Spin-lattice coupling in a ferrimagnetic spinel: Exotic H−T phase diagram of MnCr2S4 up to 110 T (original) (raw)
Related papers
Magnetodielectric coupling in frustrated spin systems: the spinels MCr 2 O 4 (M = Mn, Co and Ni)
Journal of Physics: Condensed Matter, 2010
We have studied the magnetodieletric coupling of polycrystalline samples of the spinels MCr 2 O 4 (M = Mn, Co and Ni). Dielectric anomalies are clearly observed at the onset of the magnetic spiral structure (T s ) and at the 'lock-in' transition (T f ) in MnCr 2 O 4 and CoCr 2 O 4 , and also at the onset of the canted structure (T s ) in NiCr 2 O 4 . The strength of the magnetodielectric coupling in this system can be explained by spin-orbit coupling. Moreover, the dielectric response in an applied magnetic field scales with the square of the magnetization for all three samples. Thus, the magnetodielectric coupling in this state appears to originate from the P 2 M 2 term in the free energy.
Magnetic phase transitions and magnetoelastic coupling in S
16 We combined magneto-infrared spectroscopy and first-principles calculations to unravel the role of spin-phonon coupling in the vicinity of the magnetic field-driven phase transitions in two chemically similar S = 1/2 Heisenberg antiferromagnets, CuF 2 (H 2 O) 2 (3-Clpy) and [Cu(pyz) 2 (HF 2)]PF 6. This comparison resolves questions about the conditions under which the lattice participates in magnetic-field-driven transitions and, at the same time, provides a way to predict how the lattice is likely to support microscopic spin rearrangements.
Universal Magnetic Structure of the Half-Magnetization Phase in Cr-Based Spinels
Physical Review Letters, 2010
Using an elastic neutron scattering technique under a pulsed magnetic field up to 30 T, we determined the magnetic structure in the half-magnetization plateau phase in the spinel CdCr 2 O 4 . The magnetic structure has a cubic P4 3 32 symmetry, which is the same as that observed in HgCr 2 O 4 . This suggests that despite their different zero-field ground states a universal field-induced spin-lattice coupling mechanism is at work in the Cr-based spinels.
Half-magnetization plateaux in Cr spinels
Journal of Physics: Conference Series, 2006
Magnetization plateaux, visible as anomalies in magnetic susceptibility at low temperatures, are one of the hallmarks of frustrated magnetism. An extremely robust halfmagnetization plateau is observed in the spinel oxides CdCr2O4 and HgCr2O4, where it is accompanied by a substantial lattice distortion. We give an overview of the present state experiment for CdCr2O4 and HgCr2O4, and show how such a half-magnetization plateau arises quite naturally in a simple model of these systems, once coupling to the lattice is taken into account.
Multiferroic spin-superfluid and spin-supersolid phases in MnCr2S4
Physical Review B
Spin supersolids and spin superfluids reveal complex canted spin structures with independent order of longitudinal and transverse spin components. This work addresses the question whether these exotic phases can exhibit spin-driven ferroelectricity. Here we report the results of dielectric and pyrocurrent measurements of MnCr2S4 as function of temperature and magnetic field up to 60 T. This sulfide chromium spinel exhibits a Yafet-Kittel type canted spin structure at low temperatures. As function of external magnetic field, the manganese spins undergo a sequence of ordering patterns of the transverse and longitudinal spin components, which can be mapped onto phases as predicted by lattice-gas models including solid, liquid, super-fluid, and supersolid phases. By detailed dielectric and pyrocurrent measurements, we document a zoo of multiferroic phases with sizable ferroelectric polarization strongly varying from phase to phase. Using latticegas terminology, the title compound reveals multiferroic spin-superfluid and spin-supersolid phases, while the antiferromagnetic solid is paraelectric.
Magnetocrystalline interactions in MnCr 2 O 4 spinel
In this work we present a magnetic, structural, and electron spin resonance ͑ESR͒ study of the geometrically frustrated MnCr 2 O 4 spinel in an extended range of T ͑2-1000 K͒. At the lowest temperature ͑T Ͻ 18 K͒ the ESR lineshape is compatible with the coexistence of spiral and ferrimagnetic spin ordering. Above T C ͑Ϸ41 K͒, magnetic susceptibility ͑͒ and ESR intensity coincide with each other showing the typical behavior of a ferrimagnet. From the ͑T͒ vs T dependence, absolute values for the three exchange constants J MnCr , J CrCr , and J MnMn were determined. Our results indicate that ͑i͒ these values are approximately independent of T, ͑ii͒ the antiferromagnetic direct Cr-Cr exchange is the main interaction, and ͑iii͒ J MnMn is indeed not negligible as compared with J MnCr and J CrCr . One noticeable anomaly in the temperature dependence of the ESR linewidth is observed at T Ϸ 450 K. This behavior is accounted by a 30% variation in the extrapolated high-temperature linewidth and it is attributed to a crystalline distortion not reported previously. Experiments of hightemperature x-ray diffraction allowed us to associate this distortion to a deformation of the oxygen sublattice.
Low temperature incommensurately modulated and noncollinear spin structure in FeCr 2 S 4
Journal of Physics: Condensed Matter, 2010
FeCr 2 S 4 orders magnetically at T N ≈ 170 K. According to neutron diffraction, the ordered state down to 4.2 K is a simple collinear ferrimagnet maintaining the cubic spinel structure. Later studies, however, claimed trigonal distortions below ∼60 K coupled to the formation of a spin glass type ground state. To obtain further insight, muon spin rotation/relaxation (μSR) spectroscopy was carried out between 5 and 200 K together with new 57 Fe Mössbauer measurements. Below ∼50 K, our data point to the formation of an incommensurately modulated noncollinear spin arrangement like a helical spin structure. Above 50 K, the spectra are compatible with collinear ferrimagnetism, albeit with a substantial spin disorder on the scale of a few lattice constants. These spin lattice distortions become very large at 150 K and the magnetic state is now better characterized as consisting of rapidly fluctuating short-range ordered spins. The Néel transition is of second order, but ill defined, extending over a range of ∼10 K. The Mössbauer data around 10 K confirm the onset of orbital freezing and are also compatible with the noncollinear order of iron. The absence of a major change in the quadrupole interaction around 50 K renders the distortion of crystal symmetry to be small.
We report the appearance of ferroelectricity below T S = 18 K, at which short-ranged spiral spin orders, suggesting that MnCr 2 O 4 is an improper multiferroic material. Linear heat capacity data and zero-field-cooled memory effect verify reentrant spin-glass-like state below T S. Synchrotron x-ray diffraction studies confirm significant magnetoelastic coupling at long-range ferrimagnetic order (T N = 42 K) and at T S. We argue that the release of topological spin frustration, produced due to pyrochlore structure of Cr sublattice, is manifested through the significant magnetoelastic effect at T N and T S and holds the key for spiral spin order driven ferroelectricity in MnCr 2 O 4 .