Multiple Magnetic Phase Transitions Research Articles

Multiple magnetic-phase transitions and critical behavior of charge-density wave compound TbTe3

We report multiple magnetic phase transitions and critical behavior of the 2D charge-density wave compound TbTe3 studied by μSR measurements and dc magnetization measurements. Zero-field μSR has shown three magnetic transitions below 7 K. The longitudinal field measurements under 50 G has confirmed the first transition at TN = 6.3 K. Scaling analysis from above TN gives the critical exponent w = 0.63(5), suggesting the Ising 3D antiferromagnetic nature of the ordering, which is likely mediated by the 2D correlations. However, the obtained w = 0.81(5) below TN indicates the ferromagnetic phase, which arises over the multiphase transitions at lower temperatures. Temperature-dependent transverse frequency shift gives a relatively smaller exponent γ = 1.0(1) than the Ising 3D model. The different transitions were also observed by dc magnetization measurements, suggesting two magnetic transitions at 7.4 K and 3.1 K, which correspond to the antiferromagnetic and ferromagnetic phases respectively.

Structural and cryogenic magnetic properties of rare earth rich RE11Co4In9 (RE = Gd, Dy and Ho) intermetallic compounds.

The crystal structure, magnetic properties and magnetocaloric performances of rare earth rich RE11Co4In9 (RE = Gd, Dy and Ho) intermetallic compounds are investigated systematically in this work. All compounds in this system crystallize in the orthorhombic Nd11Pd4In9-type structure with the Cmmm space group. The stacks of alternate RE and Co/In atomic layers with z = 0, 1 and z = 1/2 along the z-axis constitute the crystal structure. These compounds belong to the REx+yM2yXx family with x = 9 and y = 2, and the ratio of the AlB2-type and CsCl-type fragments in a unit cell is y : x, i.e. 2 : 9. The characteristic of multiple magnetic phase transition is revealed with a low magnetic flux density μ0H of 0.1 T for the present compounds. The ferromagnetic (FM) to paramagnetic (PM) phase transitions of the present compounds around their respective Curie temperatures (TC) are all second order phase transitions (SOPTs). Around the TC of 86, 37 and 20 K for Gd11Co4In9, Dy11Co4In9, and Ho11Co4In9 with a magnetic flux density change Δμ0H of 0-7 T, the values of the maximum magnetic entropy change (-ΔS) and temperature averaged entropy change (TEC) with 3 K span are 10.95 and 10.93 J kg-1 K-1 for Gd11Co4In9, 4.66 and 4.64 J kg-1 K-1 for Dy11Co4In9, and 12.29 and 12.09 J kg-1 K-1 for Ho11Co4In9, respectively. The corresponding values of relative cooling power (RCP) and refrigerant capacity (RC) are 538.1 and 405.9 J kg-1 for Gd11Co4In9, 213.9 and 165.9 J kg-1 for Dy11Co4In9, and 475.2 and 357.4 J kg-1 for Ho11Co4In9, respectively.

Multiple magnetic phase transitions, electrical and optical properties of FeTe2 single crystals

Single-crystalline FeTe2 in marcasite phase with orthorhombic structure was prepared via chemical vapor transport. Cooling FeTe2 single crystals from room temperature down to , multiple magnetic phase transitions were observed. Paramagnetic (PM) to antiferromagnetic (AFM) and then to ferromagnetic (FM) occurred at and for in-plane, and for out-of-plane, respectively. A strong uniaxial magnetic anisotropy was found due to FeTe6 octahedron distortion and structural modulation in FM region. The novel negative volume expansion (NVE) initiated in the vicinity of AFM to FM transition. An abrupt frequency shift of the most intense mode at and evolution of the Te–Te stretching mode near , corresponding to the phase transition from AFM to FM were observed. The temperature-dependent resistance revealed an anomaly (semiconductor to metallic transition) around AFM-FM transition, which can easily be suppressed and move to high temperature by the applied magnetic field. The results from XRD, Raman and resistivity indicated that the structural parameters, vibration frequency and transport are sensitive to the phase transition from AFM to FM. The nature of direct band gap with was identified through UV-Vis-NIR spectrum of FeTe2 single crystals at room temperature.

