Upper Critical Field and Magnetic Properties
of a Superconductor with a Ferromagnetic Component

A. M. Prokhorov*, N. P. Lyakishev**, G. S. Burkhanov**, S. A. Lachenkov**,
G. M. Leitus**, E. P. Khlybov***, and I. Warchulska****

* Institute of General Physics, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 117942 Russia
** Baikov Institute of Metallurgy, Russian Academy of Sciences, Leninskii pr. 49, Moscow, 117334 Russia
*** Vereshchagin Institute of High-Pressure Physics, Russian Academy of Sciences,
Troitsk, Moscow oblast, 142092 Russia
**** International Laboratory for Strong Magnetic Fields and Low Temperatures,
ul. Gaioviska 95 Wroclaw, 53-529 Poland

Received June 10, 1997

Abstract—A superconductor YNi_1.9B_1.2 with a critical temperature of the superconducting transition T_c equal
to 13.5 K was synthesized. The H_c2(T) curve for the compound has an anomalous portion with a positive con-
vexity in a temperature range of 9.5–13.5 K. In the normal state the compound is characterized by anomalous
temperature and field dependences of the magnetic susceptibility ; the magnetic susceptibility is temperature-
independent in a temperature range of 15–50 K in a fixed magnetic field and decreases with increasing magnetic
field from 0.214 to 4.28 kOe at a fixed temperature. It was shown that the anomalous portion of the H_c2(T) curve
may be described in terms of Werthamer–Helfand–Hohenberg theory in the Fulde–Maki approximation; the
positive convexity of the curve may be explained by the anomalous magnetic properties of the YNi_1.9B_1.2 com-
pound in the non-superconducting state.

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