Electrical resistivity and magnetic investigations of the orthorhombic Tb(Ni, Cu)2 system

doi:10.1016/0304-8853(78)90124-5

Journal of Magnetism and Magnetic Materials

Volume 8, Issue 3, June–July 1978, Pages 223-231

https://doi.org/10.1016/0304-8853(78)90124-5 Get rights and content

Abstract

The orthorhombic Tb(Ni, Cu)₂ and Gd(Ni, Cu)₂ systems (CeCu₂ structure) are closely similar according to electrical resistivity and magnetic results. The Tb(Ni_xCu_1−x)₂ system presents a transition from antiferromagnetism (AF) for x ⩽ 8% Ni to ferromagnetism (FM) for x > 8% Ni. The CeCu₂ structure becomes unstable for x > 45% Ni. The AF samples show metamagnetism at 4.2 K with critical fields. Hysteresis, which occurs for all samples at 4.2 K, is attributed to intrinsic pinning due to large anisotropy where the mechanism for the AF range is analogous to intrinsic pinning of narrow domain walls in FM samples.

Spin disorder resistivity measurements show a discontinuity at the AF-FM transition composition for both the Tb and Gd systems. This is due to a step up of the residual resistivity at 4.2 K as a result of AF ordering. This interpretation is confirmed by applying a magnetic field to destroy the AF ordering.

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Citation Excerpt :
The sample GdCu2 exhibits three metamagnetic transitions (at critical fields Hc1, Hc2 and Hc3) in both the arc-melted and melt-spun form [Fig. A1(b) and Fig. 4(a)]. These field-induced transitions in RCu2 compounds correspond to the change of antiparallel to parallel spin alignment and that of conversion of magnetic/Ising axis [19,24]. There is no remanent magnetization.
In this work, magnetic and magnetocaloric properties of melt-spun RCu₂ (R = Gd, Tb, Dy, Ho and Er) compounds have been studied. The melt-spun samples have formed in the same orthorhombic crystal structure (space group Imma, no. 74) as that of the arc-melted samples but with a development of crystallographic texture and micron-size grains. The melt-spun ribbons of RCu₂ (R = Gd, Tb, Dy, Ho and Er) order antiferromagnetically at 43 K, 51 K, 28 K, 10 K and 11 K (T_N) respectively. The ordering temperatures are almost the same as that of the arc-melted samples. The RCu₂ compounds show one or more field induced transitions below T_N. Therefore, a normal magnetocaloric effect is observed in these compounds when the magnetic field change is larger than the metamagnetic critical field and inverse magnetocaloric effect is observed for smaller field changes. The microgranularity does not seem to smear out the metamagnetic transition. The maximum of isothermal magnetic entropy change, ΔS_m^max, is about −2.1 Jkg⁻¹K⁻¹, -5.5 Jkg⁻¹K⁻¹, -5.2 Jkg⁻¹K⁻¹, -17.2 Jkg⁻¹K⁻¹ and -11.7 Jkg⁻¹K⁻¹ respectively for the melt-spun RCu₂ (R = Gd, Tb, Dy, Ho and Er) samples for 50 kOe field change. The refrigeration capacity is found to be 40 Jkg^-1, 160 Jkg^-1, 166 Jkg^-1, 230 Jkg^-1 and 207 Jkg^-1 respectively, for the above samples. These values are nearly the same as that of the arc-melted counterparts. Thus the large magnetocaloric effect in the temperature range of 10 K–70 K make these melt-spun RCu₂ samples potential materials for low temperature refrigeration applications. The results also ascertain melt-spinning process as an alternate technique for the production of magnetocaloric alloys and intermetallics.
Chapter 5 Magnetic properties of rare earth-Cu<inf>2</inf> compounds
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This chapter discusses the magnetic properties of rare earth-Cu₂ compounds. The chapter focuses on rare-earth intermetallic compounds, the RT₂ (R = rare earth, T = transition metal) with the cubic Laves phase structure. The magnetic properties of the RCu₂ are affected by the crystal field (CF) effects. The magnetic ordering temperatures in the RCu₂ compounds are low and crystal-field and exchange interactions are studied by varying temperature and/or magnetic field. Changes in the magnetic structure occur in most of the compounds below the Néel temperature and most of the compounds exhibit metamagnetic transitions below the magnetic ordering temperature. The metamagnetic transition in TbCu₂ is a typical example of a single-step transition in a metallic system. The chapter presents the magnetic properties of 4f-3d intermetallic compounds. The magnetic properties of binary rare-earth 3d-transition metals intermetallic compounds with the transition metals Mn, Fe, Co, and Ni are reviewed. The chapter also presents a short theoretical consideration of crystal-field and exchange interactions of some important magnetic properties. Experimental results on RCu₂ compounds are reviewed and a comparison of different RCu₂ compounds is provided.
Importance of higher order terms in CF Hamiltonian for interpretation of magnetization curves in Tb(Cu<inf>0.7</inf>Ni<inf>0.3</inf>)<inf>2</inf>
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Influence of Ni-concentration on the magnetic structure in Tb(Cu, Ni)<inf>2</inf> system
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A powder sample of orthorhombic Tb(Cu_0.7Ni_0.3)₂ has been studied by neutron diffraction at T = 4.2 K and above the Curie temperature. It is found that this compound is ferromagnetically ordered at 4.2 K. The magnetic moment of Tb in this compound is (9.2 ± 0.2)μ_B, with components (2.2 ± 0.2, 0, 8.9 ± 0.1)μ_B. The influence of the Ni-concentration on the magnetic structure is discussed in the whole Tb(Cu, Ni)₂ system.

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Electrical resistivity and magnetic investigations of the orthorhombic Tb(Ni, Cu)2 system

Abstract

Phys. Lett.

Solid State Comm.

J. de Physique

IEEE Trans. Mag. MAG-7

C.R. Acad. Sci. Paris

J. Appl. Phys.

Electrical resistivity and magnetic investigations of the orthorhombic Tb(Ni, Cu)₂ system