Multiple Magnetic Phase Transitions in Mn-deficient Co0.4Ni0.6Mn1−xGe Compounds

The structural and magnetic transition in Mn-deficient Co0.4Ni0.6Mn1−xGe was investigated by DC magnetization and temperature-dependent X-ray diffraction measurements. By introducing Mn vacancies in the stoichiometric Co0.4Ni0.6MnGe compound, multiple magnetic phase transitions and tunable martensitic transitions were observed. A paramagnetic martensite (Ni2In-type structure) to ferromagnetic austenite (TiNiSi-type structure) transition was realized in Co0.4Ni0.6Mn0.98Ge around 275 K. A large volume expansion of 2.6% accompanied this transition. In addition, a martensitic transition induced by the magnetic field was also observed near room temperature. Furthermore, a significant magnetic entropy variation of − 21.3 J/kg K at 263 K (∆B = 5 T) was obtained in the Co0.4Ni0.6Mn0.98Ge compound.

Phase coexistence and exchange-bias effect in LiMn2O4 nanorods

In this paper, the magnetic properties of $\mathrm{LiM}{\mathrm{n}}_{2}{\mathrm{O}}_{4}$ nanorods with an average diameter of $\ensuremath{\sim}100\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ and length of $\ensuremath{\sim}1\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$ are investigated. The temperature dependences of dc and ac susceptibility measurements show that $\mathrm{LiM}{\mathrm{n}}_{2}{\mathrm{O}}_{4}$ nanorods experience multiple magnetic phase transitions upon cooling, i.e., paramagnetic (PM), antiferromagnetic (AFM), canted antiferromagnetic (CAFM), and cluster spin glass (SG). The coexistence between a long-range ordered AFM phase due to a $\mathrm{M}{\mathrm{n}}^{4+}\text{\ensuremath{-}}\mathrm{M}{\mathrm{n}}^{4+}$ interaction and a cluster SG phase originating from frozen AFM clusters at low temperature in $\mathrm{LiM}{\mathrm{n}}_{2}{\mathrm{O}}_{4}$ nanorods is elucidated. Field-cooled hysteresis loops (FC loops) and magnetic training effect (TE) measurements confirm the presence of an exchange-bias (EB) effect in $\mathrm{LiM}{\mathrm{n}}_{2}{\mathrm{O}}_{4}$ nanorods below the N\'eel temperature $({T}_{\mathrm{N}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}\phantom{\rule{4pt}{0ex}}60\phantom{\rule{4pt}{0ex}}\mathrm{K})$. Furthermore, by analyzing the TE, we conclude that the observed EB effect originates completely from an exchange coupling interaction at the interface between the AFM and cluster SG states. A phenomenological model based on phase coexistence is proposed to interpret the origin of the EB effect below 60 K in the present compound. In turn, the appearance of the EB effect further supports the coexistence of AFM order along with a cluster SG state in $\mathrm{LiM}{\mathrm{n}}_{2}{\mathrm{O}}_{4}$ nanorods.

Evidence of Enhanced Oxygen Vacancy Defects Inducing Ferromagnetism in Multiferroic CaMn7O12 Manganite with Sintering Time

We provide the first experimental evidence of oxygen vacancy defect induced ferromagnetism in undoped multiferroic CaMn7O12 (CMO) manganite synthesized from the facile chemical combustion method. The obtained nanocrystalline is characterized by various techniques like TGA, FTIR, XRD, SEM-EDX, AFM, UV-visible, XPS, and SQUID, etc. to confirm the phase purity and crystallinity of CMO. Surface roughness increases with sintering time attributed to the increase of surface oxygen vacancy defects. X-ray photoelectron spectroscopy was carried out to confirm the oxidation state of constituent elements and also provides direct evidence of enhanced oxygen vacancies. UV–vis optical absorption used to infer band gap shift from 1.68 to 1.38 eV, respectively, is also attributed to increases in oxygen vacancy defects. Multiple magnetic phase transition temperatures of 90, 50, and 42 K, respectively, were obtained from the derivative of magnetization. A systematic decrease of full widths at half maxima (fwhm) of dM/dT vs ...

