Sharp Metamagnetic Transition Research Articles

Electronic states of the constituent magnetic elements, superior magnetic properties and spin-flip metamagnetic transition in Cu3Dy(SeO3)2O2Cl

Dy based cuprate francisite [Cu3Dy(SeO3)2O2Cl, in short DyCufr] is so far potentially the most fascinating magnetic compound in the class of francisite compounds. Synthesized DyCufr has been investigated via structural, X-ray absorption near edge structure (XANES), X-ray photoelectron spectroscopy (XPS) and magnetization measurements. XANES and XPS provide consistent and corroborative results regarding electronic states of the constituent elements. The most striking observation is that the slope of magnetization for the field induced metamagnetic transition (MMT) attains nearly infinity (perfect), hysteresis associated with MMT is substantially high, and the critical field for MMT is very low. The antiferromagnetic ordering temperature (TN), saturation magnetization (MS) are very high, and the remanent magnetization (MR) is appreciable in DyCufr in contrast to few other similar compounds. Unpaired 4f electrons of Dy3+ causing high value of effective magnetic moment and spin-flip type metamagnetism are pivotal for producing magnetically the most superior francisite. Actually, sharp MMT as evidenced in DyCufr, has the potential to be used in magneto-refrigeration and spin-electronic devices because it can produce an avalanche flip of spin structure from low-spin (antiferromagnetic) to high-spin (ferromagnetic) state.

Percolative transport and metamagnetic transition in phase separated La0.55Ca0.45Mn1-xAlxO3-δ

The Al3+ doping effects on the ferromagnetic metallic state of La0.55Ca0.45MnO3 have been studied by preparing the La0.55Ca0.45Mn1-xAlxO3-δ (x = 0, 0.05, 0.1, 0.15) ceramics. Various measurements such as ac susceptibility, relaxation, magnetization and resistivity were performed to study the magnetic and magnetotransport properties. The magnetic disorder produced by the Al3+ dopants and the oxygen vacancies suppress the long range ferromagnetic ordering and induce a short range charge ordered antiferromagnetic clusters, leading to a phase separated behavior in the Al3+-doped samples. A Griffith-like behavior is observed due to the occurrence of short range ferromagnetic clusters in the paramagnetic phase. The 15% Al3+ doping sample exhibits a spin-glass state. The 10% Al3+ doping system is blocked in a metastable state upon cooling at zero field, and a sharp metamagnetic transition is induced by applying a high magnetic field, in which the antiferromagnetic phase is transformed into ferromagnetic phase and the ferromagnetic clusters grow in size. The ferromagnetic domains grows rapidly when applying a high magnetic field. Once the conducting ferromagnetic domains are interconnected throughout the sample, a percolative insulating-to-metallic state transition would occur, accompanied by a sharp drop in resistivity.

Enhanced mechanical strength in hot-rolled La-Fe-Si/Fe magnetocaloric composites by microstructure manipulation

La-Fe-Si-based alloys possess a giant magnetocaloric effect due to the sharp itinerant-electron metamagnetic transition. However, the relatively poor mechanical strength of these alloys impedes their practical application in the magnetic refrigeration system. In this study, we employed hot rolling to manipulate the microstructure, and thus to improve the mechanical strength of LaFe11.6Si1.4/Fe composites. The microstructure and magnetic phase transition behavior have been systematically investigated by X-ray tomography, high-resolution transmission electron microscope and digital image correlation technique. We found that the bending strength of the hot-rolled LaFe11.6Si1.4/Fe reached up to 176 MPa, which is about 26% higher than the non-rolled one. The refinement of the α-Fe particles plays a key role in hindering crack propagation and enhancing the mechanical strength of the hot-rolled sample. Additionally, the reduction of the La-rich phase and large-size pores is found to be beneficial to the mechanical strength enhancement. The hot-rolled composite shows a sharp metamagnetic transition with a maximum magnetic entropy change of 17 J kg−1 K−1 for 2 T magnetic field change. This study demonstrates that microstructure manipulation based on hot rolling is a feasible approach to improve the mechanical strength of La-Fe-Si materials.

