Precise measurements of radio-frequency magnetic susceptibility in (anti)ferromagnetic materials

TL;DR

This study employs a 14 MHz tunnel diode oscillator to precisely measure the magnetic susceptibility of various (anti)ferromagnetic materials, revealing distinct behaviors between local and itinerant magnetic orders and detecting spin and metamagnetic transitions.

Contribution

It introduces a highly sensitive TDO-based method to distinguish local versus itinerant magnetic orders and to detect spin and metamagnetic transitions in intermetallic materials.

Findings

Local moment ferromagnets show a sharp peak in susceptibility near T_c.

Itinerant ferromagnets exhibit a broad maximum in susceptibility.

TDO measurements can distinguish magnetic order types and detect transitions.

Abstract

Dynamic magnetic susceptibility, $\chi$, was studied in several intermetallic materials exhibiting ferromagnetic, antiferromagnetic and metamagnetic transitions. Precise measurements by using a 14 MHz tunnel diode oscillator (TDO) allow detailed insight into the field and temperature dependence of $\chi$. In particular, local moment ferromagnets show a sharp peak in $\chi(T)$ near the Curie temperature, $T_c$. The peak amplitude decreases and shifts to higher temperatures with very small applied dc fields. Anisotropic measurements of CeVSb$_3$ show that this peak is present provided the magnetic easy axis is aligned with the excitation field. In a striking contrast, small moment, itinerant ferromagnets (i.e., ZrZn$_2$) show a broad maximum in $\chi(T)$ that responds differently to applied field. We believe that TDO measurements provide a very sensitive way to distinguish between local and itinerant moment magnetic orders. Local moment antiferromagnets do not show a peak at the N\'eel temperature, $T_N$, but only a sharp decrease of $\chi$ below $T_N$ due to the loss of spin-disorder scattering changing the penetration depth of the ac excitation field. Furthermore, we show that the TDO is capable of detecting changes in spin order as well as metamagnetic transitions. Finally, critical scaling of $\chi(T,H)$ in the vicinity of $T_C$ is discussed in CeVSb$_3$ and CeAgSb$_2$.