Critical behavior near the ferromagnetic-paramagnetic transformation in the austenite phase of Ni43Mn46Sn8X3 (X = In and Cr) Heusler alloys

In this work, we present a detailed study on the magnetic property and critical behavior in the austenitic phase of Ni43Mn46Sn8X3 alloys with X=Cr and In, which were prepared by an arc-melting method in an argon ambience. The M(T) curve of the Cr sample (X=Cr) exhibits a single magnetic phase transition at the Curie temperature of the ferromagnetic (FM) austenitic phase with TAC=303K. In contrast, the In sample (X=In) exhibits multiple magnetic phase transitions, including a magnetic phase transition from a FM state to weakly magnetic state at TMC=165K of the martensitic phase, a martensitic transition from the weakly magnetic to the FM austenite phase at TM-A=259K, and a magnetic phase transition from the FM to paramagnetic (PM) at TAC=297K of the austenite phase. Based on the Landau theory and M(H) data measured at different temperatures, we pointed that the FM-PM phase transitions around TAC in both samples were the second-order phase transition. Our results suggest an existence of the long-range FM interactions in the austenite phase. A small deviation from the mean-field theory of the critical exponents has been also observed pointing out an existence of the inhomogeneous magnetism that could be associated with the presence of the anti-FM interactions in these samples. Besides, their effective exponents βeff(ε) and γeff(ε) have been also calculated.

Magnetic and Transport Properties of Mn2Ni1.8In0.2 Alloy

The structural, magnetic, and transport properties of the Mn2Ni1.8In0.2 alloy have been presented. It was observed to form in tetragonal structure. Multiple magnetic phase transitions have been detected in magnetization data over the temperature range from 2 to 350 K. From the resistivity, ac susceptibility, and heat capacity data, the superconducting transition are observed at T = 5.6 K. The alloy is considered to be one of the potential candidates from the Mn-rich alloys, which has shown both magnetic and superconducting properties, which can be useful from application point of view.

Effect of the Mn/Fe Ratio on the Microstructure and Magnetic Properties in the Powder Form (Fe1−x Mn x )2P System

The structure, morphology, and magnetic properties of the mechanically alloyed iron manganese phosphides (Fe1−xMnx)2P with 0.15 ≤ x ≤ 0.75 (Mn/Fe ratio = 0.17, 0.33, 0.66, and 3) have been studied by means of X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectrometry, and BS1 and BS2 magnetometry. The powder form (Fe1−xMnx)2P compounds exhibit multiphase structures that contain Fe(Mn)-type solid solution and Fe2P-type, Mn2P-type, Fe3P-type, and MnP/FeP-type phosphides. The magnetization versus temperature reveals the existence of multiple magnetic phase transitions. The saturation magnetization, coercivity, and squarness Mr/Ms ratio values are discussed as a function of both the Mn content and the temperature. From the approach to saturation magnetization studies, several fundamental magnetic parameters were extracted. The local magnetic anisotropy constant K1 was determined.

Complex magnetic phase diagram with multistep spin-flop transitions in La0.25Pr0.75Co2P2

$\mathrm{L}{\mathrm{a}}_{0.25}\mathrm{P}{\mathrm{r}}_{0.75}\mathrm{C}{\mathrm{o}}_{2}{\mathrm{P}}_{2}$ crystallizes in the tetragonal $\mathrm{ThC}{\mathrm{r}}_{2}\mathrm{S}{\mathrm{i}}_{2}$ structure type and shows multiple magnetic phase transitions driven by changes in temperature and magnetic field. The nature of these transitions was investigated by a combination of magnetic and magnetoresistance measurements and both single crystal and powder neutron diffraction. The Co magnetic moments order ferromagnetically (FM) parallel to the $c$ axis at 282 K, followed by antiferromagnetic (AFM) ordering at 225 K. In the AFM structure, the Co magnetic moments align along the $c$ axis with FM $[\mathrm{C}{\mathrm{o}}_{2}{\mathrm{P}}_{2}]$ layers arranged in an alternating sequence, $\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\downarrow}$, which leads to the doubling of the $c$ axis in the magnetic unit cell. Another AFM transition is observed at 27 K, due to the ordering of a half of Pr moments in the $ab$ plane. The other half of Pr moments undergoes AFM ordering along the $c$ axis at 11 K, causing simultaneous reorientation of the previously ordered Pr moments into an AFM structure with the moments being canted with respect to the $c$ axis. This AFM transition causes an abrupt decrease in electrical resistivity at 11 K. Under applied magnetic field, two metamagnetic transitions are observed in the Pr sublattice at 0.8 and 5.4 T. They correlate with two anomalies in magnetoresistance measurements at the same critical fields. A comparison of the temperature- and field-dependent magnetic properties of $\mathrm{L}{\mathrm{a}}_{0.25}\mathrm{P}{\mathrm{r}}_{0.75}\mathrm{C}{\mathrm{o}}_{2}{\mathrm{P}}_{2}$ to the magnetic behavior of $\mathrm{PrC}{\mathrm{o}}_{2}{\mathrm{P}}_{2}$ is provided.