Square lattice antiferromagnets (NO)M(NO3)3 (M = Co, Ni): Effects of anisotropy

Two novel transition metal nitrates (NO)M(NO3)3 (M = Co, Ni) have been characterized in thermodynamic measurements. The structure of these compounds provides a unique opportunity for accommodation of Jahn – Teller cation with odd number of electrons Co2+ (3d7), and non – Jahn - Teller one with even number of electrons Ni2+ (3d8), in similar crystallographic position. Both compounds order antiferromagnetically at TNCo = 12.8 K and TNNi = 23.8 K. The single ion anisotropies of Co2+D = 7.2 K and Ni2+D = 2 K ensure qualitatively different behavior under external magnetic field. The cobalt nitrate demonstrates sharp metamagnetic transition at BM = 2.2 T while the nickel nitrate evidences smooth deflection at spin-flop transition BSF ∼ 6 T. To gain microscopic understanding of the magnetic properties of (NO)M(NO3)3 the first principles density functional theory calculations have been performed.

Disorder and epitaxial strain control of metamagnetic transition, large saturation magnetization, and magneto-terahertz properties of YMn0.5Cr0.5O3 polycrystals and thin films

The multiferroic YMn0.5Cr0.5O3 (YMCO) compound possesses magnetic phases that are debatable for their origin in intrinsic and extrinsic attributes. To extract the contribution of the polycrystalline disorder as well as determine the effect of structural modifications and epitaxial strain on the magnetic properties, we have formed YMCO bulk in polycrystalline pellet and powder forms, and epitaxial thin films with a wide range of compressive and tensile strains. The temperature and field dependent magnetization of polycrystals discards the possibility of magnetization reversal and unveils the presence of multidomain states with soft and hard characters in powder form. The epitaxial YMCO films possess an extraordinary structural control of their magnetic properties, as the tuning of compressive strain results in an increase of 4–5 factors of magnitude in the saturation magnetic moment. This strain engineering further allows a tuning of the magnetic property from spin frustration/short-range ordering to the long-range ordering, which also induces a rare phenomenon of sharp step-like metamagnetic transition. The implementation of magneto-terahertz time-domain spectroscopy on this system does not show the manifestation of any magnon/electromaganon resonance typical of a magnetoelectric phase, thus suggesting either a very weak or lack of coupling between magnetic and electric ordered parameters in polycrystalline YMCO. This study resolves some longstanding issues on the magnetic and magnetoelectric phases in addition to the epitaxial control of large magnetization and metamagnetic transition being potentially relevant in several aspects of spintronics applications.

Large magnetocaloric effect and magnetoresistance in ErNi single crystal

The magnetic properties, magnetocaloric effect and magnetoresistance in ErNi single crystal have been investigated in detail. With decreasing temperature, ErNi single crystal undergoes two successive magnetic transitions: a paramagnetic to ferromagnetic transition at TC =11 K and a spin-reorientation transition at TSR = 5 K. Meanwhile, a sharp field-induced metamagnetic transition is observed below the TC along the a axis. ErNi single crystal possesses a giant magnetocaloric effect around TC. The maximum magnetic entropy change is -36.1 J (kg K)−1 along the a axis under the field change of 0−50 kOe. In particular, the rotating magnetocaloric effect in ErNi single crystal reaches its maximum under a relatively low field, and the maximum rotating entropy change with a value of 9.3 J (kg K)−1 is obtained by rotating the applied field from the [011] to [100] directions under 13 kOe. These results suggest that ErNi could be a promising candidate for magnetic refrigeration working at liquid-helium temperature region. Moreover, a complicated transport behavior is uncovered in ErNi single crystal, which is attributed to the complex magnetic states and magnetic polaronic effect. Both positive and negative magnetoresistance are observed. A considerable large magnetoresistance with the value of -34.5 % is acquired at 8 K under 50 kOe when the field is along the [100] direction.

Percolation like transitions in phase separated manganites La0.5Ca0.5Mn1-Al O3-

We show that the replacement of Mn with Al strongly affects the magnetization and electrical transport behaviors in La 0.5 Ca 0.5 Mn 1- x Al x O 3- δ ( x = 0, 0.05, 0.07 and 0.09). Nonmagnetic Al 3+ ions substitution at Mn sites dilutes Mn 3+ -O 2- -Mn 4+ network, thus suppresses the ferromagnetic metallic state in La 0.5 Ca 0.5 MnO 3- δ and causes a phase separation phenomenon, in which ferromagnetic phase coexists with antiferromagnetic charge ordered phase at low temperatures. With applying sufficiently high magnetic field, step-like metamagnetic transitions were observed in x = 0.05–0.09 systems below helium temperature, in which the antiferromagnetic charge ordered phase collapsed into ferromagnetic phase. Corresponding to the sharp step-like metamagnetic transitions, the resistivity decreases dramatically with increasing magnetic field, exhibiting a percolative insulator-metal transition. The variation of temperature and magnetic field changes the relative fractions of ferromagnetic and charge ordering phases, and percolative insulator-metal transition occurs due to the development of percolation paths between the growing FM domains.

