetic phase transitions can be induced inDyAg2 both by temperature and magnetic field. The detailed magnetic phase diagram ofDyAg2 is determined experimentally. It was already known thatDyAg2 undergoes an incommensurate to commensurate antiferromagnetic phase transition close to10 K. The present experimental results highlight the first order nature of this phase transition,and show that this transition can be induced by magnetic field as well. It is further shown thatanother isothermal magnetic field induced transition or metamagnetic transition exhibited byDyAg2 atstill lower temperatures is also of first order nature. The multiple magnetic phase transitions inDyAg2 give rise to large peaks in the temperature dependence of the heat capacitybelow 17 K, which indicates its potential as a magnetic regenerator material forcryocooler related applications. In addition it is found that because of the presenceof the temperature and field induced magnetic phase transitions, and becauseof short range magnetic correlations deep inside the paramagnetic regime,DyAg2 exhibits a fairly large magnetocaloric effect over a wide temperature window, e.g., between10 and 60 K.

Magnetocaloric effect in UNiGa compound with the multiple magnetic phase transitions

The magnetocaloric effect (MCE) in the UNiGa compound has been studied using the dc magnetization measurement technique. This system shows normal and inverse MCEs at low field around the paramagnetic to ferrimagnetic transition temperature (38.4 K), and the ferrimagnetic to antiferromagnetic transition temperature (34.5 K), respectively. At higher fields, the inverse MCE becomes very weak, which could be explained due to the presence of a field-induced metamagnetic phase transition. The maximum value of the magnetic entropy change - Δ S M , for Δ μ 0 H = 5 T , has been found to be 3.56 J kg - 1 K - 1 at ∼ 37.2 K with a relative cooling power of 22.5 J kg - 1 .

Re-entrant ferromagnet PrMn2Ge0.8Si1.2: Magnetocaloric effect

The structural and magnetic properties of the re-entrant ferromagnet PrMn2Ge0.8Si1.2 have been investigated by various experimental methods. Similar to the canonical re-entrant ferromagnet SmMn2Ge2, multiple magnetic phase transitions have been detected in PrMn2Ge0.8Si1.2 over the temperature range from 10to550K with re-entrant ferromagnetism occurring around ∼54K. The magnetocaloric effect has been measured in terms of the isothermal magnetocaloric entropy change and found to be positive at the re-entrant ferromagnetic transition with a maximum value of around 1.9J∕kgK at 58K for a magnetic field change of 0–3T. On the other hand, the entropy change becomes negative (∼−0.5J∕kgK) at the antiferromagnetic to ferromagnetic transition for the same field change.

Magnetism and electronic structure of the intermetallic compound Ce5CuBi3

We have studied the electronic structure as well as magnetic, electronic transport and thermodynamic properties of the intermetallic compound Ce5CuBi3. It was found that Ce5CuBi3 undergoes three successive phase transitions at 25 K, 13.7 K and 3.5 K. We attribute the multiple magnetic phase transition to be associated with the two non-equivalent magnetic sublattices of the magnetic Ce ions. The investigated compound is characterized by an enhanced ratio Cp /T at 2 K, which may be interpreted as being due to the nearness of the 4f-level to the Fermi level and some contribution of magnon excitation. The core-level photoemission spectra indicate that Ce ions in Ce5CuBi3 are very close to trivalent which is consistent with the magnetic susceptibility data. The calculated band structures using the scalar-relativistic linear muffin-tin orbital method in the atomic sphere approximation and the all-electron full potential linear augmented plane wave plus local orbitals method have been performed for the non-magnetic ground state and as well as for collinear ferromagnetic and ferrimagnetic spin alignments. The largest stabilization energy is found in the case of a ferromagnetic structure. The calculated moments on the two sites of the Ce atoms are in agreement with the experimental value (0.93 μ B /Ce). The calculations predict that the studied compound has a pseudogap in the DOS curve. Analysis of the partial DOS suggests some differences in hybridization strengths between the Ce-Bi and Ce-Cu orbitals.

Magnetism of the series of intermetallic Ce5CuM3 compounds, where M=Sn, Pb and Bi

We present a short summary of experimental and theoretical studies on the isostructural intermetallics Ce 5 CuM 3 (M = Sn, Pb and Bi), crystallizing in the hexagonal Hf 5 CuSn 3 -type structure (space group P 6 3 / mcm ). The investigated compounds are found to undergo multiple magnetic phase transitions at low temperatures. We discuss the role of f-spd hybridization on the evolution of heavy-fermion state across the series of the studied compounds. The band structure calculations not only support magnetic ground state of the studied compounds but also suggest an inequivalent contribution of Ce atoms at different positions to the density of states.