Achieving a table-like magnetocaloric effect and large refrigerant capacity in in situ multiphase Gd65Mn25Si10 alloys obtained by crystallization treatment

In situ multiphase structure Gd65Mn25Si10 alloys were fabricated by melt spinning and subsequent crystallization treatment. In the process of crystallization, the α-Gd, GdMn2 and Gd5Si3 phases precipitate in the amorphous matrix in turn. The Curie temperature (TC) values for the α-Gd crystallization phase and amorphous matrix can be tailored by tuning the crystallization treatment time. All three multiphase alloys obtained by crystallization treatment at 637 K for 20, 30 and 40 min, respectively, undergo multiple successive magnetic phase transitions. A table-like magnetic entropy change over a wide temperature range (~90–120 K) and a large full width at half maximum (ΔTFWHM) magnetic entropy change (~230 K) were achieved in the above-mentioned crystallized alloys, resulting in large refrigerant capacities (RCs). The enhanced RCs of the three crystallized alloys for a magnetic field change of 0–5 T are in the range of 541–614 J kg−1. Large ΔTFWHM and RC values and a table-like (−ΔSM)max feature obtained in in situ multiphase Gd65Mn25Si10 crystallized alloys make them suitable for potential application in efficient Ericsson-cycle magnetic refrigeration working in a temperature range from 74 to 310 K.

Magnetic and magnetocaloric properties of DyMn2Si2 compound with multiple magnetic phase transition

Structural, magnetic and magnetocaloric properties of the ternary intermetallic compound DyMn2Si2 are studied by X-ray diffraction and magnetization measurements. It is found that DyMn2Si2 crystalizes with tetragonal ThCr2S2-type structure and exhibits four successive magnetic transitions at low temperature, around 20K, 31K, 38K and 82K, named respectively as T1, T2, T3 and T4 transitions. Large values of magnetic field (>35kOe) favor antiferromagnetic clusters and give rise to exchange bias effect. The different responses of T2 and T3 to field change, induces two non-identical isothermal entropy change (-ΔSM) peaks. The maximum values of -ΔSM occur in temperatures around T3 and reaches 8.2J/kgK, for a magnetic field change of 50kOe. Also, the presence of transitions T2 and T3 close to each other induces a table-like magnetocaloric effect (MCE) in a wide temperature range. Thus, the peculiar magnetic properties observed for DyMn2Si2 compound are interesting for low temperature magnetic refrigeration.

Magnetocaloric effect in HoMn2Si2 compound with multiple magnetic phase transitions

The structural, magnetic and magnetocaloric properties of the polycrystalline compound HoMn2Si2 have been studied. The temperature variation of magnetization and heat capacity show that below room temperature the compound under goes multiple magnetic transitions, at about 80, 15 and 3.5 K respectively. Moreover, the presence of the interesting thermomagnetic irreversibility in HoMn2Si2 is detected in the magnetization versus temperature plot, which can be ascribed to the narrow domain wall pinning effect. A broad and asymmetric peak is observed for the MCE response which might suggest the underlying first-order nature of the transition and/or the spin fluctuations of the Mn subsystem. The density of states N(EF) at the Fermi level and the Debye temperature have been determined and analyzed. Large magnetocaloric effect (ΔSM = −9 J/kg-K for a field change of 5 T around 9 K) suggest that this material is suitable for the low temperature magnetic refrigeration.