Pressure-induced itinerant electron metamagnetism in UCo0.995Os0.005Al ferromagnet

The effect of external hydrostatic pressure on magnetic properties is studied for the UCo0.995Os0.005Al single crystal. At ambient pressure, the ground state is ferromagnetic. Even lowest applied pressure 0.11GPa is sufficient to suppress ferromagnetism. A sharp metamagnetic transition is observed only in magnetic fields along the c axis of the crystal, similar to previously studied itinerant electron metamagnet UCoAl. Temperature dependence of the susceptibility for various pressures shows a broad maximum at Tmax ~ 20K. The experimental data are analyzed with the theory of itinerant electron metamagnetism, which considers anisotropic thermal fluctuations of the uranium magnetic moment. The observed pressure dependence of the susceptibility at Tmax and the temperature for the disappearance of the first-order metamagnetic transition are explained with the theory.

Alloying and pressure effects on itinerant-electron metamagnetism of the UCoAl-based compounds

With the UCo1-xOsxAl single crystals, we studied interplay between alloying and pressure effects on magnetism of the itinerant electron metamagnet UCoAl. The Os alloying for x ≥ 0.005 switches the UCoAl to ferromagnetism. For the UCo0.995Os0.005Al single crystal, even lowest applied pressure 0.11 GPa is sufficient to suppress ferromagnetism. A sharp metamagnetic transition for various pressures is observed in magnetic fields along the c axis of the crystal. Concentration magnetic phase diagram of the UCo1-xOsxAl, which includes the quantum phase transition from ferromagnetic to metamagnetic state, and P–T–H phase diagram of the UCo0.995Os0.005Al are determined using the data of magnetization measurements at various pressures and temperatures.

High-field study of UCo2Si2: Magnetostriction at metamagnetic transition and influence of Fe substitution

UCo2Si2 (tetragonal crystal structure) is antiferromagnet below TN = 83K with ferromagnetic basal-plane layers of U magnetic moments oriented parallel to the c axis. The layers are coupled in +−+− sequence along this axis. In fields of 45T applied along the c axis, UCo2Si2 exhibits very sharp metamagnetic transition to ++- uncompensated antiferromagnetic state. The transition is accompanied by pronounced magnetostriction effects. The crystal expands along the c axis by 1 * 10−4 and shrinks in the basal plane by 0.5 * 10−4 (at 1.5K) resulting in negligible volume effect. Between 20K and 40K the transition changes from the first- to the second-order type. The Fe doping in UCo2Si2 reduces TN from 83K to 80K at x = 0.2 in U(Co1-xFex)2Si2. Metamagnetic transition shifts to higher fields (from 45T at x = 0–56T for x = 0.2). Magnetization jump over the transition remains practically the same which is in agreement with uranium magnetic moment determined by neutron diffraction on crystal with x = 0.1 as 1.29 μB, i.e. only slightly lower than that in UCo2Si2.

A comparative study of magnetic field induced meta-magnetic transition in nanocrystalline and bulk Pr0.65(Ca0.7Sr0.3)0.35MnO3 compound

In our present study we highlight the observations of external magnetic field induced sharp meta-magnetic transition in polycrystalline bulk as well as nanocrystalline form of Pr0.65(Ca0.7Sr0.7)0.35MnO3 compound. Interestingly, such behavior persists in the nanoparticles regardless of the disorder broadened transition. However, higher magnetic field is required for nanoparticles having average particle size ∼40nm for such meta-magnetic transition, which differs from the general trends of the pure charge ordered nano materials. The interfacial strain between the different magnetic domains plays the important role in magnetic isothermal properties of nanoparticles, when the samples are cooled down in different cooling field. Additionally, both the bulk and nanoparticle compounds exhibit spontaneous phase separation and significantly large magnetoresistance at the low temperature region due to the melting of charge ordered fraction.

Low-temperature magnetic phase diagram and specific heat of Nd2IrIn8

In this work, we report results of specific heat and magnetization measurements on a single crystal of Nd2IrIn8. The compound orders antiferromagnetically below the Néel temperature of 12.5(2)K. Nd2IrIn8 exhibits magnetic anisotropy with c as the easy axis. Two sharp metamagnetic transitions are present at 2K. The measured data have been used to construct the low-temperature phase diagram for H||c. The measured susceptibilities and specific heat are compared to results based on first-principles calculations of the crystal-field parameters.