XAS and MCD studies in Laves compounds with multi‐magnetic phase transitions

We investigated the magnetic phase transition of the Laves phases, which shows the multiple magnetic phase transition, by using X-ray absorption (XAS) and magnetic circular dichroism (MCD). XAS-MCD measurements were performed around the Fe-K and L 2,3 edges. The magnet-optical sum rule was applied to XAS and MCD spectra of L 2,3 edges. The orbital and spin magnetic moment were estimated respectively. The orbital magnetic moment increased abruptly below the magnetic phase transition temperature. The spin magnetic moment had no abrupt change at the magnetic phase transition temperature. This shows that there is a strong correlation between the multiple magnetic phase transition and the orbital magnetic moment. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetic Phase Diagrams of Ce2Fe17‐xMnx—H System: A Magnetization Study.

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Magnetic phase diagrams of Ce 2Fe 17− xMn x–H system: A magnetization study

The field-induced magnetic phase transitions of the helical phase of Ce 2Fe 17− x Mn x alloys ( x = 1.3 and 1.7) and their hydrides of Ce 2Fe 17− x Mn x H y ( y = 1 ) were investigated by isofield magnetization curves in external magnetic fields up to H = 10 kOe. The temperature dependence of the critical fields, H C inducing phase transition between ferromagnetic (F) and helical antiferromagnetic (HAFM) state are determined. On the basis of the experimental results, the H – T phase diagrams are established. The multiple magnetic phase transitions observed in the low magnetic field are discussed in terms of competing exchange contributions within the iron magnetic sublattices. Hydrogenation leads to a considerable enhancement of ferromagnetic-like exchange interactions, which causes the increase of the Curie temperature and drastically reduces the critical field H C of a metamagnetic transition.

Multiple magnetic phase transitions inPrCoAl4Observed by Muon Spin Rotation and Relaxation Measurements

Zero field muon spin rotation and relaxation $(\ensuremath{\mu}\mathrm{SR})$ measurements on a single crystal of orthorhombic $\mathrm{Pr}\mathrm{Co}{\mathrm{Al}}_{4}$ revealed the presence of spontaneous static fields, extending above the well-known incommensurately modulated antiferromagnetic structure $({T}_{N}=17\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ up to at least $110\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Two further transitions at $30\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $84\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ were clearly visible. The spontaneous fields above ${T}_{N}$ are confined to the $(b,c)$ plane and are tentatively ascribed to a spin density wave involving the Co $3d$-band electrons.

Detailed study of the magnetic phase transitions in single crystalline HoNi 2B 2C and DyNi 2B 2C

We have studied the magnetic phase transitions in single phase, single crystalline HoNi 2B 2C and DyNi 2B 2C by measuring the temperature-dependent magnetic susceptibility, specific heat, and electrical resistivity. This study was undertaken in order to clarify the question of whether DyNi 2B 2C has a second, higher temperature magnetic phase transition near 16 K. HoNi 2B 2C has a cascade of magnetic phase transitions between 5 and 6 K. In addition to the superconducting phase transition near 9 K, three magnetic transitions (6.0, 5.5, and 5.2 K) can be easily detected in both of the thermodynamic measurements and are also seen in the electrical transport. The data taken on HoNi 2B 2C clearly demonstrates that multiple magnetic phase transitions can be readily detected (when they are actually present). In the case of DyNi 2B 2C only one magnetic phase transition (at T N ∼10 K ) was detected. The only other phase transition associated with the DyNi 2B 2C sample was the lower temperature superconducting phase transition at 6.3 K. Despite extensive data collection and analysis, no sign of any phase transition between 10 and 20 K in DyNi 2B 2C could be detected. This leads us to the conclusion that there is no 16 K magnetic phase transition associated with single phase, single crystal DyNi 2B 2C.

Magnetic phase diagram of GdNi 2Ge 2: a magnetisation and specific-heat study

The antiferromagnetic body-centred tetragonal compound GdNi 2Ge 2 orders at 28 K. Successive magnetic phase transitions are observed by specific-heat and magnetisation measurements as a function of temperature in different applied magnetic fields. Plots of M 2 vs. B/ M (Arrott-plots) show various anomalies. On the basis of the experimental results, a magnetic phase diagram is constructed. The multiple magnetic phase transitions are discussed in terms of competing ordering modes in the Gd sublattice.