Large exchange bias effect in LaCr0.9Ru0.1O3

The incorporation of tetravalent Ru (10%) into antiferromagnetic spin structure of LaCrO3 leads to mixed valence states of Cr (Cr2+ and Cr3+). Highly delocalized 4d orbital of Ru induces prominent ferromagnetic (FM) component in antiferromagnetic (AFM) matrix of parent compound. The complex magnetic interaction across the interface of FM and AFM regions gives rise to large exchange bias field (HEB) of about 10kOe. The inverse and normal magnetocaloric effect for magnetic field up to 50kOe coexists in a single material due to multiple magnetic phase transitions with temperature.

Effect of In/Sn substitution on magnetism, crystal and electronic structure in Gd(In1-xSnx)3 system

The magnetic, electric transport and electronic structure of a series of polycrystalline intermetallic compounds were investigated by means of experimental and ab initio methods. For all investigated compounds, the multiple magnetic phase transition was detected by means of magnetization and resistivity measurements. Partial replacement of In by Sn atoms is reflected in the oscillating behaviour of the upper Néel temperature () and other magnetic parameters but the lower Néel temperature () remains almost constant. Electronic structure studied by method indicates that the In/Sn substitution results in an energy shift of the Gd4f and Gd4d lines and a reconstruction of the valence band (VB) near the Fermi level. Especially, the maximum intensity near the Fermi level varies with Sn content in an oscillatory manner. The observed peculiar features of the electronic structure of the alloys have been reproduced by ab initio density functional calculations. For all compounds, the calculations disclosed the presence of two, close energetically, ground-state antiferromagnetic structures of AFM-I (0 0 1) and AFM-III (1 1 0) type. The ab initio study revealed also that upon the In/Sn substitution, the ground-state magnetic structure of the compounds changes from AFM-III type for the In-rich side to AFM-I type for a higher Sn content. Our experimental and theoretical investigations demonstrated unambiguously that the observed oscillatory variation of different magnetic parameters of the is driven by the changes in the VB structure of the system upon the In/Sn substitution.

Understanding the multiple magnetic structures of the intermetallic compound NdMn1.4Co0.6Si2

Magnetic phases for the intermetallic compound NdMn1.4Co0.6Si2 have been investigated at various temperatures by dc magnetization, neutron diffraction and neutron depolarization. Our study shows multiple magnetic phase transitions with temperature (T) over 1.5–300K. In agreement with dc-magnetization and neutron depolarization results, the temperature dependence of the neutron diffraction patterns shows five distinct regions with different magnetic phases. These temperature regions are (i) T⩾215K, (ii) 215K>T⩾50K, (iii) 50K>T⩾40K, (iv) 40K>T>15K, and (v) T⩽15K. The corresponding magnetic structures are paramagnetic, commensurate collinear antiferromagnetic (AFM-I), incommensurate AFM (AFM-II), mixed ferromagnetic and AFM (FM+AFM-II), and incommensurate AFM (AFM-II), respectively.

Magnetic properties of NiMn2O4−δ (nickel manganite): Multiple magnetic phase transitions and exchange bias effect

