My research over many years has been focused on a detailed understanding of magnetic materials. Many were rare earth compounds whose interesting properties are observable only at low temperatures. The work has involved experimental studies of crystal field effects, microscopic spin-spin interactions, cooperative effects and phase transitions. The results frequently provided critical tests of theoretical predictions.

One example of such a material is dysprosium aluminum garnet (DAG) which we have studied extensively since 1962. DAG has provided a model system for studying thermodynamic relationships, metamagnetism, order-order phase transitions, critical exponents, criteria for using Ising model approximations, time reversed antiferromagnetic states, tricritical points, induced staggered fields, and magnetoelastic effects.

We also made early studies of rare earth garnets containing iron, which are ferrimagnetic at room temperature and of interest for microwave and magneto-optical applications.

Another material that we pioneered was cerium magnesium nitrate (CMN) which later became the thermometric standard for temperatures in the range 6 mK to 1 K. CMN also turned out to be the first example of a material to exhibit the two-phonon relaxation process now known as the Orbach process.

Another "first" was the discovery of ferromagnetism in magnetic insulators, initially in dysprosium ethyl sulphate, below 1 K, and then in GdCl3, above 1 K. Prior to our experiments it had been assumed that insulators order antiferromagnetically, and that only metallic systems can order ferromagnetically. Subsequently, we discovered more insulating ferromagnets including Tb(OH)3, Dy(OH)3, and Ho(OH)3, for which we continue to be the only source of crystals worldwide.

Our work has also led to a number of new experimental techniques. These have included the first use of a mutual inductance bridge with a moving sample for measuring magnetic susceptibilities; exploiting the large anisotropy of CMN to make measurements in crossed magnetic fields; using tunnel diode oscillators to make adiabatic susceptibility measurements for determining magnetic specific heats; development of a magneto-optical method for accurately calibrated ac susceptibility measurements; and use of a high sensitivity ultrasonic interferometer for the detection of magnetic phase transitions.

Among our theoretical papers one on "The raising of angular momentum degeneracy of f-electron terms by cubic crystal fields" has proved widely useful (over 1,000 citations) for predicting the low-lying energy levels of rare earth compounds. Another early paper established the framework for relating local ionic anisotropy to macroscopic magneto-crystalline anisotropy.

I have also been active as a consultant to industry and to a variety of academic institutions and as an organizer of technical conferences.

Selected Publications

"The Role of Quantum Mechanics in Understanding Magnetic Materials" (Invited paper), W.P. Wolf, Centennial Meeting of the American Physical Society, Atlanta, March 1999, Bull. Am. Phys. Soc., 44, 1400 (1999).

"Is Physics Education Adapting to a Changing World?" W.P. Wolf, Physics Today, October 1994.

"Magnetoelastic Effects in Dysprosium Aluminum Garnet: Theory," W.P. Wolf and C.H.A. Huan, Phys. Rev. B, 37, 2033 (1988); see references contained therein.

"Magnetic and Thermal Properties of Tb(OH)3," C.A. Catanese, A.T. Skjeltorp, H.E. Meissner, and W.P. Wolf, Phys. Rev. B, 8, 4223 (1973).