Electric-field control of magnetic order above room temperature

Controlling magnetism by means of electric fields is a key issue for the future development of low-power spintronics. Progress has been made in the electrical control of magnetic anisotropy, domain structure, spin polarization or critical temperatures. However, the ability to turn on and off robust ferromagnetism at room temperature and above has remained elusive. Here we use ferroelectricity in BaTiO3 crystals to tune the sharp metamagnetic transition temperature of epitaxially grown FeRh films and electrically drive a transition between antiferromagnetic and ferromagnetic order with only a few volts, just above room temperature. The detailed analysis of the data in the light of first-principles calculations indicate that the phenomenon is mediated by both strain and field effects from the BaTiO3. Our results correspond to a magnetoelectric coupling larger than previous reports by at least one order of magnitude and open new perspectives for the use of ferroelectrics in magnetic storage and spintronics.

Complex and strongly anisotropic magnetism in the pure spin system EuRh2Si2

In divalent Eu systems, the 4f local moment has a pure spin state J = S = 7/2. Although the absence of orbital moment precludes crystal electric field effects, we report a sizable magnetic anisotropy in single crystals of EuRh2Si2. We observed a surprisingly complex magnetic behavior with three successive phase transitions. The Eu2+ moments order in a probably amplitude-modulated structure below 24.5 K, undergoing a further transition to a structure that is possibly of the equal-moment type, and a first order transition at lower temperatures, presumably into a spin spiral structure. The sharp metamagnetic transition observed at low fields applied perpendicular to the hard axis is consistent with a change from a spiral to a fan structure. These magnetic structures are presumably formed by ferromagnetic planes perpendicular to the c axis, stacked antiferromagnetically along c but not of type I, at least just below the ordering temperature. Since EuRh2Si2 is isoelectronic and isostructural to EuFe2As2 at room temperature, our results are also relevant for the complex Eu-magnetism observed there, especially for the transition from an antiferromagnetic to a ferromagnetic state observed in EuFe2P2 upon substituting As by P.

Complex magnetic order in Pr2Pd3Ge5: a single crystal study

We have investigated the magnetic and electronic transport properties of single crystal Pr2Pd3Ge5 grown by the Czochralski method. Complex magnetic behaviour (multiple magnetic transitions) is clearly seen in this compound from the magnetic susceptibility χ(T), isothermal magnetization M(H) and electrical resistivity ρ(T) data. For the magnetic field applied along the crystallographic c-axis (H ‖ [001]) the χ(T) data exhibit two sharp transitions at 6.9 and 6.3 K and a broad hump near 8 K. Four anomalies at 8.0, 7.3, 6.2 and 4.9 K are observed for the magnetic field along both a- and b-directions (H ‖ [100] and H ‖ [010]). Further, the ordered state χ(T) presents a large anisotropy with an easy axis along the c-axis. The presence of magnetocrystalline anisotropy is also inferred from the isothermal M(H) data. The M(H) data measured at 1.9 K for H ‖ [001] exhibit a step-like increase due to field-induced metamagnetic transitions at T and T. For H ‖ [100] and H ‖ [010] sharp step-like field-induced metamagnetic transitions occur at T and T which are accompanied by a weak S-shaped spin-flop metamagnetic transition at T. We have extracted the H–T phase diagram from the M(H) data collected at different temperatures in the magnetically ordered state which shows the existence of three magnetic phases below TN for H ‖ [100] and H ‖ [010], and two magnetic phases for H ‖ [001]. A sharp transition due to the onset of long range antiferromagnetic order is also seen in the ρ(T) data which also exhibit anisotropic behaviour. The observation of an upturn near TN in the ρ(T) data suggests the formation of a super-zone gap and hence the existence of incommensurate magnetic structure. Further, in the ordered state, the ρ(T) data present a gap in the excitation spectrum of magnons with a characteristic energy gap Δ ∼ 0.23 meV.