We present magnetic properties of NiMn2O4−δ (nickel manganite) which was synthesized by complex polymerization synthesis method followed by successive heat treatment and final calcinations in air at 1200°C. The sample was characterized by using X-ray powder diffractometer (XRPD), scanning electron microscopy (SEM), field-emission scanning electron microscopy (FE-SEM) and superconducting quantum interference device (SQUID) magnetometer. The XRPD and FE-SEM studies revealed NiMn2O4−δ phase and good crystallinity of particles. No other impurities have been observed by XRPD. The magnetic properties of the sample have been studied by measuring the temperature and field dependence of magnetization. Magnetic measurements of M(T) reveal rather complex magnetic properties and multiple magnetic phase transitions. We show three magnetic phase transitions with transition temperatures at TM1=35K (long-range antiferromagnetic transition), TM2=101K (antiferromagnetic-type transition) and TM3=120K (ferromagnetic-like transition). We found that the TM1 transition is strongly dependent on the strength of the applied magnetic field (TM1 decreases with increasing applied field) whereas the TM3 is field independent. Otherwise, the TM2 maximum almost disappears in higher applied magnetic fields (H=1kOe and 10kOe). Magnetic measurements of M(H) show hysteretic behavior below TM3. Moreover, hysteresis properties measured after cooling of the sample in magnetic field of 10kOe show exchange bias effect with an exchange bias field |HEB|=196Oe. In summary, the properties that distinguish the investigated NiMn2O4-δ sample from other bulk, thin film, ceramic and nanoparticle NiMn2O4-δ systems are the triple magnetic transitions with sharp increase of the ZFC and FC magnetizations at 120K and the exchange bias effect. The analysis of the results and comparison with literature data allowed us to conjecture that the mixed oxidation states of Mn ions, ferromagnetic and antiferromagnetic sublattice orders and surface effects in the sample tailor these interesting magnetic properties.

Electrical detection of spin reorientation transition in ferromagnetic La0.4Sm0.3Sr0.3MnO3

Field-cooled magnetization of La0.4Sm0.3Sr0.3MnO3 samples shows an anomalous maximum at a temperature T* = 45 K within the ferromagnetic state, which is suggested to spin reorientation transition of the Mn sublattice aided by antiferromagnetic Sm(4f)-Mn(3d) interaction. While dc resistivity does not show any specific feature at T*, ac electrical impedance shows anomalous features at both T* and at the ferromagnetic transition temperature even in the absence of an external magnetic field. Our results indicate that ac electrical transport can be used to detect multiple magnetic phase transitions whose impact on the dc electrical transport is either weak or masked completely.

Magnetic properties and magnetocaloric effects in GdCo9Si2 compound with multiple magnetic phase transitions

The structure and magnetic properties of polycrystalline GdCo9Si2 compound have been investigated. It has a BaCd11 structure and undergoes two magnetic phase transitions: an antiferromagnetic to ferrimagnetic transition occurring at ∼93 K, and a ferrimagnetic to paramagnetic transition at 420 K, which results in a positive and a negative magnetic entropy change, respectively. The two peak values of magnetic entropy change are −0.6 and 1.1 J·kg−1·K−1 for ΔH = 5 T. Furthermore, there exists a metal-semiconductor transition temperature (TP), below which the resistance increases with increasing temperature, while the semiconductor characteristic is observed above TP. The magnetic domain structures are characterized by stripe and grid structures 1 μm wide. Although the MCE is small for applications, its study is useful to clearly understand the nature of multiple magnetic phase transitions in the GdCo9Si2 compound.

Spin–glass transition in La0.75Sr0.25Mn0.5Cr0.5−xAlxO3−δ perovskites

The structural and magnetic properties of the Al-doped La0.75Sr0.25Mn0.5Cr0.5−xAlxO3−δ (x=0.0, 0.1, 0.2, 0.3) were investigated by X-ray powder diffraction, neutron powder diffraction and magnetization measurements. Rietveld refinement of the diffraction data confirms that the compounds crystallize in rhombohedral symmetry (space group, R-3C). Unit cell volume decreases with increasing concentration of Al at the B-site. Upon cooling from room temperature, we have observed multiple magnetic phase transitions, i.e. paramagnetic (PM), ferromagnetic (FM), antiferromagnetic (AFM) and spin–glass (SG), in the samples. A low temperature magnetic hysteresis study demonstrates the presence of ferromagnetic domains for all compositions. The antiferromagnetic transition temperature decreases with the Al-doping AC susceptibility measurements at 97Hz and 1Oe show SG behaviors with a spin-freezing temperature close to 50K for all samples. The in-phase ac susceptibility (χ/) decreases in magnitude and spin–glass transition (TSG) increase toward higher temperature with increasing frequency. The spin–glass behavior accompanied by the anomalous magnetic transitions is due to the competing interactions between FM and AFM. The results also shows that a part of the samples lose magnetic order to form a SG state accompanied by an AFM state at low temperature.