Understanding the table-like magnetocaloric effect

In this work, we explain the table-like magnetocaloric effect as a consequence of multiple magnetic phase transitions for different temperatures. Using a Hamiltonian that takes into account the dipolar and quadrupolar interactions and the crystalline electric field, it was possible to study the magnetocaloric effect of the Γ 3–Γ 5 reduced magnetic system. We analyze the table-like magnetocaloric effect for different λ and K, dipolar and quadrupolar parameters, and for a suitable energy gap between Γ 3 and Γ 5 that permits successive magnetic orderings at different temperatures.

Thermomagnetic history effects inSmMn2Ge2

The intermetallic compound SmMn$_2$Ge$_2$, displaying multiple magnetic phase transitions, is being investigated in detail for its magnetization behavior near the 145 K first order ferromagnetic to antiferromagnetic transition occuring on cooling, in particular for thermomagnetic history effects in the magnetization data. The most unusual finding is that the thermomagnetic irreversibility, [= M$^{FCW}$(T)-M$^{ZFC}$(T)] at 135 K is higher in intermediate magnetic field strengths. By studying the response of the sample (i.e., thermomagnetic irreversibility and thermal hysteresis) to different histories of application of magnetic field and temperature, we demonstrate how the supercooling and superheating of the metastable magnetic phases across the first order transition at 145 K contribute to overall thermomagnetic irreversibility.

Reentrant spin glass behavior in Cr-doped perovskite manganite.

The magnetic and transport properties of the Cr-doped manganites La(0.46)Sr(0.54)Mn(1-y)Cr(y)O3 ( 0 < or = y < or = 0.08) with the A-type antiferromagnetic structure were investigated. Upon cooling, we find multiple magnetic phase transitions, i.e., paramagnetic, ferromagnetic (FM), antiferromagnetic (AFM), and spin glass in the y = 0.02 sample. The low temperature spin glass state is not a conventional spin glass with randomly oriented magnetic moments but has a reentrant character. The reentrant spin glass behavior accompanied by the anomalous multiple magnetic transitions might be due to the competing interactions between the FM phase and the A-type AFM matrix induced by the random Cr impurity.

Multiple phase transitions in

The magnetic-phase diagram of the system is studied by specific-heat, magnetic-susceptibility and electrical resistance measurements (x = 0.1, 0.2, 0.3, 0.6, 0.8, 0.9, 1.0). The susceptibility was measured by zero-field-cooling (ZFC) and field-cooling (FC) methods. If x < 0.1, there is no clear long-range magnetic order. When x > 0.1, starts to deviate from at . This suggests a spin-glass state below . In the range , the specific-heat measurements of show multiple magnetic phase transitions. There are three phase transitions in and . Except for x = 0, below 30 K, electrical resistivity increases continuously up to a temperature of 10 K. The drastic drop of below 10 K is due to magnetic ordering. The multiple phase transitions of are not observed in the resistance measurements. However, the slope of of changes at , which further supports multiple phase transitions in .

Multiple magnetic phase transitions in YbMn 2Si 2− xGe x

Magnetization and dilute 57Fe Mössbauer studies of YbMn 2Si 2− x Ge x at temperatures 4.2–650 K display multiple magnetic phase transitions. For YbMn 2Ge 2, T N=495(5) K while at 430, 350 and 190 K, drastic changes in canted spin structure antiferromagnetism occur.

A non-magnetic Fe probe of multiple magnetic phase transitions in RMn2Si2−x Ge x , R=rare earth

Dilute 57Fe Mossbauer-spectroscopy studies of RMn2X2 (X=Si and/or Ge, R=La, Ce, Pr, Nd, Sm, Eu and Gd) at 4.2 to 650 K yield the following results: Fe in RMn2X2 does not carry a magnetic moment. It reveals the magnetic order in the Mn and R sublattices through transferred hyperfine fields (∼100 kOe). The compounds LaMn2Si2, LaMn2Ge2, CeMn2Ge2, PrMn2Ge2, NdMn2Ge2 and SmMn2Ge2, known to be ferromagnets with T c=300–350 K, are antiferromagnetically ordered above their corresponding T c. Ther T N values extend from 385 K (SmMn2Ge2) to 470 K (LaMn2Si2). At the ferromagnetic-antiferromagnetic phase transition, a sharp reorientation of the Mn magnetic moments relative to the crystalline axes occurs. In RMn2Si2−x Ge x with intermediate x values, the Ge is much more dominant in determining the magnetic properties of the Mn sublattice. While PrMn2Si2 is an antiferromagnet (T N=365 K) and PrMn2Ge2 is a ferromagnetantiferromagnet (T c=328 K, T N=415 K), we find that in PrMn2SiGe, the magnetic behaviour is similar to that in pure PrMn2Ge2, T c=305 K and T N=395 K.