Control of magnetic ground state and sharp metamagnetic transition by impurity size in A site substituted Pr1–xCaxMnO3

Similar to the substitution of Ba or Sr for calcium, the substitution of La for praseodymium in Pr1–xCaxMnO3 (x=0·5 and 0·4) can also induce ferromagnetism and sharp magnetisation multisteps at low temperature. The La substitution is more efficient to facilitate these magnetic phenomena in Pr0·6Ca0·4MnO3 than in charge exchange type manganite Pr0·5Ca0·5MnO3 due to the fact that the pseudo-charge exchange type orbital charge ordered structure in the former system is easier to be collapsed. More importantly, by comparing the magnetic properties of Pr0·6–xLaxCa0·4MnO3 with those of Pr0·6Ca0·4–xAxMnO3 (A=Ba, Sr), the crucial role of the A site impurity size on the magnetic phenomena is emphasised. The Ba substitution exhibits a greater ability to induce such magnetic phenomena than the Sr substitution, and the ability of the latter is greater than that of the La substitution. This sequence is in agreement with that of their ionic size, i.e. Ba2+>Sr2+>La3+. Combining the 'counterdistortion' effect due to the introduction of larger size impurities on A sites with the martensitic-like model, the experimental results have been systematically discussed.

Magnetocrystalline anisotropy in RAu 2Ge 2 (R = La, Ce and Pr) single crystals

Anisotropic magnetic properties of single crystalline RAu 2Ge 2 (R=La, Ce and Pr) compounds are reported. LaAu 2Ge 2 exhibits a Pauli-paramagnetic behaviour whereas CeAu 2Ge 2 and PrAu 2Ge 2 show an antiferromagnetic ordering with Nèel temperatures T N = 13.5 and 9 K, respectively. The anisotropic magnetic response of Ce and Pr compounds establishes [0 0 1] as the easy axis of magnetization and a sharp spin-flip type metamagnetic transition is observed in the magnetic isotherms with H // [0 0 1]. The transport and magnetotransport behaviour of these compounds, in particular LaAu 2Ge 2, indicate an anisotropic Fermi surface. The magnetoresistivity of CeAu 2Ge 2 apparently reveals the presence of a residual Kondo interaction. A crystal electric field analysis of the anisotropic susceptibility in conjunction with the experimentally inferred Schottky heat capacity enables us to propose a crystal electric field level scheme for Ce and Pr compounds. For CeAu 2Ge 2 our values are in excellent agreement with the previous reports on neutron diffraction. The heat capacity data in LaAu 2Ge 2 show clearly the existence of Einstein contribution to the heat capacity.

High Field Metamagnetism of PrRh2Si2 Single Crystal Compound Having Anomalously High Nèel Temperature

High field magnetization up to 18 T and magnetic susceptibility measurements have been carried out on a PrRh2Si2 single crystal. The anomalously high Neel temperature of 70 K is confirmed. A strong uniaxial magnetic anisotropy with the easy c-axis is evidenced. A sharp metamagnetic transition appears at 16 T in the easy c-axis magnetization process while magnetization in the basal plane is very small and the curve is linear. The saturation moment obtained is 3.1μB. Crystalline electric field (CEF) effects have been analyzed to discuss the magnetic behaviors.

Pressure-induced ferromagnetic order in the weak ferromagnet YbRhSb

YbRhSb has a small spontaneous moment of 0.003 μB/Yb below Tm1= 2.7 K at ambient pressure. We have studied the pressure effect on the weak ferromagnetism by the measurements of dc magnetization for a single crystal up to 2.5 GPa. With increasing P, Tm1 (P) increases to a maximum value of 3.3 K. For 0.9 < P < 1.5 GPa, another magnetic transition occurs at Tm1 above Tm1, and Tm1(P) has a deep minimum of 2.5 K at PC = 1.7 GPa. For P > 2 GPa, a spontaneous moment of 0.3μB/Yb appears along the orthorhombic c-axis. In the ferromagnetic state above 2 GPa, magnetization curves for B ∥ a and B ∥ b exhibit sharp metamagnetic transitions at around 1.5 T. The complexity of the magnetic behaviors may be ascribed to the competition between single-ion crystal field anisotropy with easy direction ∥ a and inter-site exchange interaction with easy direction ∥ c.

Spontaneous magnetization and resistivity steps in the bilayered manganite(La0.5Nd0.5)1.2Sr1.8Mn2O7

We report a detailed study of steplike magnetization and resistivity jumps in a bilayered $({\mathrm{La}}_{0.5}{\mathrm{Nd}}_{0.5}{)}_{1.2}{\mathrm{Sr}}_{1.8}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ single crystal. The sample exhibits very sharp metamagnetic transitions at low temperature when the magnetic field is applied either in an ab plane or along the $c$ axis, which causes huge magnetization steps. The critical field depends on the cooling magnetic field as well as the sweep rate of the magnetic field. Meanwhile, the evolution with time of the magnetization exhibits a spontaneous step when both the temperature and magnetic field are constant. Similar steplike behaviors are also observed in resistivity. These results suggest that a martensiticlike transformation could happen in bilayered manganites.